effect of deep tillage on soil physical properties and maize yields on coarse textured soils

Soil & Tillage Research, 6 (1985) 31---44 31 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

EFFECT OF DEEP TILLAGE ON SOIL PHYSICAL PROPERTIES AND MAIZE YIELDS ON COARSE TEXTURED SOILS

M.R. CHAUDHARY, P.R. GAJRI, S.S. PRIHAR and ROMESH KHERA

Department of Soils, Punjab Agricultural University, Ludhiana 141 004 (India)

(Accepted 4 April 1985)

ABSTRACT

Chaudhary, M.R., Gajri, P.R., Prihar, S.S. and Khera, R., 1985. Effect of deep tillage on soil physical properties and maize yields on coarse textured soils. Soil Tillage Res., 6: 31--44.

The effects of deep tillage on soil physical properties and maize yields were evaluated on a loamy sand soil in which the bulk density distribution did not show a distinct root- limiting soil zone. Sub-soiling, mould-board ploughing and deep digging to 45 cm were compared with conventional tillage with and without irrigation. The tillage operations slightly decreased the bulk density of soil at all working depths. Sub-soiling and deep digging decreased the soil penetrat ion resistance in the 20--40-cm layer to one-tenth of that in the control. They induced deeper and greater rooting and increased profile water use compared with conventional tillage. Sub-soiling, mould-board ploughing and deep digging increased plant height by 30--35 cm and yielded 80--100% more stover and 70--350% more grain than the control in different experiments.

INTRODUCTION

Sub-soiling, which loosesns the sub-soil without inverting it, is aimed at stimulating greater and faster penetration of roots and at increasing internal drainage of the profile. Early studies with sub-soiling often showed no posi- tive effect on crop growth. Chilcott and Cole (1918) concluded that sub- soiling or other methods of deep tillage may show a favourable response at certain times and in some places, but in general, for the Great Plains as a whole, no increase of yield or amelioration of conditions could be expected from this practice. Smith (1925) also did not observe any material increase in crop yields from sub-soiling. Anderson et al. (1958) observed a consistent decrease in yields caused by sub-soiling over a 4-year period. Some of the dis- parity in earlier experimental results may well be due to (1) the soil water content at the time of sub-soiling, (2) lack of accurate identifiaction of the soil problem needing correction, or (3) large differences in the rooting characteristics and behaviour of the crops.

For maximum lifting and shattering, sub-soiling should be carried out

0167-1987/85/$03.30 © 1985 Elsevier Science Publishers B.V.

32

when the soil is dry. The depth of soil loosening depends upon the geometry and condition of the soil (Spoor and Godwin, 1978). Campbell et al. (1974), Swain (1975), Doty et al. (1975) and Kamprath et al. (1979) demonstrated that sub-soiling was warranted in those soils where there was a definite hard- pan or compact layer or horizon which impeded root growth and water movement to deeper horizons, and where the soil dried out sufficiently for effective sub-soiling.

The threshold bulk densities above which sunflower roots did not pene- trate corresponded to about 1.75 Mg m -3 for sands, and varied from 1.46 to 1.63 Mg m "3 for clays (Veihmeyer and Hendrickson, 1948). Flocker and Nielson (1960), however, reported that at low soil moisture suctions, root growth was not affected by soil bulk density. The concept of limiting soil bulk density has gradually been replaced by the more logical concept of soil strength (Barley, 1963; Taylor et al., 1966; Barley and Greacen, 1967). The soil moisture content, which changes with time, has a profound effect on soil strength (Gill, 1959; Taylor and Gardner, 1963). Therefore, it has been suggested that soil strength should be measured at or near field capacity (Pearson, 1966). Soil strength usually increase with increase in bulk density or with drying of coherent soil (Taylor and Bruce, 1968).

Apart from soil strength, the rigidity of the soil pores has an important bearing on root growth (Wiersum, 1957; Aubertin and Kardos, 1965). Coarse textured soils with rough particle surfaces simulate the rigid system by pro- viding greater inter-particle friction when pushed apart by growing roots (Cruse et al., 1980). Simultaneously, the coarse textured soils are low in water retention and dry rapidly under high evaporation. These soils impede root growth rather than water movement.

