Sep 11, 1983 - (Boone and Veen, 1982 ). Scanty available information on the effects of ...... John Wiley, New York, 350. PP. Macartney, J.C., Northwood, P.J., ...
Soil & Tillage Research, 21 ( 1991 ) 325-345
325
Elsevier Science Publishers B.V., Amsterdam
Characterizing compaction effects on soil properties and crop growth in southern Nigeria B. K a y o m b o a, R . L a l b, G . C . M r e m a c a n d H . E . J e n s e n d
aDepartment of Agricultural Engineering and Land Planning, Sokoine Universityof Agriculture, Morogoro, Tanzania bDepartment of Agronomy, The Ohio State University, Columbus, OH 43210, USA CFaculty of Agriculture, University of Botswana, Gaborone, Botswana dDepartment of Soil and Water and Plant Nutrition, The Royal Veterinaryand Agri?ultural University, Copenhagen, Denmark (Accepted 5 October 1990)
ABSTRACT Kayombo, B., Lal, R., Mrema, G.C. and Jensen, H.E., 1991. Characterizing compaction effects on soil properties and crop growth in southern Nigeria. Soil Tillage Res., 21: 325-345. A field experiment based on controlled traffic concept was conducted over three rainy seasons in a bimodal rainfall area during 1982-1983 with the objective of, firstly, determining the effects of trafficinduced compaction on soil physical properties, root growth and leaf nutrient concentration in maize (Zea mays L.), cowpea (Vigna unguiculata (L.) Walp) and soya bean (Glycine max Merr.) and secondly, characterizing soil compaction by evaluating soil physical properties which closely correlated with crop yields. Main treatments of tillage methods compared discing (to 20 cm depth followed by harrowing) to a no-tillage system. Traffic treatments of 0, 2 and 4 passes of a 2-Mg roller were subplots in a split-plot design experiment. The roller simulated field traffic in the 1.5-2,5 Mg weight range and exerted an average contact pressure of 113 kPa per pass on soil. Traffic-induced compaction decreased water infiltration rate and increased soil dry density and penetrometer resistance. Vertical root growth of maize and cowpea was consequently reduced down to 21 cm depth and that of soya bean down to 14 cm depth. Lateral root distribution was also markedly reduced. In the third consecutive growing season, traffic-induced soil compaction reduced the leaf nutrient concentration of Mg in no-tillage and P, Ca, K and Mn in discing for maize; Mg in discing for cowpea; and Ca in discing for soya bean. Traffic-induced soil compaction reduced grain yields of maize, cowpea and soya bean in all three seasons under both no-till and disced treatments, but the severity of this compaction increased considerably in the third consecutive season and was particularly more marked on the disced plots than on the no-till plots. The water infiltration rate was found to be the most sensitive soil property in characterizing soil compaction on this AIfisol in relation to crop yield.
INTRODUCTION Adverse soil compaction effects on plant growth in tropical Africa have been reported (Macartney et al., 1971; Kayombo and Lal, 1986a). Some studies on mechanical land clearing together with widespread abundance of
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326
B. KAYOMBO ET AL.
subsoil gravel horizons show that compaction severely inhibits crop root growth (Babalola and Lal, 1977a, b; Hulugalle et al., 1984). Consequently, the increased mechanical stress on the root system may reduce plant water and nutrient uptake. The effects of compaction on nutrient uptake by roots have received much less attention than effects on plant growth itself. Whereas compaction might be expected to increase the movement of ions to roots by diffusion (Kemper et al., 1971 ), restricted growth of roots generally results in smaller amounts of nutrients being absorbed from compacted than from uncompacted soil (Boone and Veen, 1982 ). Scanty available information on the effects of compaction on nutrient contents by crops in tropical Africa show some increase in nutrient contents by paddy rice (Ogunremi et al., 1986), and possible decrease in nutrient contents of maize (Babalola and Lal, 1977a, b). The consequences of compaction are particularly important when considering that increased mechanization is inevitable in tropical Africa to meet the high demand for food and crash crop production. There is, therefore, a need for further research on the effects of traffic-induced compaction on root growth and plant nutrient uptake of tropical crops. The literature available from tropical regions shows that crop yields are markedly reduced by excessive soil compaction (Seubert et al., 1977; Grewal et al., 1984; Kayombo and Lal, 1986a). Brouwer (1977) notes that the soil as a medium for plant growth not only affects the development and activity of roots directly but it also affects the growth and yield of the aboveground parts by modifying the function of the roots. As a result of soil compaction, pore size distribution is altered, total porosity is decreased, and there are changes in the movement and content of heat, air, water and nutrients in the soil (Warkentin, 1971; Kemper et al., 1971 ). The restricted growth of roots commonly observed in compacted soil has been variously attributed to all of these properties, and to the high mechanical resistance to plant roots (Taylor and Ratcliff, 1969 ). The final crop yield may, therefore, be used as a measure of the severity of soil compaction. In many tropical developing countries, resources rarely permit a complete programme of soil testing in compaction studies, and therefore, a simple and reliable diagnostic approach is needed to identify the existence of a soil compaction problem. Willcocks (1984) noted, for instance, that simple observation of the development of mature crop root systems in the field provided qualitative assessment of the need for some soil loosening in compacted Luvisols of semi-arid Botswana. The objective of this study was two-fold: (i) to determine the effects of traffic-induced compaction on soil physical properties, root growth and leaf nutrient concentration; (ii) to evaluate which of the soil physical properties is most sensitive to traffic-induced compaction and is significantly correlated with crop yield.
