GIOO

GIOI

GI02

GI03

GI04

GIOS

,/ GI06

/ GI07

GlOB

GI09

E2,ES

F3A

F3B

F3C

SCHOOL OF CROP SCIENCES

INDEX

Introduction

Pot Trial

Lime Requirement

Effect of Consolidation on Emergence

Sieve Analysis

Hec4anical Properties

Moisture Characteristic

stability to Wetting

Aggregate Analysis - P.S.A. and S.A.R.

Density and Pore Space Relations (PSR)

Air Dry 6g, Density of Solids for PSR

PSR of a Natural Soil Core

·PSR of Soil Aggregate by Wax Block

Shrinkage Curve of a Soil Paste

.' .. G100.1

ScHOOL OF CIlDI? SCIENCES

DEPARTf'lENT OF SOIL SCIENCE. ",

'METHODOLOGY - PRACTICAL WORK

Introducti on

On completion of an experiment, all of which have questions, the

student must present his laboratory notebook to a supervisor for comment

and marking. In addition, a summary of the principal results should be

prepared on a separate sheet of paper at the same time; this will be

retained by the department.

It is important that the- design of any experiment should be ba;ed on

a consideration of all information previously obtained. For example:

the moisture characteristic of the porous material may predicted

semi-quantitatively using information from the sieve analysis. This

prediction allows us to anticipate the size of the matric potential

steps so that maximum information is'obtained in the range of potential

where drainage of the majority of pores occurs. It wi 11 also permit

prediction of the maximum drainable porosity so that moisture content

variation can be measured with maximum accuracy.

The "predictive" questions concluding each. experiment are designed

to guide the student in this form of preparation for subsequent

experiments.

",

6100.2

Laboratory Notebook

A 1 abora tory record must be kept ina hardback notebook. Thi s·record

must contain all detail s of 1 aboratory practi ce where they d1fferfrom

these notes and with experimental results and errors adeq"uately tabUlated. "

Each experiment generally concl udes with a conci Sf! di scussi on of the

theory of methods used and the si.gnificance of results and "errors; See

Appendix Al/2/3 for precedure concerning errors.

Appropriate references must be cited in the text in the manner·

described in the CSIRO publication "A Guide to Authors"-or in the appendix

of currents issues of Aust. J. Soil Res. "

Laboratory Facilities

Practical work may proceed at any time when the laboratories.are not

occupied by other classes. Supervisors, however, will be availabie only

during programmed practical periods, ·There ~Ust. al~ays

be at least two. students present outside of hours in. case of accident

There are a series of calculations and .questions it the end of each experimental determination (or"group of determiiatlons). ~o not throw any experimental material away before you have" accurately com­pleted all parts of the dete.rmination and have had answers and con-clusions checked by a member of staff. .

, .

'-

.... ,

G-IOO Intro/3;

Recording of Numerical Results and Accuracy of Measurement

(1)

(2)

(3)

A tabular form is required: each line should'incluae na~e of observation; unit of measurement; equipment used, equlp­ment error; result for replicates A, Band C; 2 extra columns for evaluation of equipment C.V.' if necessary t;e. if C.V! (experimental) exceeds 10% - see. example on page B for eg.

Distinction should be made by underlining Or ,by using differ­ent colours between primary observations e.g. mass of wet -soil in the container or mass of dry soil in the conta,iner and derived quantities such as mass of water, mass of oven dry soil, an.d moisture content which are calculated from the primary observations.

The standard deviation of a piece, of equipment depends on the equipment used. This in its turn controls the number of places to which primary data should be recorded and,the coefficient of variation due to equipment. (The error of a me'asurement is often related to the difference of two observations, e.g. dry' and wet mass yield amount of water, so that ffthe standard deviation of ' the equipment applies to the'difference and hence controls the number of places to which data should be collected to-reach a predetermined_ accuracy. )

Consideration of Variability of Results

The Coefficient of Variation obtained by study of the experimental values from the replicates is generally a sufficient guide to experimental reproducibility. If, however, the Coefficient of Variation exceeds 10%, it is adVTsable to examine the equipment standard errors and hence determine whether the cause is due to the equipment or due to soil variability ptUB operator error.

In each (1 )

(2)

experiment it is necessary to decide, If the answer needs to be more or less accurate in view of its proposed use; how the method could be improved if increased accuracy is

, desirable.

Calculations involving A·tomic Absorption, Pot'entiometric Analysis and Colorimetrfc' Anal-ys-is- Results

The A A method pr-oduces results which are printed out tn the form of y moles/litre for the element in question (Colorimetric ana-lyses are read on calibration graphs of concentration either in moles/ litre versus absorption, or ppm versus absorption).

The concentration so obtained refers 'to t-he solution that was analysed. Very rarely is this the same as the extract obtained from the soil. -

I

,c;..IOI) , 'Introf4.

"

The following claculatlon steps are general, fcir,an'alyses 'i,n ,n1ol,es/ 1 itre. (1) .,' calculation of concentration in or.ig'iilal extract:

Original extract concentration· moles/litre 'x O.F. where ,O.F. is the'dilution factor. '

(2) calculation of concentration in'o.d. solI:

(3 )

y x D.F. x (volume of extract/unit mass of o.~. SRil).

= V (1 +881 '1 -1

y x D.F. x W x 100. mo es 9 ,

where W is mass of soil used in g. of'initial moisture con­tent e- 9 g-l. and V is volume of extract 'in mI. The 1000 in thegdenominator converts ml to litres.'

The volume of the extract in many insiances 'includes the water,in the original sample. i.e. W'x ego p~UB the amount of solution added. v in ml

i.e. V· v + W x 8g If. however. the final volume is made up'to volume as in a volumetric flask. e.g. the Ag thiourea extract for Cation Exchange Capacity. the water in the soil initially fs already include~ in the final volume. --

Often the answer for the extract is required in mg!,ll.i­equivalents/litre ~r for the dry soil in m~9uiv

(1) multiply answer in either case by TOOO x z where z Is valency of ion in ques·tion; , ' '

For many experiments the values of V. 8g and W, are constan't between experiments and a constant mulJ;,l p1 ier' can be used for step (2).

(4) Calculation of concentration in Jlgg- l of o.d. soil (ppm)

The answer in (2) is multiplied by M X I06,where M Is the Molecular or Atomic weight of the ~lement in question.

SOIL SCIENCE I V PMCTICAL I'lANUAL . .Introduction Paga S-

~£[ Instrument Accuracies (Assuming equipment 10 go~d repair anp used correctly)·

Balances

Volumetric flasks

Pipettes graduated

Pipettes bulb

Burettes

Measuring cylinders

Instrument

P1200and K7 Mettler Mettler H4 Mettler P120 Mettler Hl0T\ll Mettler AE1S0 Mettler AW200 Mettler PE3S0 PE3S0 Delta range

.Sartorius 1219MP 1219MP Delta range

50 mL 100 mL 500 nL

2nL 5mL

5mL 10'mL 25 mL

100 nL

50 mL (A grade for Volumetric chern.) 50 mL (others)

100 mL 500 mL

pH meter measuring to ± 0.5 mV pH meter Radiometer

. AccUracy' .

± 0.03 9 ± 0.001 9 ± 0.003 9 ± 0.0005 9 ± 0,0001 9 ± 0.0001 9 ± 0.01 9 ± 0.001 g' ± 0.01 9 ± 0.001 9

± 0.1 nL ±0.15nL ± 0.3 nL

± 0.03 nL/delivery. ± 0.05 nL/graduated

± 0.05 mL!delivery ± 0.05 mL!delivery ± 0.10 nL!delivery ± 0.12 nL!d.livery

± 0.05 nL/reading ± O.lS.nL!reading

± 0.05 nL/reading ± 2.0 nL!reading

± 0.009 pH ± 0.005 pH

(

"

!:

" "

..

"

'Af.1 APPENDIX . ,."

Calculati~n of the standard deviation and the coefficient of vari~tion attributable

to the equipment used in a determination. and speclm~n layout

The standard deviation for a measurement using particular equipment 'is often suppl ied by the manufacturer or can. be 'determined by repetitive obser.vations. a wjll be used to indicate the standard dev"iation for these circumstances. The values given reflect the cumulative ,experience in 'these laboratories, and are therefore subject to refine­ment.

1. The simplest case is when all experimental measurements are independent. Let the oper ational quantities w,x,y and z have variance a~ etc. Provided that aw «W, i.e. that the coefficient of variation of each component is small, .

then a~ c Var (X) c. X2~(va:2w), where Xis the quantity to be determined and is a function of w, x, y, z such that X c c.f(w,x,Y,z) and c is a constant multiplier.

Hence aX = X It(Varz'!!.) or C.V. of.X c It(coeff.' of variation of w to z)2. W w

Example 1: Estimation of Exchangeable Sodium Concentration ,in soil in milli-,equiv. g-l, x = ~. and c = 1 z

Measurement Unit Experimental Value C.V, in

(C.V.)2 a A B C terms of· sample A+

Oil ution - .175 w = 10.0 ;175/10 .000,306,25 factor - -

Extraction .02 xc 50 .02/50, .000,000,16 factor - - -Concentration

:o..175xlO-4 -4 .1 75xl 0-4/l 0-4 of analysed Molar y = 10 - - .000 i306 ,25 sol tition

Mass of soil g .003xl2* x c 10.00 - - .003xl2/l0 '.OOO,OOO,IB

Sum (C.V.) I t.OOO, 612 ,84

t Strictly the C.V. should be determined for the mean of sub sites A,8', and' C. But the error in calculating C.V. (equip) by-using experimental values of A alone is usually small.

, * Difference of two readings ,+ 12

Derived quantity

Concentriltion m-e~viv. "E c .024,756 in soil .

I< •• 5 XIE .. .5(~024;756) g - - aX c

mean X .. XA+XB+XC .. .012,38

c c.v. (equip) , .. .025

jhiS t c. Vh of .025 is entirely attributable to the equipment: ' Other contributio'ns ue 0 t e operator, to variability within a sample, to variability between sa les

~!l:t~iteh~nd t~ variability between sites can be incorporated,using thet(C.V~2 ons p. ence it, is possible to partition the experimental'C.V, into that

caused by the equipment and caused by,soll/site/operator sources. '

(

(.

N2

2. When t..h.: experimentally derived quantity, X, involves ~cai'culation

<; c.f(x,y etc.} where one of the 'measurements is ,used more than once in,'

the calculation or where the operational quantities are non-independent,

the procedure for calculation of Ox is,more complex in ,that 'th.e covariance

of the non-independent quantities has to be intro~£ed.

Exampl e: .Determinatibn 'of Moisture Contentsg

where Mr •. Mass of wet sol1

M2 • Mass of o.d. sol1

Wl = Mass of wet sol1 plus container

W2 = Mass of o.d. soil plus container

W3 = Mass of container

OB ,= s.d. of balance.'. var (x) 2 = var (y) = 2"B

2 2 2 2Cf~ x2 Hence Variance (Sg). = = 2"B + 2CfBX + CfS "7 ? -4 y

2 2 2 And C.V. of '6' = "s = [2Cf~ + ,2oB + 2"B]"

9 Sg XZ" x x.y

Rearranging C.V. of 6g - /{(C.V.x)2 + (C.V.y)2 +, (C.V.x) (C.V.y))

Notice.,~ecause of the non-independence, this expression has an additional

interactive term when compared with the expression appropriate for inde­

pendence.

A/3

.Calculated Example 2 and Specimen Layout:

. -

. Expe ri men ta 1 aB Experi men ta 1 Value C.V • 2

quantity Unit B C of A

(C.V.) A

Mass of tin 9 .03 for K7 35.82=W3 36.53 37.82

Mass of tin 9 .03 Balance 70.35=Wl 71.58 73.29 and wet soil

Mass of tin 9 .03 6L50=~2 68.63 70.33 and dry so11 !

~

I Derived I

quantities a

o:d. soil 9 .03 X I 2 31. 68=M2 32:10 32.51 .Oof34 .000,001,795,6 , water

9 • 03. x 12 2. 85=Ml -M2 2.95 2-:-96 .01489 .000,221,712,1' . .000,019,952,6*

<Sum (C.V.)2.·· E. 000,243,460,3

Additional term C,V'M2

x C:V' M M .

1- 2

Derived quantity

69

99-1 .0900=X .0919 .0910 Mean 8

9 gg-l .0910

s (expt1) .00095 as c'S IE.· .0".015,60 9 • • 00140

C.V. (exptl) .0105 C.V. (equip) c .0156

C.V.(expt1) < C.V.(equip) and mean of s values provides' a good estimate of the exper­imental value of 8g of .091g.

This value of 8g and the C.V.(equip) of .0156 can now be used in the derivation of.

