Western Kentucky UniversityTopSCHOLAR®

Masters Theses & Specialist Projects Graduate School

1977

Movement of Soil Nitrate Through a PembrokeSoil as Affected by Tillage Method and Time ofNitrogen ApplicationNoel T. Johnston

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Recommended CitationJohnston, Noel T., "Movement of Soil Nitrate Through a Pembroke Soil as Affected by Tillage Method and Time of NitrogenApplication" (1977). Masters Theses & Specialist Projects. Paper 1718.http://digitalcommons.wku.edu/theses/1718

MOVEMENT OF SOIL NITRATE THROUGH A PEMBROKE SOIL AS AFFECTED BY TILLAGE METHOD AND

TIME OF NITROGEN APPLICATION

A Thesis PreSented to the

FaCUlty of the Department of Agricul ture Western Kentucky University

BOwling Grep- , Kentucky

In Partial Fulfillment of the Requirements for the Degree

Master of Science

by

Noe l T. Johnston 1977

MOVEMENT OF SOIL NITRATE l 'HROUGH A PEMBROKE SOIL AS AFFECTED BY TILLAGE METHOD AND

TIME OP NITROGEN APPLICATION

Approved:

Approved :

AC KNOWLEDGEMENTS

The authoc wishe s t o expr ess his sincere apprecia ­

tion to the following:

Dr . Ray Johnson f or his inspiration , assistance,

and valuable counselling during the course of study and for

his aid in the preparation of this thesis.

Dr . Willia m H. Stroube, Dr . Wilbert C. No rmand, and

Dr . Elmer Gray for their assistance and cOoperation during

this study and for their critical r ~adin9 of this manuscript.

Dh. Robert Blevins and Dr. Grant Thomas (Un iversity

of Kentucky) for their assistance with the study,

Mr . James A. Lowe for his assistance on obtaining

and analyzing the data . ,

Special thanks are extended t o my wife , Ca r olyn , for

her understanding, patience, and encou ragement during the

entir e Course o f s tudy .

iii

TABLE OP CONTENTS

ACKNOWLEDGEMENTS iii . . . . . . .

Chapter

I INTRODUCTION . . 1

II REVIEW or LITERATURE

Nitrogen Conversions . 3 Time ~f Application 6 Movement of Nitrate Through the Soil

Pro file 8 Effect of Tillage Practices on Ni trate

Movement . . 10

III MATERIALS AND METHODS.

Pield Studies . Laboratory Studies. Statistical Analysis.

11 15 16

IV RESULTS AND DISCUSSION .

Conventional Tillage versus No - Tillage. 17 Soil Moisture . . . . . 17 Soil Nitrate Levels. . . 27

Time of Nit r ogen Application. 27 Soil Moisture 27 Soil Nitrate Levels . 33

V CORN YIELDS 38

SUMMARY 40

iv

TABLES

1. The Detailed Description of the Pembroke So il Series Used in this Study . . . . . . .

2 . The Effect of Time of Nitrogen Application and Tillage Method on Corn Yields (k/ h)

v

12

39

FIGURES

1. Rainfall Data Collected At Bowling Green Airport From January To June For 1971. 18

2 . Rainfal l Data Collected At Bowling Green Airport From June Thro ugh October For 1971. 19

3. Mois ture Comparison At The 0-15 Centimeter Depth Over Several Sampling Dates For Conventional Tillage And No-tillage Practices. . 20

4. Moisture Comparison At The 15-30 Centimeter Depth Over Several Sampling Dates For Conventional Tillage And No-tillage Practices . . . . . . 22

5 . Moisture Comparison At The 30-60 Centimeter Depth Over Several Sampling Dates For Conventional Tillage And N~ ~ illage Practices . . . . .. 23

6. Moisture Comparison At The 60-90 Centimeter Depth Over Several Sampling Dates For Conventional Tillage And No- tillage Practices . . . .. 25

7. Comparison Of Moisture And No-tillage Over Dates .. .

Between Conventional Tillage All Depths For Several Sampling

8. Comparison Of Nit rate Concentrations Between Conven­tional Tillage And No-tillage Fo r The 0-15 Centi­meter Depth And 15-30 Centimeter Depth Over Several

26

Sampling Dates. . . . .. ........ 28

9. Comparison o f Nitrate Concentrations Between Conven­tional Tillage And No-tillage For The 30-60 Centi-meter Depth Over Several Sampling Dates . . 29

10. Comparison Of Soil Moisture Between Different Da tes Of Application For The 0-15 Centimeter Depth And 15-30 Centimeter Depth Over Several Sampling Dates. 30

11 . Comparison Of Soil Moisture At Different Dates Of Application For The 30-60 Centimeter Depth And 60- 90 Centimeter Depth Over Several Sampling Dates. 31

vi

FIGURES--Continued

12 . Comparison Of Nitrate Concentrations Between Dif ­ferent Fertilizer Application Date s At The 0-15 Centimeter Depth Over Several Sampling Dates . 34

13. Comparison Of Nitrate Concentrations Between Dif­ferent Fertilizer Application Dates At The 15-30 Centimeter Depth Over Seve ral Sampling Dates .. 36

vii

CHAPTER I

INTRODUCT I ON

Of al l the plant nutrients , nitrogen has been

subjected t o t he most extensive study . The amount of

inorganic nitrogen in the soi l is small while the quan t ity

needed annually by c~ops is compa~atively la~ge . Of t he

macronutr ients usually applied in comme rcial fertilizers ,

nitrogen seems to have the q u ickest and most pronounced

effect on plant g ~owth .

I n applying a nitrc~en fertilizer fo r crop us e ,

one must be concerned with placement, form, and availability,

and with keep ing the fe~tilize~ whe~e it is placed throughout

the c ritica l pa rt o f t he q rowinq season. The nitrogen supply

mo lded by non-leguminous 91ants is of ext r eme importance and

its avai l abi lity is complicated by the fact that nitrogen in

soi l s is easi l y conve rted into forms which are more o r less

mobi l e and avai l able .

The time of applicatlon of nitrogen fertilizer can

signi fi ca ntly affect its availability . It commonly is appl i ed

in e ithe r the spring o r fall i n r ow c r op cultur e . Under our

climatic conditions , nitrogen applied in t he fall tends to

be los t by denltrification and l each ing over the winter

period, and the practice is not economical. The re are also

1

2

disadvantages associated with sprinq application of nitrogen.

Application is needed at a time when the farme r is extremely

busy and whe re the soil may be too wet to support the appli­

cation equipment.

