Soil & Tillage Research, 4 (1984) 199--213 199 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

E F F E C T OF I N D U C E D C O M P A C T I O N BY W H E E L T R A F F I C ON S O I L P H Y S I C A L P R O P E R T I E S A N D Y I E L D O F M A I Z E IN R O M A N I A

ANDREI CANARACHE', IULIU COLIBAS 2, MARIA COLIBAS 2, ION HOROBEANU 3, VIORICA PATRU 4, HORIA SIMOTA 4 and THEODOR TRANDAFIRESCU'

'Research Institute of Soil Science and Agrochemistry, Bd. M~r~ti 61, Bucharest 71331 (Romania) 2Agricultural Research Station, Calea Aradului 5, Oradea 3700 (Bihor County) (Romania) 3Agricultural Research Station, Albota 0310 (Arges County) (Romania) 4Research Station for Irrigated Crops, Valul lui Traian 8763 (Constanta County) (Romania)

(Accepted 26 July 1983)

ABSTRACT

Canarache, A., Coliba~, I., Coliba~, M., Horobeanu, I., P~Itru, V., Simota, H. and Tranda- firescu, T., 1984. Effect of induced compaction by wheel traffic on soil physical properties and yield of maize in Romania. Soil Tillage Res., 4: 199--213.

Results of field experiments with soil compaction induced by wheel traffic applied uniformly to cover the entire surface of the experimental plots are reported. Compaction was done immediately before sowing, and each year, in each location, the same treat- ments were repeated on the same plots. The number of tractor passes varied between 0 and 30. The experiments were conducted during the 1978--1981 period in four locations with different soil and climatic conditions.

Changes in soil physical properties, as well as in the yield of maize grain, were shown to be related to the number of tractor passes according to regression formulae of the type: Y = a X b. Most of the changes were recorded between 0 and 8--10 passes, while with more than 15--20 passes changes became negligible. The average maximum increase in bulk density was 20--25% as compared with the non-compacted control plot, and the average maximum decrease in yield was 46%. Moisture content in the compacted plots was 2--3% (w/w) lower than in the control plot, except for the soils with poor drainage where the lower part of the compacted topsoil showed an increase in moisture content. Air content in the compacted plots often dropped below 10, and occasionally to nearly 0% (v/v). For three of the four locations, grain yield of maize linearly decreased by 13 kg ha-' (or 0.18% of the control plot yield) for each 1 kg m -3 increase in bulk densi- ty.

INTRODUCTION

In the last f i f ty years , i.e. since agr icul tura l m e c h a n i z a t i o n s t a r t ed to ex- pand , the adverse e f fec t s o f soil c o m p a c t i o n b y f ield t raf f ic on soil p rope r - ties and yie lds have been ex tens ive ly s tudied in m a n y countr ies . I t will

0167-1987/84/$03.00 © 1984 Elsevier Science Publishers B.V.

200

suffice to quote here the reviews on this subject by Barnes et al. {1971), Chancellor {1977), and Soane et al. (1981a, 1981b, 1982). Most of the published papers refer to a particular field experiment and, consequently, a comparison of results under various soil conditions is difficult.

In Romania, earlier pot experiments with various bulk densities, and moisture and air contents, for different soils, crops and fertilizer treatments, have helped in finding the general trends of compact ion effects on soil properties and yields (Canarache and Thaler, 1962; Canarache and Vintil~l, 1962; Canarache and Berindei, 1972). Berindei et al. {1968) carried out field experiments with potatoes, showing traffic effects on tuber development and yield in adjacent crop rows. Soil physical properties under wheel tracks were studied in orchards (Iancu and Neamtu, 1979), and in common field crops with intensive field traffic {Florescu and Canarache, 1965; Canarache et al., 1979a; Marin et al., 1979; Canarache et al., 1979b).

In 1978 a series of experimental fields was set up in an integrated project to include the main arable softs of Romania. Its objective was to get a better quantitative understanding of the damage due to compaction under various soil conditions.

MATERIALS AND METHODS

Experiments were conducted in four fields with various soil {Table I) and climatic {Table II) conditions.