327
COMPACTION EFFECTS ON SOIL AND CROPS IN NIGERIA
MATERIALS AND METHODS
A field experiment based on the controlled traffic concept was conducted in three consecutive growing seasons during 1982-1983 at the International Institute of Tropical Agriculture (IITA) near Ibadan, Nigeria. The predominant soil series at the experimental site is Egbeda, whose distinct features are coarse-textured surface horizons and the predominance of angular and subangular quartz gravel in subsoil horizons. The soil is derived from fine-grained biotite gneiss and schist parent material and is classified as an Alfisol (Oxic Paleustalf) according to Soil Taxonomy (Soil Survey Staff, 1975 ). There are two growing seasons in this ecological zone: the first from April to July, and the second season from late August to mid-November. The total annual rainfall varied from 908 mm in 1982 to 921 mm in 1983. The weather during the three growing seasons is shown in Table 1. Rainfall in the second season in 1982 was much below moisture demand. In 1983, however, the rainfall exceeded open pan evaporation during May-July in the first season, and during September in the second season. Prior to initiation of the experiment, the site was disc-ploughed and cropped to maize for 4 years and subsequently put under vegetation fallow for 2 years. TABLE 1
Growing season rainfall, open pan evaporation, and air temperature at IITA Second season 1982
Rainfall ( m m ) Departure ~ Mean air temp. ( ° C ) O p e n pan evap. ( r a m )
August
September
76.0 -34.0 24.0 89
66.8 - 115.2 25.5 97
April
May
October 103.5 -62.0 25.7 125
November
Total
10.4 -22.6 27.0 136
256.7 -238.8 447
July
Total
First season 1983
Rainfall ( m m ) Departure ~
Mean air temp. ( ° C ) O p e n pan evap. ( m m )
80.8 - 59.2 29.0 170
236.2 86.2 27.5 155
August
September
June 160.8 - 20.0 25.9 119
108.4 - 37.6 24.7 86
586.2 - 30.6 530
Second season 1983
Rainfall (ram) Departure ~ Mean air temp. ( ° C ) O p e n pan evap. ( m m )
36.1 - 85.9 24.0 75
Departure from a 30-year average.
139.2 - 42.0 25.4 94
October 38.3 - 133.7 26.9 129
November 28.6 - 3.4 27.8 145
Total 242.2 - 265.0 443
328
B. KAYOMBO ET A L
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 subplots for different levels of seedbed traffic. Discing was done by a tractor-drawn disc plough to 20 cm depth followed by harrowing. No-till plots were sprayed with paraquat (1-1'dimethyl-4,4'-bipyridylium ion) at the rate of 2.5 1 ha-1 using a manually operated knapsack sprayer 1 week before planting. Traffic treatments consisting of 0 (zero), 2 (moderate) and 4 (heavy) passes o f a 2-Mg roller (60 cm in diameter and 180 cm long) pulled by a 33.6 kW tractor, were then performed on both disced and no-till plots. The roller was used as a compacting tool for its easy manoeuvrability and suitability for uniform compaction of coarse-textured soils on small-sized plots (Capper and Cassie, 1976 ). The roller simulated field traffic in the range of 1.5-2.5 Mg. The contact area between the roller and the soil was 0.1729 m 2. Thus the average 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 ). Each subplot was divided into three equal portions, each of which was planted to either maize (cv. 'TZPB'), cowpea (cv. 'IT82E-9') or soya bean (cv. 'TGx 306-036C'). Randomization was used to allocate a crop to a portion of a particular subplot. The size of the subplot was 82 m 2. All roller traffic was controlled so that it always occurred in the same place season after season. There was neither cultivation on trafficked plots before planting nor additional traffic after planting. Tractor wheel tracks (as a result of pulling the roller) were not considered when sampling. Crops were planted manually using dibblers at spacings of 25 X 75 cm for maize and cowpea, and 5 X 75 cm for soya bean. Soya bean seeds received no rhizobia inoculation before planting because the variety used nodulated freely with rhizobia indigenous in the experimental soil. Fertilizer applied uniformly at planting consisted of 120 kg h a - ~ N (40 kg at planting time and 80 kg 4 weeks later) as urea for maize, 26 kg ha-1 p as single superphosphate and 30 kg h a - 1 K as muriate of potash for maize, cowpea and soya bean. Cowpea and soya bean received no N. First season crops were planted during mid-April; second season crops during