No - tillage farming , wh ich is relative ly new , apparently

increases the rate of nitrogen movement through the soil pro­

fil e . No-tillage r esults in a mulch of dead plant materia l

on th e surface . The mulch tends to keep more moisture in the

soi l. This extra moisture can be benefic ia l to the crop but

it also permits the nit rogen t o move mo re rapidl y through the

soil.

The present study was initiated t o study the effects

of tillage practice and time of nit ~en application o n the

movement of nitrate thro ugh a Pembroke silt loam soil . This

soil is typical of tr.e well-draine d limestone soils found in

Southern Kentucky.

CHAPTER II

REVIEW OF LITERATURE

Nitrogen Conversions

In a ll soils there is considerabl e gain and loss o f

nitrogen in the course of a year. Th e sour ce of nitrogen

in a r a ble soils 1S derived from such material s as commercia l

fertilizer , c r op res "dues, g r een and farm manur es , and

ammonium and nit r ate sal ts brought down by precipitation.

In a dditio n the fixat ' o n of atmosphe r ic nit r o ae n by certa in

microrgan isms living o n soil o r ganic matter o r on the roots

o f l eg umes accounts fo r significant additions o f nitrogen

t o the s oi l. Ni trogen l oss is due to c r op r emoval, leaching ,

e r osion , and t he escape of gaseous nitrogen ( 4 ).

The mechanism by which simple o r ganic nitrogen com­

pounds a r e changed t o fo r ms that r esist breakdown is still

not c l ea rl y understood . Immobilized nitrogen in the microbal

tissue becomes an integr al pa rt of the soil organic matter.

In t his o r ganic form , it is slowly mine ralized into compounds

which can be used by higher p l ants (4 ).

The gener al t e rm "mine r alization" cover s a series of

r e actions. As a r esult of enzymatic di ges tion t he more c om­

p lex prote ins and a llied compounds are simplifed and hydro­

lized. The e nd p roduct, NH3 is formed by the bacte rial

3

4

enzymatic p rocess of mineralization (4):

R - NH2 + HOH e n zymic R - OH + NH) + ene r gy hyd r olys1S

Mi ne r alization p r oceeds most rapid l y in well-drained ae r ated

soils . The fate of ammoni c al nitrogen is fourfold (2 4 ) :

1 . Consider able amounts are appropriated by o r ganisms capable of using ammonium forms of nitrogen.

2. lIigher p lant s can use the ammonium form of nitrogen .

3. Ammonium ions are subj e ct to fixation by some of t he clay minerals and organic matte r. Thi s is especially true o f clays with e x pand ing l attices .

4. After plant and animal syntheses ace t e mporaril y sa ti sf i ed , the remaining ammonium nil r ogen may be o xid ized to nitrate by ce r tain spec ial-purpose bacte r ia.

The biological oxidation of ammonia to nitrate is

known as nitrification . Nitrification is a two step process

by which ammonia is first converted t o n it r ite (N02

- ) then

to the nit r ate (NO)-) fo r m. Conversion to n i trite LS brought

about by obligate autot r oohic bacte ri a of the genus Ni troso-

monas. The r eac tion can be r epr esented by ( 4 ):

The conve r sion f r om nitrit e to nitrate is affected primarily

by obligate autotrop1c bacteria termed ~itrobacter. This

reaction represents the change from nitrite to nitrate .

From the standpoint of soil fertilization, the NH 4+ N02

and NO) ion forms are o f greatest importance. The ammonium,

nitrite, and nIt r ate fora. arlse fro the nor..l •• robic

decompoSltlon of 80il orqanlc -atter or fro. Addltlon of

commerclal fertlllzers (4).

SOlIs dlffer . n thelr capaClty to nitrlfy added

ammonium co~pound.. Factors that .ay be responslble for

varlation are:

1. Presence of dlffer~nt .'ze populatlons of nitrlfu.rs ( 4).

2. SolI aereatl0n - The nltrODacterla are obll­qate autotrophlc aerobes. T ey 111 not pro­duce nItrates In the Abaence o f -alecular oxyqen. S011s that are coarse-teKtured or po.se •• good structure 4Cllltste a rapld exchanqe of qaaes ~nd .ns~re An Adequate sup­ply of oxygen tor the nltrobacterla.

1. 5011 -alsture - T e nltrobacterl. are ~r. sensltive to excess ~J.tuz. than 0 dry .011 conditions.

4. The relatlonshlp bet en nltrlflc tlon and 8011 teaperature has be n studled for 10ft9 tl Win er t-.perature aus' be 1 to prevent nltriflCatlon of the ad d ..anlua nIt r n oc the nltrate nltrogen 111 be 10 t by erOSlO percolatlon, Or 1 achln be o re lt 18 8 by the crop une foIl Inq y ac .

The catIonIC nature of H · ~r.lt. Ita .b Orptlon

and retentlon by sOil collolds. It ls q ner lly not as

sub ) ct to reaoval by leachlnq as 1. the nltrate foea . If

condItIon. tor nItrIfIcatIon are unf.vor.bl.~ ..-onlua oltro-

gen aay be retaln d In sOlis for long perlods of tla..

sOli. of tlne texture WIthout appreclable 10 •• by leachlng

o 0 where teaperatures re841n below)1 - 40 r (9).

6

The presence of nitrogen in the cationic form, how­

ever , does not insure against loss by leaching . The soil

must have a sufficiently high exchange capacity to retain

the added ammonium nitrogen or it will be removed by perco­

la~ing water (9).

Time of Application

The literature concerning time of application of

nit rogen indicates that fall-appli ed nitrogen has resulted

in a lower g ra in yield of corn that that obtained from

spring applications. Pearson (21) working with seve ral soil

textures in Alabama, Georg1a , and Mississippi , found that

~ i trogen broadcasted in o vember or December was 49 percent

less effective in increasing corn yie lds than the corres­

ponding sprinq applications . In t e rms of nitrogen r ecover ed

the relative effectiveness was 62 percent.

It is believed that den i trificat ion may be the most

plausible explanation for the low efficiency of fall-a pp lled

nitrogen compa r ed t o spring applied nitrogen. In r ecent

studies Anderson (1) concluded that nitrification can occur

at an appreciable rate at temperatures only a few degrees

above freezing. Thus, fall applications of nitrogen f e rt i ­

li zer, even if it was added in the ammonium form, would be

susceptible to denitrificatio n.

Soils can become waterlogged during the winter r e ­

sulting in denitrification of the nitrate nitrogen . However,

denitrification can occur under well-aerated soil conditions

7

whe r e o r ganic materials a r e under going rapid d ecompoSi t ion ,

and the micr o-environment of the bacteria may become

essentially anaerobic. This condition r esults from the i n­

c r eased biological oxygen demand in the soil (1).

