Mulching Effects on Runoff,
Soil Erosion, and Crop Response
on Alfisols in Western Nigeria
R. Lal
ABSTRACT. Soil quality and resilience characteristics determine
productivity, sustainability, and risks of soil and environmental degradation. Soil surface management, comprising residue mulch and
tillage methods, affects soil quality and resilience. Field experiments
were conducted in western Nigeria on soils prone to erosion and
degradation to evaluate the effects of mulch rates on runoff, soil
erosion and crop yield. Effects of five mulch rates (4, 3, 2, 1 and 0
Mg/ha/season of rice straw mulch) with notill on crop response were
compared with that of plow till treatment on field runoff plots for
four consecutive years from 1981 to 1984. Runoff and soil erosion
effects of different mulch rates were measured for only 1981 and
1984. Maize grain yield was significantly affected by mulching in 1
out of 3 seasons, and was the highest at 5.4 Mg/ha for 4 Mg/ha
mulch rate and the lowest at 3.5 Mg/ha for 1 Mg/ha mulch rate, a
difference of 54%. Soybean grain yield was significantly higher at
1.4 Mg/ha for 4 Mg/ha mulch rate than 0.8 Mg/ha for 1 Mg/ha mulch
rate, a difference of 62.5%. Mean cowpea yield was the highest at
about 1 Mg/ha for 4 Mg/ha mulch rate and the lowest at 0.7 Mg/ha
for unmulched plots. Runoff and soil erosion were lower in 1981
than in 1984, with higher losses generally for the plow till treatment.
The index of relative mean annual soil erosion was in the order 100
(plow till), 35.1 (0 Mg/ha mulch rate), 25.0 (1 Mg/ha mulch rate),
30.9 (2 Mg/ha mulch rate), 20.8 (3 Mg/ha mulch rate), and 16.1 (4
Mg/ha mulch rate). Reductions in soil erosion by mulching were due
both to decreased runoff and to lower sediment concentration in
R. Lal is affiliated with the School of Natural Resources, The Ohio State
University, Columbus, OH 43210.
Journal of Sustainable Agriculture, Vol. 11(2/3) 1998
E 1998 by The Haworth Press, Inc. All rights reserved.
135
136
JOURNAL OF SUSTAINABLE AGRICULTURE
runoff. The data show that the desirable mulch rate for soil and water
conservation is about 4 Mg/ha/season for these soils. [Article copies
available for a fee from The Haworth Document Delivery Service: 1-800342-9678. E-mail address: [email protected]]
INTRODUCTION
Strategies for sustainable use of soil resources in harsh environments
depend on knowledge of soil quality, soil resilience and factors affecting
these interacting and complex attributes. Soil quality, capacity to produce
economic goods and services, and protection of the environment depend
on soil inherent properties, farming/cropping systems, and management
(Doran and Parkin, 1994). Soil resilience, the soil’s ability to restore its
quality following a stress or perturbation, also depends on inherent properties (endogenous factors), climate, and management (exogenous factors)
(Lal, 1994). Management factors crucial to enhancing soil quality and
resilience are those that minimize risks of accelerated soil erosion and
structural degradation, enhance soil organic matter content and activity
and species diversity of soil fauna, and strengthen nutrient recycling
mechanisms. Accelerated soil erosion is a major problem in soils of west
Africa (Lal, 1976; 1990). Use of crop residue mulch and notill system are
effective techniques to reduce risks of erosion-induced soil degradation
(Lal, 1994), conserve water, improve soil quality and enhance soil resilience (Lal, 1997).
Using organic wastes and by-products is an important strategy to improve soils (USDA, 1978). Crop residue mulch, applied as a layer at the
soil-air interface, protects the soil against raindrop impact, decreases
runoff velocity and its shearing strength, and reduces runoff amount and
rate. Consequently, residue mulch decreases risks of accelerated erosion
(Wischmeier, 1973; Lal, 1976). In addition to soil conservation, there are
also distinct benefits of mulching in soil-water conservation in the root
zone (Dudley and Russell, 1939; Russell, 1939; Unger, 1978; Greb et al.,
1979; Larson et al., 1972; 1978; 1982; Lal, 1975; 1986; 1990).
Because of its favorable effect on soil quality and resilience, and its
moderating influence on soil temperature and moisture regimes, mulching
has beneficial effects on crop growth and yield (Jurion and Henry, 1969;
Venkateswarlu, 1987; Klaij and Serafini, 1988; Geiger et al., 1992). The
benefits are especially important and notable for subsistence farming systems that are based on low external inputs. However, crop residues, that
provide the major source of mulch material are also needed for several
alternative uses such as fodder, fuel, and construction material. Therefore,
Research, Reviews, Practices, Policy and Technology
137
defining mulch requirements is crucial to determining the optimum use of
limited resources.
Crop residue requirements for erosion control depend on numerous
factors (Unger, 1988). Important among these factors are soil properties
and slope gradient. Requirements for crop residues may be influenced by
soil texture. The objective of this experiment was to evaluate the effects of
the rate of application of crop residues mulch on runoff, soil erosion, and
crop response on a coarse-textured soil.