Fatehpur soil is loamy sand throughout the profile and dries out rapidly. It does not have any distinct root-restricting layer of high bulk density. Pre- liminary observation showed that very few maize roots penetrated beyond 60 cm into the soil. Field experiments were conducted to determine the response of maize to sub-soiling in this soil.

MATERIALS AND METHODS

Field experiments were conducted to evaluate sub-soiling by a chisel tine as a management practice for maize on Fatehpur loamy sand (typic ustip- samment). The textural composition and available water retention capacity of the typic pedon (Table I) show that the clay content ranges from 3 to 5% and the water retention capacity is rather low. Two types of experiment were conducted.

Experiment 1

In this experiment, the following four treatments were compared in four replications:

33

(i) conventional tillage -- one disc harrowing followed by two cross-runs of a tine cultivator followed by planking;

(ii) sub-soiling 40 cm deep at 30--35-cm intervals followed by conventional tillage;

(iii} mould-board ploughing to 20 cm depth followed by conventional tillage;

(iv) soil manually dug to 45 cm depth and filled back in the natural layer sequence, followed by conventional tillage.

TABLE I

Characteristics of experimental soil

Horizon Soil separates (%) Water content (% v/v) at: Bulk depth density (cm) Sand Silt Clay Field 1.5 (Mg m -3)

capacity' MPa

0- 16 88 8 4 13.8 7.1 1.54 16--31 84 11 5 14.2 6.4 1.60 31--73 87 8 5 16.0 7.8 1.60 73--88 89 8 3 15.5 6.8 1.52 88--115 91 6 3 11.8 5.2 1.45

115 91 6 3 10.1 4.9 1.45

' In situ (Peters, 1965).

This experiment was conducted for 2 years, i.e. 1981 and 1982. The sub- soiling was done with a tractor-drawn one-tine chisel sub-soiler (Fig. 1), before pre-sowing irrigation, when the soil was dry. Other tillage operations were carried out after the pre-sowing irrigation. The fertilizers to supply 60 kg N, 60 kg P2Os, 60 kg K~O and 25 kg ZnSO4"7H20 per hectare were applied by drilling before sowing. Maize seeds (Zea mays L., cultivar Partap) were sown 15 cm apart in rows 60 cm apart. The second application of 60 kg N ha -1 was made 30 days after sowing.

In 1981, half of the plots were provided with normal irrigation, and the other half were left unirrigated to provide water stress to the plants. In 1982, normal irrigation (7.5 cm of water at each application) was given to all the plots. The rainfall distribution pat tern and irrigation dates are shown in Fig. 2.

During the crop growth period in 1982, the soil bulk density (all treatments) and pore size distribution (Treatments (i) and (iv) only) were determined on undisturbed soil cores collected from different depths. Pore size distribution was calculated from moisture-release curves. In 1982, the penetration resistance of soil from sub-soiled and control plots was measured periodically after irrigation. The penetrat ion resistance was measured by manually pushing a proving ring cone penet rometer {cone angle 30 ~ and base

34

Fig. 1. The chisel-tine used for sub-soiling in different experiments.

E u

Z

I,,- :3 =E (J

30

25

20

15

10

5

• 29-7 1982 F

, r ~, I, TIME OF iRRIGATION i 2/.,.9 ', 1981

1 1981 ! [ - - J 2 1 9 8 2 ~ . . . . . . . . . . _.~

2 2 1 1 ( ', 1 2 2

. :_r 7 - - J

y+:-<~ _ _ V " '-'

J r ' - " J

l t" . . . . I" " ' - " + " " " - J I I I I l

0 10 20 31 10 20 31

JULY ; ,I ~ AUGUST

Fig. 2. Rainfall distribution and irrigation times during the two maize growth seasons.

35

diameter 13 mm) into the soil. The maximum dial reading for each depth- interval was recorded. All values of penetrat ion resistance were expressed at 10% gravimetric soil water content by interpolation from a plot of penetration resistance vs. soil water content . During crop growth, root distribution on different days at different depths was determined by extracting soil cores of 7.5 cm diameter at a depth-interval of 15 cm with the help of a metallic tube. These were taken from the base of a representative plant growing near the middle of a row. The three samples for any one depth were com- bined to give one sample per plot per depth. The roots were separated from the soft by gentle washing over a 1-mm screen, and their length was determined by the line interception method of Newman {1965). Periodic plant heights and crop yields at harvest were also recorded.

