Soil & Tillage Research, 7 (1986) 117--134 117 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

E F F E C T S O F S O I L C O M P A C T I O N B Y R O L L I N G O N S O I L S T R U C T U R E A N D D E V E L O P M E N T O F M A I Z E I N N O - T I L L A N D D I S C P L O U G H I N G S Y S T E M S O N A T R O P I C A L A L F I S O L

B. KAYOMBO' and R. LAL 2

I Sokoine University of Agriculture, Morogoro (Tanzania) International Institute of Tropical Agriculture, Ibadan (Nigeria)

(Accepted for publication 10 December 1985)

ABSTRACT

Kayombo, B. and Lal, R., 1986. Effects of soil compact ion by rolling on soil structure and development of maize in no-till and disc ploughing systems on a tropical Alfisol. Soil Tillage Res., 7: 117--134.

A field experiment conducted over three consecutive rainy seasons during 1982-- 1983 investigated the effects of three levels of seedbed traffic, but with no subsequent traffic, on soil physical propert ies and growth of maize (Zea mays) using the no-tillage and disc ploughing systems of seedbed preparation. The main treatments consisted of disc ploughing to 20 cm depth followed by harrowing, compared with the no-til- lage system. Traffic treatments of 0, 2 and 4 passes of a tractor-drawn 2 Mg roller were sub-plots in a split-plot design experiment. All tillage and traffic treatments were con- trolled so they always occurred in the same place, season after season. The 4-pass treat- ment significantly increased penetrometer resistance and dry-soil bulk density, and considerably decreased total porosity, saturated hydraulic conductivity and infiltra- t ion rate, more so in disced plots than in no-till plots. The 2-pass t reatment had a sig- nificant but less marked effect on soil physical propert ies than the 4-pass treatment. Soil compaction thus resulted in reduced percent emergence, plant height, leaf area index and root growth. Eight weeks after seeding, the root densities in the 0--7 cm soil layer were 2.8, 1.6 and 1.3 mg cm -3 for no-till, and 2.1, 1.3 and 0.9 mg cm -3 for disced plots for 0, 2 and 4 passes, respectively. The 4-pass t reatment reduced the mean maize grain yield over three consecutive seasons by 48 and 63% in no-till and disc-plough- ed systems, respectively, compared to the zero traffic treatment.

INTRODUCTION

C o m p a c t i o n o f a g r i c u l t u r a l so i l s c a n r e s u l t f r o m t h e t r a f f i c o f f a r m m a - c h i n e r y a n d s o i l - e n g a g i n g i m p l e m e n t s . So i l c o m p a c t i o n i n c r e a s e s b u l k d e n s i t y a n d s h e a r s t r e n g t h , a n d d e c r e a s e s p o r o s i t y a n d p e r m e a b i l i t y t o a i r a n d w a t e r f l o w (Dav i e s e t a l . , 1 9 7 3 ) . I n c r e a s e d m e c h a n i z a t i o n is t h u s v i e w e d w i t h c o n c e r n , b e c a u s e t h e r e s u l t i n g soft c o m p a c t i o n can s i g n i f i c a n t l y h a m p e r t h e p e r f o r m a n c e o f v a r i o u s c r o p s ( B a r n e s e t al . , 1 9 7 1 ; C h a n c e l l o r , 1 9 7 6 ; R a g h a v a n e t al . , 1 9 7 8 ; S o a n e e t al . , 1 9 8 2 ; C a n a r a c h e e t al . , 1 9 8 4 ) .

0167-1987/86/$03.50 © 1986 Elsevier Science Publishers B.V.

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Although in tropical Africa mechanization is increasing, the research in- formation concerning the effects of compact ion on soil properties and crop growth is rather scanty. In tropical Africa, compact ion caused by mechanical land clearing has serious implications for post-clearing land management (Cunningham, 1963; Ahn, 1968; Lal and Cummings, 1979; Hulugalle et al., 1984). In East Africa, Pereira and Jones (1954) demon- strated the disadvantage of progressive soil structural deterioration with ploughing and discing in successive seasons. Work at the International Insti tute of Tropical Agriculture in Nigeria showed that compaction by mechanized farm operations for cultivating grain crops was severe, par- ticularly on the headlands, whereas with manual operations of seeding, spraying and harvesting, soil compact ion was not a problem even after 11 years of cont inuous cropping (Lal, 1982, 1985). Soils with clays of low cation activity are particularly hard setting. The mechanisms respon- sible for this behaviour are not ye t completely understood. There is, there- fore, a need for further research on the effects of traffic-induced com- paction on soil properties and resulting crop performance, as well as on the methods and advantages o f controlled traffic in crop production.

The objective of the present s tudy was to evaluate the effects of three levels of seedbed traffic including zero traffic, but with no subsequent traffic, on changes in physical properties of an Alfisol and on the growth and yield of maize in no-till and in disc-ploughed systems of seedbed pre- paration.