C.V.(equip) of other experiments involving 8 in which the other measurements are 9 .

independent using the procedure of 1. i.e.ll:(C.V.)2. Notice that altho'ugh 8g has.

a C.V.(equip) of .0156, the C.V.(equip) of the mass of so11 is only.00134. (See

1st line of derived quantities). As can be seen in Example 1 for exchangeable sod­

ium, i~ was z and its C.V.(equip) that were relevant, not 8g - zwas derived from the wet wei 9ht corrected for 8. .

. 9

*This example2is given to show.layout and calculation steps. In practice the·C:V. of A and (C.V.) two right hand" columns would not liave been calculated because C.V. (experimental) is 0.01 or 1%. For many experiments < 10% is acceptable and does not warrant analysis of er.rors... . .

Reference

Kendall & Stuart (1963). 'Advanced Theory of Statistics Vol. I~.P:231. 2nd Ed. 'Gr'iffi,

(\ .

Gioo . .il!4

References

In addition to references cited specifically in the Practical Notes for

a particular experiment, the following texts will be useful:

Black: C.A. (ed) 1965. "Methods of Soil Analysis. Part I".

(Am. Soc. Agron.,Madison).

Childs, E.C. 1969. "Physical Basis of Soil and Water Phenomena".

(Wiley-Interscience).

Crank, J. 1964. "The Mathematics of Diffusion".

(Oxford U. P., London) .

Hagan, R.M., Haise, H.R. and Edminister, T.W. (eds) 1967.

"Irrigation of Agricultural Lands". (Am. Soc. Agron., Madison).

Kirkham, D. and Powers, W.L. 1972. "Advanced Soil Physics".

(Wiley, New York).

Luthin, J.N. (ed) 1957. "Drainage of Agricultural Lands".

(Am. Soc. Agron., Madison).

Phil ip, J .R. 1969. "Theory of Infiltration" in Advances in Hydroscience

5:215-296.

Rose, C.W. 1967. "Agricultural Physics". (Pergamon, London).

Loveday, J. (ed) 1974. Methods for Analysis of Irrigated Soils.

Tech. Comrn. No. 54 (C.A.B.).

';" ,

G101.1

Pot Trial Glass House Assessment of Soil Fertility

1.1 Introducti on

.2

One of the most common methods of assessing soil fertility is to conduct a'pot trial in which nutrients are added to the soil in various combinations.

There ~re two principal designs:-Omission trial - where an overall "plus" treatment with nutrients ln quantities and ratios known to produce maximal growth of the test plant is added to one treatment (pot) and one nutrient at a time is omitted from all other treatment. Factorial trial - where additions in various combinations are made to a "control" or untreated soil.

For this assessment a randomized complete block factorial design each at 2 root temperatures will be used. The chemical design incorporates both a modified Andersop-Jenny trial where a single (N or p) nutrient is omitted in each treatment, and a simple factorial (control + K, + N, + P, + NP).

In total there are therefore 6 chemical treatments:

Control, - N, - P, - NP, + NPK, - NPK; where - NPK represents a treatment to which all basic and minor elements necessary for growth are added (i.e. Mo and CaC03).

N.B. "Control" has CaC03 added when the test crop is lettuce. (There is little point, as well as being statistically undesirable, to design trials to produce zero yields for some trea tmen ts. )

Study the questions which need to be considered at the conclusion of the exercise before starting the experiment, to ensure no aspect of the data collection is omitted.

Preliminaries

Prior to setting up the pot trial the following data should be obtained or be calculated:

(i) the moisture content of the soil at field capacity; (ii) the moisture content of the sample; (iii) the quantity of lime required to bring the soil to

pH 6.5 for the wei ght of soi 1 used. (Desi gn for approximately 52 post/soil each containing46.o g wet soil at Field Capacity moisture content. see Expt. G106);

(iv) a plan of each (temperature) tank showing the position of each pot. Ensure that the soils and treatments have been randomized within each replicate block. A suggested code for marking each pot is:

Temperature Block Soil Treatment (7 0 C - 0 I :; 0 .A :; 0 C - 0 ~~oC - 1 II :; 1 B :; 1 + :; 1 (+ NPK)

III - 2 c " z. -N - 2 ~+ PK) IV :; 3 0 ~ 3 -P :; 3 + NK)

-NP :; 4 (+ K)

I \

.3

( v)

(vi)

(vii)

the calibration of the delivery rate of the spray when the water tap is full open; . the total quantity of water required to bring the amount of soil required for the pot trial to ~ field capacity; the amount of soil·at half field capacity to be packed into each pot;

(viii) the weight of a pot with polythene beads and hence gross wei ght when contai ni ng 1/90 g wet soi 1.

Preparation of the Soil

Soil in the field condition is ground in the soil grinder, where possible, and mixed in plastic garbage bins to ensure that the sample is homogeneous. A weight of field soil convenient for the trial (approx. 52 ·pots each containing #6n g of soil at Field Capacity), is weighed on the steel yard and ·transferred to the concrete mixer. The calcium carbonate required to bring the soil to pH 6.5 is added and the soi 1 and CaC03 mi xed for a few minutes. (Care must be taken to add CaC03 slowly if soil is moist.)

Sufficient water is now sprayed onto the soil, while the mixer is turning, to raise the water content to an equivalent of ~ field capacity. The soil is then transferred to plastic bins, re-mixed and taken to the glasshouse .

• 4 Patti ng (one opera tor)

The soil at half field capacity is then filled into the labelled tared polythene plastic pots. It is essential that the pots be filled in such a way as to result in the same apparent density in each pot and to avoid any layering of the soil*. Sufficient soil should be filled into each pot to result in a total mass of soil at field capacity of7'~O g. (For this stage and all subsequent stages, only one operator should carry out the entire stage to reduce varia­bility caused by different operators.) * Consu~the demonstrator when swelling soils are used .

.. 5 Addition of Nutrients (one operator)

Nutrients are added according to the plan

Nutrient Plan

given:

Control All nutri ents " " " "

" " " "

Treatment

0 1 2 3 4 5

minus N minus P minus Nand P minus N, P and K

Rates

Ca(H2P04)2* ·H20

0.164 0.164

of Appl i cation

NH4N03 K2S04 0.474M 0.079M

6 ml 2 ml 2 ml

6 ml 2 ml 2 ml

--

Code o 1 2 3 4 5

CaC03

xx xx xx xx xx xx

Na2MOOj II 2.05 g 1

2 ml 2 ml 2 ml 2 ml 2. ml

(

, ' ,

* Ca(H2P04)2 ; H20 is added as a solid l>" below'surface of soil in the pot.

xx Amount is that determined by "linear" Ca(OH)2 lime requirement method and is added to the soil in the cenient mixer,' ,

II May be varied depending on known history of soil and identified trace .element deficiencies.

NOTE that the phosphate is applied as Ca(H2P04)2 . H20 at the rate of 0.164 g ± 0.001 g per pot placed 1;;" below the surface of the soil in the po't. This should be weighted into vials prior to setting up the experiment.

The other nutrients** are added in solution from automatic pipette syringes. The appropriate aliquots of all solutions should be run into 150 ml beakers, diluted to 10 ml and poured onto the pot. N.B. Care should be taken to ensure that the total volume of water added -- in the nutrients and washings of the beaker does not exceed the volume

.6

required to raise the soil in the pot to exactly field capacity. Weigh the pot and add sufficient water to bring the soil to field capacity. ** Calculate the rate of application of nutrients in mg per pot and

in kg per hectare (relative to area of pot).

Sowing (one operator)

Using lettuce as the test crop, six pregerminated seeds (migonette lettuce, Green variety) treated with "Coversan" are sown shallowly about ),;" below the soil surface in each pot. Great care in handling the germinated seed is necessary. They must be sown radical down­wards and care taken that there is not varying soil density above the seed .

. 7 Taring (one operator)

/

.8

Check the weight, add water if necessary to bring all pots to common Field Capacity mass.

Finally, approximately 20 g of ~ythene chips is placed on the top of the pot. All pots should be brought to a common tare in the process to facilitate watering.

Establishment

When the seeds have established, thin out to 2 plants per pot selecting plants of similar size, well spaced in the pot. (Always sow down a spare pot of untreated soil for replacement.)

.9 Watering

The success of the trial depends on the care with which the watering programme is carried out as even a temporary water stress can lead to differences in yield. It is essential that students adopt a rosterto keep the soil at field capacity throughout the trial. After the 3rd week of growth, allowance for the wet weight of the crop must be made. This is conveniently made by assuming a linear increase in wet weight of the crop in all treatments other than the "control" and "-P". (Total growth in these treatments may be so small that the effect can be neglected.)

The following table will serve as a guide to the allowances to be made for the growth of the lettuce in the Michaelmas term for the + treatment.

3rd week add 20 g to pot ,tare 4th " " 40 g " " " 5th " " 60 9 " " " 6th " " 80 9 " " " 7th " " 100 9 " " "

G101.4

Allowance must be made for applying extra water over the weekends so that the plant will not experience water stress. The amount to be applied can be estimated from the record of water losses. A record of the water lost from each of the pots should be kept throughout 'the trial and at the end a graph.made of the weekly loss from the average of each treatment (based on means of acceptabl e repl i cates) .

. 10 Environment Records

Ensure that solar radiation records, air temperature and humidity records and soil temperature records are kept during the trial.

Produce a graph of weekly solar radiation.

Also graph: Weekly average temperature

(MAX + MIN for 7 days) ; 2

Weekly relative humidity

(MAX + MIN for 7 days) 2

Weekly soil temperature in the pots as a function of depth .

. 11 Visual Assessment Scoring

Once a week representative plants from each treatment and soil are to be scored in terms of relative vegetative production. It is not easy to maintain a common scale from week to week, and so it is suggested that a score scale of 0 to 5 is used, where 5 is the largest plant on a particular day.

Note all symptoms that you are able to ;see: chlorosis, mottling of leaves, red coloration of stem, etc. Consult Wallace (1961) for symptom correlations .

. 12 Harvesting

All pots must be brought to Field Capacity about 2 hours before harvest. Weighing tins must be oven dried and weighed before harvesting.

Plants are harvested at 6 weeks by cutting at soil level with a scalpel. Avoid the inclusion of polythene chips in the harvested material. Since the number of pots involved is small, both wet and dry weight yields of the plants should be obtained. Harvesting should be completed in a minimum of time and tins weighed rapidly to obtain accurate wet weights. (Tin and plant weights should be taken to 0.001 g to overcome errors with small plant weights.) The plant material is then dried at 700C in the forced draft oven, firstly for one hour without removing lid to cause wilting. When dry after 2 days, put lids on tins and cool, otherwise since plant material is hygroscopic a desiccator must be used.

Weigh:, Determine mass of oven dry, dry matter per pot Determine mass of water per g oven dry matter ..

For each treatment, select· plants with average weight (to eliminate false treatments) bulk the mate~ial for each treatment, and store in labelled polythene bags for subsequent anaiysis •

• 13 Soil for subsequent analysis

Soil from some treatments will need to be stored for subsequent analysis. These can only be specified once the dry weight data has been obtained, but they will generally includ·e treatments that allow estimates before and after growing plants of:

(1) .p mineralisation and N status; (2) P characteristics (both + P and - P pots), (3) K characteristic (ONLY if responses).

DOOOOOOOOOOOO

2 Statistical analysis of results

Dry weight results should be examined statistically using the analysis procedure outlined. It may be necessary to use a missing plot technique if growth in some pots is zero.

2.1 A guide to the statistical analysis of a randomised complete block factorial within temperatures Pot Trial (prepared by the Department of Biometry).

The basic data is as follows:

2 soils; 6 chemical treatments which are quadruplicated (i.e., 4 blocks), 2 root temperatures (20°C and 2S o C). These are not

replicated so there is no Between Temperature Effect; The model for each temperature may be represented as follows:

where

K. 'k ~J

=

i = block: i = 0, 1, 2, 3;

j soil: j = 0, 1,

k

11

S. ~

a. J

ak

(aa) jk

chern. treatment: k = a, 1, 2, 3, 4, 5;

is an effect common to all pots;

is the effect of the ith block,

is the effect of the jth soil,

is the effect of the kth chemical treatment,

is the interaction of the jth soil with the kth chemical treatment,

is the remaining term which is normal~y distributed with mean zero and variance cr2 •

s

Prepare a two way table,. for each temperature, of treatment totals.

Chemical _Treatments Soil Total

C + -N -p -NP

Soils j=O X.OO X. Ol X. 02 X.03 X. 04

j=l X. IO X. ll X

.12 X

.13 X. 14

Chemical X X X X X Total •• 0 •. 1 •• 2 •• 3 .• 4

Sources of variation d.f. Sum of Squares 2. 2.

L. X. X A. Between Blocks 3

l 1. •• R --=

12 48

X2. 2. E- X

B. Between Soils 1. J • J •. -'-'-'- =. S 24 48

2. X2. Lk X .• k"

C. Between Chemical 5 --= C 8 48 Treatments

-NPK

X.Os

X .15

X •• 5

Mean Square s.s. d.f.