MATERIALS AND METHODS
These experiments were conducted for 4 consecutive years from 1981
to 1984 at the research farm of the International Institute of Tropical
Agriculture (IITA). The IITA is located approximately 30 km south of
the northern limit of the lowland rainforest. The average annual rainfall
of about 1250 mm is received over two distinct growing seasons in a
bimodal distribution. The first longer growing season lasts from late
March to early July. The second shorter growing season is from late
August to early November. Therefore, there are two dry seasons, a short
one from late July to late August and a long one from early November to
late March.
The soil of the experimental site belongs to Ibadan series (Moormann et
al., 1975), and is classified as clayey, skeletal, isohyperthermic, Kaolinitic
Oxic Paleustalf. The soil is sandy near the surface and contains a well
defined gravelly horizon between 25 and 60 cm depth. The gravel concentration, primarily quartz ranging from 2 to 15 mm in size, is highly
variable ranging from 30 to 70% by weight.
These experiments were conducted on field runoff plots measuring 20
m 2 m established on natural slopes of about 8%. Plots were established
on a soil that had been fallow for about 5 years. Grass and shrub regrowth
were cut manually and removed from the experimental plots. There were
six treatments comprising five mulch rates of 4, 3, 2, 1 and 0 Mg/ha used
with a notill system, and a plowed treatment. Rice straw was used as
mulch, was applied to all plots at the time of sowing for each of the two
seasons, and was left in place. Much material was uniformly distributed
over the plot, but especially between the rows. The stover/straw (of maize,
cowpea or soybean) harvested at the end of the season was weighed and
removed from the plot. Rice straw was used as a mulch material because
the control (uncropped) plots had no residue and all plots received mulch
of a uniform material with slow decomposition rate. Soybean or cowpea
produce little residue, and these residues also decompose very quickly
138
JOURNAL OF SUSTAINABLE AGRICULTURE
(Lal et al., 1980). All treatments were replicated three times as per the
randomized block design.
Each runoff plot was equipped with runoff and erosion monitoring
equipment of the type described by Mtakwa et al. (1987). Runoff and
erosion were monitored for each rainfall event that produced measurable
runoff. The runoff amount was calculated by dividing the total runoff
volume collected in a tank by the plot area. Two 1-liter samples of runoff,
collected after thoroughly stirring the contents in the tank, were used to
determine sediment concentration by filtering through a fine filter paper
and drying in the oven. Total soil erosion was computed as the sum of
sediments deposited in the flume and those contained in the runoff. Runoff
and erosion data for each storm were summed for each season. The C-factor for crop/soil management was computed as a ratio of the runoff or soil
erosion from a treatment to that of the runoff and soil erosion from the
plowtill uncropped plot for the same period. All of the 18 runoff plots
were sown to maize-cowpea rotation. Maize was planted around mid April
during the first growing season and cowpea around the end of August
during the second. This rotation was followed from 1981 to 1983. In 1984,
maize was replaced with soybeans. Therefore, in all, there were 3 crops of
maize, 1 of soybean and 4 of cowpea.
All notill plots were sprayed with paraquat (1, 1i dimethyl 4, 4i bipyridilium ion) at 0.5 kg ha1 a.i. All plow till plots were plowed with a
2-wheel tractor every season, until crop residues were plowed under.
Maize was sown at a spacing of 75 cm 25 cm. Maize and soybean
received fertilizer at 100 kg N/ha as urea, 30 kg P/ha as single superphosphate, and 30 kg K/ha as KCl. Cowpea did not receive any fertilizer. Grain
and straw/stover yields were measured at maturity. The entire plot was
harvested and grain and stover weights were recorded separately. After
determining the field moisture content by drying grains in the oven at
105_C and straw at 60_C, grain yields were reported at 15% moisture
content and straw yield on oven dry basis.
There were 5 additional runoff plots. These plots received 4 mulch rates
of 4, 3, 2 and 0 Mg/ha as notill and the plowed treatments. These plots
were managed the same way as the other 18 plots, except that no crop was
grown in them. There was no vegetative cover other than crop residue
mulch, and weeds were effectively controlled.
Soil samples from 0-5 cm and 5-10 cm depths were obtained during
the dry season of 1984-85 to evaluate treatment effects on soil physical
properties. Particle size distribution was measured by the hydrometer
method (Gee and Bauder, 1986). Soil moisture retention characteristics
were measured using tension table and pressure plate extractors (Klute,
139
Research, Reviews, Practices, Policy and Technology
1986). Data were analyzed to compute analysis of variance and the least
significant difference assuming the normal distribution (Steel and Torrie,
1980).
RESULTS
The mean seasonal total of erosive rainfall events was 630 mm for the
first season, 342 mm for the second season and 972 mm for the annual
total. There were more erosive rains during 1981 and 1984 compared with
1982 and 1983.
Crop Yields
Maize grain yield was significantly affected by mulch treatment in only
one (1982) out of three years (Table 1). Maize grain yield in 1982 was the
highest at 5.4 Mg/ha for 4 Mg/ha mulch rate and the lowest at 3.5 Mg/ha
for 1 Mg/ha mulch rate, a difference of 54%. There were also significant
differences in soybean grain yield, which was significantly more by 62.5%
for 4 Mg/ha mulch rate than 3 Mg/ha and 1 Mg/ha mulch rates. Stover
TABLE 1. Mulching effects on maize and soybean grain yield.