Experiment 2

This experiment was conducted during 1982 only. Sub-soiling with a chisel-tine to a depth of 40 cm in rows 30--35 cm apart was compared with conventional tillage. Irrigation of 7.5 cm water was applied during two rain- less periods when the ratio of irrigation water (IW) to cumulative pan evaporation since the previous wetting (PE) equalled 1.2 in one case and 0.75 in the other.

This experiment was conducted for two sowing dates, viz. the last week in June (normal date of sowing) and the first week in August (late sowing). Each t reatment was repeated four times.

In Experiment 2, root distribution in the 37-day-old crop was studied by the pin-board method. The gravimetric soil water content after harvest was determined on soil samples drawn from different depths by a screw auger. These were converted to volumetric water content by multiplying them with soil bulk density values at the respective depths. These samples were taken from two places in each plot.

RESULTS

Tillage and soil properties

Tillage of a specific soil volume lowered the bulk density (Table II). The bulk density in the chisel furrows and in the plots dug to 45 cm depth tended to be slightly less than that in the control plots and in the area between the chisel furrows to a depth o f 40 cm. The bulk density of the upper 10-cm layer was slightly lower than in the lower soil layers in the control plots and mould-board plots.

Penetrometer resistance in the 20--40-cm layer in the chisel furrows was about one-tenth of that at the same depth in the control plots (Table III).

To s tudy the effect o f soft loosening on pore size distributions, the latter were calculated from the soil moisture release curve. Undisturbed cores were

36

TABLE II

Soil bulk density in the surface 40 cm of soil as affected by different tillage treatments in Experiment 1 (1982)

Soil depth Bulk density (Mg m -3) in different treatments (cm)

Control Sub-soiling

Between In chisel chisel furrows furrows

Digging Mould- board

0--10 1.52 1.58 1.56 1.49 1.52 (0.01)' (1.01) (0.02) (0.01) (0.02)

10--20 1.62 1.60 1.54 1.51 1.59 (0.06) (0.06) (0.02) (0.01) (0.02)

20--30 1.60 1.70 1.51 1.51 1.61 (0.02) (0.01) (0.01) (0.01) (0.01)

30--40 1.60 1.62 1.50 1.62 1.63 (0.01) (0.01) (0.01) (0.01) (0.01)

'Values in parentheses are standard deviations for four observations.

TABLE III

Penetration resistance' of Fatehpur loamy sand in sub-soiled and control plots, corrected to a soil water content of 10% by weight in Experiment 1 (1982)

Soil depth Penetration resistance (MPa) (cm)

Sub-soiling Control

0--I0 0.18 0.85 10--20 0.16 I . I I 20--30 0.I0 1.03 30--40 0.I0 1.39 40--50 1.08 2.38 50-60 2.17 2.17

'Measured at various soil water contents with a cone diameter of 13 ram; inclusive angle 30 °. Each value is a mean of 15 observations.

taken from control and manually dug plots in 1982 and the results are given in Table IV. In the upper 10-cm soil layer, the pore size distribution was similar in both cases, but in the 10--20- and 3 0 - 3 5 - c m layers, soil loosening increased the propor t ion of pores which were 18--600 #m in diameter.

Root grow th

Figure 3 shows the root systems of 37.day-old irrigated maize plants from sub-soiled and control plots in Experiment 2a. Roots in chiselled plots had

37

TABLE IV

Pore size distribution of Fatehpur loamy sand as affected by loosening with digging in Experiment 1 (1982)

Treatment Soil depth (cm)

% space occupied by pores of size:

>600 ~m 85-- 18-- 7-- <7 #m 600 #m 85 #m 18 ~m

Digging

Control

0--10 12 1 12 3 15 10--20 12 1 13 3 15 30--35 9 2 14 4 14 50--55 2 4 16 3 14

0--10 13 1 12 4 13 10--20 13 0 9 3 14 30--35 9 1 11 4 15 5 0 - 5 5 5 2 12 8 13

grown to 100 cm depth as compared to 40 cm in the control plots. In 1981, the roots of 52~lay-old maize plants had penetrated to 150 cm depth in sub- soiled plots as against 90 cm in control plots (Fig. 4). Similar effects from soil loosening were also observed under non-irrigated conditions. Where the soil was dug to 45 cm depth in 1981, roots of 70-day-old non-irrigated maize plants had penetrated down to 180 cm, compared with 135 cm in control

E u

U.I

0

10

2O

30

4C

5C

6oi 70

8O

90

100

m

- Control Subsoiling ~

Fig. 3. Root system of 37-day-old maize plants as affected by sub-soiling in Experiment 2a (1982).