R/3

Sil

ciS

F

X .0.

X .1.

X

test

(R/3) 1/

2. Sis = FI

(CiS) Is 2.

=

FO

F 2

D. soils x Treatments 5 s.C. s.c/s 2 (S.c/s)/s =F3

Residual variation

Total variation

where S.C. = 2.

L .LkX .k J .J 4

33

47

E

X

48

- Soil Sum of Squares

E/33 2.

s

- Chern. Treatment Sum of Squares

E Total S.S. - Block S.S. - Soil S.S. - Chern. Treat. 5.5.

- soil x Chern. Treat. s.s.

i.e. E = Total - R - S - C - S.C. (and s2 = Estimate of Variance) = E

33

It should be noted that the chemical treatments used in this experiment are such that a difference between the Variance of the errors applicable to the control and the Variance of the errors applicable to the other 5 chemical treatments might be anticipated. A decision to include or exclude the control yields from the analysis might be made on the basis of the relative yields. If the yields of the control are on average less than one fifth those of the other treatments, exclude the control. The exclusion of the control will necessitate adjustments to the degrees of freedom.

The overall analysis includes the determination of interaction effect with temperature. The observation on a particular plot is now designated Xijm where m refers to the temperature, and m = 0 at 20°C. and 1 at 2s o C.

I

Sources of Variation

Between Block within temp.

Between Soils within temp.

Average Soil Effect

Soil x Temperature

Between Chern. Treatment within temperature

Average Chern. Treatment effect

Chem. Treatment x temp.

d.f.

3+3 = 6

HI = =?

1

1"

lO~

5-,

5 ~.

GIOl. 7

sinn of Squares

RO + R· 1

So + Sl ~ ST 2 2 2

X X X . 0 .• .1. . SA + =

48 48 96

S -T SA

Co + C1 = CT

2 X2 X .. k. k = CA 16 96

Soil x Chern. Treatment within temperature

(s.C.) 0 + (S.C.) 1 (S,C')T

Average Soil x Chemical Treatment

Soil x Chern. Treatment x Temp.

Error

Total

Temperature

66

95

1

Note that the total sum of squares .

2 EEX ok

• J • jk 8

2 X

96

(average soil Sum of Squares)

-(Av.Chem.Treat.Sum of Squares)

=(S,C')A

(S,C')T - (S,C')A

2 EEEEXo

~jkm

2 2 (EEEX

ijk for temp. 20°) + (EEEXijk for temp. 25°).

In order to compute the sum of squares in the overall analysis it is necessary to prepare 2- and 3- way tables where the 3-way table is a composite of the 2-way tables used for each temperature as per next page.

Tests of significance of main effects and interactions are made by a series of F tests with Error mean square as the divisor.

GlO1.8

m = temperature 0 1

Soils j - 0 1 0 1

Chemical treatments k = 0 X.OOO X.IOO X.OOI X.IOI

- 1 X.OIO X.110 X.Oll .X.lll

2 X.020 X.120 X.021 X.121

3 X.030 X.l30 X.031 X.131

4 X.040 X.140 X.041 X.141

S X.OSO X.ISO X.OSI X.ISI

Soils j = 0 1 Totals

Chemical treatments k = 0 X.OO. X.IO. X .• O.

1 X.OL X.IL X •. l.

2 X.02. X.12. X .• 2.

3 X.03. X.l3 . X •• 3.

4 X.04. X.14. X .• 4.

S X.OS. X.IS. X •. S.

Totals X.O .. X.L. X ..•.

Temperature m= 0 1 Totals

Chemical treatments k= 0 X .. 00 X .. Ol X .• 0.

1 X .. 10 X .• 11 X •. l.

2 X .• 20 X .. 21 X •• 2.

3 X .. 30 X .. 31 X .. 3.

4 X .• 40 X .. 41 X .• 4.

S X .• SO X .. Sl X .. S.

Totals X .•. 0 X •.. 1 X .•.•

Temperatures m= 0 1 Totals

Soils j = 0 x.o.o X.O.l X.O ..

1 X.LO X.Ll X.l. •

Totals X .•. 0 X ... 1 X •.•.

' . GI01.9

• 2 Prepare a summary table of the average visual scores· for each treatment and soil .

• 3 . Prepare a summary table of the average weekly environment of the plants during the trail.

.4 Prepare a summary table of average weekly water usage by various treatments for each soil.

3.1 What would you conclude about the nutrient status of the soils from the statistical analysis of the data?

.2 What laboratory analyses should confirm these conclusions?

.3 Why is lettuce used as an indicator crop? '

.4 Could this particular design be used for a leguminous crop?

.5 Does the Nitrogenous fertilizer offset the affect of higher temperature? Does Nitrogenous fertilizer affect the wet weight/dry weight ratios and the transpiration ratios?

.6 What is the significance of using soil in field condition instead of drying at 70 D C before use?

.7 Is there a relationship between water loss and either solar radiation or relative humidity or soil temperature? Explain the conclusions in terms of the surface energy balance equation .

. 8 Do the visual symptoms of deficiency correlate with vegetative production?

.9 Can visual scoring be developed to replace actual harvesting and weighing of the test plants?

4 Notes

(1) General to illustrate minus technique in field:

A.J. ANDERSON (1946) - Fertilizers in Pasture Development on Peat Soils in the Lower South-East of South Australia. J.C.S.I.R. :uL: 394-405.

or A.J. ANDERSON (1952) - Testing pastures for mineral deficiencies. C.S.I.R.O. Rural Research £.

(2) JENNY, E.A., VLAMIS, J., & MARTIN, W.E. (1950) -Greenhouse Assay of Fertility of California Soils. Hilaardia. 20: 1_

(

G101.10

(3) STEFANSON, R.C. & COLLIS-GEORGE, N. (l974) - The importance of environmental factors in soil fertility assessments. I. Dry matter production. Aust. J. Agric. Res. 25: 299-308.

STEFANSON, R.C. & COLLIS-GEORGE, N. (l974) - The importance of environmental factors in soil fertility assessments. II. Nutrient concentration and uptake. Aust. J. Agric. Res. 25: 309-316.

(4) SPRAGUE, H.B. (1964) - Hunger signs in crops. 3rd edit. Amer. Soc. Agronomy.

(5) WALLACE, T. (1961) - The diagnosis of mineral deficiencies in plants by visual symptoms. H.M.S.O.

1.1

2.1

.2

3.1

II

1.1

6102.1

A COMPARATIVE STUDY OF THREE METHODS FOR DETERMINING THE LIME

REQUIREMENT OF ACID SOILS (Item 1.2 (iiil, p. 1 of E62 A)

"Linear Lime Requirement Method" (fudified)

Procedure:

(1) Weigh the equivalent of 10 g OVen Dry (0.0.) < 2 mm, soil into seven 35 ml centrifuge tubes.

(2) Then add the 1}50 Ca(OH)2 solution and deionized water to the tubes as follows:

Tube No. 1 2 3 4 5 6

ml.deion.HgO 25.0 22.5 20.0 17.5 15.0 10.0

7

5 M

M1.--:'~O Ca(OH) g 0 2.5 5.0 7.5 10.0 15.0 20.0

(3)

(4)

(5)

( 6)

Close each tube with a well fitting.plastic cap and place on shaking wheel for 1 hour.

Standardize the!'l.1s Ca(OH) g by titrating 5 ml 0.1 N Hcl + 100 ml COg free Sater in a 250 ml Erlenmeyer flask using

bromo-cresol green indicator.

Standardize pH meter.

Determine the pH of the soil suspensions after allowing about 5 minutes I settling time.

Construct a plot of suspension pH vs. volume of ~ Ca(OH)g added. 50

Calculate the ';"quivalent quantity"of CaCo, in q, of caC03 per kg 0.0. soil to bring 1 kg of soil to pH 6.~. (Twice the latter quantity is empirically found to be the correct lime requirement for growth of lettuce in the pot trial experiment.)

Would your result have been the same, if you had only'used tube No.s 1 and 6, as in the original linear lime requirement method?

Hutchinson-McLennan Method for Lime Requirement.

Procedure:

(1) Weigh the equivalent of 10 gros 0.0. < 2 mm soil into three 200 ml centrifuge bottles. Add 100 ml of recently filtered Ca(HC03)g, secure the bottles with a firmly fitting cap, and place on shaking wheel for 1 hour.

(The Ca(HC03)g solution is made by slowly bubbling CO2

into a suspension of CaCO in water for 24 hours with occasional stirring to prevent the lime from settling out. Just before using, filter 'only as much 'of the Ca(HCOt)g solution as

* 'required. This solution is unstable and should also be ·standardized immediate Iv before us:j_no_

III

GI02.2·

(2) Fil.ter the 1. hour equilibrated suspensions through a Whatman No. 5 filter paper, discarding the first few rus.

(3) Titrate 50 ml. of the filtrate with 50 m1 of standard O.I. ~ Hel, using bromocres~l green as indicator.

(4) Titrate 50 ml of the original bicarbonate (ca(HCO) } solution in the same way. . 3 2

The difference in titre between (4) and (3) represents the amount ca(IlC0312 that has reacted with the ~+ of the soil. It is equivalent to the ·amount of ea.++ taken up by 5 g-of soil. Explain why ·this is so.

(5) Measure the pH of remainder of Ca(HC03'2 filtrate that is not used in the titration and that of the original. Ca{HC0

3' 2

sol.ution.

2.1 Calculate the lime requirement by the H.M. method in equivalents of caco 3 per kg. of 0.0. soil and in 9 of caco 3 per kg 0.0. soil.

3.1

1.1

Exp1ain why this value is different from the value obtained by the "Linear Lime Requirement Method".

BaCl, - Triethanolamine (pH 8) Method (Modified)

Procedure:

(1) Weigh the equivalent of 10 9" O. D. soil « 2 mm) into three 200 ml centrifuge bottles, add 100 ml of approx. 0.25 -!!BaClZ - 0.055 ~ Triethanolamine pH 8 solution, secure with firmly fitting ca~s, and place on shaker wheel for 3 hours.

(2) Standardize the Baell - TEA solution by titrating 250 mls in a 500 ml Erlenmeyer flask with Standard O. 2 ~ HCl, using 5 drops of the bromocresol green-Methyl red indicator in the 500 ml flask.

(3) After 3 hours, transfer the contents of the centrifuge bottle~ to a filter funnel, fitted with a flutted 11 cm diameter Whatman No. 5 filter paper and collect filtrate in a 250 ml volumetric flask.

(4) Continue washing the soil that has collected on the filter paper by adding small partions of the extracting solution at a time until about 225 IIll of filtrate has bee~--ccliected in ,the 250 IIll volumetric flask. Each portion of the added extracting solution should be allowed to drain before addition of the next portion.

(5) Make-up to volume (250 mls) with the extracting solution. Pour the filtrate into a 500 ml Erlenmeyer flask, add 5 drops of mixed indicator solution, and titrate with 0.2 ~ Hel, as stated in step 2.

(6) Rinse the volumetric flask with some of the titrated solution and complete the titration.

N.B. With some soils the end point will fade (pH increases) upon standing, owing to the slow dissolution of-aluminium hydroxide, but this colour fading should be ignored.

G102.3

2.1 Let B equal the ml. of o. 2 ~ HC]' required to titrate 250 ml. of the original extracting solution and let S equal the ml. of 0.2 M HCl required to titrate 250 ml. of the soil extract, then L the lime requirement in g of caC03/kg.of 0.0 •. ~9tl « 2 1IlIIl) is? --.-.... _- ..

3.1 Compare this value with the values that you obtained in Methods I and II above. What reasons can you give about the different values that are obtained by the three methods. Support your reasons by writing the appropriate chemical reactions for each method .

. 2 A commonly used "rule of thumb 1l is that a hectare furrow slice of 15 em depth is equivalent to approximately 2.2 x 106 kg of 0.0. soil.

What bulk density does this "rule of thumb" assume? Using your own lime requirement values, calculate the metric tonnes of lime per hectare that each method would recommend •

. 3 Noting the fact that you used < 2 mID sieved soil in all of your lime requirement methods I what would the effect of the size fraction > 2 mrn have on your lime requirement value? How would you correct the value that you determined in the laboratory?

.4 Discuss the merits and disadvantages of all three methods. Suggest the circumstances in which you might recommend one method in preference to another.

G103.1

Effect of Consolidation on Emergence

1.1 Use the soil and pots from the pot tri al . . . . . .. x 2 soi ls Remove soil to 4 cm (the original chemical treatment is irrelevant) leaving 5 cm of consolidated soil in each pot.

.2 Sow 10 presoaked (16 hours) wheat per pot on the layer of consolidated soils .