Mulch rate
(mg/ha)
Soybeans
grain yield
Maize grain yield
1981
1982
1983
Mean maize
grain yield
1984
. . . . . . . . . . . . . . . . . . . . . . . . . Mg/ha . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
3
2
1
0
Plow till
Mean
CV (%)
LSD (.05)
5.2a
4.3a
4.2a
3.9a
4.1a
4.5a
4.4
18.3
1.5
5.4a
3.8ab
4.6ab
3.5b
4.2ab
4.4ab
4.3
21.5
1.7
4.8a
4.7a
4.3a
4.3a
4.5a
4.7a
4.6
17.6
1.5
1.3a
0.8b
1.1ab
0.8b
1.2ab
1.0ab
1.1
23.7
0.5
5.1a
4.3a
4.4a
3.9a
4.3a
4.5a
4.4
38.1
1.1
Means followed by the same letter in the column are not significantly different at 5% probability
level.
140
JOURNAL OF SUSTAINABLE AGRICULTURE
yield of maize was significantly affected by mulch in 2 out of 3 years, and
the highest stover yield was obtained for the plowtill treatment in 2 out of
3 years (Table 2). The mean maize stover yield, with a range of 4.7 to 6.0
Mg/ha, did not differ among treatments, as was also the case with stover
yield in 1982. There were no differences in soybean straw yield among
mulch rate treatments.
Mulching treatments had significant effects on cowpea grain yield in 3
out of 4 seasons (Table 3). Mean cowpea yield (average of all 4 seasons)
was the highest at about 1 Mg/ha for 4 Mg/ha mulch rate and the least at
0.7 Mg/ha for 0 Mg/ha mulch rate, a difference of 30%. Among notill
treatments for 1982 and 1984, the highest cowpea grain yield was always
obtained for the 4 Mg/ha mulch rate, and the difference between the
highest and the lowest grain yield was 52% in 1982 and 22% in 1984.
Cowpea grain yield in 1983 was low, highly variable, and did not differ
among treatments. For the first year, in 1981, effects of notill on soil
properties were similar to those of the plow-till because of drastic soil
disturbance.
Water Runoff
The data on water runoff were highly variable with CV ranging from
22% to 33% (Table 4). Nonetheless, there were significant differences in
runoff amount among mulch treatments. The least runoff was generally
TABLE 2. Mulching effects on stover yield of maize and soybeans.
Mulch rate
(Mg/ha)
Maize stover yield
1981
1982
1983
Soybean
straw yield
Mean
maize
1984
stover yield
. . . . . . . . . . . . . . . . . . . . . . . . . Mg/ha . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
3
2
1
0
Plow till
Mean
CV(%)
LSD (.05)
5.86ab
5.11ab
5.77ab
3.94c
5.79ab
6.57a
5.51
14.1
1.41
7.22a
6.55a
6.71a
6.75a
6.80a
7.36a
6.90
12.2
1.53
4.79a
3.34b
4.13ab
3.44b
3.43b
4.01ab
3.86
16.9
1.19
1.48a
1.32a
1.26a
1.17a
1.34a
1.29a
1.31
29.7
0.71
5.96a
5.00a
5.54a
4.71a
5.34a
5.98a
5.42
35.8
1.86
Research, Reviews, Practices, Policy and Technology
141
TABLE 3. Mulching effects on cowpea grain yield.
Grain yield
Mulch rate (Mg/ha)
1981
1982
1983
1984
Mean
. . . . . . . . . . . . . . . . . . . Mg/ha . . . . . . . . . . . . . . . . . . . . . . . .
4
3
2
1
0
Plow till
Mean
CV (%)
LSD (.05)
0.72ab
0.66ab
0.70ab
0.76ab
0.41b
1.04a
0.71
41.5
0.38
1.08a
0.71b
0.90ab
0.72b
0.78ab
0.89ab
0.85
20.4
0.22
0.51a
0.26a
0.49a
0.34a
0.39a
0.53a
0.42
37.9
0.29
1.55a
1.45ab
1.36ab
1.23bc
1.27ab
0.96c
1.30
12.8
0.21
0.97
0.77
0.86
0.76
0.71
0.86
0.82
Means followed by the same letter in the column are not significantly different at 5% probability
level.
TABLE 4. Mulch effects on runoff under maize and soybeans (first season)
and cowpea (second season) rotation.
1981
Mulch rate
(Mg/ha)
First
season
Second
season
1984
Annual
total
First
season
Second
season
Annual
total
Mean
annual
. . . . . . . . . . . . . . . . . . . . . percent of rainfall . . . . . . . . . . . . . . . . . . . . . . . . . .