38

plots (Fig. 5). In the irrigated crop, the roots penetrated to 120 and 90 cm depths in the dug and control plots, respectively.

Apart from inducing deeper rooting, soil loosening by sub-soiling and digging increased rooting density in comparable soil layers as compared with controls.

i- w Q

ROOT LENGTH

0 0.2 0-/~ 0 -6 0.8 I J I I

0 / i

45

7 5

-- 10,5 o

135

150

Contro l

DENSITY, cm cn33

0 0.2 0 .4 0 .6

i I I 0 I

0 s /

0 $1 / . o / . - - . Irri te, b O, s

o .... -o Unirr igated a e

J ~ O

£

Subsoiling

0.8 I

Fig. 4. Root distribution of 52-day-old maize plants in control and sub-soiled plots under irrigated and non-irrigated conditions (1981).

ROOT LENGTH DENSITY, cm cry3

E 45 U

ff ~ 75 n iJJ

• .J 105 u o

0

15

135

165

180

0.2 O'4 O~S '

/ - p

a t

?

i

I

CONTROL

0-8 09 0 | i

t I O

. #1

0.2 0"4 0"6 0"8 1-0 1-2 i ! i i i ,

/ /" * I rr igated -- 7 o Unirr igated

p,

DIGGING

Fig. 5. Root distribution of 70-day-old maize plants in control and dug plots under irrigated and non-irrigated conditions (1981).

39

Water uptake

Figure 6 shows the soil moisture profiles at harvest of the maize in Experi- men t 2 (1982) as affected by sub-soiling under irrigated and non-ixrigated conditions. There was less water in the subsoi led compared with the control plots under both irrigated and non-irrigated conditions. However, the differences were larger in the irrigated than in the non-irrigated plots.

. r . ' l p- n ILl C3

- J

o u3

SOIL WATER CONTENT, % VlV

0 2 4 6 8 10 12 0

60

120

180

0

60

120

180

14 I i l l ! ! ! i

: Sontro!. ~ ~ - ' ~ ~ ' - - - ' - I ~uosomng f L

I [. .11. \2 . / N t -.,q

IRRIGATED ,If

UNIRRIGATED

Fig. 6. Moisture profiles at harvest as affected by sub-soiling and irrigation in Experiment 2a (1982).

Crop growth and yield

The periodic height of plants in different tillage treatments is shown in Fig. 7. The plants in the mould-board ploughed, sub-soiled and deep-dug plots were taller than those in control plots. However, differences among these deep tillage treatments were non-significant.

40

E u

I - -r

I , I :E

I -

Z

,.J

195

190

1.50

120

go

60

30 1 1981

&

A o

• Control o Mould board & Subso i l i ng x Digging [ C.D.at 5%

1982

0 ~ 0 10 20 30 ~0 50 60 70 80 0 10 20 30 &0 50 60

DAYS AFTER PLANTING

Fig. 7. Progressive height of irrigated maize plants under different tillage treatments.

Maize stover yields from different experiments are summarised in Table V. In 1981, stover yields in the mould board ploughed, sub-soiled and deep-dug plots were about 80--90 and 100--120% greater than those of control plots under non.irrigated and irrigated conditions, respectively. In 1982, these treatments also significantly increased stover yields above the control.

In Experiment 2a (1982), sub-soiling increased maize stover yield by about 35% under both irrigation levels in early-sown crops. In the later-sown crops (Experiment 2b), yield increase by sub-soiling was 47% under lower irrigation levels and 27% under the higher irrigation level.

Grain yields in different treatments generally followed the same trend as stover yield (Table VI). In 1981, irrigation did not have any significant effect on grain yields. Mould-board ploughing gave substantially lower yields than sub-soiling or digging under irrigated conditions, although this was not true for non-irrigated conditions. Compared with the 1982 yields, the yields in 1981 were lower with irrigation but much higher without irrigation.