mid-September. Compaction-induced changes in soil dry density, soil moisture content and cumulative infiltration were measured by standard methods described by Black et al. (1965). All soil physical parameters, except infiltration, were measured immediately after the application of tillage and traffic treatments. Soil density was measured on undisturbed cores (5 cm in diameter and 5 cm high) down to 20 cm depth. In addition, penetrometer resistance was measured with a recording penetrometer from 5 to 30 cm depth in 5-cm increments. Soil moisture was measured gravimetrically in the 0-10 cm layer. Cumulative infiltration was measured by a double ring infiltrometer in January
COMPACTION EFFECTS ON SOIL AND CROPS IN NIGERIA
329
during the dry season. The results of the infiltration tests were analyzed according to Phillip's ( 1957 ) equation to compute equilibrium infiltration rates. In the first season of 1983, root density in the row was measured by taking soil cores (7 cm in diameter and 7 cm deep) at 2-week intervals down to 21 cm depth. Root density was also measured at 21 cm lateral distance from the row by core sampling at 7-cm lateral intervals. The cores were saturated overnight and then washed with a gentle spray of water over a 2-mm sieve. Washed roots were dried in the oven at 60 °C and then weighed. Ear leaf samples for maize at flowering and upper canopy leaf samples for cowpea and soya bean at anthesis, were collected each season. The leaf samples were oven-dried and ground to pass a 425/~m screen. Total N was determined colorimetrically using a Technicon Auto-Analyzer. P, K, Ca, Mg, Zn and Mn were determined by emission or atomic absorption spectrophotometry after wet digestion. Grain yield was recorded at 10% ( w / w ) moisture content at maturity. Measured soil properties were related to grain yield. Simple correlation coefficients were calculated according to Little and Hills (1978), and the stepwise regression procedure to determine the soil physical parameters which most affected crop yields according to Weisberg (1980). RESULTS AND DISCUSSION
Soil physical properties Soil bulk density Moderate and heavy traffic significantly (P~< 0.05) increased the soil dry density of both disced and no-till plots down to 10 cm depth in September 1982 compared with the nontracked (zero pass) treatments (Table 2). 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 in no-till plots and 20 cm depth in disced plots. This effect was partially due to cumulative compaction effects from the previous season, and partly due to the high rainfall received in September 1983 which made the soil more susceptible to roller traffic. The soil dry density of the nontracked soil of both no-till and disced plots was comparatively higher in September 1983 than during the two previous periods of measurement owing to continuous cropping in previous seasons.
Penetrometer resistance The penetrometer resistance of the trafficked treatments significantly increased down to 15, 20 and 25 cm soil depths in September 1982, April and September 1983, respectively, compared with those of nontracked treatments (Fig. 1 ). The gap in penetrometer resistance between the nontracked treatments and those of trafficked treatments considerably widened in September
330
B. KAYOMBO ET AL.
TABLE 2
Effects of tillage and traffic treatments on d r y b u l k d e n s i t y ( M g m - 3 ) of the soil t Tillage
Roller
Soil d e p t h ( c m )
passes 0-5
5-10
10-15
15-20
0
1.32 d
2
1.47 c
1.45 b
1.52 a
1.55
1.50 b
1.53 a
4
1.54
1.57 ab
1.58 a
1.55 a
1,56
0 2
1.29 d 1.48 b~
1.40 ~ 1.44 b~
1.38 b 1.42 b
1.47 1,49
4
1.61 a
1.58 ~
1.46 ab
15 September 1982 No-tillage
Discing
1.51 NS
11 April 1983 No-tillage
Discing
0 2
1.22 d 1.53 b
1.29 c 1.50 b
1.37 c 1.48 b
1.43 b 1.49 ab
4 0 2
1.67 a 1.05 e 1.47 c
1.64 a 1.13 a 1.46 b
1.60 a 1.25 d 1.39 c
1.54 ~ 1.33 c 1.51 a
4
1.71 ~
1.69 a
1.62 a
1.56 a
11 September 1983 No-tillage
Discing
0
1.51 b
1.54 c
1.56 c
1.59 bc
2
1.73 a
1.64 b
1.63 b
1.66 a
4
1.71 a
1.70 ab
1.60 bc
1.65 ab
0
1.37 c
1.39 a
1.36 a
1.52 c
2
1.76 ~
1.73 a
1.67 ab
1.66 ~
4
1.79 a
1.79 a
1.72 a
1.70 ~
~For each period of measurement, means within a column followed by the same superscript are not significantly different using Duncan's multiple range test at the 5% level of p r o b a b i l i t y . N S = n o t significant.