... x 2 varieties

. 3 Cover the seed with a known weight of aggregates x 2 sizes (~ - ~ mm) to form a 5 cm layer.

The aggregates would be wetted by mist· spray and then equilibrated at -100 cm for 16 hours before use .

. 4 The upper layer is then either left loosely packed (estimate the bulk density from the weights in (3) .. x 3 Consolidate every third pot by adding a load equivalent to 1000 g/cm2 for 10 minutes - estimate p.

. 5

Consolidate the remaining third pot by adding a load equivalent to 2000 ·g/cm2 for 1 minute - estimate p.

Dupl i cate each treatment ... plus extra pots without seed to _test for . strength at t = 0 and at emergence, i.e. 4x3 .

. 6 Use torsional shear box to determine shear strength of the surface layers at 2.5 cm depth, at t = 0 and at emergencejduplicated .

. 7 Place all pots in 200c tank .

. 8 Count emergent shoqts daily for 14 days .

60 pots in total

. 9 In laboratory at 200 C -- use tension t~ble at -10 cm to find viability of a batch of both cultivars which have been presoaked for 16 hours.

2.1 Use analysis- of variance if necessary to determine the effect of properties of surface layers (choose one day for analysis).

3.1 Briefly outline the various types of seed bed and/or management practice to which each treatment corresponds .

. 21 Can a preferred management practice be recommended for either soil?

.22 What are the restrictions on its use?

(

•

Determination of Particle Size by Sieve Analysis

G104.1

Di stri buti on ..

1.1 Thoroughly mix the sample of material provided and using a·dry sieving technique determine the particle size distributions of 100 g aliquots. It will be necessary by trial and error to find the range of sieves needed as the vibrator will not accommodate all sieves. (For a soil sampl~ as distinct from a sand, the vibrator will cause breakdown of some aggregate sizes. Sieving· times of 4, 16, 36 minutes should be used and the means of each fraction plotted against the Itime. Extrapolation to zero time will give the original amounts of each aggregate size range.)

.2 Examine specimens of the most frequent sized particles using the binocular microscope. Draw and describe these particles. In particular note:

(1) if axes are of equal length (2) if particles are smooth or angular (3) if regular crystal gr0l1th is detectable (4) if concoidal surfaces are present (5) if the granules are stained, coloured or clean.

2. Present the results as:

.1 histogram showing fraction of sample plotted as a function of particle size range;

.2 cumulative plot showing cumulative fraction of sample as a function of increasing particle size. (Use log scal e for size.)

.3 gravimet~ic weighting of sieve analyses: Sieve Mean si ze Mass on sma 11 er First moment

Openings sieve

>a to a >a a 1.laa

a to b a + b a 2 a + b ·a 2

b to c b + c 2

y b + c

2 'y

c to d c + d 0

2 c + d '0

2

e to etc. ~ m

La = 100 g a Laa aa

1st moment weighted diameter = La" La

.4 coefficient of uniformity:

From plot ~. 2): defi ned as si ze " 60% of fi nes size - 90% of fines (or 10% coarse)

The smaller the number the more uniform the sample.

G104.2

3.1 How reproducible was the sampling technique?

.2 What is the principal source of error in the method?

.3 Calculate the pore entry pressure and the matric potential at which the pores, in a close-packed bed of this material,

_ should fill using the 1st moment weighted diameter. . Identify the assumptions necessary in your calculations .

. 4 What is the probable origin of the specimen as deduced from its appearance? Do you expect the angle of internal friction, $, (see later experiment) to be greater than 300 ?

4. Notes

.1 Dallavale, J.M. 1943. "Micromeritics". Pitman Publ. Corporation, N.Y.).

1A

.1

.2

Variation of Shear Strength of Soils with Moisture Content

. G105.1

A simple experimental apparatus is shown in the accompanying diagram :- constant load - varying ~.

The apparatus is set up so that the matric potential at the plate surface is zero. (In the case of soils that slake or disperse, the initial matric potential should be <-50 cm.)

The cylindrical mould, provided with the equipment, is placed upon the sintered disc and sand or fine soil carefully packed into it. It may be necessary to line the mould with a thin polythene film if the mould cannot be subsequently removed without deforming the sample. It is essential that the same degree of packing, that is the same bulk density, 'be attained in each experiment on the same material. Either overfill the mould or use.an extra length of moulding to help in packing, and consolidate after the sample is wetted by tapping .

. 3 The burette is firstly raised in order to saturate the moulded sample with water, and then lowered in order to impose a matric potential of -10 cm at the surface of the disc .

. 4 The excess soil above the mould is removed, the mould is removed and the first stress experiment can begin .

. 5 Impose a known matric potential say -10 cm on the plate, .allow to 'equilibrate until water movement ceases. The range of ~ used will depend on the moisture characteristic of the sand but at least two values in saturated and two in partly drained soil are required. The pore entry pressure (or grade) of the sintered plate must be greater than the ~ imposed on the sample, but at the same time the hydraulic conductivity of the plate must be large enough to allow re-equilibration of water in the sample when it fails and deforms .

. 6 Carefully place a mass M on a tared aluminium disc on the top of the sample .

. 7 With a minimum of disturbance, increase the matric potential (i.e. as a first approximation relative to the mid-height of the specimen) in approximately 2 cm increments until the matric potential for failure is approached. (This point should be determined approximately in an initial exploratory experiment.) Then proceed in smaller increments until the sample fails. The best procedure for increasing the matric potential is by adding water in approximately 2 ml increments or less, to the burette, from a wash bottle. This avoids the vibration that accompanies the movement of the burette.

(I) record the matric potential at which the sample failed, and (2) the total load M' (=M + tared disc) (3) Note the form of the failure pattern - brittle or multiple

shatter and (4) where possible measure a the angle of the failure plane to

the vertical and (5) height X above the plate corresponding to the mid point of

the failure plane.

\.

G105.2

.8 Remove all the soil from the plate to a tared container and determine- (a) mass of wet soil (Mw + Ms) and after oven drying, (b) mass of oven dry soil Ms. This is needed for calculation of p as well as 6g .

. 9 Repeat the experiment (1.1-1.8) for the load, M, to get a more accurate result in the light of the first experiment .

. 10 Repeat at greater I~I and hence greater load .

. 11 Repeat at a ~ where sample has drained. The ab·ove technique (1.5-1.7) will need modification when the sample has drained under the initial ~:

in this case ~ will be kept constant and the load, M, increased until the sample just fails. This will require several repetitions of the experiment for each ~ to home­in on the correct M. N. B. is taken re 1 ati ve to mi d-hei ght of the

failure plane of the sample.

1B Constant $ -- varying load

A more sophisticated apparatus can be used to study the drained part of the strength curve. In this case a lever with a Mechanical Advantage of 2 is used to load the soil, ~ is kept constant and M, the load, is applied by adding water to the lever. The equipment is particularly useful for drained samples.

1C Routine measurements

(a) Shear Box -- engineering (b) Unconfined compression test (c) Torsional shear box (d) Penetrometer.

See: Soils I E21.

.1 Field samples will be provided .

. 2 Soils samples should be prepared from sieved soil at various 6 and if possible, two values of P. They should be allowed to equilibrate for at least 24 hours before testing. (It is well documented that soil strengthens dn ageing.) The prepared samples will need to be of various sizes to be used with the above equipment.

The results from the various tests should be compared and, in particular, the assumptions inherent in each calculation need. to be noted.

· G105.3

2.1 The effective major principal·stress is

al = ~ + ~I~I + p(l + 6g)(L-X)

where the last term can often be neglected relative to the first term. It is the overburden of the wet soil column acting on the mid-height, X, of the failure plane of the column of length, L. Experimentally the third term =

(L-X) (Mw + Ms) (-L-)· - A

i.e a~ = * + ~I~I + (Mw ; Ms)

(check) .

L-X -C-

.2 The effective Minor principal stress, a; = ~I~I

.3 Analysis of the Mohr circle defines its center as a; + a; and its radius as 2

.4 Calculate al

and a3

for the saturated systems, (~=1),

plot as in 2.3 and from the slope of the common tangent find $ and the intercept, C.

-(a l F = - a3 ) cos $ 2 .5 - A

-N = ( a, of" a 3 ) - (al - a 3) sin $ 2 2

- B

Combination of F and N yields for a cohesionless soil 11 al - a3

sin 4> = = - C 11 + Za3 ai + a3

where 11 is the deviator stress -= al - a 3.

Hence calculate 4> for each trial, find the mean value of 4>

and S.D. Redraw the eye-fitted common tangent of (2.4) using the mean value of $.

From A and B, calculate F and N for the saturated sample. Draw a graph of F vs. N. Give the Coulomb equation, with constants, C and $ appropriate to your soil .

. 6 For the drained samples, fl <1, the deviator stress is known but not a; or a; individually.

. 7

.8

~-'= 11(1 - sin $) However, from C, U3 2 sin 4> - 0

Hence calculate a;, and a; = a3 + 11, for each drained test. From A and B calculate F and N values for each drained test. Superimpose these values on the existing F and N graph for the drained samples.

Calculate ~ for each drained test where fl = a; /I~I. Graph F versus ~ for the complete experimental range .

Graph F versus 6g. (Superimpose ~ vs e on same graph.) (If Moisture Characteristic is availabl~ superimpose this ~~,~+~~~-~~- -,-- \

(

GIOS.4

3.1 Comment on the accuracy and reproducibility of the results from 1A and lB .

. 2 Does the strength of a soil depend directly on its moisture content or on its moisture potential?

.3 Why does a change in bulk density change the F - 8 or F - I~I relationship?

.4 What difference will a change in the angularity or lack of roundness of the soil particles make to the slope of the Coulomb line?

.S If your soil were tested in the field and its matric potential at sampling was -50 cm, what would be "the apparent "cohesion"

. 6

of the soil using the original Coulomb equation in an unconfined compression test? Your argument should consider the difference between internal and external stresses. In the original Coulomb equation, N was for external stresses only, and hence C is an apparent cohesion which varies as T changes.

a is sometimes approximated to Sr the degree of Does this approximation apply to your material? a reason .

saturation . If not suggest

. 7 Which methods in lC have undertain numerical interpretation, when compared with experiments 1A and IB?

.8 Suggest situations when any of the methods in lC would be useful for characterizing field soils.

4 Notes

.1 Collis-George, N. and Williams, J. 196B. Comparison of the effects of soil matric potential and isotropic effective stress on the germination of Lactuca sativa. Aust. J. Soil Res. 7:91-8 .

. 2 Collis-George, N. and Lloyd, Jocelyn E. 1979. The basis for a procedure to specify soil physical properties of a seed bed for wheat. Aust. J. Agric. Res. 30:831-46 .

. 3 Lloyd, Jocelyn E. and Collis-George, N. 1982. A torsional shear box for determining the shear strength of agricultural soils. Aust. J. Soil Res. 20: 203-11.

F C + N

101 • -2

2. = w +

tan ~ o ~1

. GIOS.S

Shear 'strength of Soils

• •

(1)

(2 )

- - -,--- (3)

~(4)

s s

(5)

Mohr-Coulomb Diagram

Cylindrical "brass load of . Mass M

Aluminium disc

Approximate plane, in the cylinder of porous material, about which the inclined failure plane occurs. The matric potential at this plane is r = -h em of water

h em

Free water surface in burette connected through flexible tubing to the sintered glass plate. The burette is free to move vertically so that any arbitrary matric potential (within the

"limits imposed by the mean pore size of the sintered plate) may be imposed

The unit of ern of water =. unit of g/om2

a stress term since density of water is unity

in effective stress units for a "cohesionless soil"

Coulomb equation in applied stress units.

cos rf! Coulomb equation in effective stress units.

~ where • is angle of shear plane.

· Gl06.1

A. SOIL MOISTURE CHARACTERISTIC - THE VACUUM DESICCATOR METHOD

1 .. 1 Weigh a number of containers to 0.001 g. Transfer soil. at sticky point to each of a series' of dry numbered and weighed containers; keep the soll granulated; do not pack tightly into the containers; the thickness of the layer must not exceed Q 5 em Pl.ace each in one of a series of vacuum desiccators he1d at·a constant relative humidity .. (Four relative humidities and duptication is sufficient,. ..

These desiccators, with their complement of soi1, wi11 be evacuated to allow rapid equilibrium of the soil with the controll.ed water vapour pressure. Onder constant temperature conditions, two weeks should be' sufficient for equilibration •

• 2 Open the desiccator, remove each container one at a time and weigh quickly and accurately to 0.001 g. Do not 1eave the soll exposed to the atmosphere before weighing •

• 3 OVen dry, cool in dessicator and weigh to 0.001 g. u woo 0 0 0 a 0 0 0 0 0

2.1 Calculate the water content of each specimen .

. 2 The soil water potential, ~, (in centimeters of water) in equilihrium with a water vapour pressure p is given by the relation

where

plpo

R

relative vapour

gas constant in

pressure at -1 -1

J mol K

temperature TOK.

of water vapour.

g gravitational constant, and

M molecular weight of water_in kg mol -1

In MKS units and at 25 D c

5 -1

k9-JI' = 3.12. x 10 10g10 (p/po) J kg

(1J _ p.2 r.' V20 Note that since p > p,0o/mw~ti be negative, i.e. the free energy is less than thatOof a free pure water surface.

calculate the water potentials equiValent to the relative humidities used .