DISCUSSION

Loosening of soil by tillage decreased soil bulk density and soil strength. However, the decrease in bulk density was only of the order of 0.1 Mg m -3,

41

T A B L E V

M a i z e s t o v e r y i e l d s in d i f f e r e n t e x p e r i m e n t s i n v o l v i n g v a r i o u s t i l l age t r e a t m e n t s

T r e a t m e n t s

I r r i g a t i o n I T i l l age

Stover yield (kg ha -~)

M a i z e Ma ize 1 9 8 2 1 9 8 1 , E x p . 1 E x p . 1 E x p . 2a E x p . 2b ~

N o o r l ow

Yes o r h i g h

LSD at P = 0.05

C o n t r o l 2 5 6 4 * - - 2 9 9 0 * 2 9 7 5 M o u l d - b o a r d 4 6 2 9 * - - - - - - S u b - s o i l i n g 4 6 9 6 * - - 4 0 1 0 " 4 3 7 5 D i g g i n g 4 9 8 0 * - - - - - -

C o n t r o l 1 7 7 8 4 0 7 6 4 6 8 0 4 9 3 8 M o u l d - b o a r d 3 4 2 2 6 0 8 1 - - - - S u b - s o i l i n g 4 0 2 6 6 6 6 4 6 3 4 0 6 2 5 0 D i g g i n g 4 0 4 4 7 7 6 4 - - - -

T i l l a g e 8 3 8 1 4 3 1 6 1 2 1 0 3 I r r i g a t i o n 5 9 2 - - 6 1 2 105 I n t e r a c t i o n N S - - NS NS

ZLow, IW/PE = 0 . 7 5 ; h i g h , IW/PE = 1 .2 . N o i r r i g a t i o n .

T A B L E VI

M a i z e g r a i n y i e l d in d i f f e r e n t e x p e r i m e n t s i n v o l v i n g v a r i o u s t i l l age t r e a t m e n t s

T r e a t m e n t s

I r r i g a t i o n I T i l l age

G r a i n y i e l d (kg h a -~)

M a i z e M a i z e 1 9 8 2 1 9 8 1 , E x p . 1 E x p . 1 E x p . 2a E x p . 2 b ~

No or low

Yes o r h i g h

L S D a t P = 0 . 0 5

C o n t r o l 6 4 3 * - - 4 2 8 * 5 1 2 M o u l d - b o a r d 1 6 4 5 " - - - - - - S u b - s o i l i n g 1 7 7 5 * - - 8 9 6 * 8 1 6 D i g g i n g 1 7 6 1 " - - - - - -

C o n t r o l 4 9 5 1 3 3 7 2 7 0 5 2 1 7 6 M o u l d - b o a r d 1 2 1 3 3 5 1 5 - - - - S u b - s o i l i n g 2 1 3 6 3 6 2 7 4 0 2 0 3 5 4 2 D i g g i n g 2 2 2 1 4 1 4 7 - - - -

T i l l a g e 6 4 4 1 1 9 8 3 5 7 3 4 8 I r r i g a t i o n NS - - 3 5 7 3 4 8 I n t e r a c t i on N S - - 5 0 6 4 9 2

1Low IW/PE ffi 0 . 7 5 ; h i g h IW/PE = 1.2. N o i r r i g a t i o n .

42

as compared to a 10-fold decrease in soil strength. The bulk density is only related to the total porosity of the soil. Soil strength, on the other hand, is a composite property related to many factors such as size and continuity of pores, rigidity of soil, displaceability of particles, number of particle-to- particle contacts, etc. (Kaddah, 1976). Evidently, therefore, disturbance by sub-soiling reduced soil strength (as measured by impedance to penetration) by effecting changes in these factors without causing material changes in bulk density. An increase in soil strength from 3 to 15 bars has been observed (Taylor et al., 1966) to cause a drastic reduction in root penetration. If these values are valid for this soil also, the soil strength (Table III) of undisturbed Fatehpur loamy sand becomes quite damaging, even at the 10% gravimetric water content which is achieved shortly after irrigation. There- fore, reduction of soil strength to about 0.1 MPa to a depth of 40 cm greatly increased root growth and penetration to deeper layers.