MATERIALS AND METHODS

Following preliminary observations that mechanized planting and her- bicide spraying adversely affected crop emergence and plant establishment (as a result of wheel traffic during these operations), and may affect sub- sequent yields on both disc-ploughed and no-till land (I.I.T.A., 1981), a field experiment based on the controlled traffic concept was conducted in three consecutive growing seasons during 1982--1983 at the experi- mental farm of the International Institute of Tropical Agriculture (I.I.T.A.), Ibadan, Nigeria. I.I.T.A. is located in a region of bi-modal rainfall distri- bution with two distinct growing seasons, one from April to July and the other from August to November. The total annual rainfall varied from 908 mm in 1982 to 921 mm in 1983. The weather parameters during the three growing seasons are shown in Table I. Rainfall in the second growing season of 1982 was much below the soil-moisture demand. In 1983, how- ever, the rainfall exceeded evaporation during May--July in the first season, and during September in the second season. The predominant soil series at the experimental site is Egbeda (Moormann et al., 1975), the dominant features of which are the coarse-textured surface horizons and the pre- dominance of angular and sub-angular quartz gravel in the subsoil. The soil is derived from fine-grained bioti te gneiss and schist parent material

TABLE I

Growing season rainfall, open pan evaporation and air temperature at I.I.T.A.

119

Second season 1982 August September October November Total

Rainfall (ram) 76.0 66.8 103.5 10.4 256.7 departure ' (mm) -34 .0 -115 .2 -62 .0 -22 .6 -233.8

Mean air temp. (°C) 24.0 25.5 25.7 27.0 -- Open pan evap. (ram) 89 97 125 136 447

First season 1983 April May June July Total

Rainfall (ram) 80.8 236.2 160.8 108.4 586.2 departure' (ram) -59 .2 86.2 -20 .0 -37 .6 -30 .6

Mean air temp. (°C) 29.0 27.5 25.9 24.7 -- Open pan evap. (mm) 170 155 119 86 530

Second season 1983 August Septerhber October November Total

Rainfall (mm) 36.1 139.2 38.3 28.6 242.2 departure ' (mm) -85 .9 -42 .0 -133.7 -3 .4 -265 .0

Mean air temp. (°C) 24.0 25.4 26.9 27.8 -- Open pan evap. (mm) 75 94 129 145 443

' Departure from a 30-year average.

and is classified as an Alfisol (Oxic Paleustalf) according to Soil Taxonomy {Soil Survey Staff, 1975).

Prior to the initiation of the experiment, the site was disc-ploughed and cropped to maize for four years and subsequently put under vegeta- tion fallow for two years. Beginning in September of 1982, treatments were laid out in a split-plot design with three replications. Discing (D) and no-tillage (NT) were the main treatments with sub-plots for different levels of seedbed traffic. Discing was performed by a tractor-drawn disc plough to a depth of 20 cm followed by harrowing. The no-tillage plots were sprayed with paraquat (1-1' dimethyl-4, 4'-bipyridylium ion) at the rate of 2.5 l ha -1. Traffic treatments consisting of 0, 2 and 4 passes of a 2-Mg roller (50 cm diameter and 180 cm length) pulled by a 33.6-kW tractor were then performed on both disced and no-tilled plots. The roller was chosen as a compacting device due to its easy manoeuvrability and suitability for uniform compaction of coarse-textured soils on small-sized plots of 14.9 X 5.5 m (Capper and Cassie, 1976). The roller simulated normal field traffic in the weight range of 1.5--2.5 Mg. The contact area between the roller and the soil was 0.1729 m:. Thus, the contact pressure exerted by the roller on the soil was 113 kPa per pass, well within the typical range of 100--300 kPa observed on wheel-tracked soils under cereal crop production (Voorhees et al., 1985). All roller traffic was controlled, so it always occurred in the same location, season after season. Tractor wheel tracks (resulting from the action of pulling the roller) were not considered

120

when sampling. There was neither cultivation on trafficked plots before sowing nor additional roller traffic after seeding.

Maize (Zeq mays L.; cv. TZPB) was sown manually using dibblers at a row spacing of 75 cm, plants being spaced at 25 cm in the row. Fertilizer consisted of 120 kg ha -1 N (40 kg at planting and 80 kg four weeks later) as urea, 26 kg ha -1 P as single superphosphate, and 30 kg ha -1 K as muriate of potash. Maize was planted on 17 September 1982 {second season), and on 13 April (first season), and 13 September 1983 (second season).

Soil bulk density was measured immediately after the application of traffic t reatments by the core method (Blake, 1965) down to a depth of 20 cm in 5-cm increments. Total porosity was calculated from the re- lationship between bulk density and particle density. Penetrometer resis- tance was measured with a pocket penetrometer on the soil surface, and with a recording penetrometer from 5 to 30 cm in 5-cm increments. Satu- rated hydraulic conductivi ty was determined on undisturbed cores using a constant-head permeameter (Klute, 1965), the samples being soaked for 24 h prior to measurements being made. Soil moisture was measured gravi- metrically in the 0--10-cm layer immediately after the application of traffic treatments. Weekly measurements of soil moisture content at 0--10 cm depth were made gravimetrically during the first season of 1983. Water infiltration capacity was determined with a double ring infiltrometer for a 3 h period in January during the dry season. The infiltration data were analysed according to the method of Phillip (1957) to obtain equilibrium infiltration rates.