4
3
2
1
0
Plow till
Mean
CV (%)
LSD (.05)
Rainfall (mm)
4.1c
7.7b
5.6c
6.4bc
7.0b
6.6bc
8.4ab 12.2ab
10.0abc
10.0a
11.7ab
10.7ab
9.0ab 13.0ab
10.6ab
10.6a
18.3a
13.7a
8.1
11.7
9.5
21.8
32.7
26.0
3.2
6.9
3.2
642.1
432.4
1074.5
20.1ab
8.8b
24.0ab
23.3ab
24.7ab
28.9a
23.3
22.6
9.6
681.6
18.2ab
12.7b
19.0ab
19.2ab
16.2ab
24.0a
18.2
27.2
6.4
480.6
19.3ab
16.3b
21.9ab
21.6ab
21.2ab
26.9a
21.2
23.8
6.5
1162.2
12.5
11.5
16.0
16.1
15.9
20.3
15.4
Means followed by the same letter in the column are not significantly different at 5% probability
level.
142
JOURNAL OF SUSTAINABLE AGRICULTURE
observed for high mulch rates of 4 or 3 Mg/ha, and the highest for the
plow till treatments. The mean annual (average of both years) runoff
ranged from 11.5 percent for 3 Mg/ha mulch rate to 20.3 percent for the
plow till treatment. The seasonal runoff for 1981 was low, ranging from
4.1 percent for 4 Mg/ha mulch rate to 10.6 percent for plow till treatment,
probably because of favorable soil structure following a 5-year fallow. The
second season runoff in 1981 was relatively high and ranged from 7.0
percent of rainfall for 3 Mg/ha mulch rate to 18.3 percent for the plow till
treatment.
The runoff in 1984 was much greater than that in 1981, probably because
of decline in infiltration rate due to surface sealing and crust formation. The
annual total runoff ranged from a low of 16.3 percent for 3 Mg/ha mulch
rate to a high of 26.9 percent for plow till treatment. Similar trends were
observed in runoff loss for both seasons (Table 4). Mulch effects on runoff
from uncropped plots are shown in Table 5. In general, runoff increased
with decreasing mulch rate and the highest runoff was always observed for
the plowtill treatment. The C-factor for runoff increased with decreasing
mulch rate for both cropped and uncropped treatments (Table 6). The highest C-factor was generally obtained for the plowtill treatment.
Mulch rate effects on mean seasonal and annual total runoff for cropped
versus uncropped plots show drastic reductions in runoff at high mulch
rate on uncropped plots (Figure 1). However, uncropped plots were not
TABLE 5. Mulching effects on runoff from uncropped plots.
1981
Mulch rate
(Mg/ha)
First
season
Second
season
1984
Annual
total
First
season
Second
season
Annual
total
. . . . . . . . . . . . . . . . . . . . . . percent of rain . . . . . . . . . . . . . . . . . . . . . . . . . .
4
8.3
11.1
9.5
30.4
22.6
27.2
3
12.4
13.6
12.9
30.0
28.7
29.4
2
12.0
15.8
13.5
34.5
37.4
35.7
0
12.2
22.3
16.3
59.2
48.1
54.6
Plow till
18.9
26.6
20.2
60.4
51.4
56.7
Mean
12.8
17.9
14.5
42.9
37.6
40.7
3.8
6.4
4.0
15.5
12.3
14.0
642.1
432.4
1074.5
681.6
480.6
1162.2
SD
Rainfall (mm)
143
Research, Reviews, Practices, Policy and Technology
TABLE 6. Mulch effect on mean C-factor for runoff.
Mulch rate
(Mg/ha)
1981
1984
Maize
Cowpea
Uncropped
Maize
Cowpea
Uncropped
4
0.22
0.29
0.42
0.33
0.35
0.44
3
2
1
0
0.34
0.44
0.53
0.48
0.26
0.46
0.44
0.49
0.51
0.59
---0.84
0.15
0.40
0.39
0.41
0.25
0.37
0.37
0.35
0.56
0.73
---0.94
Plow till
0.43
0.69
1.0
0.48
0.47
1.0
replicated and the curves for the cropped plots are based on three times the
data points as the uncropped plots.
Soil Erosion
The data on soil erosion were even more variable than those on runoff,
and the CV ranged from 23% to 116%. Similar to runoff, however, soil
erosion was also low for 1981, and increased drastically for 1984, 1250
kg/ha vs. 3343 kg/ha (Table 7). Soil erosion decreased drastically with
increasing mulch rate in all notill treatments. The mean first season
(average of both first seasons for maize and soybean) soil erosion was
511 kg/ha for 4 Mg/ha mulch rate, 626 kg/ha for 3 Mg/ha mulch rate, 841
kg/ha for 2 Mg/ha mulch rate, 963 kg/ha for 1 Mg/ha mulch rate, 994
kg/ha for 0 Mg/ha mulch rate, and 3836 kg/ha for plow till treatment. The
mean second season soil erosion under cowpea was 460 kg/ha for 4
Mg/ha mulch rate, 630 kg/ha for 3 Mg/ha mulch rate, 1027 kg/ha for 2
Mg/ha mulch rate, 550 kg/ha for 1 Mg/ha mulch rate, 1131 kg/ha for 0
Mg/ha mulch rate, and 2209 kg/ha for plow till treatment. The relative
mean annual soil erosion was in the order 100 (plow till), 35.1 (0 Mg/ha
mulch), 25.0 (1 Mg/ha mulch), 30.9 (2 Mg/ha mulch), 20.8 (3 Mg/ha
mulch) and 16.1 (4 Mg/ha mulch). The data in Figure 2 highlight the
importance of crop cover in reducing soil erosion. Soil erosion risks were
drastically reduced with protective effect of canopy cover, even in case
of the open row maize. Within the cropped treatments, however, the
highest soil erosion was always measured for the plow till treatment.