• 3 Plot the results for this experiment on the Bame graph and

3.1

with the same co-ordinates as the results for "The filter paper equilibration method".

D DOD o 0 0 0

Explain conciselY the theory of the method.

.2 Do you know if the soil has reached equilibrium? How would you test?

.3 Why do you evacuate the desiccator?

.4 What is the approximate moisture potential equivalent to that of that of air dry sail?

.5 What is the advantage of using saturated salts in the presence of solid salt rather than sulphuric acid solutions?

.6 What is the relative vapour pressure in equilibrium with M/20 NaCl?

.7 Why is temperature control important?

.8 Which components of the total potential of the soil water does this method reflect?

(

G106.2

4. A table of some of the more common saturated salt solutions used to obtain constant relative h~dities is presented together with various' concentrations of sulphuric acid us.ed for the same purpose.

Substance

CaClZ .6HzO

Zn(N03JZ6HZO

KZC03 .2HZO

Ca(N03JZ .4Hz O

NaZCrZ07 .2HZO

NH"OH, KN03

NH"Cl

(NH"Jz SO"

KBr

ZnSO" .7HzO

NaZSO" .10HzO

CuSO" • 5HzO

Sulphuric Acid at 20°C

S.G.

1.0

1.1

1.2

1.3

R.H.%

100.0%

93.9

80.5

58.3

Temp

20 QC

20 QC

20 QC

24.SQC

20 QC

20 QC

20°C

20 QC

20 QC

20 QC

20 QC

20 QC

S.G.

1.4

1.5

1.6

1.7

ReI. Humidity

32.3%

42.0%

43.5%

51.0%

52.0%

72.6%

79.5%

81.0%

84.0%

90.0%

93.0%

98.0%

R.H.%

37.1

18.8

8.5

3.2

(

SOIL MOISTURE CHARACTERISTIC Supplementary Exercises

B.. The Eeodoroff Field Capacity Estimation

6106.3

1.1 Fill a tube (10 cm high, diameter 3 em) open at one end and sealed at the other end by a nylon gauze with "fine" earth to a depth of 4 em. To pack homogeneously fill the tube slowly while continually tapping. Stand the tube plus soil in 0.5 em of water and leave until the sample is saturated .

• 2 Remove the tube plus saturated soil from the water. Place it on the topmost surface of soil in a 400 cc beaker containing 150 cc of the same air dry soil. It is essential to ensure that there is a good contact between the soil in the tube and the air dry soil and that this contact is maintained during the experiment .

. 3 Cover the whole apparatus with plastic sheet, to minimize evaporation and also to help wedge the tube upright and leave for 48 hours .

. 4 At the end of 48 hours remove the soil from the tube and determine the moisture content by weighing, oven drying and reweighing.

2.1 Express the results as gIg 0.0. soil and also as glunit volume.

3.1 What is the theoretical basis for Feodoroff's procedure?

.2 Has it proved useful for the range of soils you have worked with?

.3 What values of moisture potential does it appear to equate to?

.4 Would you recommend any change in equilibrium time?

c. The Determination of Wilting Point using the Sunflower Method of Vei hmeyer

1.1 Thoroughly mix the soil at a moisture content of about half the value of field capacity moisture content*. Take duplicate sub-samples to determine the gravimetric moisture content .

. 2 Fill several weighed po1ythene jars with this soil to·within 1 in. of the neck of the jar and weigh. Add sufficient water to raise the soil in the jar ·fo approx. field capacity and plant 5 sunflower seeds (HeLianthus annus drawf var.). Weigh the jar and contents. Place in the greenhouse, leaving the lids off until the seeds have germinated.

.3 After germination, remove all but the best seedling and lead it through the hole in the lid. Allow to grow, irrigate when necessary, until three or four sets of leaves (in addition to the original cotyledons) have developed. At this stage the plant will weigh 2-5 g. Place the container and contents on a balance and add· enough water to bring the gross mass to a value equivalent to field capacity then add approx. 5 g additional to allow for the weight of the plant. Close the lid tightly and pack cotton wool around the stem where it enters the lid. Protect the sides of the jars from the direct rays of the sun •

• 4 After sufficient time has elapsed, the first signs of wilting will appear in the lower leaves and dropping of the next set of leaves will follow rapidly. When all but the upper whorl of small leaves show wilting symptoms, transfer the container and plant to a .darkened humid chamber containing water in the bottom.

Gi06.4

.5 If the plant remains wilted after several hours in the test chamber, the permanent wilting point has been reached. If instead the leaves regain their turgor, remove from the test chamber and wait until wilting symptoms again develop, then test as before •

. 6 When the permanent wilting point has been reached, cut off the stem at the surface of the soil and weigh plant and container separately .

• 7 Then oven dry the jar of soil at 1OSoC and reweigh to find the moisture content of the soil plus roots. Assuming (1

2) that the roots contain 80% water by weight.

( ) the mass of roots equals half the mass of stem plus leaves.

2.1 Calculate the soil moisture content at permanent wilting point.

3.1 What philosophical advantage does the Sun Flower method have over the purely physical procedures for determining Permanent Wilting Percentage?

4 Note

.1 It is conveni ent and introduces 1 ittl e error to negl ect the oven dry wei ght of the roots .

• 2 The number of repl i cati ons necessary for obtai ni ng the desi red precision depends upon a number of factors, including the technique of the operator and the properties of the soil. The standard deviation is generally about 0.4% of the oven dry weight, tending towards lower values for coarse-textured soils and higher values for fine-textured soils .

. 3 *If the soil will not granulate at ~ F. Cap. so that the pots would be filled with a coherent soil mass with little soil air, mix the soil with up to ~ its mass of coarse sand. The calculation of P.W.P. will need to be appropriately rescaled.

(

G106.5

D The Pressure Membrane r~ethod

1.1 Use the pressure plate in exactly the same way as outlined in FlB, for pressures of 1 bar, 3 bars and 10 bars (i.e. 100, 300 and 1000 J kg-I).

Ei Sucti on Pl ate Method

1.la EITHER: Use the plate as outlined in the reference texts listed in FIB to obtain 6g at -1 cm, -50 cm and -100 cm;

.lb OR: Use a sintered plate-hanging column as in the High Energy moisture characteristic G105 at -1 cm, -50 cm and -100 cm;

.lc OR: Use a pressurized sintered plate at -1 cm, -50 cm and -100 cm.

Note: 1.lb or 1.lc are more convenient for a few samples as the water is monitored by outflow and only one set of weighings is needed.

1.la requires weighing at each moisture content but many samples can be equilibrated simultaneously.

GW6.6

F SOIL MOISTURE CHARACTERISTIC COMPOSITE "CURVE.

1. Draw a smooth curve through the points obtained by the various "Soil Moisture Characteristic" methods. . Note the curve .can have alternate X axes 8g or Bvo .

Extend this curve to 10g10 '1-1I: 1 = 7 (pF) noting that pF 7 is the arbitrary value of potential. corresponding to oven dry moisture content. (6g = 0).' Al.so extend into the range of low pF by el} taking the moisture content and appropriate matric potentials measured in the "The -high energy moisture characteristic" experiment whe.t::e available and, (2) by using the results of the bulk density or Hydraulic COnductivity cores to find porosity at ponding and hence theoretical 6g saturation.

2. From this curve redetermine:

.1 The permanent wilting point moisture content •

• 2 The moisture cont~nt corresponding to field capacity •

• 3 The available water expressed as gig oven dry soi1 •

• 4 The avai1able water expressed as inches,of water/inch of soil and em/em.

3.1

Are these values significantly different to the single point values?

Sketch the wetting scanning curve of the moisture character~stic.

.2 To what extent is this curve dominated by the crumb size obtained in the 2 mm fraction?

.3 What is the average relative humidity in agricultural soils to nearest percent? What percentage of all gases present does this represent at 20 D C?

.4 Many plants begin to become inefficient, i.e., Net Photosynthesis decreases relative to transpiration, when water potentials fall to approximately -3 bar. In your soil what percentage of availab1e water is efficiently used?

.5 If the daily evaporation rate is approximately 5 nun what watering regime is needed for a crop with 50 cm rooting range if it is to lie within a -1/3rd to -3 bar moisture potential range1

.6 What parts of the characteristic are dominated by osmotic forces, surface forces and capillary forces for your soil?

.7 Do osmotic effects contribute significantly to the moisture potential at P.W.P. for this soil?

.8 If bulk density is changing with Bg ~ee Soils II F3A, F3B, F3C) sketch on a new .diagram the moisture-air characteristics. (Hint -- At each ~(pF) there is a Bv and an fair -- the sum of these is the total porosity.).

(

GI07.1

THE STABILITY OF SOIL STRUCTURE TO QUICK AND· SLOW W ETING

This method wa~ developed by E.C. Childs (1940), and has been applied (1) to drainage systems which have a short effective l.ife and (2) to reclamation sites particularly where the upper horizons have been stored separately from underlying horizons as we1l as i.n irrigation areas.

Basically the procedure is to compare the moisture characteristic of a completely stable system (quartz sand) with the characteristics

obtained from the soil under study.

An arbitrary granular size (e.g. 3:i-~ rom) is. chosen and used for sand and soil. If the characteristics of soil and sand are similar the soil granules are stable to the wetting procedure under test.

A. The "high energy moisture characteristic of sand"

1.1 Refer to the diagram in Figure 1. for'details of the apparatus referred to in this script.

Before adding sand to the funnel it is convenient but not mandatory to arrange the apparatus. by adding or removing water from the burette and by adjusting the height of the burette, so that:

(i)

(ii) (iii)

(hi - II) H 70 CID

Vi = 40 cm3

1.5 cm approximately (approx) above bench (approx) •

top

Clamp the funnel firmly, do not move until after sand is removed.

2 Measure out 20 crn3 of the sand (~-~ mm) and also weigh it.'

pour this sand into the water in the funnel of the apparatus. carefully tap the funnel to pack and level the sand, and to expel any entrapped air. Adjust the burette so that there is about 2 rom of water standing above the surface of the sand.

Allow the system to reach equilibrium. i.e. for the water levels in the burette and funnel to become equal •

• 3 Record on graph paper, Vl and hI (i.e. the initial equilibrium

.4

values of Vi and hi)' (It will be convenient to allow-in the plot for 15 .. cm3 change of Vi and SO cm change of hi if 1.1 is followed). See Fig. 2 for the suggested layout of. the axes of the graph.

In addition to the concurrent graphing of results as the data is determine~ also produce a table of results and derived results with column headings,

bV M +

(the last two columns are respectively the coordinates 6g T i of the moisture characteristic) •

! and

• 5 Lower the burette 2.5 em. Allow the system to come to static equilibrium again. The levels in the funnel and burette are probably still equal. Record and plot V2 and h2 •

• 6 Continue lowering the burette after equilibration, until the meniscus height is level with the top of the sand, recording V 3, h 3, etc, and plo tting the results.

1.7

G107.2

Then proceed in approximately 3 em increments until h. = 50 em and then in 5 em increments to hi = 20 em = h final.. ~ (These are rel.ative to an initial hi of hi = 70 em)

Plot the equilibrium values of Vi and h{ after each increment4 For ~ - ~ mm sand equilibrium is generally reached in 10 minutes up to hi = 50 em and is generally reached in 20 minu,tes up to hi = 20 em •

• 8 without moving the apparatus, remove a sample of sand and determine its moisture content, egfin~'"

2 It can be assumed that zero matric potential. obtains throughout the sample when the matric potential. at the surface of the sample is zero, i.e. when the free water surface coincides with the surface of the sample.

.1

The following procedure is illustrated on the attached specimen graph Fig. 2.

From the graph determine the height (ha) at which water ceases to be drawn through the sand and the latter is just saturated. (This point is marked by a rapid change in slope see Note 4.1). using this value of ha recalculate the scale of the h axis in terms of matric potential Ti where Ti = -(ho - hi) cm, on the original graph and complete the last column of the table •

• 2 Similarly the value of V corresponding to ho (which we shall designate Vol represents the situation when the sample is saturated with water, but with no free water above the surface and is found from the coordinates of the graph at the point of rapid change of slope •

• 3 Vfinal is the volume of water in the burette corresponding to

.4

. s

the last equilibrium point hf and to 9gfinal. Hence complete the third column of the table but do not calculate V for values greater than Va - Vfinal. This latter volume corresponds to water which was drained from the pares. Water in excess of this was ponded above the sand and is not "soil" water.