1983. This apparent grouping of the penetrometer resistance values was attributed to the continuous cropping and cumulative compaction effects from the two previous growing seasons. Soil moisture Significant differences in soil moisture content between treatments occurred in April 1983, and in no-till plots in September 1983 (Table 3). 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 example, the soil moisture content in the heavily trafficked treatment was reduced by 2.1% ( w / w ) in the r/o-till and by 4.0% ( w / w ) in the disced treatment compared with the nontracked no-till control. The merits of a no-tillage system, including soil moisture retention, in biostructurally active soils have been documented for some tropical regions (Lal, 1985 ).
COMPACTION EFFECTS ON SOIL AND CROPS IN NIGERIA
331
IS September 1882
25 30 i
i
i
i
1
2
3
/-
0
11 April 1983
S 10
E u
15
2o 28 30 1
2 II
3
September
o----'o2
o-. h
i~
l
5 LSO (5 °/*)
it::
i
=
2
3
Penetrometer
L 1983
~"'
resistance,
i
/.
MPa
Fig. 1. Variation of penetrometer resistance with depth immediately after tillage and traffic treatments.
Infiltration After one cropping season, the 3-h cumulative infiltration for the nontracked 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 h - l in January 1983 ( Fig. 2 ). The infiltration rates for moderate and heavy traffic were 12.3 and 9.1 cm h -~ under no-tillage, and 28.1 and 13.1 cm h - t under discing, respectively. However, the gap in the infiltration rate between nontracked and trafficked treatments considerably widened in January 1984. The infiltration rates o f the moderately and heavily trafficked plots were also markedly lower than identical treatments in January 1983. This distinct reduction in infiltration rates was attributed to a cumulative increase in soil compaction of the trafficked plots as a result o f two seasons of consecutive cropping. Infiltration tests conducted on mechanically-cleared plots show similar, and in many cases, severe reductions in water infiltration rate (Dias and Nortcliff, 1985 ).
332
B. KAYOMBO ET AL.
TABLE 3 Soil moisture content at 0-10 cm depth immediately after tillage and traffic treatments ~
Tillage
Roller passes
No-tillage
Soil moisture content (% w/w)
0 2 4 0 2 4
Discing
15 Sept. 1982
11 April 1983
11 Sept. 1983
7.6 7.9 7.8 8.5 8.4 7.7 NS
5. l" 3.6 b 3.0 ~ 1.6 d 1.9 a 1.1 e
10.3" 8.2 b 8.4 b 8.5 ~b 10.6" 9.0"
'For each period of measurement, means within a column followed by the same superscript are not significantly different using Duncan's multiple range test at the 5% level of probability. NS=not significant.
160
January NT
120 D 8O E u c o
-
-
-
-
o
~
~o/~ / ~o/
0
cJ
e - e---~ 2 c-~ : :0 ! - - -.I 2 o--.--oL
~e ~ o
4O
0
E ~6
1983
160
30
60
Jonuory
1984
30
60
90
120
150
180
90
120
150
180
120
8O
40
0
0
Time,rain
Fig. 2. Change in cumulative infiltration owing to traffic treatments under no-tillage and discing.
Root growth patterns T h e r e w e r e s i g n i f i c a n t d i f f e r e n c e s in r o o t d e n s i t y o f m a i z e u n d e r the r o w 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 f o r b o t h no-tillage a n d discing t h r o u g h o u t the d e p t h o f m e a s u r e m e n t (Fig. 3 ). At e a c h level o f s e e d b e d traffic, the r o o t d e n s i t y in no-tillage w a s h i g h e r t h a n in discing. At 8 w e e k s a f t e r
COMPACTION
333
EFFECTS ON SOIL AND CROPS IN NIGERIA.