Seedling emergence was determined in each experimental unit until no additional germination occurred. The number of leaves and plant height were determined every two weeks. Leaf area was measured every two weeks by means of a leaf area meter {Lambda Instrument Corporation, Lincoln, NE). The leaf area index was obtained by dividing the leaf area by the unit land area occupied by the plant. During the first season of 1983, root samples were taken by the core method {BShm, 1979) at two-week intervals in 7-cm increments down to 21 cm from areas where shoots had been removed for measurements of growth. These samples were saturated overnight and then washed with a gentle spray of water over a 2-mm sieve. Washed roots were picked up by forceps, rewashed and then dried at 60°C. Roo t density was expressed as the weight of dry roots per unit volume of soil (mg cm-3). At maturi ty, the maize was harvested manually, shelled and the grain yield recorded at 10% (w/w) moisture content .

RESULTS AND DISCUSSION

Soil properties

Dry bulk density Changes in the dry bulk density resulting from tillage and traffic treat-

ments are given in Table II. Moderate (2 roller passes) and heavy (4 roller

121

passes) traffic significantly (P < 0.05) increased the dry bulk density of both disced and no-till soil down to 10 cm depth in September 1982 com- pared to the non-tracked (0 roller pass) treatments. In April and September 1983, marked increases of dry bulk density of the moderately and heavily trafficked treatments were generally detected down to 15 cm depth in no-till plots and up to 20 cm depth in disced plots. This was partly due to cumulative compaction effects from the previous season, and partly due to the high rainfall received in September 1983 (Table I) which made the soil more susceptible to roller traffic. Due to continuous cropping in subsequent seasons (Khatibu et al., 1984), the dry bulk density of the non- tracked soil of both no-till and disced plots was comparatively higher in September 1983 than during the two previous periods of measurement (Table II).

T A B L E II

Ef fec ts of til lage and t raf f ic t r e a t m e n t s o n d ry bu lk dens i ty (Mg m -3) of the soil '

Tillage Rol ler Soil d e p t h ( cm) passes

0--5 5--10 1 0 - - 1 5 15--20

15 S e p t e m b e r 1982 No -till

Discing

11 Apri l 1983 No -till

Discing

11 S e p t e m b e r 1983 No -till

Discing

0 1 .32d 1 .45b 1.52a 1 .55a 2 1 .47c 1 .50b 1 .53a 1.54a 4 1 .57ab 1 .58a 1 .55a 1 .56a

0 1 .29d 1.40c 1 .38b 1.47a 2 1 .48bc 1 .44bc 1 .42b 1.49a 4 1 .61a 1.58a 1 .46ab 1.51a

0 1 .22d 1 .29c 1.37c 1 .43b 2 1 .53b 1 .50b 1 .48b 1 .49ab 4 1 .67a 1 .64a 1.60a 1.54a

0 1 .05e 1 .13d 1 .25d 1.33c 2 1 .47c 1 .46b 1.39c 1.51a 4 1 .71a 1 .69a 1.62a 1.56a

0 1 .51b 1 .54c 1 .56c 1 .59bc 2 1 .73a 1 .64b 1 .63b 1.66a 4 1 .71a 1 .70ab 1 .60bc 1 .65ab

0 1 .37c 1 .39d 1.36d 1.52c 2 1 .76a 1 .73a 1 .67ab 1.66a 4 1 .79a 1 .79a 1.72a 1.70a

' The le t te rs a---e d e n o t e s ignif icance at the 5% level using D u n c a n ' s new mul t ip le range test . Means w i th same le t te r are n o t s igni f icant ly d i f fe ren t .

122

To tal porosity Moderate and heavy traffic considerably decreased the total porosity

of the soil in both no-till and disced plots down to 10 cm depth in Septem- ber 1982 and down to 20 cm depth in April 1983 (Table III). For instance, in April 1983, moderate and heavy traffic decreased the total porosity by 5.8 and 10.8% under no-tillage and by 12.3 and 21.3% under discing at 0--5 cm depth, respectively, compared to the values of the non-tracked treatments. The corresponding total porosity reductions at 15--20 cm depth were 2.8 and 4.0% under no-tillage and 4.7 and 8.3% under discing. In September 1983, roller traffic significantly reduced the total porosity of no-till soil down to 10 cm depth, whilst that of disced plots was markedly decreased down to 20 cm depth. Significant decreases in the total porosity of trafficked plots under discing (as compared to those of the relatively undisturbed no-till soil) were possibly due to the high rainfall in September 1983 and the cumulative compaction effects from previous seasons.

TABLE III

Effects of tillage and traffic treatments on total porosity (%, v/v) of the soiP

Tillage Roller Soil depth (cm) passes

0--5 5--10 10--15 15--20

15 September 1982 No -till

Discing

11 April 1983 No-till

Discing

11 September 1983 No-till

Discing

0 50.5a 46.0a 43.0b 42.3a 2 44.5bc 44.2bc 43.0b 42.9a 4 41.5cd 41.3cd 41.7b 41.8a

0 52.3a 47.5a 48.4a 44.7a 2 45.4b 45.5ab 46.8a 43.7a 4 39.6d 40.5d 45.5ab 43.4a

0 47.8b 47.6b 47.3b 46.0b 2 42.0d 43.8c 44.0c 43.2bc 4 37.0e 38.0d 39.8d 42.0c

0 57.0a 54.7a 52.8a 49.7a 2 44.7c 45.3bc 48.0b 45.0b 4 35.7e 36.3d 38.6d 41.4c

0 43.0b 41.9b 41.1b 40.0ab 2 34.7c 38.1c 38.5bc 37.4bc 4 35.5c 35.9c 39.6b 37.7b

0 48.3a 47.6a 48.7a 42.6a 2 33.6c 34.7cd 37.0cd 37.4bc 4 32.5c 32.5d 35.1d 35.9c

i The letters a--e denote significance at the 5% level using Duncan's new multiple range test. Means with same letter are not significantly different.