Calculate the final moisture content (9gfinal as a percentage of the oven-dry weight •

of the sample

Recalculate the scale of the V axis in terms of 9g, as in the fourth column of the table. This follows from the definition of the moisture content, 9g, that

where 99i is V = Vii and

.Y.i. - Vfinal M

9g. = 99f inal , . +

the moisture content of the sample when M is the total mass of sand.

3.1 Explain the theory of the method •

• 2 What is the effective mean pore radius of the sand?

.3 Sketch the prirM.ry wetting scanning curve of the sand. Assume the sand to be composed of uniform spheres and close packed as in Figures 2.8 and 4.5 of Blake (l967).

GIG7 • 3

3.4 What is the gas pressure (mbars) greater than atmospheric pressure you would haye to impose in a pressure membrane cell to caus-e the most common pore in the sand sample to drain? - known as the pore entry pressure?

4 Notes

.1 The theoretical slopes of the Vi hi results when there is free water above the sample i.e. from VI hI to Va ho is equal to the ratio of the diameters of the burette and the sintered funnel •

. 2 This characteristic curve of the sand is now used as a yardstick to compare .the behaviour of soils of initially the same aggregate size.

Childs produced a second curve, the pore size distribution, by plotting the slope of the characteristic, ~, versus' i [more properly this should be 1 1. . d·'i

'i See Russell, E.W. Soil Conditions and plant Growth, 9th Edn, p427 (Longmans (1961».

de 1 Produce a table of d'i versus 'i .and TL in 5 em steps of 'i'

. de 1 Plot -- vs and identify the matric potential of the most common

dt. " J. * L

pore, "'[ .'. What is its radius.? The dividing head of a drawing board is the mo~t convenient and accurate way to measure slopes. This is now superseded by 4.4 below .

. 3 A common mistake is to ascribe the slope of the characteristic in the region 0 to -5 em Li to pore drainage. Examination-of the relation

'{ = - .15/r

shows that if pores did drain in.this region they would be larger than is possible. II Drainage " in this region is therefore due to structural rearrangements, e.g. repacking, shrinkage, and need not be taken into account when deriving the graph in 4.2

.4 Collis-George, N. and B.S. Figueroa (1984). The use of the high energy moisture characteristic to assess soil stability.

They introduced a definition of Structural Index = ~8/'d as defined by the construction lines on GI07.5

It is not necessary to convert burette readings to 8g or 8v if the same volume of soil/sand is taken in each experiment, as the Structural Index is a relative measurement that allows comparison of soils if experimental conditions are identical. Note the construction lines are approximately parallel to each other and allow for shrinkage as distinct from pore emptying.

l

Fig. 1

...

Burette ,.

Sintered 1:unnel

Sample

Flexible tubing

' .... '" ...... .

High energy moisture characteristic -

sintered funnel technique.

GI07.4

" .., .::,

11

e ~ ..., '" 'tl ..., " W

.r!

" W > " 0 u

'" 0 ..., w > .r! ..., '" .-l W ... ..., -" 0>

.r! W -" ~ ~ u ~

.r! C W e

a • r! ...

( -" .r! .-l . r! ~ 0'

'"

o

'"

N on

'" on

o

'"

GIO?5

EXPERIMENTAL POINTS AND MANIPULATION FOR HIGH ENERGY

MOISTURE CHARACTERISTIC OF SAND.

Moisture content 8g (final) 8g(a)

( determined here (V final h final) Va - Vfinal

• ~ 6V ~ -'-"'---":":==~ + 8g (final) I M

•

• \ • 1\ '"\ I '''.

\ . .~ \ <

\

\

, "-,1tJ ~ k __ .........•...... _ .... _. > \. \'''---. -- \

! -""\. •

= 6V + 8g(final) M

I & M = mass of sand in funnel.

I

~ I

I 7J

\ • \ • .\ I Point (Va, ho)

'\/ ~----_ (V' h'l

'["=0 - 11 ______ • ~ ~ L-----.-----,------.-----.-----r-------~ .~

28

Fig. 2

30 32 34

Equilibrium volume of water in burette (ml) [V iJ

36 38

G1D.7.6

B. COMPARISONS OF SOILS IN TERMS OF SOIL STRUCTUAAL- STABILITY 'TO WATER.

1.1

Q1.2

• 3 +.8

S1.2

The high energy moisture characteristic may be used to describe the pore size ti{stribution of an undisturbed field soil, e.g. in a core or of a bed of soil aggregates of a restricted arbitrary particle size.

It may therefore be used to measure changes in pore size distribution consequent on a particular soil treatment relative to the behaviour of an intert stable rigid material as a standard. (See N. C011is-George and B.S. Figueroa 19B4) •

For each soil prepare two samples of aggregates (Q and 5) of 20 cm3

a.d. soil which lie in the range 1 rom to , rnm.

Weigh each sample.

Quick wetting: - Arrange the apparatus as for the sand experiment, but with a slightly deeper layer of water in the funnel (2.5 cm instead of 1.5 em). Pour in the soil Q making sure the soil granules never build up above the water surface. Very gently level the surface of the soil, do not tap or vibrate. Note the thickness of the sample. If the depth of water is more than 2 rom remove with a pipette.

carry out steps A 1.3 to be much longer than with mount a cardboard slider

1.B as in G10?/1 • The time invervals will the sand. To test if equilihrium is reached, on the burette and check the water level

movement every 10 minutes. Notice if dispersed clay comes through the sintered plate. It may be necessary to run the epxeriment over two days. In which case, use a connecting tube between the burette and funnel to minimise evaporation.

o 0 0 0 0 0 0 0 0 0 0

Slow wetting: arrange the apparatus to meet

(i) (ii) (iii)

(hi - H) H

v. , o - 50 70 em (approx) above bench top 20 em3 (approx)

The funnel is not to be moved until after soil is removed. Dry the inside of the funneL

(i)

(H)

(iii)

(iv)

(v)

Pour the soilS onto the relatively dry plate, level. Note the thickness of the sample. Le.ave for 20 min;

Reduce (hi - H) to -30 em by raising the burette, leave for 10 min.

Reduce (h. - H) to -15 em by raising the burette, , leave for 10 min;

Reduce (hi - H) to -5 em by raising the burette, leave for 10 min. (DO not vibrate the bench or apparatus during this stage or the next one.)

Make the pressure +ve so that there is a layer of water 2 rom thick above the soil, leave for 10 min. The sample is now 'saturated' and has been slowly wetted. Measure its thickness.

.3+ .B Follow the procedure of A1.3 - 1.B in GlO?1. If the structure is stable the drainage characteristic will be produced in 1-2 hours.

Q/S 2

3.1

.2

.3

. 4 (

.5

Notes:

4.1

c· .2

Determine 66 and Td for each system as in A4.4 where 66 is volume of water that drains as distinct from water lost by and Ld is matric potential at which the mean pore drains. the stability index of each soil = 66

Td

G107.7

shrinkage Calculate

Calculate the Stability Ratio for each soil relative to the sand of the same initial sieved size.

o 0 0 0 a 0 0 0 0 0 0 0

Why are sieved soil samples of same size us'ed?

Why is the moisture content of a soil greater than that of the sand at all matric potentials?

Plot the basic moisture characteristics of G107.5 on one graph and using the Stability Ratios from 2 determine if the soil is stable to quick wetting or to standing in water (slow wetting).

Explain why the stability ratio can be greater than unity •

Compare this result with (i) the aggregate' analysis experiment, GIOB.1 (ii) the S.A.R. results, G10B.6

and (iii) the slaking/dispersion test of Emerson (1967) E42 Soil Science I Manual.

What differences to the experimental results would have developed if the funnels are filled with M CaC1

2 instead of distilled water ?

.100

000000000000

Russell, E.W. (1961) - Soil conditions and plant growth. Chap. IX pp427-B (Longmans Green, London) .

Collis-George, N., and B.S. Frgueroa (19B4). Aust. J. Soil Res. 22: 349-56.

No analysis of errors is needed for this set of exercises, as generally the contrast between soils is very marked.

a 0 '0 0 0 0 0 0 0 0 0

(

(

G10B.1

AGGREGATE ANALYSIS

The degree of aggregation is arbitrarily defined by the ratio:

% of of diam. > d which area d o u tlmate partlc es 0

There is no widely adopted arbitrary value for d; in these experiments four. values, 0.002, 0.005,0.02 and 0.3·mm; will be.used.

The extent to which the finer particles of the soil cohere naturally into larger aggregates is important, and affects resistance of the soil to erosion as well as affecting the rate of infiltration of water and the degree of aeration of the soil.

An empirical measure of the degree of aggregation can be obtained by subjecting the soil to a milder dispersion treatment and comparing the particle size distribution with that obtained by mechanical analysis treatment.

Many arbitrary procedures have developed and become standardized against field correlations (N.B. Russel, 1947). In America, there has been a move to standardize on wet sieving techniques (Proc. Soil Sci. Soc. Am. 1951 -Report of Committee). For our purpose it is necessary to emphasize the empirical nature of all procedures and the following techniques (1.1, 1.2) should be compared on soils used in particle size analysis and in quick and slow wetting, high energy moisture characteristics.

1.1 Use, in this ex~eriment, exactly the same mass of oven dry sieved soil as prescribed for the particle size analysis experiment, F2, in the Soils II Practical Manual.

One sawpiemay be brought to an arbitrary moisture content, e.g. -100 cm, before the analysis (discuss this with your demonstrator).

Transfer the appropriate mass of air dry sieved soil to a shaking bottle, add 250 ml of distilled water and shake for one hour on the wheel shaker.

Transfer with a minimum of disturbance to a 500 ml graduated cylinder and make up to the mark with distilled water.

Measure the temperature of the-suspension. Shake by inverting 30x, and using a calibrated soils hydrometer measure the amount of suspended material remaining after 4 min 48 s, 76.8 min and 8 h or at appropriate times for the temperature of the suspension. The readings obtained represent, respectively, the quantities of material finer than 0.02, 0.005 and 0.002 mm found to be 'disaggregated' by this gentle treatment .

. 2 Sieve a second 10 g sample of dry soil through a 0.3 mm sieve, over white paper, in small portions, at a time. Weigh the residue (M2 ) which consists of all particles, ultimate and aggregated, of size >0.3 mm.

The wei ght of aggregate of size >0.3 mm = (M2 - Md g where. Mr is the weight of ultimate particles,>0.3 mm size, found by particle size analysi s.

( ,---

GI08.2

2.1 Express the results obtained in 1.1 as a percent of the hydrometer readings obtained for the size fractions (0.02, 0.005 and 0.002 mm) found by particle size analysis. Calculate the degree of aggregation for the 0.02 and 0.005 mm size fractions and the Ritchie Dispersal Index for the clay fraction .

. 2 Calculate the degree of aggregation for the results obtained in 1.2.

3.1 Why do you work with a sieved soil sample?

.2 Is the soil "stable"? What is meant by the term stable in this context? Compare your ans\~er with Quick and Slow wetting treatment and with the S.A.R. results .

. 3 What effect did the initial moisture content have on the experiment in 1.11 -

.4 \~hat forces effect "disaggregation" in the hydrometer method (1.1) as compared with the dry sieving method (1.2)?

.5 Do the descriptions of aggregation obtained by the various methods agree?

.6 Are the results consistent with the results obtained from:

% Exchangeable Cations, Cation Exchange Capacity, % Organic Matter, Stability to Quick and Slow Wetting, The field profile descriptions of structure.

4.1 Other methods in use are wet and dry sieving but the results are very sensitive to small technique differences. The hydrometer method is. useful in that it identifies stable microaggregates in the 20 to 5 ~m range. The dry sieving technique is useful for identifying air dry macroaggregates that are likely to resist mechanical forces as in wind erosion and cultivation.

GI08.3

PARTICLE SIZE·ANALYSIS

The purpose of this exercise is to provide particle size information for interpreting the results derived from aggregate size analysis, moisture characteristic. plastic limits, etc. and for comparing estimates of the clay fraction by hydrometer and pipetting procedures.

1.1 Follow the procedure of the hydrometer method F2 in the Soils II practical notes .

. 2 Include in your hydrometer measurements a reading at 76.8 mm •

. 3 Following the 8 h hydrometer reading, restir. the suspension and let it stand for an additional 8 h •

. 4 Fit a 10 ml pipette with a cork so that, when the cork is lying flat on the mouth of the cylinder, the tip of the pipette just touches the surface of the suspension. Measure the distance from the cork to the tip of the pipette, then push the latter down so that this distance is increased exactly by 10 em .

. 5 Fill the pipette slowly but steadily and transfer the sample to al preweighed tin, weighed to the nearest ±O.OOOI g. Allow to evaporate in a low temperature oven (70De) or sand bath until almost dry. then oven dry at 1050 C overnight. Cool and reweigh. The weight difference is 1/50th of the clay «0.002 mm) in the original soil sample .