Similar to runoff, the C-factor for soil erosion also decreased with increasing mulch rate (Table 8); with one exception, the highest C-factor
was observed for the plowtill treatment.
144
JOURNAL OF SUSTAINABLE AGRICULTURE
FIGURE 1. Mulch rate effect on mean runoff for (A) first season, (B) second
season and (C) annual total loss. Runoff for the cropped and uncropped plow
till treatment, respectively, was 19.8% and 39.7% for the first season, 21.2%
and 39.0% for the second season, and 20.3% and 40.0% for the annual total.
40
(A) First Season
35
30
25
20
Uncropped
Runoff (percent of rainfall)
15
Cropped
10
40
(B) Second Season
35
30
25
20
Uncropped
15
Cropped
10
5
40
(C) Annual Total
35
30
25
20
Uncropped
15
Cropped
10
0
1
3
2
Mulch Rate (Mg/ha)
4
145
Research, Reviews, Practices, Policy and Technology
TABLE 7. Mulching effects on soil erosion for maize and soybeans (first
season) and cowpea (second season) rotation.
Maize-cowpea rotation in 1981
First
Second
Annual
season
season
total
Mulch rate
(Mg/ha)
Soybean-cowpea rotation in 1984
First
Second
Annual Mean
season
season
total
annual
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . kg/ha . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
247c
164b
411c
775b
756b
1531b
975
3
389bc
222b
611bc
863b
1037b
1900b
1256
2
586abc
586ab
1172bc
1096b
1467b
2583b
1868
1
720abc
454ab
1174bc
1205b
645b
1850b
1512
0
778ab
Plow till
1701a
1032a
2479a
1209b
561b
1770b
2125
626ab
1658ab
6640a
3792a
10432a
6045
2297
Mean
625
625
1250
1965
1378
3343
CV (%)
45.0
116.0
54.2
22.5
55.4
26.5
LSD (.05)
362
930
872
569
981
1141
Means followed by the same letter in the column are not significantly different at 5% probability
level.
TABLE 8. Mulch effect on mean C-factor for soil erosion.
Mulch rate
1981
1984
(Mg/ha)
Maize
Cowpea
Uncropped
Maize
Cowpea
Uncropped
4
0.094
0.169
0.183
0.028
0.036
0.037
3
2
1
0
0.149
0.224
0.275
0.297
0.229
0.605
0.469
1.755
0.175
0.182
---0.861
0.032
0.040
0.044
0.044
0.050
0.070
0.031
0.027
0.074
0.555
---0.796
Plow till
0.394
0.646
1.00
0.242
0.181
1.00
Sediment Concentration
Data on sediment concentration for selective rainfall events for 1984
are shown in Tables 9 and 10. Data in Table 9 show that sediment concentration was generally the highest for the plow till treatment, and
showed a decreasing trend with increasing mulch rate. The mean (average
146
JOURNAL OF SUSTAINABLE AGRICULTURE
FIGURE 2. Mulch rate effect on mean soil erosion for (A) first season, (B) second season and (C) annual total loss. Mean soil erosion for the cropped and
uncropped plow till treatment, respectively, was 3836 kg/ha and 14983 kg/ha
for the first season, 2298 kg/ha and 14160 kg/ha for the second season, and
6045 kg/ha and 29089 kg/ha for the annual total.
12500
(A) First Season
10000
7500
5000
2500
Uncropped
Cropped
0
10000
Soil Erosion (kg/ha)
(B) Second Season
8000
6000
4000
Uncropped
2000
Cropped
0
25000
(C) Annual Total Loss
20000
15000
10000
Uncropped
5000
Cropped
0
0
1
2
3
Mulch Rate (Mg/ha)
4
147
Research, Reviews, Practices, Policy and Technology
TABLE 9. Mulching effects on sediment concentration in runoff under soybeans-cowpea rotation during the first and second growing season 1984.
Mulch
rate
(Mg/ha)
31 May
1 June
18 July
31 August
13 September 16 October Mean
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . g/L . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
0.91ab
0.71bc
0.57abc
3
2
0.20b
0.27c
0.51bc
1.22a
1.16a
0.66a
0.67
0.54ab
1.05abc 0.98ab
1.93a
1.47a
1.06a
1.17
1
0.73ab
2.33ab
1.19a
1.37a
0.46a
1.15
0
1.09ab
1.83abc 0.70abc
1.44a
0.73a
0.52a
1.05
Plow till
1.50a
2.57a
0.37c
2.32a
2.60a
1.09a
1.74
Mean
0.83
1.46
0.66
1.52
1.36
0.78
1.10
CV (%)
LSD (.05)
60.5
0.64
65.1
1.23
0.82ab
36.2
0.31
1.03a
50.4
0.98
0.81a
83.2
1.45
0.91a
0.82
63.6
0.64
Means followed by the same letter in the column are not significantly different at 5% probability
level.