Texture in the arable layer is moderate to fine in all four locations. In Valul lui Traian the soil is deep, loose and permeable throughout the profile. In the other three locations the deeper horizons are more finely textured and denser than the topsoil, and they have a low or very low permeability. In Sfn Martin, and especially in Albota, the soils are poorly drained, and lower horizons are pseudogleyed.

The climate is droughty in Valul lui Traian {where the experimental field was irrigated), and moderately humid in the other three locations. Of the four years of research, 1978 and 1980 were cooler and rainfall was above average.

Results reported here refer to 1978--1981 for Valul lui Traian and Sfn Martin, to 1979--1981 for Moara Domneasc~t, and to 1981 for Albota.

The experimental design consisted of nine parallel strips of 7.2 × 60 m s. For soil sampling and yield recording, each strip was divided into four plots {replications) of I5 m length. The control t reatment (no compaction, normal soil management) was repeated every three strips. Each year, in each loca- tion, the same treatments were repeated on the same plots.

In all locations compact ion was done with a free-running 48-kW wheeled tractor with an overall weight of 3620 kg (1170 kg on the front axle, and 2450 kg on the rear axle) at a speed of 2.3 m s -1. The contact area between tyres and soil was 0.0326 m s and 0.1342 m 2 for the front and rear tyres, respectively. Thus, the specific load was 179 kPa and 91 kPa for the front

TA

BL

E I

So

il d

ata

fo

r th

e e

xp

eri

me

nta

l si

tes

Lo

ca

tio

n

Sof

t H

ori

zo

n

De

pth

C

lay

B

ulk

H

50

~m

H

yd

rau

lic

F

ield

H

um

us

pH

(U

S T

ax

on

om

y

(m)

co

nte

nt

de

nsi

ty a

p

ore

c

on

du

cti

vit

y a

ca

pa

cit

y

(%,

w/w

) (w

ate

r)

and

lo

cal

(%,

w/w

) (k

g m

-3)

v

olu

me

a (r

am

h -

1)

(%,

w/w

) b

clas

sifi

cati

on

) (%

, v

/v)

Val

ul

lui

Ty

pic

Ve

rmu

sto

ils

Ap

0

.00

---0

.20

3

2

13

00

1

4

10

.0

27

.0

3.1

8

.0

Tra

jan

(V

erm

ic C

he

rno

ze

m)

Am

0

.20

--0

.64

3

3

12

30

1

5

12

.0

26

.0

2.5

8

.1

AC

0

.64

--

29

1

25

0

16

1

5.0

2

5.0

0

.8

8.3

Mo

ara

Ud

oll

ic

Ap

0

.00

---0

.20

3

2

13

60

1

7

15

.0

25

.0

2.2

5

.5

Do

mn

ea

sc~

A

rgiu

stal

fs

Am

0

.20

---0

.38

3

6

14

10

1

2

9.0

2

4.0

1

.9

6.8

(M

oll

ic R

ed

dis

h

Bt

0.3

8--

- 4

1

15

80

8

1.8

2

3.0

0

.5

6.8

B

row

n)

Sin

Mar

tin

A

qu

ic H

aplu

stal

fs

Am

0

.00

---0

.20

2

5

14

40

1

2

7.0

2

7.0

2

.8

5.1

(P

seu

do

gle

ye

d

El

0.2

0--

0.4

8

29

1

49

0

11

4

.0

26

.0

1.4

5

.2

Lu

vic

Bro

wn

) B

tw

0.4

8--

4

3

15

30

6

0.4

2

4.0

0

.8

5.6

Alb

ota

V

erti

c A

qu

ic

Am

0

.00

--0

.20

4

0

14

00

8

0.7

2

6.0

2

.2

5,7

H

aplu

stal

fs

E1

0.2

0--

0.3

8

37

1

41

0

4 0

.3

25

.0

1.1

5

.4

(Pse

ud

og

ley

ed

Ver

tic

Btw

y

0.3

8--

- 3

8

14

80

3

0.1

2

3.0

1

.1

5.9

L

uv

ic B

row

n)

aAv

erag

e o

f d

ete

rmin

ati

on

s in

Ju

ly--

Au

gu

st i

n n

on

-co

mp

ac

ted

plo

ts.

bF

ield

de

term

ina

tio

n.

b~

O

202

TABLE II

Climatic data for the experimental sites

Location Year Annual rainfall a Annual mean temperature (ram) (°C)