2.L
F;S~q 2~
16
NT o ' ~ o 0 o----o 2 o-. -o/. 0 = --0 e----e 2 e--eL
1.2
0.8
,
,
I
I
0./-
(1
i
,
,
i
L
6
8
10
~
~
~
,'o
Weeks after planting
Fig. 3. Variation of root density (under row) of maize with depth as affected by tillage and traffic treatments in the first season of 1983. DISCING
NO-TILLAGE u E
16
2 pass
0 pass
h pass
1.sl
0 pass
2 pass
/, pass
[
@° [18
0.8
Q:
0
IL
I/. ox
ZO
~,
~o
2,0
16
t,6
1,2
12
0a
0,8
0L
0
0p
p
• O~ 6x
Fig. 4. Effects of tillage methods and traffic treatments on root system development of maize at 6 weeks (top) and 10 weeks (bottom) after planting.
planting, root densities in the top 7 cm o f soil for zero, moderate and heavy traffic were 2.3, 1.6 and 1.3 mg c m - 3 under no-tillage and 2. l, 1.3 and 0.9 mg c m - 3 under discing, respectively. Root density declined sharply with increasing soil depth. This was possibly caused by an increased gravel concentration with depth which was observed in the course o f the present root sampling. Seedbed traffic markedly affected the lateral spread o f roots between tillage treatments, particularly at 10 weeks after planting (Fig. 4). Lateral root de-
334
a. K A Y O M B O ET AL.
velopment of maize generally declined with increasing traffic intensity under both no-till and discing systems. However, at each level of seedbed traffic, the root density of maize in the surface 0-7 cm of soil was high throughout the 0-21 cm lateral distance under no-tillage, whereas it was restricted to 0-7 cm lateral distance under discing. Root density of cowpea under the row was significantly reduced by seedbed traffic in the measured 0-21 cm depth (Fig. 5 ). At 8 weeks after planting, the root densities at 0-7 cm depth for zero, moderate and heavy traffic were 0.5, 0.4 and 0.3 mg cm -3 under no-tillage and 0.4, 0.3 and 0.2 mg cm -3 under discing, respectively. Unlike maize, the root density of cowpea declined very gradually with increasing soil depth. This was possibly due to the deep rooting habit of cowpea, which has been shown to penetrate soils of high bulk density and strength (Maurya and Lal, 1979). Lateral root development of cowpea 10 weeks after planting showed that, regardless of traffic intensity, roots near the plant stem grew to 14 cm depth in no-tillage whereas under discing lateral root spread to 21 cm lateral distance was limited to the soil layers near the surface (Fig. 6). The root growth of soya bean under the row is shown in Fig. 7. At each period of measurement, seedbed traffic significantly reduced soya bean root density in the 0-7 and 7-14 cm depths. At 10 weeks after planting, root densities at 0-7 cm depth for zero, moderate and heavy traffic were 1.8, 1.3 and 0.8 mg cm -3 under no-tillage and 1.6, 0.7 and 0.6 mg cm -3 under discing, respectively. Soya bean root density declined sharply at 7-14 and 14-21 cm depths. This could be attributed to the inability of the soya bean root system to penetrate into soils having high bulk density and strength resulting from high concentration of gravels at deeper soil depths (Maurya and Lal, 1979, 1980). Lateral root development of soya bean generally declined with increasing traffic intensity under both no-till and discing systems (Fig. 8). At 10
a E u
O8
06
i
i
I
N'I c ' ~ - o 0 c.- ---o Z o,--..-o /, D *,~e0 e---e 2 e-. -e ~
i
.~11 I°
o
02
L
5
8
10
Weeks after p l a n t i n g
Fig. 5. Variation of root density (under row) of cowpea with depth as affected by tillage and traffic treatments in the first season of 1983.
COMPACTION
335
EFFECTS ON SOIL AND CROPS IN NIGERIA
DISCING
NO-TILLAGE 16
0 pass
2 pass
4 pass
161
2 pass
0 pass
l, pass
I
@o. 0.8
OL
= °l
I •%
6,~
?
1.2
1.2
°l
I 7 14.! IL, 'T X
Fig. 6. Effects of tillage methods and traffic treatments on root system development of cowpea at 6 weeks (top) and 10 weeks (bottom) after planting. ZO
!
16 i
12 >. .~
0.8
NTO~0 0----02 ~--oL D : --0
e---o 2
e---eL
x LSOI(5"/') [
[J
/-
t0
DC 0.~
I
I
i
i
t
6
Weeks
6 after
8
/-
6
8
10
ptonting
Fig. 7. Variation of root density (under row) of soya bean with depth as affected by tillage and traffic treatments in the first season of 1983.
10 weeks after planting, the root density of soya bean in the surface and subsurface soil horizons was higher throughout the 0-21 cm lateral distance under no-tillage than under discing for all levels o f seedbed traffic.
Leaf nutrient concentration Results o f nutrient contents o f maize ear leaf are shown in Table 4. In the second season o f 1982, no-tillage resulted in lower leaf nutrient concentrations o f Mg and Zn compared with discing, regardless o f traffic intensity. In
336
B. KAYOMBO ET AL. NO-TILLAGE
'E 16
E
0 pass
2 pass
DISCING 4 pass
16
08
08
0k
0
0 pass
2 po.ss
/, pass
o ' 7i~i, "I, ~ I ' 7 o
'E 1.6
I6
12
12
0a
oa
0L
O.