There are some soils f or which fall application of

nitrogen de f initely i s not recommended. These include all

sandy soils and soils which are unf r ozen throughout much of

the winter. In these soils excessive leaching of fall-appli ed

nit rogen wi l l OCCur. Also, nit rogen should not be fall-appli ed

on any soil which tends to be poorly drained. On wate r - l ogged

soils muen of the nitrate nitrogen 15 los t by denitrification

occurring within two o r three days af ter application (25).

~ ~lications of nitrate fe r til izers in the fall or

winter are likely to r e sult i n movement and l eaching of the

nitr ate . This leaching is related to the fact that in winter

there is extensive water movement t h rough the soil unless th e

soil is frozen. Several expe r l ments have shown that COver

c r ops will g reatly re duce the amoun t o f nitrate l eachi ng

du r ing winter month s (23). The cover crop r e duces the loss

of nitrate by absorbing the ion and by r emoving water from the

soil.

Agronomists have concluded that for cer tain areas of

the country the economic loss f rom a fall application o f

nitrogen mo r e than offsets its advantages and , therefor e ,

recomme nd t hat it not be applied in the fall (6).

8

Movement of Nitrate Through the Soil Profile

With increasing use of nitrogen fertilizers, there

a r e greater losses due to leaching; and it becomes more

important to determine the magnitude of leaching losses so

that nitrates may be more effectively managed. There are

many factors involved in the movement and leaching of nitrate

in the soil (2).

Leaching and movement of nitrate are dependent upon

the rate and amoun t of precipi t ation and upon the soil

moisture characteri s tics . Nitrate is highly s oluble in water

and does not form insoluble compounds with t he 50 11 consti ­

tuents nor does it adhere to the surface of the soil. Thus,

nitrates ar e r eadily transported by the soil water movements

(7, 13).

Rainfall, in an amount sufficient to cause water to

percolate through the soil p rofil e, will gradually remove

nitrates from th e topsoil . The depth which nitrate l eac hes

depends upon the amount and rate o f water passing through

the soi l profile. As a result of large amounts of water pe r­

colating through the soil , there are high accumulations of

nitrate in the subsoil at depths of 1, 2 , or 3 feet and eve n

down to 5 f e et (5 , 18).

Loss of nitrate by leaching depends upon the water

holding capacity and the moisture content of the soil at the

time precipitation occurs. Once soil water intake exceeds

field capacity . downward movement and leaching occur at a

high r ate. However , leaching is retarded, to an extent, when

9

soil water is below field capacity (2 , 3, 5 , 7 , 12 , 16 , 18).

As the upper layers of the soil dry, there is

appreciable upwa r d moveme nt of soil water fro m the subsoil.

Thi s upward movement is due t o capilla r y action , which also

moves nitrate from the subsoil t o t he root zone and even to

th e soi l surface . As soi l water moves upward and is l ost

by e vaporation , nitrates tend to accumulate at the surface of

the soil (2, 3) .

Lysime t e r stud 'es , often used to measure amounts and

rates of nitrate movement , continua ll y emphasize t he importance

of soi l texture a nd porosity o n t he amoun t and rate of nitrate

l eachi ng . Texture and porosity a r e determined by t te various

soil t ypes (sand , loam , c ay , etc . ) and much researc h work

has e mphasized the a ffec t s o f varying soil textural types on

nitrate l eaching. In a compa ri son of three soil types, it

was f o und that the greatest l eaching losses occurred from a

sandy l oam soil , l ess from a medium clay l oam, and the sma l lest

l oss was from the c lay loam (3) . In each study coa r se r -textured

sandy so il s resulted in highe r amounts of nitrate leaching than

all othe r fine r textur e d soil ty ~es . Bates and Tisdale found

tha t downward moving nitrates were concentrated in the subsoil

of a silt l o am and often we r e returned to the surface by

cap illary wate r s in the summer . They also found that a deep

c lay loam subsoi l markedly reta rded the movement of nitrates

from a clay l oam soi l ( 3) .

10

Effect of Tillage Practices o n Nitrate Movement

It has been well es t ablished that tillage increases

evaporation of soil moisture and thus inc r eases the rate of

soil drying . It also is an unquestioned fact that the pri­

~ary pu r pose of a soil mulch is to reduce evaporation (6).

The p r actice of no-ti llage farming, which is the

plantinq o f seed in a micro-seedbed, created with a minimum

of soil disturbance minimizes the soil moistu r e loss. That

is, tillage is eliminated and a mulch is left on the surface.

The additional moisture under no -t illage c o nditions thus re­

sults in faster movement of t he nitrogen through the soil in

periods of relatively heavy r a! nfall (1 , 23). Ma ny field

st- Ales have been conducted b y the University Agricultural

Experiment Station under Kentuc ky farm conditions to deter­

mine the needs and the extent of any needs for primary

nutrients. About 56-112 (K/ H) of nitrogen is recommended

for conventional - tillage on a well-drained soil. The

r ecommended rate f o r no-tillage on a well-draine d s oi l i s

112-140 (K/ H) of nitrogen . This me thod o f plant i ng is so

new that only time and further rese arch will show the e ffects

of soil, texture , porosity and other properties on the rate s

of nit rate movement unde r these conditions.

CHAPTER III

MAT~RIALS AND METHODS

Field Studies

In January 1971, an experiment was initiated on the

Western Kentucky University Farm to study nitrate leaching

as a function of time of application and method of tillage.

Pembroke silt loam, which is a ty?ical upland limestone­

derived soil in this area, was used for the study. A detailed

description of the Pembroke series is give~ in Table t.

Th e experimental area was divided into four replica­

tions. Each r eplica tion was divided in to three treatments.

The treatments were: (1) nitrate application in the fall ,

( 2) nitrate application in the spring, or (3) no nitrate

application. Each of these t r eatments was furthe r divided

into conventional tillage and no-tillage treatments.

Soil samples were taken from each plot at twelve

diffe r ent dates beginning March 18 and continuing through

October 5 . The samples were taken at four differe nt depths:

0-15 centimeters. 15-30 centimeters, 30-60 centimeters, and

60-90 cen timeters. On each date, three samples at each depth

were taken for e ach plot and combined for further analysis.

These samples were used to dete rmine moisture and movement

of nitrogen through the soil profile .

11

12

Table I

The Detailed Description of the Pembroke Soil Series Used in This Study (1 7 )

The Pembroke series is a member of the fire-silty, mixed,

thermic family of Molli c Paleudalfs. The se soils have

dark brown silt loam A horizons and red silty clay loam

B2t horizons that g rade to dark red silty clay C horizons.