Multi-annual Valul lui Traian b average 401 10.6

1978 477 10.1 1979 319 10.8 1980 397 9.8 1981 368 10.6

Multi-annual Moara Domneasc~f average 551 10.3

1979 859 10.4 1980 643 9.7 1981 627 10.5

Multi-annual S fn Martin average 635 10.5

1978 831 9.1 1979 545 10.1 1980 670 9.4 1981 727 10.0

Multi-annual Albota average 694 9.8

1981 665 9.9

al October (preceding year) to 30 September. bIrrigated, 240--320 mm per year.

and rea r wheels , respect ive ly . The inf la t ion pressure was 300 kPa in the f r o n t tyres , and 150 kPa in the rea r ty res .

T r e a t m e n t s , including 0, 1, 3, 5, 10, 20, and 30 whee l -by-whee l passes, and a lways cover ing the ent i re p lo t , were carr ied ou t i m m e d i a t e l y be fo re sowing in March or Apri l , on soil which had been p loughed to 0 .20 - -0 .25 m d e p t h in the p reced ing a u t u m n . C o m p a c t i o n was fo l lowed b y suf f ic ien t ly intensive seedbed p r e p a r a t i o n (disc, ha r row, cu l t iva tor ) to enab le sowing and ge rmina t ion . Soil m o i s t u r e c o n t e n t a t c o m p a c t i o n was usual ly close to field capac i ty t h r o u g h o u t the profi le , and in the arable l ayer as s h o w n in Tab le I I I .

In all cases ma ize (Zea mays) was sown at seed ra tes o f 20 - -25 kg ha -1 and at a r o w d is tance o f 0.7 m. In each l oca t i on a p p r o p r i a t e cult ivars were used: HS 218 in Valul lui Tra ian , HD 412 in Moara Domneasc,~i, H T 215 in S in Mart in , and H D 120 in Albo ta . The p reced ing c rop was maize in Valul lui Tra ian and Albo ta , s o y b e a n s in Moara Domneasc~ , and win te r whea t in S in Mart in . Usual obse rva t ions were m a d e on c rop d e v e l o p m e n t , grain yields were r ecorded , and soil m o i s t u r e c o n t e n t was d e t e r m i n e d per iodical ly .

203

TABLE III

Soil moisture content (0--0.20 m depth) at compaction

Location Year Date of Moisture content compaction (%, w/w)

Valul lui Traian 1978 17 April 22.5 1979 9 April 24.2 1980 22 March 23.1 1981 2 April 24.5

Moara Domneasc~ 1979 24 April 21.8 1980 10 April 25.0 1981 8 April 24.6

Sfn Martin 1978 11 April 22.8 1979 11 April 22.6 1980 19 April 25.2 1981 18 April 17.5

Albota 1981 15 April 24.0

During the second half of the vegetation period (July--August), in each t rea tment eight small pits were dug. Horizontal surfaces were exposed in each pit at 0.05, 0.15, 0.25, and 0.35 m depths, and at each depth four un- disturbed soil cores were taken by pushing brass cylinders of 10 -3 m 3 vertically into the soft, using a hammer when necessary. Bulk density, saturated hydraulic conductivi ty, the moisture characteristic, and resistance to penetra t ion were determined in the laboratory using standard procedures (Obrejanu et al., 1964). Total porosi ty and pore size distribution were calculated. Unsaturated hydraulic conductivi ty was estimated according to the procedure proposed by Mualem and Dagan (1978).

In Moara Domneasc,~i the draft requirement for ploughing was determined. In Valul lui Traian disturbed soil samples were taken and soil structure was determined according to the H~nin--Feodoroff method (H~nin et al., 1960).

Most of the soil properties determined were used to calculate the "agro- physical index" (Canarache, 1978), which expresses the physical status of the soil in a single value.

RESULTS AND DISCUSSION

Physical soil properties

As expected, bulk density increased with increasing number of wheel passes. This increase could be approximated by regression formulae of the type:

204

Y = a X b

where Y = bulk density (kg m-a), X = number of passes, a and b = empirical parameters (Fig. 1). The increase in bulk density was somewhat greater with soils having a lower humus content and a poorer drainage. Most of the changes were recorded between 0 and 8--10 passes, while with more than 15--20 passes the change in bulk density was negligible. The maximum in- crease in bulk density was 20--25%, and the maximum value obtained was ]ess than 1600 kg m -a. The increase in bulk density was less obvious in Sfn Martin, where initial bulk density was higher.