Ol
i
7 ILJ. 7 o~ ~, %,~ " I'L~,:~o,.
Fig. 8, Effectsof tillage methods and traffic treatments on root system developmentof soya bean at 6 weeks (top) and l0 weeks (bottom) after planting. the first season of 1983, no-tillage resulted in a higher nutrient concentration of P, but lower concentrations of N, Ca and Mg compared with discing. In the second season of 1983, heavy traffic reduced the ear leaf nutrient concentration of Mg under no-tillage and the ear leaf nutrient concentrations of P, Ca, Mg, K and Mn under discing, compared with the nontracked treatments. Results of cowpea leaf analyses are shown in Table 5. In the second season of 1982, the leaf nutrient status in cowpea was not affected by the treatments. In the first season of 1983, discing resulted in lower leaf nutrient concentrations of P and Mn compared with no-tillage, regardless of traffic intensity. In the second season of 1983, discing resulted in a lower leaf nutrient concentration of Mn compared with no-tillage, regardless of traffic intensity. However, moderate and heavy traffic reduced the nutrient concentration of Mg compared with the nontracked no-till plot. The leaf nutrient status of soya bean was also influenced by tillage and seedbed traffic (Table 6 ). In the second season of 1982, no-tillage resulted in a higher leaf nutrient concentration of Mn but a lower nutrient concentration of N compared with discing. Moderate and heavy traffic reduced the leaf nutrient concentration of Ca in no-tillage. In 1983, moderate and heavy traffic reduced the leaf nutrient concentration of Mn (in the first season) and Ca (in the second season) under discing, compared with the nontracked treatment. The effects of tillage and soil compaction on the leaf nutrient concentration, as reported above, could possibly be explained in the following way. In the second season of 1982 and the first season of 1983, the reduced leaf nutrient concentration of N, Ca, Mg and Zn in no-tillage as compared with disc-
337
COMPACTION EFFECTS ON SOIL AND CROPS IN NIGERIA TABLE 4 E a r l e a f nutrient contents of maize at tasseling ~ Tillage
Roller
Total
Total
Ca
Mg
K
Mn
Zn
passes
N
P
(%)
(%)
(%)
(%)
(%)
(ppm)
(ppm)
0 2
1.81 1.96
0.26 0.27
0.27 ~ 0.22 b
0 . 1 6 ~d 0.14 d
4.02 3.69
76 77
26 b 23 ~
4 0 2 4
1.72 2.16 1.82 2.12
0.29 0.23 0.25 0.24
0.28 a 0.32 a 0.37 a 0 . 2 7 ~b
0.18 b~ 0.21 a 0.20 a 0 . 1 9 ab
3.69 3.55 4.17 3.61
76 77 65 77
23 ~
NS
NS
0.22 d 2 . 4 4 cd 2.23 d 2.76 ~ 3.09 ab 3.26 a
0.30 a 0 . 2 9 ab 0.31 a 0.22 c 0.22 ~ 0 . 2 4 ~c
Second season, 1982 No-tillage
Discing
NS
NS
3.54 3.57 3.48 3.60 3.64 3.54
83 123 87 96 97 105
NS
NS
2 7 ~b
28 a 30 ~
First season, 1983 No-tillage
Discing
0 2 4 0 2 4
0 . 5 0 bc 0.47 c 0.42 c 0 . 6 3 ab
0.66 a 0.51 b
0.16 b 0 . 1 5 b~ 0.13 c 0.19 b 0.24 a 0.18 b
5b 9b
10 b 48 a 13 b 16 b
Second season, 1983 No-tillage
0
2.84
0.39 a
0.71 a
0.33 a
5.37 a
213 a
58
Discing
2 4 0 2 4
2.21 2.25 2.94 2.45 2.55
0.35 a 0 . 3 2 ab 0.32 a 0.29 b 0.27 b
0.71 a 0.51 ab 0.52 a 0.55 ~ 0.42 b
0.34 a 0.26 bc 0.31 ab 0.27 b 0.25 c
6.21 a 4.71 ab 4.88 a 5.55 a 4.60 b
190 a 178 ab 179 a 167 b 160 b
40 48 39 41 43
NS
NS
' F o r each season, means within a column followed by the same superscript are not significantly different using Duncan's multiple range test at the 5% level of probability. N S = not significant.