Typifying Pedon:

Ap 0-9"

Blt 9-1""

B2lt -- 16-33"

B22t -- 33-4S"

B23t -- 4S-7S"

Pembroke Silt Loam - Cultivated (Color for moist soil)

Dark brown (7 . SYR 3/ 2) silt loam; weak to moderate fine granular structure: very friable; many roots: neutral; clear smooth boundary. (6 to 14 inches thick)

Reddish-brown (SY R 4/ 4 ) to yellowish-red (SYR 4/6 ) silty c lay loam; weak fine subangular blocky structure ; friable; many roots: few Clay films; common very small black concretions; slightly acid; gradual smooth boundary. (J to 12 inches thick)

Red (2.SYR 4/ 6) silty clay loam; moderate medium subang ular blocky structure: friable; common roots; common clay films: common very small black conc retions; medium acid: gradual smooth boundary. (12 to 22 inches thick)

Dark red (2.SYR 3/6) heavy silty clay l oam: moderate medium subanqular blocky structure: friable: few roo ts: common clay films; common black sta1ns on peds; common black conc r etions; few small chert fragments; strongly acid: gradual smooth boundary. (10 to 2S inches thick)

Dark red (2 . SYR-IOR 3/6) silty clay; moderate medium blocky structure; firm: common clay films; common black stains on peds; common black concretions; few small chert fragments; strongly acid; gradual wavy boundary. (17 to 3S inches thick)

C -- 7 5-1 08"

R -- 108"

Type Location:

13

Dark red (2 . 5YR-10R 3/6) silty clay, common medium distinct variegations o f strong brown (7.5YR 5/ 6) and light brownish-gray (lOYR 6/ 2); weak coarse angular blocky structure; very firm , sticky, plasti c ; few black concretions; f ew small chert fragments; very strongly acid. (12 to 15 inches thick )

Limestone.

Warren County , Ken t ucky; along U. S . High­wa y 31, 10 miles south of Bowling Green.

1 4

Initially the e xperimental area was c o ve red with

ba r ley , which se rve d as a winte r cov e r c r op . The barley

wa s kille d by spr ayi ng with Pa r aq ua t (2 pt/ A) on May 4.

On Ma y 11 t he dead material was chopped up with a r o t a r y

mo we r. Late r , o n May 22 , the conventional - ti ll e d p l o ts we r e

worked wi th a heavy d i sk to l oosen the soil and i ncor porate

the r e sidue s . On May 23 , Sl lA , an F- 2 cross wh i t e corn

hy b rid , was p l a nted. The conven tional l y t i l led p l o t s we r e

sprayed with a t r ~ z ine and a l ach l os , whi l e the no - ti l l age

p l o t s we r e spr ayed with Pa r aqua t (1 - 2 p t / A) and atrazine

(4- 6 pt / A) a t r ecommended rates.

Sod i um n itrate was th e source of nitr cgen fe r tilizer

used . It wa s b r oadcast applie d at t he r ate o f 168 kilograms

pe r hec t a r e . The f all applica t ion was made on Jan uar y 6 and

t he sp r i ng appl ica t ion o n May 25. (The t e r m "fall" is used

i n t hi s thesis for c o nvenience and in keeping with the li tera-

t ure re po rts o n t imes of fe r ti l izer app l ica tion . ' Po t ssium

K20 a t a r a t e o f 11 2 ki l og r ams pe r hecta r e a nd phospho r us at

the r ate of 11 2 ki l ogr ams P205

pe r hecta r e we r e added t o all

o f t he p l o t s on this da t e .

Weed cont ro l was effected during the summer months

by the use of he r bicides , cu l tivat ion , and r e mova l by hand.

Weeds were cont r o lled on the c o nventional - tilled plot s by

me an s of tracto r c u l t iva t ion and the chemica l a trazine .

Paraq ua t and l as s o , a t recomme nded r a t es , we r e used t o Con­

trol weed s o n the no -tillage plots . The johnsong ra ss was

r e move d by hand from bo th conve ntional t i l l age and no- t illage

15

p l o t s . The her bicides used in this expe r iment seemed to

have very little effect on johnsongrass and only moderate

control was obtained with hand weedinq.

The corn was harvested on Oc tobe r 25 for yie ld

determination by taking a 6 met e r section ou t of the middle

two rows o f 8 row plots . Moi sture was determined using a

Model ReT Steinlite electronic moisture tester and y ields

were expressed at a constant moisture level of 15. 5 pe rcent.

Laboratory Studies

The soil samples take n were used t o determine mois ture

content and moveme nt o f nitrogen th r ough the soil p r ofi le.

Mo s t of these samples were taken after rainf a l l amounts of

one inch or greater. The se samples were take~ to the lab and

weighed . They we re then placed in an oven and allowed to dry

for 24 hours at a temperature of 10 5 C and reweighed. The

difference in the two weights was t he soil moisture conten t.

A sub-sample of each dried soil s ampl e was then used

for nitrate determination. Th e t esting instrument used was

a Model 401 Orion S peci fic Ion Meter . Two e l ect r odes wer e

connected t o the ion meter, a ni tra te ion electrode and a

r eference electrode. These electrodes w~ re placed in a nitro­

gen solution and pa r ts per millio n o f nitrate we r e read

directl y on the meter . The meter was calibrated us ing pure

solutions of sodium nitrate of known concentrations. A

soil sampl e s u spension was formed by adding 20 g rams of the

sample to 40 ml. of water. The suspension was placed on a

1 6

s ha ker and al l owed t o shake fo r 15 minu t es . Af t e r the sus ­

pension was a llowed to se t for 10 minutes , the liquid po r­

t i o n was r e moved and tested. Parts per million of nitrate

we re read direc tly f rom the me t e r after placing e l ect rodes

in the liquid.

Stati s tical Ana l ys is

The data were analyzed t o de t e rmine tre atme nt dif ­

fere nces and in t e rac tio ns . A split - split - pl o t arrangement o f

trea tme nts wa s used t o s tudy nitrogen data t o dete r mine

differences in nitrate movement through the so il profile at

d iffe ren t application dates . An F-Tes t and analys is o f

variance we r e u sed to de ' ~ rmine significance . The main plots

nitroge n treatme nts and control. The split p l ots were con ­

ve ntional till age versus no -tillage . The split-split-p1ots

used we re soil depths (0 -15 centimeter s , 15-30 centimers,

30-60 centimeters , 60 - 9 0 centime ters . )

CHAPTER I V

RESULTS AND DISCUSSION

conventional Tillage Versus No-Tillage

Soil Moisture

Rainfall data collec t ed at the Bowling Green Airport

are given in Figure~ 1 and 2.