Fig. 2 shows that the 0 .10-0 .20 m soil layer was most affected, some compaction being detectable down to 0.30 m and, with 30 passes, in some instances, even to 0.40 m. This variation of bulk density with depth was noticed in all four locations, but it was much more obvious in Valul lui Traian, where the soil was originally in a loose condition throughout the profile (Fig. 2B).

Compared with the non compacted soils, the pore size distribution of maximally compacted soils (30 passes) showed a distinct decrease in medium-size pores (30-0 .2 pm), and usually also in coarse pores (> 30 ~m), accompanied by an increase in very fine pores (< 0.2 pm) (Fig. 3).

Similar changes were observed in other soil physical properties, and they could be described using the same type of regression curves as for bulk densi-

1800

_ 1700 A t b o t o

n e o s c o o~ 1600 × / " /

x • + / o

og',~l I + . I " +

c 1400 o • /

• /

/ + Va tu t tui T r a i a n y =1320 X 0"047 130C / r = 0.84 'm~

_~ 7 • M o a r a Domneasc~ Y = 1440 × 0.025 r = 0 . 8 2 * "

oS?n Mort in Y = 1 4 8 0 X 0 . 0 1 3 120C r = 0 6 8 ~

+ x A l b o t a y = 1 4 6 0 X 0 . 0 4 8 r = 0.98 ~

1100 ~3 1'0 2~0 30

N u m b e r o f p Q s s e s

Fig. 1. Relationship b e t w e e n the number of w h e e l passes and mean bulk density of the surface layer (0~0.20 m depth).

205

Bu lk d e n s i t y { kg / m 3 ) 1250 1 3 0 0 1350 1400 1450 1500 1550 1600

X2 00. ~ C~D oio5 £D

i

o4k

A Averoge of otl yeors ond tocet ions

B u l k d e n s i t y ( k g / m 3 ) 1250 1300 1350 1400 1450 1500 1550 1600

° - l L ' IT-

0.1 0 "\ . 1 ~ 3 ~ . 5 ~ 1 ( } " ' - . 2 0 ~ . 3 0

0 3 . ......

r f i l / B. Votul tui TrQion , 1978-1981

Fig. 2. V a r i a t i o n o f b u | k d e n s i t y w i t h d e p t h as re la ted t o t he n u m b e r o f whee l passes.

ty (Table IV). Similarly, most of the changes were recorded between 0 and 8--10 passes, with only minor further change for more than 20--25 passes. For maximally compacted soils (30 passes) there was a 10% (v/v) decrease in total porosity, a 30--50% decrease in macroporosity, a 4--5-fold decrease in saturated hydraulic conductivity, a 2--3-fold increase in water-stable aggregates (%, w/w), a 2 0 - 2 5 % decrease in dispersion, a 1 0 - 2 0 % decrease in structure instability, a 2 0 - 3 0 % increase in specific ploughing resistance, etc. It should be stressed that the increase in water-stable aggregates was due mainly to mechanical effects of compaction, and not to a real improvement in soil structure.

The agrophysical index, which accounts in a single value for most of the soil physical properties, fol lowed a similar trend (Fig. 4).

At maximum compact ion (30 wheel passes), the moisture characteristic (Fig. 5) showed a serious decrease of moisture content in the drainable

206

30 VALUL LUI TRAIAN MOARA DOMNEASCA

• N u 0 r21_

m

30

SIN MARTIN ALBOTA O c~ 20

10

>300 300- 30- '(012 >300 300- 30- <02 30 02 30 012

Di a me t e r o f po r e s (/u.m)

[ ~ Not compacted ~ Maximum compaction (30wheet passes)

Fig. 3. Change in pore size distribution of the surface layer (0--0.20 m depth) by maxi- mum soil compaction (30 wheel passes).

porosi ty range (pF < 2), and some decrease in available water (pF 2--4.2). Also the unsaturated hydraulic conductivi ty was clearly decreased (Fig. 6).