ing, were a result of: (i) the surface application of a low rate of superphosphate containing P, Ca and S which may have restricted the uptake of these elements; (ii) the antagonistic effect of increased concentrations of K (from fertilizer) at the soil surface on Ca and Mg uptake (Hargrove, 1985); (iii) greater nitrogen immobilization by crop residues. Although moderate and heavy traffic reduced leaf nutrient concentration more in disced plots than in no-till ones, the main effect of compaction was on root growth. The effects of mechanical impedance on water and nutrient uptake are related to the volume of soil explored by the roots (Shierlaw and Alston, 1984). Root distribution was restricted by traffic-induced compaction and decreased the volume of soil explored more in the disced soil than in the no-till soil. Hence, compacting freshly disced soil during field operations may reduce root growth
B. KAYOMBO ET AL.
338 TA BLE 5
Leaf nutrient contents o f c o w p e a at flowering ~ Tillage
Roller
passes
Total N (%)
Total P (%)
Ca (%)
Mg (% )
K (%)
Mn (ppm)
Zn (ppm)
4.63 4.49 4.55 4.20 4.56 4.33 NS
0.41 0.36 0.36 0.41 0.35 0.37 NS
2.91 2.35 2.62 2.90 2.67 2.94 NS
0.43 0.37 0.39 0.49 0.40 0.47 NS
4.08 3.49 3.78 3.77 3.59 3.82 NS
473 568 488 408 445 556 NS
44 46 45 42 70 55 NS
4.84 5.02 4.81 4.73 4.95 4.92 NS
0.44 a 0.358 0.40 a 0.38 ab 0.330 0.358
2.76 2.55 2.74 2.90 2.82 2.81 NS
0.41 ab 0.38 b 0.41 a 0.46 a 0.43 a 0.41 a
3.54 a 3.328 3.55 a 3.45 ab 3.30 b 3.49 a
539 a 645 ~ 766 a 4448 3988 516 ab
20 19 18 22 19 23 NS
3.48 3.21 3.19 3.67 3.70 3.73 NS
0.21 b 0.22 b 0.29 a 0.23 ab 0.22 b 0.228
3.19 a 2.52 b 2.44 b 2.82 ab 2.40 b 2.37 b
0.47 a 0.40 b 0.39 b 0.47 a 0.44 a 0.43 ab
4.03 b 4.29 a 4.43 a 4.76 a 4.078 4.13 a8
478 a 61 I a 557 a 353 b 3228 438 a8
30 34 35 31 36 36 NS
Secondseason, 1982 No-tillage
Discing
0 2 4 0 2 4
First season, 1983 No-tillage
Discing
0 2 4 0 2 4
Second season, 1983 No-tillage
Discing
0 2 4 0 2 4
~For each season, means within a column followed by the same superscript are not significantly different using Duncan's multiple range test at the 5% level of proba bi l i t y. NS = not significant.
and nutrient uptake to a greater extent than when plants are grown in initially more compacted soil of reduced tillage systems.
Grain yields Moderate and heavy traffic reduced the grain yields o f maize, cowpea and soya bean in all three growing seasons under both no-till and disced treatments, but the severity o f the effects o f rollertrack compaction increased considerably in the third consecutive season (i.e. the second season of 1983 ) and was particularly more marked on the disced plots than on the no-till ones (Fig. 9). In the second season o f 1983, grain yields for zero, moderate and heavy traffic were 4.7 > 3.0 > 2.3 Mg h a - ~ under no-tillage and 5.4 > 1.6 > 1.4 Mg h a - ~ under discing in maize, 1.0 > 0.7 > 0.6 Mg h a - ~ under no-tillage and
COMPACTION EFFECTS ON SOIL AND CROPS IN NIGERIA
339
TABLE 6 Leaf nutrient contents of soya bean at flowering ~ Tillage
Roller
passes Second season, 1982 No-tillage 0 2 4 Discing 0 2 4
First season, 1983 No-tillage 0 2 4 Discing 0 2 4
Second season, 1983 No-tillage 0 2 4 Discing 0 2 4
Total N (%)
Total P
3.81 b 3.80 b 3.80 b 4.57" 4.50" 4.06 "b
Ca (%)
Mg (%)
K (%)
Mn (ppm)
Zn (ppm)
0.25 0.28 0.28 0.27 0.28 0.25 NS
1.09" 0.97 b 0.97 b 1.20" 1.11" 1.03 "b
0.32 0.33 0.34 0.37 0.38 0.37 NS
3.01 3.33 3.35 3.30 3.19 3.40 NS
225" 216" 214" 180 bc 158 c 195 ab
63a 61" 57 a 55 ~b
2.69 2.56 2.31 3.21 2.85 2.68 NS
0.32 0.27 0.25 0.26 0.26 0.24 NS
1.38 1.36 1.35 1.39 1.42 1.36 NS
0.42 0.41 0.40 0.45 0.42 0.46 NS
2.43 3.08 2.83 2.61 3.00 2.76 NS
202 a 189" 171 "b 175 ~ 138 b 158 b
21 16 19 32 18 31 NS
2.98 b 3.26 b 3.41 ab 4.05 a 2.94 b 3.14 b
0.20 0.20 0.20 0.18 0.20 0.18 NS
1.28" 1.09" 1.05 ab 1.11" 0.97 b 0.99 b
0.44 0.45 0.44 0.44 0.39 0.43 NS
2.55 2.76 2.90 2.44 2.82 2.90 NS
207 199 181 181 200 220 NS
35 b 40 b 34 b
(%)
51 b
67 a
38 b
41 b 51 a
~For each season, means within a column followed by the same superscript are not significantly different using Duncan's multiple range test at the 5% level of probability. N S = n o t significant.