TABLE 10. Mulching effects on sediment concentration in runoff from uncropped plots in 1984.
Mulch
rate
(M/ha)
31 May
1 June
18 July
31 Aug.
13 Sept.
16 Oct.
Mean
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . g/L . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
4
0.80
1.72
1.06
2.20
1.40
0.84
1.35b
3
1.04
1.68
1.00
1.30
0.80
0.20
1.03 b
2
1.70
1.34
0.98
4.74
0.94
0.84
1.76b
0
6.58
8.66
1.68
9.00
1.88
4.62
4.57a
Plow till
5.22
6.16
1.90
2.16
3.00
3.30
3.62a
Mean
3.07
3.91
1.32
3.88
1.60
1.96
2.47
SD
2.65
3.32
0.43
3.14
0.89
1.90
1.55
LSD (.05)
1.72
148
JOURNAL OF SUSTAINABLE AGRICULTURE
of all events) sediment concentration in plow till treatment was more by
52.9 percent compared with 4 Mg/ha mulch rate and 39.7 percent
compared with 0 Mg/ha mulch rate. Data on sediment concentration for
the uncropped treatment shown in Table 10 indicate the highest sediment
concentration of 4.6 g/L for 0 mulch rate followed by that of the plowed
treatment at 3.6 g/L. Mean sediment concentration for the uncropped plots
was 2.47 g/L compared with 1.10 g/L for the cropped plots, a difference of
2.25 times.
Soil Properties
Mulching and tillage effects on soil properties for 0 to 5 cm depth are
shown in Table 11. Four years of mulching and tillage treatments caused
some differences in soil texture. Unmulched treatments with and without
plowing had generally the highest sand and the lowest clay content. Consequently, soil moisture retention at different suctions was also higher for
notill plots with high than low mulch rates. Similar trends in soil properties
are observed for 5-10 cm depth. Soil samples from unmulched plots of
notill and plow till treatments contained 3 to 4% more sand, 1 to 2% less
clay, 2.0 to 2.5% less water at field capacity (0.01 MPa suction) and 0.5%
less water at the permanent wilting point (1.5 MPa suction) (Table 12).
TABLE 11. Mulch rate effects on particle size and moisture retention characteristics for 0-5 cm depth.
Mulch rate
Sand
Silt
Clay
(Mg/ha)
Moisture retention at different suctions (MPa)
0.003
0.01
0.1
0.5
1.5
. . . . . . . . . . . . . . . . . . . . . . . Percent by weight . . . . . . . . . . . . . . . . . . . . . . .
4
62.9
13.3
23.8
22.9
15.2
11.4
8.4
8.2
3
67.1
10.9
22.1
23.0
13.3
9.9
7.1
6.5
2
64.0
11.5
24.4
19.7
14.1
9.5
7.0
6.9
1
68.1
8.9
23.1
17.6
11.5
8.8
6.0
6.0
0
68.4
12.0
19.6
20.0
13.1
9.1
7.4
7.2
Plow till
67.7
12.0
20.3
21.3
14.5
8.8
7.2
7.0
Mean
66.4
11.4
22.2
21.1
14.0
9.9
7.2
7.0
9.0
28.7
20.3
18.3
21.0
22.2
20.2
22.5
10.8
5.9
8.3
5.0
5.3
4.0
2.6
3.0
CV (%)
LSD (.05)
Research, Reviews, Practices, Policy and Technology
149
TABLE 12. Mulch rate effects on particle size and moisture retention characteristics of 5-10 cm depth.
Mulch rate
Sand
Silt
Clay
(Mg/ha)
Moisture retention at different suctions (MPa)
0.003
0.01
0.1
0.5
1.5
. . . . . . . . . . . . . . . . . . . . . . . Percent by weight . . . . . . . . . . . . . . . . . . . . . . .
4
62.2
12.3
25.5
26.1
16.6
10.5
8.1
7.5
3
62.1
11.9
26.1
24.4
13.7
9.4
6.9
6.5
2
61.3
11.9
26.8
22.5
12.5
8.4
6.4
6.2
1
65.1
8.5
26.4
20.8
12.0
7.8
5.7
5.4
0
65.4
11.3
23.3
24.6
14.0
9.4
7.3
7.0
Plow till
66.1
9.0
24.9
25.9
14.0
10.0
7.5
7.0
Mean
63.7
10.8
25.5
24.1
13.8
9.3
7.0
6.6
CV (%)
7.1
24.4
19.3
12.6
21.6
24.0
26.0
20.7
LSD (.05)
8.1
4.8
6.3
5.5
5.4
4.0
3.3
2.8
Therefore, application of residue mulch at about 4 Mg/ha/season improved
soil quality even over a short period of 4 years.
GENERAL DISCUSSION AND CONCLUSIONS
Beneficial effects of mulch treatments are due to several interacting
factors, including improvements in soil quality and resilience. Mulching
decreased the rate of decline of soil structure by improving soil moisture
and temperature regimes (Lal, 1986), stimulating activity of soil fauna,
and decreasing runoff and soil erosion. Low runoff and soil erosion were
reflected in higher clay and silt contents of the surface horizons of plots
receiving high mulch rates. Plots receiving high mulch rates were also
characterized with high soil moisture retention at low suctions (Tables 11
and 12). Improvements in soil moisture characteristics by mulching are
due to favorable soil organic matter content and high activity of soil fauna,
e.g., earthworms and termites (Lal, 1986).