Soil moisture data at the 0-15 centimeter l eve l on

the various sampling dates from March to October are given in

Figure 3 . The comparison between conventional t . llage and

no-tillage began on June 14, which was the firs t sampling

date after tillage and planting. The moisture was probably

just below field capacity on March 1, but there was a signifi ­

cant increase in soil moisture on March 18, as a result of the

increased rainfall at this time. Moisture was above normal

from June 14 until October due to the high amounts of rainfall

during these months. The rainfall was 4.06 inches in June.

7.66 inches in July , a nd 7 . 71 inches in August. The moisture

was somewhat lowe r on June 14 due to the low amounts of rain­

fall prior to thi s sampling date (see Figure 2) and evapora­

tion from the exposed soil surface .

The no-tillage plots wer e consistently higher in soil

moisture than the conventionally tilled plots . The presence

of the killed bar l ey mulch on soil surface in the no-tillage

plots presumably caused this difference. However, the

17

" o

3 . 5

3.0

.-< ... 2.5 .. ... . -< 0-.-< 2.0 u CIl ... Ilo 1.5 Ul CIl ., U " 1.0 H

.5

Jan 1 Feb 1 Mar 1 Apr 1 Months

May 1 June 1

Figure 1. Rainfall Data collected At Bowling Green Airport from January to June for 1971.

3.5

c o ...

3 . 0

~ 2.5 :l ... no ';j 2.0 Q)

'" n. <Il 1. 5 Q) ., u ~ 1.0

. 5

· ·

· ·

I Jl \1 I. -.-

June 1 July 1

. \1 i I II. I •

Aug 1 Sept 1 Months

I L I

Oct 1

figure 2. Rainfall Data collected At Bowling Green Airport from June Through October for 1971.

<> N

36

34 ., '" 32 .. .. " ., 30 0 ... ., .,. 28 ., ... " 26 .. Ul .... ~ 24

... .... 22 0

til

20

18

MaY 1

T _ conventional Tillage NT - No- Tillage

..:-~-:-~-;-;-,-~-~----------------------

June 1 July 1 ~ug 1 Sept 1 Oc t 1

NT

T

Figure 3. Moisture comparison ~t The 0- 15 Centimeter Depth over Several Sampling oates For conventional Tillage ~d No-tillage practices.

Mar 1 ~pr 1 Months

21

moisture level in this surface layer was relatively high

on all sampling per iods because each sampling date was

intentionally chosen two or three days af t e r rainfall amounts

of one inch o r greater had occurred. Therefore , any signi ­

ficant differences in soil moisture l evels resulting from

t illage practices should be mor e evident below the 15 centi ­

mete r dep th .

Moisture percentage of the soil at the 15-30 centi ­

meter depth is gi v en by Figure 4. The moisture content was

r ather high and the trends a r e similar to those found in the

0-1 5 centimeter l ayer as pr eviously shown. The greatest

difference b~tween ti llage treat~ents was obtaine d at the

last samp l ing date which, as indica t ed in Figure ~ , was the

only extended dry period durinq the entire g rowing season.

This is an indication of the advantage that would be expected

in moistur e conservation wi th no-tillage in a -normal - or dry

g r owi ng s easo n.

It is generally agreed among soil scientists that

soil cover ed with dead s a d will have a g reater infiltration

over a growing s e ason than the same soil a ft e r normal p l o wing

and cultiva t ion. The p resence o f the undisturbed bu t deca)~ng

plant roots in the soil and old root channels may serve as a

r eady avenue f or water infiltration into th e soil . Th1S

e nables the soil to store more water following appreciable

rainfa ll .

Moisture content of the 30-60 cent ime ter layer i3

shown in Figure 5. At this depth there was less difference

N N

35 34 33

.. 32 ",31 .. ., 3D

" .. 29 ~ 28 ..

Q, 27 .. 26 ~ 25 ., <1124

~ ~~ :: 21 ~ 20

19 18

Mar 1 Apr 1 May 1

T - Conventional Ti llage NT - NO-Tillage

-- --- NT -----_T June 1 July 1

Months Aug 1 Sept 1 Oct 1

Figure 4. Moisture Comparison At The 15-30 Centimeter Depth Over Several Sampling Dates For Conventional and No-tillage Practices.

,., '"

32

31 ~ 30

'" ... 29 c

28 .. u

27 ... .. 26 0.. .. 25 ...

::J 24 ... U) 23 0-< 0 22 :>:

21 .-< 0-< 20 0

'" 19 18

Mar 1 Apr 1 May 1

T -NT -

June 1 July 1 ~!onth s

Conventional NO- Tillage

._- ----_.

Aug 1

Tillage

, NT ,

..... _--_._---_. T

Sept 1 oct 1

Figure 5. Moisture Comparison At The 30- 60 Cent imete r Depth Ove r Several Sampling Dates Fo r Conventional T i llage And No-tillage Practices .

24

betwee n the conventional and no - tillage plots than was

evident at s hal l owe r depths . No- tillage plots were about

. 1 to . 2 % higher in moisture than the conven tional til l age

plots . This is consistent with other findings such as

those of Blev i ns and Coo k (6) and is a p robable indication

of minimal e v aporation from this depth.

Moistur e content at the 60 - 90 centimete r layer is

given by Figur e 6. The differe nces at this depth were small

and inco nsistent. Th e results obtained on August 14 cannot

readil y be e xplained a ~d are not consistent with comparative

results for this date a t the other depths. Beyond 60 centi­

meters , systems of tillage seemed to have llttl e ef f ec t on

moistu r e as evidenced ~y this study .

A comparison between no - tillage and conventional

til l age over all depths is given by Figure 7. The no-t i llage

plots were consistently about .6 t o .7 % highe r in moisture

througho ut the growing season. This aqrees with experiments

conducted by others such as Thomas (23) and Ble vins and Cook

(6) at the University of Kentucky.

The conservati on o f moisture under no-tillage c ropping

is assoc iated with soil conditions that maintain good surface

in filtration throughout the cropping season, r eduction i n

evaporation du e to the su rfa ce mulch a nd the absorptive pro­

perties of the decaying roots and surface mulch . This pr ovides

a g reater rese rv ior of soil moistur e in the major plant

r ooting zone , as previous l y indicated . The advantages for

no - ti l lage wou l d l i ke l y ha v e been g r eater in a drier season.

OIl N

.. '" .. ... c: .. u ... .. a. .. ... ::J ... U) ... 0 :.:

.... ... 0 til

32 31 30

29 28 27 26 25 24 23 22

21 20 19 18

Mar 1 Apr 1 May 1

T - Conventional Tillage NT - No-Tillage

'.-

June 1 July 1 Aug 1 Sept 1 Months Oct 1

T NT

Figur e 6. Moisture Comparison At The 60-90 Centimeter Depth Ove r Seve ral Sampling Dates For Conventional Tillage And No-tillage Practice s .