Generally, in the 0--0.20 m soil layer, there was a 1--3% (w/w) decrease in moisture content in the severely compacted plots (Table V). This could be at tr ibuted to the lower water retention for equal pF values in the compact- ed plots, as shown by the change in the moisture characteristic discussed above. Such a decrease could be seen in all locations, including Valul lui Traian where, due to irrigation, an opt imum moisture status was maintained throughout the growing season. The overall decrease in moisture content was well expressed in Albota, but it should be noted that here the data refer to only one year, which was relatively dry.

Within this general trend, a different situation developed in soils with an impermeable Bt clay-illuvial horizon in the lower part of the 0--0.40 m soil layer (Sin Martin, and especially Albota). In the compacted plots, this part of the investigated soil profile showed a somewhat increased moisture con- tent. This increase, statistically significant in Albota, is shown in the average figures in Table V. It was even greater (up to 6--8%, w/w) in several particular observation periods (data no t presented here). Probably, in the compacted plots of these soils, drainage through the deeper soft layers was impeded be- cause of their low permeability, loss by evaporation was low due to the re-

207

TABLE IV

Values of coefficients a and b of the empirical equation Y = a X b (where Y = soil property (0---0.20 m depth), X = number of passes) and of the correlation coefficients

Soil property a b Correlation coefficient

Bulk density (kg m -3) 1320--1480 0.013--0.048 0.68--0.98

Total porosity (%, v/v) 44--50 --0.018 to --0.049 --0.62 to --0.96

Macroporosity (%, v/v) 5--12 --0.090 to --0.220 --0.44 to --0.92

Hydraulic conductivity (mm h -1 ) 0.09--6.30 --0.090 to --0.610 --0.37 to --0.91

Water stable aggregates (%, w/w) a 3.5 0.310 0.94

Dispersion a 6.3 0.130 0.92

Structure instability a 1.6 --0.093 --0.53

Resistance to penetration (MPa) 3.70--4.70 0.220--0.330 0.71--0.92

Specific ploughing resistance (kPa) b 618 0.044 0.82

aDetermined only in Valul lui Traian in 1980. bDetermined only in Moara Domneasc~ in 1979.

050 \ \ ,A Vatu[ tui T ra ian \ / v - n 4 ~ X - 0 . ] 5

x 0 4 0 ÷ \ / . . . . . . M o a r a Domneasc6 ', ~ r - 0 9 7 ~ / 023 "o ! - " / Y = 0 . 2 2 X -

- 0 54

~ 0 . 2 0 ~ / o S , n Mart,n t o I / ,~.,~. / / r = 0 9 6 "

~: x ', f f Y =O.07X "0.15

~ ' "" "-~.~'- . . . . . . . J- . . . . . . o . / Y =012X . . . . . . . . . . ; . . . . . . . . . . . . . . . . . . . . 0 % "

I

0 10 20 30 Number of passes

Fig. 4. Relationship between the number of wheel passes and the agrophysical index of the surface layer (0--0.20 m depth).

duced unsaturated hydraulic conductivity, and water consumption by crops was limited due to the weak development of the root system. It may be considered that a "captive" stock of water developed.

Marked differences between control and compacted plots are to be seen in soil air content, and they were due mainly to the already discussed higher bulk densities. In the deeper layers in Sin Martin and Albota, due to the

2 0 8

50 " ' , , - - - ~ VALUL LUI TRAIAN MOARA DOMNEASCA

=,o . . . . _.., ~\ < -

x ~

D

o 0 1 2 3 L 0 1 2 3 4

pF pF

5O

S'IN MARTIN ALBOTA

~ x x

~30, ~ ~

2 2 0

8

~ 10 "~ Not compacted 5 ~: - - - Maximum compaction

0 I 2 3 L 0 I 2 3 Z,

pF pF

Fig. 5. Change in the moisture characteristic (0---0.20 m depth) by maximum soil compac- tion (30 wheel passes).

"captive" water, air content was especially low, in some cases even zero. Values lower than 10% (v/v), the assumed minimum air content for normal plant growth, were often recorded in these two locations and, occasionally, also in the other two.