Agronomic Productivity
Improvements in soil quality by mulching had beneficial effects on
agronomic productivity (Figure 3). Maize grain yield increased with in-
150
JOURNAL OF SUSTAINABLE AGRICULTURE
FIGURE 3. Mulch rate effects on mean grain yield of maize, soybean and
cowpea. Grain yield for the plow till treatment was 4.54 Mg/ha for maize, 1.01
Mg/ha for soybean and 0.86 Mg/ha for cowpea. Low soybean yields were
due to crop failure in that season.
6
Maize
Grain Yield (Mg/ha)
5
4
3
2
Cowpea
Soybean
1
0
0
1
2
3
4
Mulch Rate (Mg/ha)
creasing mulch rate, which may be due to several factors including (i)
water conservation, (ii) favorable soil temperature, (iii) improved soil
structure as reflected in high infiltration rate, and (iv) favorable nutrient
status due to low nutrient losses in runoff and eroded sediments.
Sustainability
A relevant index of agronomic sustainability in these soils with high
erosion risks is productivity per unit loss of runoff and soil. Productivity
per unit loss of soil erosion increased with increasing mulch rate (Tables 13
and 14). The data in Table 13 show that maize:runoff ratio was 197.6
kg/mm for 4 Mg/ha mulch rate compared with 70.9 kg/mm for 0 mulch in
notill and 66.1 kg/mm in plowtill treatment. The ratio of cowpea grain
Research, Reviews, Practices, Policy and Technology
151
Table 13. Crop yield in relation to runoff and soil erosion for different mulch
rates in 1981.
Mulch rate
(Mg/ha)
Yield/Runoff
Maize
Cowpea
. . . . . km/mm . . . . . . . . .
4
3
2
1
0
Plow till
Mean
SD
197.6
104.6
77.9
60.7
70.9
66.1
96.3
51.9
21.6
21.8
13.3
15.0
7.3
13.1
15.4
5.7
Yield/Erosion
Maize
Cowpea
. . . . . . kg/kg . . . . . . . . . .
21.1
11.1
7.2
5.4
5.3
4.4
9.1
6.4
0.93
0.76
0.64
0.63
0.34
0.16
0.58
0.28
TABLE 14. Crop yield in relation to runoff and soil erosion for different mulch
rates in 1984.
Mulch rate
(Mg/ha)
Runoff
Soybean
Cowpea
. . . . . . kg/mm . . . . . . . .
4
3
2
1
0
Plow till
Mean
SD
10.8
22.0
7.7
7.4
7.9
6.5
10.4
5.9
17.7
23.7
14.9
13.3
16.3
8.3
15.7
5.1
Erosion
Soybean
Cowpea
. . . . . . kg/kg . . . . . . . . .
1.68
0.93
1.00
0.66
0.99
0.15
0.90
0.50
20.5
0.76
0.93
1.90
2.26
0.25
1.36
0.82
yield to runoff decreased from 21.6 kg/mm for 4 Mg/ha mulch rate to 7.3
kg/mm for 0 mulch rate. The beneficial effects of mulching were even
more pronounced in terms of grain yield:soil erosion ratio, especially for
maize which ranged from 21.1 kg/kg for 4 Mg/ha mulch rate to 5.3 kg/kg
for 0 mulch rate. Although the data were rather variable, similar trends in
yield: runoff and yield:erosion ratios were observed for 1984 seasons.
152
JOURNAL OF SUSTAINABLE AGRICULTURE
Beneficial effects of mulching on soil erosion control are apparently
due to the following:
i. Low runoff losses due to high infiltration rate: Mulch improves infiltration rate by minimizing crusting, and improving macropores.
ii. Low sediment concentration: Mulching decreases sediment concentration by minimizing inter-rill/rill erosion through improvements in soil structure and protective effects of crop residue against
raindrop impact and inter-rill erosion.
High soil erosion with plow till treatment may be attributed to the
following:
i. Lack of the protective effects of crop residue mulch,
ii. Decline in infiltration rate due to plowing, and
iii. Increased susceptibility to surface sealing and crust formation.
Establishment of ground/canopy cover had an important effect on reducing soil erosion, even without the residue mulch. Therefore, cropping
systems should be developed that provide ground cover at all times especially during the periods of intense rains. It is in this regard that the
importance of residue mulch and canopy cover cannot be overemphasized
(Lal, 1986).
The data show that the minimum mulch rate required for soil and water
conservation is about 4 Mg/ha/season. Application or maintenance of
mulch at this rate would facilitate using additional crop residue for other
purposes while conserving soil and water, improving soil quality, and
enhancing agricultural sustainability.
REFERENCES
Doran, J.W. and T.B. Parkin, 1994. Defining and assessing soil quality. In ‘‘Defining Soil Quality for a Sustainable Environment,’’ SSSA Special Publication
No. 35, Madison, WI: 3-21.