'" N

24 T-Conventional Tillage

NT-NO-Tillage OJ 23

'" '" ., / "' ... - - _ ....... c , 22 , OJ , ..... ~ . u ,

" , OJ , , , , , 0. 21 ,

, NT , , OJ

" , -- ---, .--" ., 20 .,

T .... 0 :.:

.-< 19 .... 0

U)

18

17

June 1 July 1 AU3 1 Se pt 1 Oct 1 M nths Figure 7. Comparison Of Moisture Between Conventional Tillage And No-tillage Over All De pths For Several Sampl ing Dates .

27

Soil Nit rate Levels

Figure 8 presents the nitrate data comparison be­

tween conventional tillage and no-tillage practices at the

0-15 centimeters and 15-30 centime t e rs depths.

The ni t rate levels in the 30 - 60 centimeter and

60-90 centimeter soil layers are given in Figure 9 . There

is little or no evidence of any nitrate accumulation in

either of these layers at any sampling date.

The data show the nitrate levels to be about the

same at harvest time regardless of tillage methods. Most

of the nitrate is conce ntrated in the 0-30 centimeter por ­

tion of the soil and this amount was very smal l when compa r ed

to the original applic ~ ion of 168 kilograms of nitrate

nitr ogen.

Overall there was very little difference in nitrate

distribution in the soil profile as a result of tillage

method. On all dates except July 7, th e re was no s ignificant

difference between tillage methods. This could have resulted

from the high rainfall during the summer months causing

nitrate to l each out of the soil profile or from loss by

denitrification dur ing periods when the sojl was water saturated.

Since the soil was near field capacity during the entire

growing season , the nitrate would have moved at a pproximately

the same rate r ega rdless of tillage method.

Time of Nitrogen Application

Soil Moisture

A comparison of moisture at different fertilizer

application times is shown in Figures 10 and 11 . The soil

70

60

" '" '" 50 0 ... .., "., z 40

M 0 Z

:>: 30 Q. Q.

20

10

" '" 30 " 0 ... '" "., 20 z M

0 z 10 :>: Q. Q.

June 1

:

, I

I I

, I ,

" I •

28

T - Conventional Tillage NT - No-Tillage

I • 0-15 centimeter depth I •

•

• • • I

• • I

I I I I • \ ....... -

", , -'- .. .. '"

July 1 Aug 1 Sept 1 Oct 1 Months

1 5-30 centimeter d epth

.'_'_-- -- ' -------... .. .. ... ~- T " .' "'····--'---~T - ' ... '

J une 1 July 1 Aug 1 Sept 1 Oct 1

NT T

!'Iontha Figure 8. Comparison of N~trate Concentrations Be tween Con-

vention 1 Tillage and No-tillage For The 0-15 Centimeter Depth and 15-30 Centimeter Depth Over Several Sampllng Dates

c

" '" 0

" .oJ 0.., z

"" 0 z :E 0.. 0..

c

"

30

20

10

'" 30 o " .oJ

0.., z 20

"" o z :E 0.. 0..

10

June 1

June 1

----- - .~ ,

July 1

,

July 1

29

T - Conventional Tillage NT - NO-Tillage

30-60 centimeter depth

---'---

Aug 1 M<.-n ths

Sept 1

___ r_ .NT

Oct 1

60-9 0 centimeter depth

c" _c--- ______________ .~T Aug 1 Months

Sept 1 Oct 1

Figure 9 . Comparison Of Nitrate Concentrations Between Conventional Tillage And No-tillage For The 30-60 Centimeter Depth And The 60-70 Centimeter Depth Over Several Sampling Dates

30

0-15 centimeter depth

III 22 '" '" ., .-c , , III 21 , -0 , ;K "

, , III , '" ,

20 ,

III ,

" .' " ., '" 19 .... .-1 0 --:0: ,,-

.-< 18 .... 0

'" )7

June 1 July 1 Aug 1 Sept 1 Oct 1 Months

23

15-30 centimeter depth III 22 '" '" , ., , , c , III 21 , 0 , " III 0.

III 20 , " ,

\ " ;.; ., '" 19

\~ .... 0 :0:

.... 18 .... 0

'" 17

June 1 July 1 Aug 1 Sept 1 Oct 1 Months

Figure 10. Comparison Of Soil Moisture Between Different Dates Of App1~cation For The 0-15 Centimeter Depth And 15-30 Centimeter Depth Over Several Sampling Dates

., 23

'" '" ., c 22 ., 0 .. ., '" 21 ., .. " ., 20 III .... 0 :.: .... 19 .... 0 til

18

17

June 1

24

23 ., '" '" .,

22 c ., 0 .. .,

21 '" ., .. " 20 ., III .... 0 :.:

19 .... .... 0 til

18

17 June 1

• • I

/ • •

Ju l y

July 1

1

--

Aug 1 Months

\ \

\ '.-

Aug 1 Months

31

30-60 centimeter depth

--' F ~ ----- 0 '. ---\ -- S

Sept 1 Oct 1

60-90 centimeter depth

F -- -- --\ ~. - - - - - s

\ ___ --- 0

Sept 1 Oct 1

Figure 11. Compar ison Of Soil Moi s ture At Different Dates Of Applicat i on For The 30-60 Centimeter Depth And 60-90 Centime t er Depth Over Severa l Sampling Dates

32

moisture level was consistently higher in the upper 0-15

centimeter layer in the plots that had received a fall appli­

cation of nitrate as compared to the spring application

anc check plots. The one exception was on J~ly 21 when the

soil moisture l eve l was slightly higher in the plots that

received nitrate application in the spring_ One explanation

is that the barley growth was greater on the plots receiving

a fal l application of nitrogen and acted as a better mulch

where the nitrogen was applied in the spring or where none

was applied. Th e same type results occurred in the 15-30

centimeter layer probably for t he same r eason . The additio nal

moisture in the plots receiv ing a fall application of nitr ogen

was especially evident late in le season at this soil d e pth.

The re was e ssentially no difference between tillage

methods at the 30-90 centimeter depth because thi s moisture

apparently was not affected by crop use or was not sUbject to

drying conditions. Howeve r, there was a general trend of

decreasing soil moisture from the first to the last sampling

period in both the 30-60 centimeter and the 60 -9 0 centimeter

d epths . The moisture levels were higher at the 30-60 cen t i ­

me t e r depth than 0-30 centimete~ layer . One reason for th e

difference is the highe r clay content at the lower depths.