123

Throughout the range of depths measured, the total porosi ty of the disced non-tracked (0 roller pass) t rea tment was highest (Table III). Similar results were repor ted for ferruginous sandy loam soils in Botswana (Will- cocks, 1981), Senegal (Chopart, 1983) and Kikuyu red loam (Rhodic Paleu- dult) soils of East Africa (Hosegood, 1964).

Penetrometer resistance Moderate and heavy traffic significantly increased the penet rometer

resistance on the soil surface of both no-till and disced plots (Table IV).

TABLE IV

Average values of penetrometer resistance (kPa) of the soil surface of various tillage and traffic treatments 1

Tillage Roller 15 September 1982 11 April 1983 11 September 1983 passes

No-till 0 165c 196d 111c 2 300b 314b 348b 4 339ab 431a 424a

Discing 0 2 - - - - - -

2 310b 264c 378b 4 407a 431a 438a

The letters a--d denote significance at the 5% level using Duncan's new multiple range test. Means with same letter are not significantly different. 2 Soil was too soft to register any values.

Penet rometer resistances measured by a recording penet rometer down to 30 cm depth are shown in Fig. 1. The penet rometer resistances of the trafficked t reatments significantly increased down to 15, 20 and 25-cm soil depths in September 1982, April and September 1983, respectively, in comparison to those of non-tracked treatments. The gap in penetro- meter resistance between the non-tracked treatments and those of traf- ficked t reatments considerably widened in September 1983. At the "nor- mal" ploughing depth of 20 cm, for instance, the penet rometer resistances o f the non-tracked treatments were 3.3 MPa for no-tillage and 3.0 MPa for discing, whereas moderate and heavy traffic recorded penet rometer resistances of 4.2 and 4.5 MPa under no-tillage and 4.3 and 4.4 MPa under discing, respectively. This apparent grouping of the penet rometer resis- tances between the non-tracked and trafficked t reatments in September 1983 was at t r ibuted to the cont inuous cropping and cumulative compac- tion effects f rom the two previous growing seasons.

Saturated hydraulic conductivity The saturated hydraulic conduct ivi ty of the non-tracked no-till and disced

plots was higher than that o f modera te ly and heavily t raff icked t reatments

124

0

5

i0

15

20

25

30

0

5

I0

15

20

~ 2s

0

5

10

15

20

25

30

15 Sept 1982

,

I 2 3 4 5

11 Aprit 1983

1 2 3 4 5

11 Sept 19B3 LSD (5%)

o - - ~ 2 I

o-.. -o 40 ::

1 2 3 4 5 6

Penetrometer resistance ~a

Fig. 1. Variation of penetrometer resistance with depth immediately after tillage and traffic treatments.

of either no-tillage or discing over a 0--15-cm depth (Table V). Moderate and heavy traffic significantly reduced the saturated hydraulic conductivity in the 0--15-cm depth layer. However, there was considerable variation in saturated hydraulic conductivity values for all treatments in the 10--20- cm depth layer. This variation was possibly due to a considerable spatial variation in gravel concentration of these soils (Lal, 1979). Babalola (1978) reported a variation in the coefficient of variation of 48--147% in saturated hydraulic conductivity measurements of an Alfisol (Oxic Paleustalf) near Ibadan, Nigeria.

Infiltra tion After one cropping season, the 3-h cumulative infiltration for the non-

tracked treatment was 84.2 cm under no-tillage and 135.5 cm under discing, and their respective equilibrium infiltration rates were 23.4 and 41.6 cm

125

TABLE V

Effects of tillage and traffic treatments on saturated hydraulic conductivity (cm h - ' ) of the soiP

Tillage Roller Soil depth (cm) passes

0--5 5--10 10--15 15--20

15 September 1982 No -till

Discing

11 April 1983 No-till

Discing

11 September 1983 No -till

Discing

0 125.0a 112.5a 118.7a 113.8a 2 72.5bc 76.3bc 87.5ab 93.2a 4 38.1c 40.0c 60.0b 71.2a

0 106.4ab l l 0 . 0 a b 97.6a 100.0a 2 57.5c 62.5c 67.7b 87.4a 4 37.5c 48.8c 67.7b 75.0a

0 172.5a 166.3a 152.5a 97.4a 2 70.0b 66.2b 105.0b 107.9a 4 41.1cd 61.3b 80.8b 90.0a

0 153.6a 155.0a 157.4a 152.5a 2 50.0bc 61.3b 67.5b 93.7a 4 24.4d 40.0b 67.5b 82.5a