Y i e l d s

Decrease in maize grain yield as related to the number of tractor passes, as shown in Fig. 7, could also be approximated by regressions of the type: Y = a X b. The decrease tended to be greater with softs having a lower productivity in the order Valul lui Traian--Moara Domneasc~l--Si'n Martin--

209

VALUL LUI 7RAIAN MOARA DOMNEASCA

"'%.

s i f"" ~ - 6 ~ ~

0 ! 2 3 ° 1 2 3 pF pF

S]'N MARTIN ALBOTA

E ~ -2 ~I0 -- Not compacted

> -- - Maximum compaction

X \ 25 "o

0 I 2 3 0 I 2 3

pF pF

Fig. 6. Change in the unsaturated hydraulic conductivity (0--0.20 m depth) by maximum soil compact ion (30 wheel passes).

Albota. This also refers to years with different yield levels in the same loca- tion (data not shown separately). Most of the decrease in yield was noticed between 0 and 8--10 passes, and it became negligible with more than 20--25 passes. The average decrease in yield due to compaction for all locations and years, as compared to the control, was 38% for 10 passes, and 46% for maximum compaction.

When assessing these results, it should be noted that the experimental plots discussed here were located on old agricultural fields, with soils al- ready having an unfavourable physical status. It is not unlikely that for a soil with an opt imum physical status the decrease in yield due to compaction would be even greater. It must also be taken into account that within the growing season 10 wheel passes, let alone 2 0 - 3 0 passes, are not usual in common practice, although they may occur in special crops, for example orchards or potatoes. Wheel-by-wheel tracks, i.e. compaction covering the

210

TABLE V

Soil moisture content and air content after 0 and 30 wheel passes (means for all years and seasons, totalling 248 determinations)

Location Depth Moisture content Air content at field moisture (m) (%, w/w) content (%, v/v)

Not Maximum Not Maximum compacted compaction compacted compaction

Valul lu iTraian 0 --0.1 21.5 19.2 27.0 14.3 0.1--0.2 21.9 20.6 21.9 9.9 0 .2 -0 .3 22.1 21.7 20.4 12.7 0.3--0.4 21.6 21.5 22.1 21.9

Moara Domneasc~t 0 - 0 . 1 20.2 17.5 20.6 14.0 0.1--0.2 20.6 19.4 18.5 12.1 0 .2 -0 .3 20.3 19.8 18.1 12.6 0.3--0.4 20.9 20.6 17.4 15.4

Sfn Martin 0 --0.1 18.7 18.6 21.1 15.3 0.1--0.2 18.6 18.7 17.2 12.2 0 .2 -0 .3 18.8 18.9 15.9 10.1 0 .3 -0 .4 19.4 20.2 14.4 10.8

Albota 0 - 0 . 1 20.5 13.7 21.3 13.6 0 .1 -0 .2 22.7 17.9 15.5 7.0 0.2--0.3 26.8 24.3 10.3 3.2 0.3--0.4 31.9 34.2 6.5 0.0

LSD (0.05) 2.2 5.0

10 x + Vatul tui T r a j a n

Y : 8.3X IO 111

- - ~ / Y = 5 . 1 X - 0 . 8 . . . . . "o ~ obln l'¢0rlln _ / r-OOy"

f iAt bota o

Y = 4 .9X-031 x

r = 0.96 ~*

0 0 10 20 30

N u m b e r of posses

Fig. 7. Relationship between number of wheel passes and yield of maize grain (average for all years studied).

211

I0 ~ +

g * / * V a t u l tut .Tralan ~ Y :228-@0111X

8 \ ~ . . < - - - ' J "~÷ F : 0,6s "~

oS'~n Martin ~----",",",",",",","x~ o + o " o ~ + "D° 6 Y = 52.4-0.0326 X . . " ".,.,,, ~. .

r : O 70 % -< +

- . M o a r a Domneasc6 ~ ~ ~ . + " >- 3 ', ~ . . . _ ~ - - ~ A l b o t a

Y = 22.5-0 0126X ,, Y =24 6-0.0136X o o

: 0.47 Oo, ,o "~ \ r = 0 9 8 " " 2 o , --.

1 o ~ o o

0 1100 12'00 1300 14'00 1500 1600 1700

B u t k d e n s i t y { k g / m 3 )

Fig. 8. Relationships between soil bulk density (0--0.20 m depth) and yield of maize grain (average for all years studied).