. 6 After sampling. carefully pour away a major portion of the supernatant suspension and follow the decantation procedure for separating the fine and course sand fractions.

2.1 Calculate the suspension concentration in gllitre (R-RL), corrected for temperature at each time of measurement N.B. R = hydrometer reading of the soil suspension.

RL= hydrometer reading of the calgon solution without the soil.

If both Rand RL readings are made at the same temperature, no temperature correction is necessary .

. 2 Calculate sunmation percentage, P%, as percent of original mass of o.d. soil

N.B. %P = 100 CICo where C = R - RL and Co is the original o.d. wei ght of soi 1 .

. 3 Calculate particle diameter, d, in microns at each sampling time from the formula

d = _B_

It where t is in minutes. and

B = 1000[ 30 nh l ~ g(ps - PL) J

where h = distance in cm from the surface of the suspension to the center of the hydrometer bulk, n = the viscosity, Ps = density of the solid and P

L = the density of the liquid .

. 4 An example, illustrating values of a at 300 C,_ is provided in the following table: (where R is hydrometer reading of soil suspension)

R = -5 B = 50.4 ~= -.25 aR R = 10 e = 46.7 ae _ -.28 R = 25 e = 42.5 aR -

R = 40 a = 38.0 ae a]l= -.30

G108.4

2.5 This table, taken from Day or Black, is applicable at 300 C. These values of e must be adjusted by square root of the viscosity~ if the R value was not taken at 300 C. Values of viscosity versus temperature can be found in Tables,' but approximate values are:

Temperature 150 200 250 300 Centigrade Viscosity 1.140 1.005 0.894 0.801 Centipoise

2.6 Express your results in three ways as described in section 2.2 a, band c of F2 in the Soils II Practical Notes, and also compare the triangular plotting method of Toogood (1958) with that of Marshall (1947).

3.1 What are the relative advantages of expressing the results in terms of: (i) U.S. triangular diagram; (ii) Marshall IS triangular diagram;

(iii) Histogram; (iv) Summation curve?

.2 Why are the results from the two procedures (hydrometer and pipette) not identical?

.3 What are the reasons and special c·ircumstances for selecting one procedure in preference to the other?

.4 With what other soil physical and soil chemical characters do these resul ts correlate for the profiles?

.5 What % waterat-15 atmospheres potential would you predict from the clay content? (see Nielsen & Shaw)

.6 What % water at field capacity would you predict from the clay content? (see Burrows & Kirkham)

.7 What pedological processes do the results suggest? Are these consistent with the parent material and other soil forming factors associated with this soil? Refer to Stace et al. and identify the appropriate soil.

4. Notes

Baver, L.D. 1965. "Soil Physics". Wiley, N.Y. Chap. 2. 8urrows, W.C. and Kirkham, O. 1958. Soil Sci. Soc. Am. Proc. 22:103.

Day, P.R. 1956. Soil Sci. Soc. Am. Proc. 2D:168. Marshall, T.J. 1947. C.S.I.R. 8ull. No. 224. Neilsen, O. and Shaw, B.T. 1958. Soil SCi. 86:103. Stace et al. 196B. "Handbook of Australian Soils". Rellim Publ. Co. Adelaide.

Toogood, J.A. 195B. Can. J. Soil Sci. 38:54.

8lack, C.A. 1967.

Loveday, J. (ed.) Comm. No. 54.

Methods of Soil Analysis. Agron. Monograph 9. 1974. Methods for Analysis of Irrigated Soils. Tech. Conmonwealth Agricultural Bureaux Farnham Royal.

, ,

THE RELATION OF SODIUM ADSORPTION RATIO'· AND CATION "EQUIVALENT CONCENTRATION" TO AGGREGATE STABILITY

1.1 Using about 20 9 of the IIfine li earth, preparei (1) a 1/5 soil water suspension and (ii) a saturation mixture as defined by the water content of the upper Plastic Limit, Notice if the soils are either dispersed or flocculated on allowing the 1/5 suspension to sand for lz hour. Filter the 5011 water extract using a macerated filter paper pad and buchner funnel where the sample is dispersed, and by gravity filtration where the sample is coagulated. Some improvisation may be necessary to obtain sufficient extract from the saturation mixture for the subsequent analysis, Analyze the extracts for Na, K, Ca and Mg as per Soils II Manual. N.B. That suppressants will be required for the analysis of Ca and Mg.

2.1 Calculate the r (soluble cation) and the S.A.R. in m-equivalents per litre for each soil water ratio.

Di spersed S.A.R.

Coagul ated Fi g. 1. r Soluble Cations m-equiv 1-1

.2 Given that the slope of the line in Fig. 1 is 4/1 for kaolinite, III for illite and 1/4 for montmorillonite, plot the results for the appropriate clay type (obtained from Cation Exchange Capacity and Mechanical Analysis data).

3.1 Is the soil dispersed in terms of this relationship for 1:5 'extracts?

.2 In what way does the relationship differ for saturation extracts as soil:water ratio changes?

.3 What effect would Organic Matter have on the slope of the relationship S.A.R. vs ~ soluble cations?

PLASTIC LII~ITS

A. Lower Plastic Limit (LPL)

The lower plastic limit is defined as "the lowest moisture content, expressed as a percentage of the weight of the oven-dried soil. at which the soil can be rolled into threads 1/8 inch in diameter without the thread breaking into pieces" -- Atterberg.

1.1 Prepare a stiff paste of the soil, roll a small amount on the glass plate, lightly beneath the fingers. If a long, limp thread is formed, which does not break 'into small pieces, it it too wet. Add more dry soil to the mass and rework until uniformly moist. Retest •

. 2 If it is too dry, it will crumble before threads can be formed. At the required wetness, the slight loss of water on rolling will cause crumbling of the threads. When certain that the whole mass is at this moisture content. detennine the moisture content by weighing and .. oven drying.

(

GI0B.6

B. Upper Plastic Limit (UPL) (or Liquid Limit)

The Upper Plastic Limit is defined as lithe moisture content at which a V-shaped furrow in a cake of soil in a dish will just begin to exhibit flow when sharply jarred by hand" -- Atterberg. (This test as defined does not specify the number or intensity of flows. These requirements have been catered for by a standard but empirical apparatus, Liquid Limit Apparatus, used'by engineers.)

1.1 Thoroughly mix a sample of air dry, fine soil weighing approximately 100 g with distilled water to produce a thick paste •

• 2 Place a portion of this paste in the brass cup of the liquid limit apparatus and level it to a maximum depth of 1 em diameter through the center of the hinge at the same time holding it perpendicular to the cup .

. 3 Turn the crank of the apparatus at the rate of two revolutions per second and count the number of shocks required for the two parts of the sample to come in contact over a length of 1.3 em .

. 4 Remix the soil and repeat the test until two consecutive. tests agree within two shocks .

. 5 Record this number of shocks, and defennine the moisture content of a SUb-sample of the paste.

.6 Bring the paste to a different moistu're content by adding distilled water and repeat the experiment .

. 7 In all, four moisture contents shOUld be chosen which effectively span the interval from 10 to 50 shocks.

2.1 Plot the results as the logarithm of number of shocks against moisture content. a I on semi-log paper. and draw the best fitting line through the points~ The liquid limit is the gravimetric moisture content equivalent to 25 shocks.

3.1 Calculate the plasticity index =UPL - LPL

.2 Activity is defined as plastic~f&y Index

Does this vary down the profile in the same way as aggregation or Ritchie's Dispersal Index?

.3 Refer to the Plasticity Chart and the Unified Soil Classification Chart cited by Ritchie and determine the Soil Group to which your soil belongs.

A Discuss its possible use as an earth dam construction material.

4. Notes

Collis-George, N. and Laryea, K.B. 1972. Aust. J. Soil Res • .!.Q.:15-24.

Collis-George, N. and Smiles, O.E. 1963. J. Soil 5ci.14:21-32. Emerson, W.W. 1967. Aust. J. Soil Res. 5:47-57. Evans, 0.0. 1954. Soil Sci. Soc. Am. Proc.l0:12. Quirk, J.P. and Schofield, R.R. 1955. J. Soil Sci.£.:163-7B.

*Ritchie, J.A. 1963. J. Soil Cons. 5erv.N.5.W. 19:111-29.

Russel, M.B. 1949. Soil Sci.6B:25-35.

*This reference must be stUdied. Ritchie used 2 hours to determine ",,0.002 mm fraction~', presumably following a mistake in the 1958 IVth

Vear Soils Practical Manual which reproduced the original Bouyoucos method.

G109.1

Determination of (1) Solid Density and (2) Bulk Density.and Pore Space Relations of non-swelling soils

I.A To determine true density of soil solids of all materials. See: ES, Soils I .Practical Manual

B The bulk density, solid density and pore space relations

of non-swelling soils:

Weigh 50 g of dry "sand" into a measuring cylinder.

Tap cylinder until the sand attains a minimum volume. Note

this volume.

Pour sand into a beaker. Place 50 ml of water in the

measuring cylinder, add the sand and tap to pack the sand

and to remove air bubbles.

and water.

Note the total volume of sand

2. Calculate:

.l The bulk density of the sand;

.2 The solid density of the sand;

.3 The percentage porosity of the sand;

.4 Estimate mean, s, and cv%.

3.1-ft Discussion and conclusions of ESt Soils I Practical

Manual (4 questions)

.5 Compare the values of the solid density determined by the

two methods .

. 6 Is the porosity consistent with close packing of ultimate

particles?

Close packing of spherical solid particles yields a porosity

of 0.30 whereas open packing has a porosity of 0.476 .

. 7 Ske tch a "shr inkage curve" for this rna terial .

. 8 Calculate the void ratio .

. 9 Comment on the accuracy and reproducibility of the two

procedures.

4. Notes

.1 The bulk density methods and the paste shrinkage

experiment of F3 Soils II practical course should be

consulted .

. 2 Dallavale, J.N. 1943. "Micromeritics". Pitman Publ.

Corp., N.Y .

. 3 The major error is associated with the transference.

a) Use a polythene funnel with a short stem.

b) reuse the relatively clear fluid in the flask several

times if need be, leaving the larger particles in the

flask.

(

(1-)

EXERCISE 2

::J.l AI/f

To determine the air dry moisture content of Boil.

2.2 METHOD

N.H. Experimaut extends ovar 2 clA~5. determination in duplicate.

Carry out the

Take 2 dry aluminium "leighin8' tins with lids and label both with name and duplicate letter (A and B) using felt pen:J with heat-proof ink. 'Haigh tha tins and racord the maximum precision error of the balance (for the t~~,'weighing Mettler balanceB this error has a minimum" valua of ± 0.03 g and applies to every da term­ination). Place about 35 g air, dry «2 mm) soil in each tin aU'd weigh again; record the' error .•

Place in an ove~ at 105°c on the shelf allocated to . your group. After 41? houts cover the 1':1n with the lid. remove from the oven, and place in a.desiccator. When.cool",weigh again and racord the error.

2.3 RESULTS

LAYER NO

Quantity Units A n Precision M Errors ax %,

Haso air dry soil + tin g

Huss oven dry Boil + tin g

HasB tin g

l1:u6 S water lost g

l1a88 oven dry 80il g

Gravimetric moisture content Hg gg-l

(

E2

(ii)

2.4 CALCULATION

A. Errol's

The ruies for calculating maximum and percentage pre­CiBio~ errors are:

(i) When adding or subtrattiiig experimental quantit-ias add maximum pracision errors. Maximum

precision <!rror!l nre 11 charaetaristic of each piece of equip~Dht and arc usually sdecified by the ~anufaeturer8.

Hhen multiplying or dividing experimental quantities add percentage precisioner~ors~

Percentage precision error max. ; precision error-

~ experimental q·uantityX 100

The essence of duplication is that sample A and B be of similar . .size and be treated identically.. It is there­fo-i:~., o':'ly necessary to. calculate errors ior one sample. For si..IJ{plicity percentage errors are recorded .to near­est ~7hole percent. Al'>7ays complete error calculation as tha experiment proceeds. N.B.This method of calculation over estimates the maximum precision error. B. Answers

Calculate the gravimet·ric moisture content

9 g

c Ha Ds ~7ater. Has S ovan dry

aud o-ecord in Table of 2.3

Calculate mean 6 = B

A + B 2

soil

Calculate maximum precision error in Bg ~

+_ %. Precision Error ~ Bg - 100 x

Calc~late practical experimantal error - ± A - B A + B

(

., , .'.~ H':,. :.

--,~, 1 AI [-I

(1.)