0 137.5a 137.5a 135.0a 125.3a 2 50.0b 87.5b 100.0b 87.8a 4 25.0b 62.6bc 82.5bc 100.0a

0 190.0a 150.9a 157.7a 125.3a 2 21.2b 50.0c 90.0b 120.1a 4 21.2b 42.5c 74.8c 106.9a

' The letters a--d denote significance at the 5% level using Duncan's new multiple range test. Means with same letter are not significantly different.

h - ' ' in J a n u a r y 1 9 8 3 (F ig . 2) . T h e i n f i l t r a t i o n r a t e s f o r m o d e r a t e a n d h e a v y t r a f f i c w e r e 12 .3 a n d 9.1 c m h - ' u n d e r n o - t i l l a g e , a n d 28 .1 a n d 13 .1 c m h - ' u n d e r d i s c ing , r e s p e c t i v e l y . H o w e v e r , t h e g a p in t h e i n f i l t r a t i o n r a t e b e t w e e n n o n - t r a c k e d a n d t r a f f i c k e d t r e a t m e n t s w i d e n e d c o n s i d e r a b l y in J a n u a r y 1 9 8 4 . T h e e q u i l i b r i u m i n f i l t r a t i o n r a t e s f o r t h e n o n - t r a c k e d t r e a t m e n t w e r e 4 3 . 8 c m h - ' u n d e r n o - t i l l a g e a n d 4 4 . 3 c m h -~ u n d e r d i sc ing . M o d e - r a t e l y a n d h e a v i l y t r a f f i c k e d t r e a t m e n t s r e c o r d e d i n f i l t r a t i o n r a t e s o f 11 .9 a n d 10 .4 c m h -~ u n d e r n o - t i l l a g e a n d 6 .8 a n d 1.9 c m h - ' u n d e r d i s c ing , r e s p e c t i v e l y (F ig . 2) . Th i s g a p in t h e i n f i l t r a t i o n r a t e b e t w e e n n o n - t r a c k e d a n d t r a f f i c k e d t r e a t m e n t s was a t t r i b u t e d t o a c u m u l a t i v e i n c r e a s e in so i l c o m p a c t i o n o f t h e t r a f f i c k e d p l o t s as a r e s u l t o f t w o s e a s o n s o f c o n s e c u t i v e c r o p p i n g .

126

150

I00

5O

o =

0

150 >

1 0 0

J a n u a r y 1 9 8 3

NT a-----o 0 c-- --~ 2

e~.- .. - - o 4

i~-- . . - - e 4

~: . . -~? :~ : : : : :~ ' " - " - -

l

30 60 90 120 150 180

January 1984

50 ~

0

3 0 6 0 9 0 1 2 0 1 5 0 1 8 0

Time (min)

Fig. 2. Cumulative infiltration curves in disc-ploughed and no-till plots for different levels o f seedbed traff ic , measured in January 1 9 8 3 and January 1 9 8 4 .

T A B L E VI

Soi l mois ture c o n t e n t (%, w / w ) at 0 - - 1 0 cm depth i m m e d i a t e l y after ti l lage and traffic treatments '

Til lage Rol ler 15 September 1 9 8 2 11 April 1 9 8 3 11 September 1 9 8 3 passes

No-t i l l 0 7 .6a 5 .1a 10 .3a 2 7 .9a 3 .6b 8 .2b 4 7 .8a 3 .0c 8 .4b

Discing 0 8 .5a 1 .6d 8 .5ab 2 8 .4a 1 .9d 10 .6a 4 7 .7a 1 .1e 9 .0a

' The letters a--e d e n o t e s ignif icance at the 5% level using Duncan's n e w mult ip le range test . Means w i th same letter are no t s igni f icant ly dif ferent .

127

Soil moisture Significant differences in soil moisture content between treatments

occurred in April 1983, and on no-till plots in September 1983 (Table VI). In April 1983, the soil moisture content in the no-till plots was higher than in the disced treatments for all levels of roller traffic. For instance, the soil moisture content in the heavily trafficked treatment was reduced by 2.1% (w/w) in the no-till and by 4.0% (w/w) in the disced t reatment compared to non-tracked no-till control. Lal (1974, 1976) also observed that soil moisture contents in no-till plots were higher than in disced plots. An increase in soil moisture retention capacity in untilled soils renders more water available for crop use. Soil moisture reserves in non-tracked no-till and disced plots were generally higher than those of the moderately and heavily trafficked treatments of either tillage system throughout the first season of 1983 (Fig. 3).

80

50

4O

2O

April

20

NT

15 D

_r . I ~ i i I i

May June Jul

~ 0

o----~ 2 o-.. -e 4

= ~ 0 • --~ 2 ~--..--4 4

A p r i l M a y .Tune July

Fig. 3. Soil moisture content as affected by tillage methods and traffic treatments in the first season of 1983.