1 . 2 > 0 . 7 > 0 . 5 Mg ha -1 under discing in cowpea, and 1.6> 1.3> 1.2 Mg ha -j under no-tillage and 1.7 > 1.0 > 0.6 Mg ha-~ under discing in soya bean, respectively. In the second season of 1982, and the first and second seasons of 1983, heavy traffic reduced the grain yields by 51, 41 and 52% under notillage and by 53, 61 and 75% under discing in maize; by 38, 42 and 40% under no-tillage and by 38, 50 and 58% under discing in cowpea; and by 50, 64 and 25% under no-tillage and by 42, 45 and 65% under discing in soya bean, respectively, compared with the yield of nontracked plots. Reduced grain yields in trafficked treatments could be attributed to adverse soil conditions which subsequently decreased root growth. These results generally agree with earlier findings in other locations under varying soil conditions (Gaultney et al., 1982; Canarache et al., 1984).
340
B. KAYOMBO ET AL.
f--I0pass [] 2passes • 4
passes
68iI~ i
MAIZfE~
L~,~)
"T
-_= E_ o2
COWPEA
LSD{S%)
SOYBEAN NO-TI LOIL1982 SCINGNO-TILDILS1983 CINGNO-TI LDILS1983 CING 2nd season 2ridseason Ist season
Fig. 9. Effectsof tillage methodsand traffic treatments on maize, cowpeaand soyabean grain yields.
Soil parameter-crop yield relationships The relationships between soil physical properties and grain yield for maize, cowpea and soya bean are shown in Table 7. All soil physical parameters, except gravimetric water content ( w / w ) , were linearly related to grain yields. However, penetrometer resistance was least related to grain yields. The linear relationships between soil dry density and grain yields obtained in the present study contradicts earlier findings in other locations under varying soil conditions. Negi et al. ( 1981 ) reported that maize yield increased with higher compaction levels up to a point and then decreased with a further increase in soil compaction on a sandy loam soil in Canada when the weather conditions were abnormally dry. Similar trends in maize and sorghum yields were recorded by Onwualu and Anazodo (1989) and Ohu and Folorunzo ( 1989 ), respectively, on sandy soils in Nigeria. In a dry area and with a loose sandy soil such as reported by these authors, it is evident that a certain amount of machinery traffic can be beneficial for crop production because of the combined advantages of better moisture storage, good germination and root proliferation and an enhanced water-and-nutrient uptake by the crop. That the results in the present study do not agree with the conclusion arrived at by these authors could be because of the high concentration of gravel at 20-40
COMPACTIONEFFECTSON SOILAND CROPS IN NIGERIA
341
TABLE 7 Relationships between soil physical properties (x) at 0-10 cm depth and grain yields (y; Mg ha-J ) Soil property
Regression equation
Correlation coefficient (r)
y = 17.3-8.8x y = 1.5+0.6x y = 2 . 8 + 12.0x y = 7 . 8 - 1.7x
-0.88*** 0.82*** 0.17 NS -0.59*
y=3.1 - 1.4x y = 0.6 + 0.02x y=0.8 + 1.4x y= 1.5-0.2x
-0.73** 0.67** 0.12 NS -0.47*
y=4.2-2.0x y = 0.5 + 0.04X y = 0 . 9 + 8.7x y=2.1-0.5x
-0.74** 0.88*** 0.13 NS -0.58*
Maize Soil dry density (Mg m -3) Water infiltration rate (cm h -~ ) Soil moisture (% w / w ) Penetrometer resistance (MPa)
Cowpea Soil dry density (Mg m -3) Water infiltration rate (cm h - t ) Soil moisture (% w / w ) Penetrometer resistance (MPa)
Soya bean Soil dry density (Mg m -3) Water infiltration rate (cm h - ] ) Soil moisture (% w / w ) Penetrometer resistance (MPa)
*P~< 0.05, **P~