The ability of plants to exploit the water and nutrients present in the soil depends largely on the concentration of roots in different layers. Deeper rooting made the plants less vulnerable to water stress in deep-tilled plots. The xylem water potential of unstressed plants from non-irrigated sub-soiled and control plots measured at 2.30 p.m. in a 50-day-old crop averaged -0.73 and -1.08 MPa, respectively.

Better root growth and plant water status with deep tillage were reflected in better crop growth and higher yields. However, the response of deep tillage varied with the seasonal rainfall distribution. The grain yields of irrigated maize were lower in 1981 than in 1982. In 1981, irrigation on 21 July and 13 August was immediately followed by rain. This may have caused ex- cessive leaching of mobile nutrients, particularly of nitrates below the rooting depth, which resulted in the lower yield. Mahajan et al. (1981) observed that on this soil some nitrate did leach below 120 cm, even with 5 cm of water being applied at each irrigation.

The lower straw yield but higher grain yield in irrigated as compared to non-irrigated maize in 1981 suggested that there may be additional adverse effects of excess water other than leaching. When excess rain falls on pre- viously irrigated soft, plant growth may suffer as a result of low aeration (Doty et al., 1975).

CONCLUSIONS

On soils with low water retention, deep rooting of crops is especially desirable for efficient use of available water and applied nutrients. Present studies have shown that some coarse textured soils, such as Fatehpur loamy sand, do not permit adequate root penetration and development even in the absence of high bulk density layers in the profile. This behaviour appears to be associated with high mechanical resistance, even at high moisture contents, of the soil below the plough layer. High strength without high bulk density of soil could be ascribed to the rough surface of the sand particles,

43

which resists particle displacement by slippage (Cruse et al., 1980). Loosen- ing of the soil and the disturbance of particle orientation brought about by sub-soiling promoted root penetration and development by increasing particle displaceability. These findings suggest that bulk density--root growth relationships may be significantly influenced by the surface roughness of soft, in addition to other factors such as soil wetness, aeration and root mor- phology. These points should receive more attention in future research.

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Anderson, J.C., Neal, D.R., Vomocil, J.A. and Brill, G.D., 1958. Effect of subsoiling and rotation on yield of corn. Agron. J., 50 : 603--604.

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Barley, K.P., 1963, Influence of soil strength on growth of roots. Soil Sci., 96: 175--180. Barley, K.P. and Greacen, E.L., 1967. Mechanical resistance as a soil factor influencing

the growth of roots and underground shoots. Adv. Agron., 19: 1--43. Campbell, R.B., Reicosky, D.C. and Doty, C.W., 1975. Physical properties and tillage of

paleudults in the south eastern coastal plains. J. Soil Water Cons., 29: 220--224. Chilcott, E.C. and Cole, J.S., 1918. Subsoiling, deep tillage and soil dynamiting in the

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densification of coarse textured soil. Soil Sci. Soc. Am. J., 44: 692--697. Doty, C.W., Campbell, R.B. and Reicosky, D.C., 1975. Crop response to chiselling and

irrigation in soils with compact A2 horizon. Trans. Am. Soc. Agric. Eng., 18: 668-- 672.

Flocker, W.J. and Nielsen, D.R., 1960. Relationship between soil moisture and air space associated with levels of bulk density that influence growing of tomato. Trans. 7th Int. Congr. Soil Sci., Madison, WI, 1: 347--359.

Gill, W.R., 1959. Soil compaction by traffic. Agric. Eng., 40: 392--394, 400, 402. Kaddah, M.T., 1976. Subsoil chiseling and slip plowing effects on soil properties and

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Swain, R.W., 1975. Subsoiling. In: Soil Physical Conditions and Crop Production. Proc. Conf. Soil Scientists of the Agricultural Development and Advisory Service, 3--5 January 1972, London, pp. 189--204.

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Taylor, H.M. and Bruce, R.R., 1968. Effect of soil strength on root growth and crop yield in the southern United States. Trans. 9th Int. Congr. Soil Sci., Adelaide, Australia, ISSS and Angus and Robertson, Melbourne, Vol. 1 pp. 803--811.

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effect of deep tillage on soil physical properties and maize yields on coarse textured soils

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