Duley, F.L. and J.C. Russell, 1939. The use of crop residues for soil and moisture
conservation. J. Am. Soc. Agron. 31: 703-709.
Gee, G.W. and J.W. Bauder, 1986. Particle size analysis. In: A. Klute (ed) Method
of Soil Analysis, Part 1, ASA Monograph 9, Madison, WI: 377-382.
Geiger, S.C., A. Manu, and A. Bationo, 1992. Changes in a sandy sahelian soil
following crop residue and fertilizer additions. Soil Sci. Soc. Am. J. 56:
172-177.
Greb, B.W., D.E. Smika, and J.R. Welsh, 1979. Technology and wheat yields in
the Central Great Plains, experiment station advances. J. Soil Water Conserv.
34: 264-268.
Research, Reviews, Practices, Policy and Technology
153
Jurion, F. and J. Henry, 1969. Can primitive farming be modernized? I.N.E.A.C.
Hors Series, Yangambi, Zaire, 457 pp.
Klaij, M.C. and P.G. Serafini, 1988. Management options for intensifying milletbased crop production systems on sandy soils in the Sahel. In: Challenges in
Dryland Agriculture: A Global Perspective. Proceedings of International Conference on Dryland Farming, August 15-19th, 1988. Amarillo, TX, Texan
Agricultural Experiment Station, pp. 501-503.
Klute, A., 1986. Water retention: laboratory methods. In A. Klute (ed) Methods of
Soil Analysis, Part 1, ASA Monograph 9, Madison, WI: 635-660.
Lal, R., 1975. Role of mulching techniques in soil and water conservation in the
tropics. IITA Tech. Bull. 1, Ibadan, Nigeria, 38 pp.
Lal, R., 1976. Soil erosion problems on alfisols in Western Nigeria and their
control. IITA Monograph 1, Ibadan, Nigeria, 208 pp.
Lal, R., D. DeVleeschauwer and R.M. Nganje, 1980. Changes in properties of a
newly cleared tropical alfisol was affected by mulching. Soil Sci. Soc. Am. J.
44: 827-833.
Lal, R., 1986. Soil surface management in the tropics for intensive land use and
high and sustained production. Adv. Soil Sci. 5: 1-110.
Lal, R., 1990. Soil erosion in the tropics: principles and management. McGraw
Hill, NY, 580 pp.
Lal, R., 1994. Sustainable land use systems and soil resilience. In D.J. Greenland
and I. Szabolcs (eds) Soil Resilience and Sustainable Land Use, CAB International, Wallingford, U.K.: 41-67.
Lal, R., 1997. Degradation and resilience of soils. Phil. Trans. R. Soc. London (in
Press).
Larson, W.E., C.E. Clapp, W.H. Pierre, and Y.B. Morachan, 1972. Effects of
increasing amounts of organic residues on continuous corn II. Organic carbon,
nitrogen, phosphorous and sulfur. Agron. J. 64: 204-208.
Larson, W.E., R.F. Holt, and C.W. Carlson, 1978. Residues for soil conservation.
In: W.R. Oschwald (ed) Crop Residue Management Systems, ASA Spec. Pub.
31: 1-15.
Larson, W.E., J.B. Swan, and F.J. Pierce, 1982. Agronomic implications of using
crop residues for energy. In: W. Lockertz (ed) Agriculture as a Producer and
Consumer of Energy, AAAS Selected Symposium 78: 91-122.
Moormann, F.R., R. Lal, and A.S.R. Juo, 1975. Soils of IITA. Tech. Bull. 3, IITA,
Ibadan, Nigeria, 48 pp.
Mtakwa, P.W., R. Lal, and R.B. Sharma, 1987. An evaluation of the Universal
Soil Loss Equation and field techniques for assessing soil erosion on a tropical
alfisol in western Nigeria. Hydrological Processes 1: 199-209.
Russell, J.C., 1939. The effect of surface cover on soil moisture losses by evaporation. Soil Sci. Soc. Am. Proc. 4: 65-70.
Steel, R.G. and J.H. Torrie, 1980. Principles and procedures of statistics. Second
edition. McGraw Hill, New York.
Unger, P.W., 1978. Straw mulch rate effect on soil water storage and sorghum
yield. Soil Sci. Soc. Am. J. 42: 486-491.
154
JOURNAL OF SUSTAINABLE AGRICULTURE
Unger, P.W., 1988. Residue management for dryland farming. In: Challenges in
Dryland Agriculture: A Global Perspective. Proceedings of International Conference on Dryland Farming, August 15-19th, 1988. Amarillo, TX, Texan
Agricultural Experiment Station, pp. 483-489.
USDA, 1978. Improving soils with organic wastes. Report to Congress in response to Section 1961 of the Food and Agric. Act of 1977 (P.L. 95-113).
USDA, Washington, D.C.
Venkateswarlu, J., 1987. Efficient resource management systems for drylands of
India. Adv. Soil Sci. 7: 165-222.
Wischmeier, W.H., 1973. Conservation tillage to control water erosion. In: Conservation Tillage, Soil Cons. Soc. Am., Ankeny, Iowa, pp. 133-141.
RECEIVED: 01/30/97
REVISED: 06/04/97
ACCEPTED: 06/09/97