The fact that these areas show very little c hange in

moisture l eve ls at the 30-90 centimeter depths is a good in­

dication that moisture was not limiting growth , since

moisture at this d epth would not be replinished by low amounts

of r ainfa ll throughout the year as would moisture in the

0-15 centimeter l ayer.

33

Soil Nitrate Leve ls

The data presented in thi s section are averages of

the two t i llage methods use d. Nitrate levels were dete r­

mined to a depth of 90 cen timete rs but significant amounts

of nitrate were found o nly in the ~-15 centim~ters and 15-

30 centimeters layers. Therefore , on l y the results from

the upper two sampling depths wi l l be presented in this sec­

tion. A comparison o f soil nitrate levels at different dates

of application in the 0-15 cen timete r laye r of the soil pro­

file is shown by Figure 12. It will be noted that most of

the fall-appli e d nitrogen had moved out of this layer by

Ma r c h 18. Undoubtedly , part of this nitro gen lost j uring

this relative l y s hort tim period in late winte r was much

too great to be accounted for by this mechan i sm. The r emain ­

ing nitrate must have been l ost from the soil either by

denitrification o r l eaching. There was a buildup of nitrate

in this layer again in June and J uly which probably r esulted

from mi ne ralization o f the barley residue. There was mor e

mineralization on th e plots that rece ived a fall application

of nitrogen. This would be expe cted as a result of more

growth and n i trogen uptake by the barley from t he fall

fe rtili zation .

There was a l a rge decrease in spring-a pplied nitrate

from July 7 to July 21 in the uppe r layer. Some of this was

take n up by the corn crop, but a l arge part was probably

moving on through the sailor lost by den i trification as pr e ­

viously suggested for the fall-applied nitrate. The nitrate

70

66 62 58 54

0:: 50 ~ 46

e 42 .!: 38 Z 36 ..,32 ~ 28 >: 24

'" 2 '" 16

12

Jan 1 Fe b 1 Mar 1 Apr 1 May 1 June 1 Months

S - Sprinq-applied nitrate F - Fall-applied nitrate o - No n i trate applied

I I

I

I

I I

I I

I

~ I I

I

I I

_---- -- ------- S

J ul y 1 Aug 1 Sept 1 Oct 1

Figure 1 2 . Compa r ison of Ni tra t e Concentr ation s Between Di ffere nt Fertil izer App l ication Dates At The 0 +1 5 Cen timeter Depth Ove r Seve r al Sampling Da t es .

35

level remained at approximately 10 ppm through the growing

season from the spring application, but the soil nitrate

l e vel was very low from the fall applicatio n and , in f act,

was very close to the nitrate leve l in th e check plots.

A comparison of nitrate leve ls f o r diffe rent da tes

of applicat i o n at the 15-30 centimeter layer of the soil

profile is p rese nted in Figure 13. Th e s e results indicate

a buildup o f nitrate during February, whi ch result~d from

the large amount l o st from the 0-1 5 cen time ter laye r at t he

same time . The nitrate level i n s oi l r eceiving ni tra t e in

the f a ll i s essentially no differen t than that o f the check

plots th rough the r e mainder of the growing s eason . Tne

nitra ~ l evel where applied in the spring is somewhat higher

throughout t he growing season , bu t this r e su l ts from movement

from the 0-15 c e ntime ter layer . Mos t of the nitrate was

contained in the 0-30 c e nt i meter portion o f the soi l . There

was not enough nitrate in the 30 - 90 centimeter layers to be

detecte d. As a result , those data a re no t p r esente d.

From Figur es 1 2 and 13, it is evident that the nitrate

a ppli ed in the fall had d isappea r e d fr om the sampled so il

profil e by March 18 . Undo ubtedly, some o f t he nitrate was

taken up by the barley cover crop, but most of it was probably

lost by denitrification. Chances of leaching we r e very

s mall because the nitrate was not found in the l o wer layers

of the soil . From the March 18 r esults, it wo uld appear that

the o nly nitrate available from the fall application for c r op

'" M

c:

40

35

30

III 25 8' " ., .... 20 z

M o Z 15 :E .. ..

10

5

Jan 1

S - Spring-applied nitrate F - Fall- applied nitrate o - No nitrate applied

--""\ ... -- \

\ \ ---- .. , ,--

\ ",/" , , \ ,,, '

-- --- -~ --~ S

L ______ -:-_, --. ------ ------------ --. ---

~~ \ ... ' /" ,

, F ,-- ------________ 0

Aug 1 Sept 1 Oct 1 July 1 Fe b 1 Mar 1 Apr 1 May 1 June 1

Months

Figure 13. Comparison Of Nitrate Concentrations Be tween Different Fertilizer Application Dates At The 15-30 Centimeter Depth Over Seve ral Sampling Dates.

37

use was that which resulted from mineralization in June.

However, there was some spring-applied nitrate still present

at bo th sampling depths throughout the season and , therefore,

presumably available for plant use.

At all dates, the nitrate levels from the spring

application were significantly higher at the . 05 level of

significance as compared to fall application. As previously

stated in this section , this difference was primarily a

result of the large losses of nitrate from the sampled profile

from the fall application treatments prior to the time of

spring applicat ion of nitrate.

CHAPTER V

CORN YIELDS

Table 2 contains corn yield data obtained from the

experimenta l a r ea. The yields were low when compared to

the average yields obtained in Southern Kentucky . There was

also no significant differe nce in yields as a result of nitro­

gen applicatio ns. There we re several possible reasons f or the

low yields. The seed used was a low yielding white corn,

and there was a heavy infestation of ~ ~hnsongrass in the plots.

The European corn borer also caused considerable damage. At

any rate , nitrogen apparently was not a limiting factor for

corn production and it cannot be determined from these results

whether much of the fertilizer-applied nitrogen was absorbed

by th e corn crop . Also, there was no advantage to the no­

tillage system under conditions for this one year. However,

with a higher producing variety of corn and lower precipita­

tion , yield differenc es as a result of these management prac­

tices might have been evident.

38

TABLE 2

The Effe ct of Time of Nitroge n Application and Tillage Methods on Co rn Yields (kilograms / hec tare )

Time of Tillage Replicatio ns Overall Applica tion Method 1 2 3 4 Average

Fall Conventional 3425 3737 4257 4124 3886 No-Tillage 4185 3681 4047 3816 3933

Spring Conventional 4491 3768 3871 3583 3928 No-Tillage 4691 3130 3092 3371 3571

Zero Conventional 3496 3612 4445 3859 3853 No-Tillage 2854 3761 3782 3157 3372

SUMMARY

The r e was no supportive e vidence o f NO) leaching

through the soil pr ofile beyond the 30 centimeter depth , at

the same time there was ver y little NO) - l e ft in the soil

at the e nd of th e gr owing season. Unde r cond itions found

at the exper i menta l site with a g rowinq crop and this level

of NO) applica t ion , l eac hing losses did not seem to be a

pr obl e m.