_ 120[

I . . . . o + ~ + o Y = 351-0.187X Lg! o + r:0.6g" • + ÷

÷ + •

- - ! + o ° x

>" [ '0 i -

t o

- 40 + Vatul tui T r a i a n • ~,~

" Moara O0rnneosc~ o \ o 30 _ o S~n Martin o o x e, 20 × A t b o t a n-"

10

0 1100 12~00 13'00 14'00 15'00 16'00-- 17'00 -

B u l k d e n s i t y ( k g / m 3 }

Fig. 9. Relationship between soil bulk density (0---0.20 m depth) and relative yield of maize grain (% of yield on non~ompacted plots; average for all years studied).

entire field, are seldom employed in practice, although they may occur, for example in the case of levelling or other earth-moving activities. Results in the present experiments, as well as in others using the same approach, are to be considered mainly as indicating a long term trend based on a year to year accumulation of compaction effects.

Fig. 8 shows linear relationships between bulk density, the main soil parameter expressing compaction, and the yield of maize grain. There was an

212

overall decrease in yield of 13 kg ha -1 for each 1 kg m -3 increase in bulk density, an exception being the Sin Martin soil with a stronger drop in yield. The somewhat limited range of bulk density values for this soil might offer an explanation for this particular result. Differences between the other three softs refer mainly to the level of the yield figures (which, at the same bulk density, was higher for the more productive soil in Valul lui Traian), and not to the rate of decrease of yield.

When yields were expressed in relative figures (control plot = 100%), the results from all four locations could be pooled in a single regression line, which showed a 0.18% decrease in yield for each 1 kg m -3 increase in bulk density (Fig. 9).

CONCLUSIONS

(1) Induced soil compact ion by t ractor wheels on old agricultural fields led to changes in soil physical properties and in maize grain yield which were related to the number of t ractor passes according to regressions of the type: Y = a X b . The regression curves showed a maximum bulk density of about 1600 kg m -3 at 15--20 passes. On average, yields decreased to 62% for 10 passes, and to 54% for 30 passes, as compared with non-compacted plots.

(2) Yields followed a negative linear trend with increasing bulk density. For three of the four experimental fields, yield decrease was about 13 kg ha -1 for each 1 kg m -3 increase in bulk density. On average, for all four sites, for each 1 kg m -3 increase in bulk density, a decrease of 0.18%, relative to the yield on the non-compacted plot, was noticed.

(3) Compact ion reduced moisture and air content in the arable layer but, on poorly drained soils with an impermeable Bt-horizon, compaction in- duced an excess of water and a large deficit in the air content in the lower part of the measured profile (0.40 m).

REFERENCES

Barnes, K.K., Carleton, W.M., Taylor, H.M., Throckmorton, R.I. and Vanden Berg, G.E. (Editors), 1971. Compaction of Agricultural Soils. American Society of Agricultural Engineers, St. Joseph, MI, 471 pp.

Berindei, M., Florescu, C.I., C~lug~ru, V., T~n~sescu, E. and C~ndea, I., 1968. InfluenZa m~rimii pneurilor de la ro~ile tractorului §i a distan~ei fntre rfndurile de cartof asupra produc~iei de tuberculi (in Romanian). (Effect of size of tractor tyres and of potato row distance on tuber yield.) An. Inst. Cercet. Cult. Cartofului Sfeclei Zah~r, Brasov, Set. Cartoful, 1: 149--161.

Canarache, A., 1978. Un indice pentru exprimarea gintetic~ a st~rii fizice a solului (in Romanian). (A synthetic index to describe soil physical status.)Stiin~a Solului, Nout~i , 1 : 33--43.

Canarache, A. and Berindei, M., 1972. Vlijanie mekhanicheskogo sostava pochvy na kultury kartofelja (in Russian, with English summary). (Effect of soil texture on pota- to growth.) In: Pyrvi Natsionalen Kongress po Pochvoznanie, Sofia, pp. 111--116.

213

Canarache, A. and Thaler, R., 1962. K voprosu obespechenija rastenii vlagoi i vozdukhom pri razlichnom uplotnenii pochv (in Russian, with English summary). (The rate of soil compact ion and the supply of moisture and air as plant growth factors.) Pochvovede- nie, 5: 106--113.