IlXRRCISE 5

Datel'minaUOll of -Gl'uail.cnnity of 8Qit 80UdaPD

1.2 N8TEIVD

Iloigh a 400 Dl boaker and placa about 20 B air' dry soil in it and weigh, Il.dd 30 ml water to t.ha ao11 in the henker nnd boil for 2-3 minutoa. Allow to cool.

Fill n 1.00 rol volumetric fl.ask .\11th water to truL gradua tion mark mid 'wai B11 it.. Erop ty the flask', Tranafer nll tho 60il salida to the flaak.

Hake up to the graduation mark. and reweigh.

Rocord thc datn in the. table balowl

S,3 RESULTS:

Prec~Bion

Units t-. B C Max

Haes oI' _b.~nker KaBB o.f b-e'aker +

dry io:Ll ..

HnaE air d'ry soil .

(I,.. 8 a f' 'oven d'ry Boil*

lIa88 11aak + .oil + water

lias s' 'fla8k + water

llas8,of water '-

displaced by aoil "*

'rruo dnnBi ty. 60il Bolida p. ***

* Calculate the mnss of"'ovcn dry 'soil aquivn.1ent to the masu of air dry Boil u8cd in the abova experi~ant,

68 Wfl8 dctermined in Exerciae 2.

II. B • 1 g oven dry Boil - ( 1 + 6g) !l air dry soil

t B air dry Boil a' t dry Boil· • ( 1+6!!)

g ovc.n

"* ***

are defined on the fa llo"ing page. "

or,rare

X

"

.5. ~

£5 .

(U)

** Calcula·te the volume of the Boil solids

mass c·f ,~ater di·spla·ced by· the solids (PR20 " 1).

(mass flask + water) + oven dry mass of ioil used -

(maas fla~k + soil + water)

c

oven dry mas~ soil solids

volume soil solids

The densities of some soil constituents are given belowi'

Soil Con-ati tuen ts

Qu"artz lCandi te Sl!lectite Goethite Hemstite Feldspar Air Soil Organic Hatter

DISCUSSIOH AND CONCLUSIONS

Boi~s1JUd denaity Ps

2.59 - 2.66 2.60 - 2.63

2.80 4.00 - 4.40 4.90 - 5.30

2.56. 0.0012

1. 2 1,5

Comment on the value of the densit~_of soil solids (Ps) of your ~aterial in the light of the abo~e table.

Will the deriGity of soil solids (n ) depend on the tel!lpcirature used to define 8g ovenS dry7 Consider temperatures from BOoC to 300 0 C.

£5 (iii)

Why is the determination of the density of soil solids (ps) carried out?

What conclusions can you dra,~ frota Ps about tha physi.cal properti.eo of your soil?

F3A/2

Pore Relations of.a Core

3.1 Will th'e bulk density of this soil be limiting to plant growth in either moisture state?

3.2 Will the aeration of this soil be limiting in either state? Why?

3.3 Calculate in em the total amount of water, at the time of sampling, contained in the soil layer with which you are working. .

3.4 Compare the 0.1 bar result with the value obtained in F1B.

Notes:

4.1 The main source of error is the contact between the base of sample and the equilibrating potential. The inevitable consequence is to restrict drainage from the sample and give rise to an enhanced ego

4.2· In same situations up to 12 replicates are needed to obtain a reliable estimate of the bulk density which is sensitive not only to sampling procedure but to climatic and management practices.

4.3 If swelling has occurred in 1.4. Comparison of weights gives the propor­tionate swelling.

4.4 ps can be estimated by assuming the mineral sol ids have a density of 2.65gcm-3 and soil organic matter has a density ofl.49cm-3(See Soils r,ES).

hence pS = (100 - (0) x 2.65 + OM x 1.4 9 cm-3

100 100

where OM is % of organic matter oven dry soil as estimated in F4A.

F3A/1 PORE SPACE RELATIONS OF A NATURAL SOIL CORE

Measurements are often carried out on samples which are collected when the 5011 is in "Field Capacity" condition. When this is not possible the samples are examined both in the field condition and after equilibration at 0.1 bar.

• The procedure for the standard determination and calculations is listed in E10 pages (i) and (ii). The fo110wing·modifications should allow field and 0.1 bar conditions to be examined for each core.

*

1.2

If the core of soil in the cylindrical samp1er has not been trimned in the field, trim sharp knife, so that the soil is level with the ends of the tube. N.B. The cores are NORMALLY trimmed in the field and would not be trimmed again in the laboratory. Ensure that all soil in the plastic bag is incl-uded in the analysis. -

Label clearly. Weigh on a K7 balance.

1.3 Fasten a fine nylon gauze around the base of the corer. Place in a dish wi~h a 1 cm layer of water and allow ~o wet for. one day.

1.4 Place either in a Pressure Plate at 0.1 bar or on a suction table. In either case a layer of very fine sand is needed between the sample and the plate/table to ensure good contact.

1.5 Allow to equilibrate for 2 weeks:- this will be carried out by lab. staff. Remove the nylon gauze carefully, and weigh, (retrim if necessary and reweigh

1.6 Remove the trimmed sample of 5011 from the'corer using a spatula and knife. Transfer to a weighed dry beaker •

. Weigh the beaker plus soil.

1. 7 Measure, with calipers, the internal dimensions of the sampler. Each dim­ension should be measured at least twice.

1.8 Dry the soil in' the beaker in a well ventilated oven at lOSoC for 24-48 hrs. Cool in a desiccator, and when cool, weigh the container and oven dry soil.

2 Calculate:

2.1 The gravimetric moisture content, 8g, of the soil core in field condition and at 0.1 bar.

2.2 The bulk density, p, of the soil in both conditions;

2.3 The pore space relations of the soils, in both conditions:

(i) the volumetric moisture content, Bv' where Volume of water

8V = Total volume of soil

(ii) the volumetric content of solid, pIps

JL.. = Volume of 5011 solid Ps Total volume of sOlI

For this calculation use the result of the determination "The Density of Sol1 Solids"ES from Soils I. Failing this,-see Note 4.4.

(iii) the volumetric air content, fair

fair = Volume of air IOtdl volume or soil •

F38/1

PORE SPACE RELATIONSHIPS' OF AN:IRREGUUIRLY SHAPED' AGGREGATE

. '\'lAX' BL8CK 'PROCEDURE

The wax block procedure is primarily used to determine the volume of irregular shaped objects, such as soil ,aggregates and deformed blocks from the shrinkage curve experiment.

l.l Tie a length of thread to the block of soil and ~Ieigh it. Quickly dip this block in wax at a temperature just above the melting point of wax, taking care that the wax is not too hot. The wax covering must be complete so that water cannot enter the block subsequently but neither must the skin of wax be excessively thick. Weigh the wax covered block in air. Hence the mass of ~Iax is known.

N.B. For moist samples from the shrinkage curve experiment it may be necessary to wax the block before tying the thread on. Take the block and quickly dip half in paraffin ~Iax and allow to dry. Holding the waxed half, quickly dip the unwaxed part into the wax. Examine the block to ensure a seal has been made at the wax junction. Tie a length of thread to the waxed block.

2.2 Heigh a beaker of water on a top weighing balance, and then record the weight when the wax covered block is suspended from a fixed support and wholly immersed in the water. By Archimedes' principle, the apparent increase in weight of the beaker of water is equal to the volume of the wax covered bloc k.

2.3 If the soil is not o.d. the moisture content must be determined. Peel off the wax to produce as large a mass of wax free soil as possible. Place the soil in a tared container and weigh.

Over dry and rewe,igh.

2.1 The volume of the block equals the volume of the block plus wax less the volume of the wax. (Assuming the density of wax to be 0.92 g cm-3 and knowing the mass of wax, the volume of wax can be calculated.)

2.2 The moisture content of the original mass in 1.1, so that the mass of water and hence the volume of water in the original aggregate can be calculated.

2.3 Follow the calculations outlined in F3A to find the hence the volume of air in the original aggregate. as the fractional volumetric content of each phase.

vol ume of sol ids and Return the results

3. See F3A.

, 'Notes:

4.1 The wax used is: A mixture of paraffin and moulding wax which, has low shrinkage when solid­ifying.

F3C/1 THE SHRINKAGE CURVE OF A SOIL PASTE·

No soil is completely structure1ess. By convention a soil system which has Noids attributable to the ultimate particle size distribution and riot to aggregate par­ticle size distribution is said to be structure1ess or to have ·on1y a textural porosity as distinct from a structural porosity

1.1 All students working on one layer will corporately carry out this exper­iment. Homogenised soil from each sub site in the layer will be mixed to produce 1500 g of fine soil.

1.2 Prepare a thoroughly mixed soil paste consisting of about 1500 g of xine soil to which is added a known amount of water sufficient· to attain a consistence approximating that of a saturated soil paste*. Lightly grease eight dry, labelled, aluminium weighing tins and weigh them on K7 balance. Transfer the soil paste into these containers, tap them gently to expel air bubbles and strike off the excess paste level with the top of the con­tainer using the back of a spatula. Weigh all containers plus paste plus 1 ids.

1.3 One sample is used to determine the specific volumes of both the saturated paste and the oven dry paste: Immediately after weighing one container of. paste, air dry for several days, follow this by oven drying to constant weight at 1050 C. {This procedure reduces the cracking that is likely to occur if the paste is rapidly oven dried}. The container plus the o.d. soil disc then cooled in a desiccator and we i ghed. The original volume of the paste is equal to the volume of the container. This is determined from measurements of height and diameter, using calipers {at least four readings are required}. The final volume of the oven dry soil block must be determined using calipers or the modified Archimedes' principle described in F3B.·

1.3 The other samples are treated as follows: Drying Technique: It is convenient to plot the shrinkage curve with experimental results spaced. at approximately equal intervals along the moisture content axis. The following method achieves this: The water content initially in each container of the soil paste is approx­imately known from the initial preparation if air dry moisture content is taken into account. Then, for each container, an equilibrium moisture con­tent is calculated so that the several tins produce approximately equal increments of moisture content over the range of moisture contents from saturation to oven dry. [i.e. for 7 there will be eight equal increments of water]. Calculate the changes in weight {container + soil + water} necessary to achieve the required moisture contents. The containers are dried and weighed individually, until they reach a total weight which is consistent with the required change. Once this total weight is reached, further loss of water is prevented by placing the lid on the container. Allow to equilibrate in the closed tin for at least 24 hrs.

1.4 Measurement of. specific volume:

The block of soil will in general, be sufficiently coherent to be removed from the container. The volume is measured either with calipers or by using Archimedes' principle F3B. Note that all wax must be removed from the block before the oven drying pro­cedure if the wax block technique for measurement of volume is adopted.

*Refer to U.S.D.A. Handbook 60. "Diagnosis and improvement of saline and alkaline soils" {1954}, p84.

F3C/2

1.5 The block is then returned to its container., re-weighed, and oven dried to constant· weight at l050 C. Cool the tin and .contents in a desiccator and re-wei gh .

. 2. Calculate for each pair of samples at each stage in the drying sequence:

2.1 the equilibrium moisture content, 6g

2.2 the equilibrium specific volume, lip

2.3 Plot (l/p) versus 6g.

3.1 Does the soil show residual shrinkage?

3.2 At what moisture content does normal shrinkage begin?

3.3 Divide into the three phases. Hence find the pore space relationships at the 6g " "Field Capacity"

3.4 Plot the results for the field core on the same diagram. What is the significance of the core results not being coincident with the paste line? .

3.5 To what other soil properties is the shrinkage curve related?

3.6 How would you determine the shrinkage curve of a field soil in undisturbed condition?

Department of Agricultural Chemistry

& Soil Science

Soil Science 4 (Agriculture) Soil Science 3 (Science)

. M.Agric. in Soil Science

"Advanced'; Soil Methods: Techniques of measurement; how they work; for .what purposes; how they are interpreted.

Aim: To provide an appreciation of a selected number of glass~ouse - . laboratory - and field techniques that are frequently used In certaIn specialized - and applied areas of soils research.

Lectures

Physical Methods

ASSESSMENT

Practical reports Examination

40% 60%

2/3 Particle size analysis (PSA) of the clay fraction and fractionation by centrifugation techniques.

4/5 Specific surface area measurements by N 2, H20 vapour., ethylene glycol (EG) and ethyieneglycol monoethylether O;:GME).

6/7 Thermocouple vs. tensiometric methods for field measurements of soil water potentials.

9/10 Gamma-neutron probe methods for measuring soil moisture content and bulk density in the field.

11/12 Thermal conductivity and time domain reflectometry (TOR) methods for monitoring soil moisture content in the field.

Physical (Chemical Methods

13/14 Measurement of redox potentials, Oz diffusion rates (ODR) and Oz/COz concentrations in soil media.

15/16 Selective ion electrodes for measurements of ion activities in soil solutions.

Mechanical Methods

17/18 Mechankal measurements of soil properties: Atterberg limits unconfined compression; compaction, oedometer and penetrometer tests.

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