Ther e was no difference in th e NO) under differen t

ti llage conditions . Possibly the .• igh r ainfall accounted

for this, since the so il r e mained near field capacity through­

out the gr o wing season . Under high moisture condition the

NO)- seemed to move at appr oximately th e same rate under both

conventional tillage and no - tillage condition s .

The r e was a significant difference found in NO) at

the differe nt application dates. Most of the fall applied

N0 3- was gone by Ma r c h 18. This was p r obably a r esult of

de nitrification or leaching . There was a large drop jn

spring applied N0 3 from July 7 to July 21. Some was p r obably

removed by the co r n crop but some was also lost by leaching

and denitrificatio n. There was very little available NO)­

r ema ining in the plo s that had received a fall application

o f nitrate as compared to the spring application and check

40

41

plots for plant growth. The plots that had received a

spring application of nitrate contained available NO) ­

for plant growth.

There was very little differ ence in moisture when

compared at different application d3tes . But there was a

difference in moisture between conventional tillage and

no-tillage . The no-tillage trea tment was higher because of

the mulch cover which held the moisture better.

The re was no significant difference in corn yields .

The yields were v e ry low, a probable result of johnsongrass

competition, an infes tation of the European corn borer, and

a low y i e lding variety 5llA white corn.

BIBLIOGRAPHY

1. Anderson , O.E. , L.S. Jones , F.C. Boswell . 1970 . Soil Temperature and Source of Nitrogen in Relation to Nitr ification in Sodded and Cultivated Soils. Agron. Journal. 62 : 206 - 211.

2 . Bartholomew , W. V. and F.E. Clark . 1965. Soil Nitrogen.

3.

4 .

Amer . Soc. Agron. Madison, Wisconsin. pp. 555-606.

Bates , T.E. and S.L. Nitrate Nitrogen Soil Mate rials. 525- 528.

Tisdale . 1957 . The Movement of Through Columns of Coarse Textured Soil Sci. Soc. Amer . P r oc. 21:

Bear , F.E. 1965. "Chemistry Of the Soil." 2nd ed. Reinhold Publishing Corporation , New York. pp. 133, 214-2 71.

5. Black , C . A. 1964 . "Soil-Plant Relationsh~p .· 3rd ed . John Wi ley & Sons , New York. pp. 205- 208.

6. Blevins, R.L . and Doyle COO~. No Tillage, Its Influence on Soil Moisture and Soil Temperature. Progress Report 187. University of Kentucky, College of Agriculture , Agricultural Experiment Station , Lexington . pp. 5-14.

7. Boswell , F.C. and O.E . Anderson. May 1964. Nitrogen Movement in Undisturbed Profiles of Fallowed Soils. Agron. Journal . 56 : 271 - 281.

8.

9 .

Bredakis, E.J. and J . E. Steckel. Nitrogen From Soils Incubated lizers. Agron. Journal. 55:

March 1963 . Leachable With Turfgrass Ferti-

145-147.

Buckman, H. O. and N.C. Brady. 1 969. "The Nature and The Macmillan Properties of Soils ." Seventh ed.

Company , New York. pp. 437-450.

10. Harding, R.B., T.W . Emblito n, W. W. Jones , and T.M. Ryan. Nov. 1963. Leaching a nd Gaseous Losses of Nitrogen From Some Non Tilled California Soils. Agron. Jou r nal. 55: 51 5-518 .

42

43

11. Jones, R.J. 1942. Nitrogen Losses From Alabama Soils in Lysimeters Influenced by Various Sys tems of Green Manure Crop Management. Agron. Journal.

1 2 .

34: 574 -585.

Krantz , B.A. and G. D. Nitrogen in Soils. 189-195 .

Scarseth. 1944. Movement of Soil Sci. Soc . Amer. Proc . 8:

13. Kurtz, L.T., L . D. Owens and R. D. Houck . Sept. 1960. Influence of Moisture on the Effectiveness of Winter Applied Nitrogen Fert i lizers. Soil Sci . Soc. Amer. Proc. 25 : 40-43.

14. Lime and Fert i li zer Re comme ndat ions . 1976. University of Kentucky. AGR-1 -7.

15. Mahendroppa, M.K . 1969. Dete ~mination of Nitrate Nitr o­gen in the Soil Extracts Using a Specific Ion Activity Electrode. Soil Sc i . 108: 132-1 36.

16 . Matthews, E.D. 1947 . Effect of Drcught and Rainfall o n Movement o f Soil Nitrogen in Cecil Soils. Georgia Exper. Station, Circular 137.

17. Na t ional Cooperat ive Soil Survey Profile Description.

18 . Norman , A.G. 1966. Press, New York..

"Advances in Ag ronomy." 19: 239-253 .

Academic

19. No-Tillage Recommendations . 1976. University of Kentucky.

20 . Olsen , R.J., R. F. Hensler , O.J . At toe, S.A. Witzel and L.A . Peterson. 1970. Fertilizer Nitrogen and Crop Rotation i n Relation to Movement of Nitrate Nitrogen Through Soil Profiles . Soil Sci . Soc. Amer. Proc. 34: 448-4 52 .

21 . Pearson , R.W. , H. V. Jordan , D.L . Be nnett, C . F. Scarsbrook, W.E. Adams , and A.W. White. 1961 . Residual Effects of Fall and Spring Applied Nitrogen Fertilizers on Crop Yields in the Southeastern United States. USDA Tech. Bull. 1 25 4.

22 . Stevenson , C.K ., C .S. Baldwin. May-June 1969. Effect of Time and Method of Nitrogen Application and Source of Nitrogen o n the Yield a nd Nitrogen Content of Corn (Zea Ma ys L.) Agroll. Journal. 61: 381-384.

23. Thoma s , G.W . July 1970 . Sources, Levels , and Availa­bility of Nitrogen in Soils . USDA 27th Southern Pasture and Forage Crop Improvement Conference , Agr. Research Service. CR-6 2- 70 .

Tisdale, S.L. and W.L . Nelson. and Fertilizers." 3rd ed. New York . pp. 5] -148 .

44

1960. "Soil Fertility The Macmillan Company,

Walsh, L.M. Sept. 1970. Let's Take Another Look at Fall Fertilizing. Crops and Soils . pp. 8- 9.