Canarache, A. and Vintil~, I., 1962. Cercet~tri fn vase de vegeta~ie cu privire la influenza st~trii de tasare §i a f n g r ~ m i n t e l o r asupra fertilit~t~ii unor orizonturi genetice ale solului brun podzol i t de la Oarja (in Romanian, with French summary). (Greenhouse experiments concerning the effect of compact ion and fertilizers on the fertility of genetical horizons of the Oarja Grey-Brown Podzolic soil.) An. Sect. Pedolog., 30: 117--123.

Canarache, A., Dumitriu, R., Dumitru, E., Trandafirescu, T. and P~tltineanu, I., 1979a. Rezultate privind compactarea ~i modificarea fnsu§irilor fizice ale solului fn condi~iile diferitelor metode de udare (in Romanian, with English summary). (Compaction and alteration of soil physical propert ies under irrigation.) In: Publica~iile Societ~i~ii Na~ionale Rom~ne de Stiin~a Solului, 17: 224--243.

Canarache, A., Postolache, T., Vasilescu, P., Trandafirescu, T. and Vine§, Gh., 1979b. Modificarea fnsu§irilor fizice ale solului sub influenza lucr~rilor solului pe cernoziomul vermic de la M~rcule§ti (in Romanian). (Changes in soil physical properties as affected by soil tillage on the Vermic Chernozem in M~rcule§ti.) In: 50 de ani de activitate §tiin~ific~ in sprijinul sporirii produc~iei agricole fn B ~ g a n u l de sud-est, M~rcule§ti, pp. 168--203.

Chancellor, W.J., 1977. Compaction of soil by agricultural equipment. University of California, Bull. No. 1881, 53 pp.

Florescu, C.I. and Canarache, A., 1965. Compactarea solului sub ac~iunea ro~ilor ma~ini- lor agricole de recoltat porumb (in Romanian, with French summary). (Soil com- paction due to wheels of maize harvesters.) An. Sect. Pedolog., 33: 21--32.

H6nin, S., F@odoroff, A., Gras, R. and Monnier, G., 1960. Le profil cultural. Soci6t6 d 'Edit ions des Ing6nieurs Agricoles, Paris, 320 pp.

Iancu, M. and Neam~u, I., 1979. Cercet~ri privind tasarea solului fntr-o livad~ intensiv~t de m~r (in Romanian, with English summary). (Soil compact ion in an apple orchard.) In: Publica~iile Societ~f~ii Na~ionale Rom~ne de Stiin~a Solului, 17: 265--287.

Marin, Gh., Chirculescu, V. and Florescu, C.I., 1979. Cercet~tri privind compactarea solului sub influenila iriga~iei fn condi~ii experimentale §i de produc~ie fn sistemul de iriga~ie Cazasu - - Br,~iila (in Romanian, with English summary). (Data concerning soil compact ion as affected by irrigation under experimental and management practices in the Irrigation District Cazasu - - Br~tila.) In: Publica~iile Societ~t~ii Na~ionale Romaine de Stiin~a Solului, 17: 244--256.

Mualem, Y. and Dagan, G., 1978. Hydraulic conductivity of soils: Unified approach to the statistical models. Soil Sci. Soc. Am. J., 42: 392--395.

Obrejanu, Gr., Serb~inescu, I., Canarache, A. and M~tnuc~t, O. (Editors), 1964. Metode de cercetare a solului (in Romanian). (Methods in Soil Investigation.) Ed. Academiei, Bucharest, 670 pp.

Soane, B.D., Blackwell, P.S., Dickson, J.W. and Painter, D.J., 1981a. Compaction by agri- cultural vehicles: a review. I. Soil and wheel characteristics. Soil Tillage Res., 1: 207-- 237.

Soane, B.D., Blackwe11, P.S., Dickson, J.W. and Painter, D.J., 1981b. Compaction by agri- cultural vehicles: a review. II. Compaction under tyres and other running gear. Soil Tillage Res., 1: 373--400.

Soane, B.D., Dickson, J.W. and Campbell, D.J., 1982. Compaction by agricultural vehicles: a review. III. Incidence and control of compact ion in crop production. Soil Tillage Res., 2: 3--36.