Crop response

Plant growth The emergence percentage of maize as affected by tillage and traffic

t reatments is shown in Table VII. Moderate traffic reduced percent emergence

128

TABLE VII

Emergence (%) of maize for various tillage and traffic treatments 1

Tillage Roller September 1982 April 1983 September 1983 passes

No-till 0 81.8a 87.8a 84.5ab 2 77.8a 91.7a 88.6a 4 66.0b 85.9a 79.1b

Di~ing 0 86.5a 88.2a 90.7a 2 83.2a 58.6b 72.9c 4 79.3a 55.1b 74.9bc

1 The letters a--c denote significance at the 5% level using Duncan's new multiple range test. Means with same letter are not significantly different.

in disced plots, whereas heavy traffic decreased the percentage emergence in both disced and no-till plots. In spite of increased cumulative soil com- paction effects in April and September 1983, the percent emergence in trafficked no-till plots was relatively high (compared to that of disced plots). Possibly this is due to the presence of old root channels which facilitated adequate supplies of water and air to emerging seedlings, and the beneficial "cushioning ef fec t" of surface plant-residues on the soil as the roller passed on top.

Differences in plant heights of maize between non-tracked and trafficked treatments markedly increased in the first and second seasons of 1983 (Fig. 4). At 8 weeks after planting during the second season of 1983, for example, moderate traffic reduced the average plant height by 35% under the no-till system and by 47% under discing. Heavy traffic reduced the plant heights of maize by 50% under no-tillage and by 62% under discing, compared to the non-tracked treatment. Comparable reductions in plant heights from moderate and heavy traffic were also reported by Raghavan et al. (1978) and Gaultney et al. (1982).

Seedbed traffic reduced the number of leaves of maize in the first grow- ing season, but the differences in leaf numbers between non-tracked and trafficked treatments increased considerably in both tillage systems in the second season of 1983 (Fig. 4). At 8 weeks after planting, the leaf numbers for zero, moderate and heavy traffic were 12.7, 10.3 and 9.5 for no-tillage, and 13.0, 9.7 and 8.8 for discing, respectively. Heavy traffic thus reduced the numbers of leaves by 25% under no-tillage, and by 34% under discing in comparison to non-tracked treatments. Similar results were obtained by Raghavan et al. (1978) in a clay soil in Canada.

Seedbed traffic reduced the leaf area index of maize at all times, but most severely in the third consecutive cropping season, namely the second season of 1983 (Fig. 4). The highest reduction in leaf area index was caused by heavy traffic on disced plots. At 8 weeks after planting, the leaf area

129

300

25oi "~200

~ iS0

ioo

N SO

0

i 0

s

z 0

4

3

z

1

0

NT ~ 0 ...../ * c-- --o 2

~"/'I I I I i J i

5D(5%1 : ]: I I [ = I

L i

2 4 6 8 i0 12

Wee~s after planting

Fig. 4. Ef fec t s of tillage m e t h o d s and t raf f ic t r e a t m e n t s o n p l an t he ight , leaf n u m b e r and leaf area index of maize in the s econd season of 1983.

index of the heavily trafficked treatments was reduced by 44% under no- tillage and by 68% under discing compared to non-tracked plots. Reduced leaf area indices in traffic treatments resulted from reductions in leaf num- bers and not from the area of the leaves.

Root growth The root growth of maize as monitored in the first season of 1983 is

shown in Fig. 5. There were significant differences in root density between non-tracked and trafficked treatments for both no-tillage and discing throughout the depth of measurement. At each level of seedbed traffic, the root density in no-till was higher than in discing. At 8 weeks after planting, the root densities in the top 7 cm of soil for zero, moderate and heavy traffic were 2.3, 1.6 and 1.3 mg cm -3 under no-tillage, and 2.1, 1.3 and 0.9 mg cm -3 under discing, respectively. Heavy traffic thus reduced the root density of maize by 42% in no-tillage and by 56% in discing. Root density declined sharply with increasing soil depth. This was possibly caused by an increased gravel concentration with depth which, as in earlier studies in the vicinity of the experimental site (Babaiola and Lai, 1977; Maurya and Lal, 1980), was observed in the course of the present root sampling.

130

2.4 2 .4 1.4

2 . 0 2.0 ~.C

1.6 ~ 1.6 LSD(S%) T .6

('// ~.2 . ~ D . : o a-..-~ 4

~ 1 . 2 2 ] ._.-. 2

"~ 0. B '! , ./ "~ o.B ~.~ _

~ /

0.4 [ 0.4 / \ . ,.4

. I o . 0 , , , o.0 L__+, , , , , , ,

4 6 8 I0 4 6 8 I0 4 6 g 1 0 Weeks a f ter plant ing

Fig. 5. R o o t growth of maize for dif ferent tillage and traffic treatments, measured in the first season of 1983 .

t,u

>.

c

u9

7

5

4

3

2

1

0

NO-TILL DISCINO

7 ~ 1 9 8 3 ~D(S%)

o

S 2 pass ~ 4 pass

4

2

1

0

NO-TILL DISCING

5

4

3

2

1

0

NO-TILL DISCING

Fig. 6. Effects o f traff ic- induced soil compact ion on maize grain yield.

131

Grain yields Seedbed traffic reduced maize grain yields in all three growing seasons

under both no-till and disced treatments, but the severity of the effects of roller-track compact ion increased considerably in the third consecutive season (i.e. the second season of 1 9 8 3 ) a n d was particularly more marked on the disced than on the no-till plots (Fig. 6). In the second season of 1983, maize yields for zero, moderate and heavy traffic were 4.7, 3.0 and 2.3 Mg ha -1 under no-tillage, and 5.4, 1.6 and 1.4 Mg ha -1 under discing. In the second season of 1982, and the first and second seasons of 1983, heavy traffic reduced maize yields by 51, 41 and 52% under no-tillage, and by 53, 61 and 75% under discing, respectively, compared to non-tracked plots. Reduced maize grain yield from trafficked treatments was due to a low grain weight per cob (Table VIII). Reduced grain yields in trafficked treatments could be at tr ibuted to adverse soil conditions, which subse- quent ly reduced root growth. Relationships between soil physical properties and maize grain yields are given in Table IX. Maize yield reductions of

T A B L E VIII

Weight o f maize grains per cob (g) as a f fec ted by tillage and t raff ic t r e a t m e n t s ~

Tillage Rol ler Second season 1982 Fi rs t season 1983 Second season 1983 passes

No-til l 0 1 4 1 . 8 b 98 .0b 113 .9b 2 89 .5d 64 .3d 72 .0c 4 68 .6e 58 .6d 54 .0d

Discing 0 172 .9a 150 .0a 136 .1a 2 114.2c 83 .2c 41 .6e 4 80 .0de 60 .8d 35.6e

The le t te rs a--e d e n o t e s ignif icance a t the 5% level using D u n c a n ' s new mul t ip le range test . Means w i th same le t te r are n o t s igni f icant ly d i f fe ren t .

T A B L E IX

Re la t i onsh ip s b e t w e e n soil p rope r t i e s (X) at 0 - -10 cm d e p t h and maize yield (Y; Mg ha -1)

Soil p r o p e r t y Regress ion e q u a t i o n Cor re la t ion coef f i c ien t (r) 1

Dry bu lk dens i ty (Mg m -3) To ta l po ros i t y ( ra t io) E q u i l i b r i u m in f i l t r a t ion ra te ( cm h -1 ) P e n e t r o m e t e r res i s tance (MPa) Soil mo i s tu r e c o n t e n t (%, w /w)

Y = 1 7 . 3 - 8 .8X 0 .80*** Y = - 6 . 3 + 23 .7X 0 .79*** Y = 1.5 + 0 .6X 0 .82*** Y = 7 . 8 - 1 .7X 0 .59* Y = 2.8 + 12 .0X 0 .17NS

NS and *, **, *** = n o t s ignif icant , and s igni f icant at P < 0 . 0 5 , P < 0.01 and P < 0 .001 , respect ively .

132

comparable magnitude resulting from moderate and heavy tractor-traffic on the soil were reported by Raghavan et al. (1978), Gaultney et al. (1982) and Canarache et al. (1984).

CONCLUSIONS

(1) Heavy traffic (4 roller passes) considerably increased the penetrometer resistance and the average dry bulk density of the soil from 0 to 20 cm depth, and significantly reduced the total porosity, the saturated hydraulic conductivity and the equilibrium infiltration rate. Moderate traffic (2 roller passes) had a significant but less marked effect on soil properties than that of heavy traffic.

(2) The effects of traffic on soil properties were more marked in the 0--10-cm depth layer than in deeper layers, and in the disc-ploughed sys- tem more than in no-tillage.

(3) Heavy traffic significantly reduced the percent emergence, plant height, leaf number and leaf area index of maize. The reduction was more marked on disced plots than on no-tilled ones.

(4) Moderate and heavy traffic significantly reduced the root growth of maize throughout the 0--21-cm depth. At each level of seedbed traffic, the root density of maize was higher under no-tillage than under discing.

(5) Moderate and heavy traffic significantly reduced the grain yield of maize. Yield reductions were more severe in the heavily trafficked treat- ments. The severity of the effect of roller-track compaction on grain yield increased with repeated traffic t reatments in subsequent seasons, and was particularly more marked on disced plots. In the second season of 1982 and the first and second seasons of 1983, heavy traffic reduced maize yields by 51, 41 and 52% under no-tillage and by 53, 61 and 75% under discing, respectively, compared to non-tracked plots. •

REFERENCES

Ahn, P.M., 1968. The effects of large scale mechanized agriculture on the physical prop- erties of West African soils. Ghana J. Agric. Sci., 1 : 35--40.

Babalola, O., 1978. Spatial variability of soil-water propert ies in tropical soils of Nigeria. Soil Sci., 126: 269--279.

Babalola, O. and Lal, R., 1977. Subsoil gravel horizon and maize root growth. II. Effects of gravel size, inter-gravel texture and natural gravel horizon. Plant Soil, 46: 347-- 357.

Barnes, K.K., Carleton, W.M., Taylor, H.M., Throckmorton, R.I. and Vanden Berg, G.E. (Editors), 1971. Compact ion of Agricultural Soils. Am. Soc. Agric. Eng., St. Joseph, MI, 471 pp.

Blake, G.R., 1965. Bulk density. In: C.A. Black, D.D. Evans, J.L. White, L.E. Ensiminger and F.E. Clark (Editors), Methods of Soil Analysis, Part 1. Am. Soc. Agron., Madison, WI, pp. 374--390.

BShm, W., 1979. Methods of Studying Root Systems. Springer-Verlag, Berlin, pp. 39--47.

133

Canarache, A., Colibas, I., Colibas, M., Horobeanu, I., Patru, V., Simota, H. and Tranda- firescu, T., 1984. Effect of compact ion by wheel traffic on soil physical propert ies and yield of maize in Romania. Soil Tillage Res., 4: 199--213.

Capper, P.L. and Cassie, W.F., 1976. The Mechanics of Engineering Soils. E. and F.N. Son, London, pp. 262--268.

Chancellor, W.J., 1976. Compaction of soil by agricultural equipment. Bull. 1881, Div. Agric. Sci., University of California, Davis, 53 pp.

Chopart, J.L., 1983. Effects of ploughing and minimum soil preparation in Senegal, Ivory Coast and Togo. In: T.O. Akobundu and A.E. Deutsch (Editors), No-tillage Crop Production in the Tropics. International Plant Protection Centre, Oregon State University, Corvallis, OR, pp. 193--194.

Cunningham, R.L., 1963. The effects of clearing a tropical forest soil. J. Soil Sci., 14: 334--345.

Davies, D.B., Finney, J.B. and Richardson, S.J., 1973. Relative effects of t ractor weight and wheel-slip in causing soil compaction. J. Soil Sci., 24: 399--409.

Gaultney, L., Krutz, G.W., Steinhardt, G.C. and Liljedahl, J.B., 1982. Effects of subsoil compact ion on corn yields. Trans. Am. Soc. Agric. Eng., 25 : 563--569, 575.

Hosegood, P.H., 1964. The effect of the Holt Basin Lister (Mark X model) on soil struc- ture, East Aft. Agric. For. J., 30: 26--30.

Hulugalle, N.R., Lal, R. and Ter Kuile, C.H.H., 1984. Soil physical changes and crop root growth following different methods of land clearing in Western Nigeria. Soil Sci., 138: 172--179.

I.I.T.A., 1981. International Insti tute of Tropical Agriculture, Annual Report for 1980. Ibadan, Nigeria, pp. 10--28.

Khatibu, A.I., Lal, R. and Jana, R.K., 1984. Effects of tillage methods and mulching on erosion and physical propert ies of a sandy clay loam in an equatorial warm humid region. Field Crops Res., 8: 2 3 9 - 2 5 4 .

Klute, A., 1965. Laboratory measurement of hydraulic conductivity of saturated soil. In: C.A. Black, D.D. Evans, J.L White, L.E. Ensiminger and F.E. Clark (Editors), Methods of Soil Analysis, Part 1. Am. Soc. Agron., Madison, WI, pp. 210--221.

Lal, R., 1974. No-tillage effects on soil properties and maize (Zea mays) production in Western Nigeria. Plant Soil, 40: 321--331.

Lal, R., 1976. No-tillage effects on soil propert ies under different crops in Western Nigeria. Soil Sci. Soc. Am. J., 40: 762--768.

Lal, R., 1979. Concentration and size of gravel in relation to neutron moisture meter and density probe calibration. Soil Sci., 127: 41--50.

Lal, R., 1982. Effect of 10 years of no-tillage and conventional ploughing on maize yield and properties of a tropical soil. Proc. 9th Conference International Soil Tillage Research Organizatio n, ISTRO, Osijek, Yugoslavia, pp. 111--117.

Lal, R., 1985. Mechanized tillage systems effects on propert ies of a tropical Alfisol in watersheds cropped to maize. Soil Tillage Res., 6: 149--161.

Lal, R. and Cummings, D.J., 1979. Clearing a tropical forest. I. Effect on soil and micro- climate. Field Crops Res., 2: 91--107.

Maurya, P.R. and Lal, R., 1980. Effects of no-tillage and ploughing on roots of maize and leguminous crops. Exp. Agric., 16: 185--193.

Moormann, F.R., Lal, R. and Juo, A.S.R., 1975. Soils of I . I .T .A. I . I .T .A. Tech. Bull. No. 3, International Insti tute of Tropical Agriculture, Ibadan, Nigeria, 48 pp.

Pereira, H.C. and Jones, P.A., 1954. A tillage study in Kenya coffee. II. The effects of tillage practices on the structure of the soil. Emp. J. Exp. Agric., 22: 323--331.

Phillip, J.R., 1957. The theory of infil tration: 4. Sorptivity and algebraic infiltration equations. Soil Sci., 84: 257--264.

Raghavan, G.S.V., McKyes, E., Gendron, G., Borglum, B. and Le, H.H., 1978. Effects of soil compact ion on development and yield of corn (maize). Can. J. Plant Sci., 58: 435--443.

134

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

Soil Survey Staff, 1975. Soil Taxonomy: A basic system of soil classification for making and interpreting soil surveys. U.S. Dep. Agric. Handbook 436 ,754 pp.

Voorhees, W.B., Evans, S.D. and Warnes, D.D., 1985. Effect of preplant wheel traffic on soil compaction, water use, and growth of spring wheat. Soil Sci. Soc. Am. J., 49: 215--220.

Willcocks, T.J., 1981. Tillage of clod-forming sandy loam soils in the semi-arid climate of Botswana. Soil Tillage Res., 1: 323--350.