Directory UMM :Data Elmu:jurnal:S:Soil & Tillage Research:Vol57.Issue4.Jan2001:
Soil & Tillage Research 57 (2001) 213±224
Predicting soil erosion in conservation tillage cotton production
systems using the revised universal soil loss equation (RUSLE)
E.Z. Nyakatawaa, K.C. Reddya,*, J.L. Lemunyonb
a
Department of Plant and Soil Science, Alabama A&M University, PO Box 1208, Normal, AL 35762, USA
b
USDA/NRCS, 510 W Felix St., Building 23, PO Box 6567, Fort Worth, TX 76115, USA
Received 6 March 2000; received in revised form 11 September 2000; accepted 27 September 2000
Abstract
Despite being one of the most pro®table crops for the southeastern USA, cotton (Gossypium hirsutum L.) is considered to
create a greater soil erosion hazard than other annual crops such as corn (Zea mays L.) and soybeans (Glycine max (L.) Merr.).
Reduced tillage systems and cover cropping can reduce soil erosion and leaching of nutrients into ground water. The
objectives of this study, which was conducted in north Alabama from 1996 to 1998, were to assess the impact of no-till and
mulch-till systems with a winter rye (Secale cereale L.) cover crop and poultry litter on soil erosion estimates in cotton plots
using the revised universal soil loss equation (RUSLE). Soil erosion estimates in conventional till plots with or without a
winter rye cover crop and ammonium nitrate fertilizer were double the 11 t haÿ1 yrÿ1 tolerance level for the Decatur series
soils. However, using poultry litter as the N source (100 kg N haÿ1) gave soil erosion estimates about 50% below the tolerance
level under conventional till. Doubling the N rate through poultry litter to 200 kg N haÿ1 under no-till system gave the lowest
soil erosion estimate level. No-till and mulch-till gave erosion estimates which were about 50% of the tolerance level with or
without cover cropping or N fertilization. This study shows that no-till and mulch-till systems with cover cropping and poultry
litter can reduce soil erosion in addition to increasing cotton growth and lint yields, and thus improve sustainability of cotton
soils in the southeastern USA. # 2001 Published by Elsevier Science B.V.
Keywords: Cotton; Cover crop; Mulch-till; No-till; Poultry litter; RUSLE; Soil erosion
1. Introduction
Soil erosion is a major environmental problem in
the US and worldwide. Eroded soils carry nutrients,
pesticides, and other harmful farm chemicals into
rivers, streams, and ground water resources (Gallaher
and Hawf, 1997). Soil erosion has been attributed
to the loss of productivity of soils in the southern
*
Corresponding author. Tel.: 1-256-858-4191;
fax: 1-256-851-5429.
E-mail address: [email protected] (K.C. Reddy).
Piedmont ranging from southern Virginia through
central Alabama which were once some of the most
productive cotton producing areas in the US. According to Brown et al. (1985), cotton yields can decline
by as much as 4% for each centimeter of top soil
loss. Erosion has been suggested as being one of the
major causes of static or declining cotton yields in
some areas in the southeast USA. Unlike gully
erosion which is easily recognized, sheet erosion
often goes unnoticed by the producer while having
a signi®cant impact on crop yields. In Alabama, soil
erosion on crop lands averages about 25 t haÿ1 yrÿ1,
which can potentially decrease cotton yields by
0167-1987/01/$ ± see front matter # 2001 Published by Elsevier Science B.V.
PII: S 0 1 6 7 - 1 9 8 7 ( 0 0 ) 0 0 1 7 8 - 1
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E.Z. Nyakatawa et al. / Soil & Tillage Research 57 (2001) 213±224
440±670 kg haÿ1, if no remedial actions are taken
(Anon., 1991).
Any tillage and planting system that leaves at least
30% of the soil surface covered with crop residues can
be called conservation tillage (CTIC, 1994; Gallaher
and Hawf, 1997). Conservation tillage, crop rotations,
and use of cover crops are acceptable mitigation
techniques to soil erosion on highly erodible sites.
The bene®ts of cover crops include improved soil
structure and tilth, addition of organic matter, reduced
soil erosion, and reduced leaching of nitrates into
water resources (Kelley et al., 1992; Schertz and
Kemper, 1994; Abdin et al., 1998; Sainju et al.,
1998; Vyn et al., 1999). The 1985 Food Security
Act and the 1990 US Federal Farm Bill restrict the
production of cotton under conventional tillage on
highly erodible sites for farmers participating in federal commodity programs such as storage loans and
subsidized prices on grain and cotton.
The revised universal soil loss equation (RUSLE) is
an empirical soil erosion model revised from the
universal soil erosion loss equation (USLE) (Wischmeier and Smith, 1965, 1978; Renard et al., 1993). It
computes the average annual soil erosion estimates
caused by rainfall and its associated overland ¯ow.
Published literature on soil erosion estimates in
reduced tillage cotton production systems, particularly
in combination with poultry litter and winter cover
cropping is lacking. This paper describes soil loss by
erosion estimated by RUSLE under conventional till,
no-till, and mulch-till systems with winter rye cover
cropping, and N from poultry litter from cotton plots
on a Decatur silt loam soil in north Alabama. The
experimental data will be useful for extension workers
and farmers who want to come up with acceptable
production practices in erosion prone areas.
2. Materials and methods
2.1. Site description and treatments
The study was conducted from 1996 to 1998 at the
Alabama Agricultural Experiment Station, Belle
Mina, AL (348410 N, 868520 W). The soil at the study
site is a Decatur silt loam soil (clayey, kaolinitic
thermic, Typic Paleudults). The study site has a slope
of about 1.5%. The treatments consisted of three
tillage systems: conventional tillage, mulch-till and
no-till; two cropping systems: cotton±winter fallow,
i.e. cotton in summer and fallow in winter, and cotton±
winter rye cropping, i.e. cotton in summer and rye
(Secale cereale L.) in winter; three nitrogen levels: 0,
100 and 200 kg N haÿ1; two nitrogen sources: ammonium nitrate and fresh poultry litter. Ammonium
nitrate was used at one N rate (100 kg N haÿ1) only.
An additional weed-free (bare) fallow treatment was
included. The bare fallow plots were not tilled and
cropped. They were kept weed-free by the use of
Roundup (glyphosate) herbicide. The purpose of these
control plots was to get an estimate of soil loss from
plots without any vegetation canopy and surface residue protection. The experimental design was a randomized complete block design with four replications.
Plot size was 8 m wide and 9 m long which resulted in
eight rows of cotton, 1 m apart.
Conventional tillage included moldboard plowing
to a depth of about 15 cm in November and disking in
April. A ®eld cultivator was used to prepare a smooth
seedbed after disking. Mulch-till included incorporating surface crop residues to a depth of about 5±7 cm
with a ®eld cultivator before planting, without performing any primary tillage. A ®eld cultivator was
used for controlling weeds in the conventional tillage
system, while spot applications of Roundup herbicide
were used to control weeds in the no-till and mulch-till
systems.
The N contents of the poultry litter used in the study
were 27 and 30 g kgÿ1 N in 1997 and 1998, respectively, on dry weight basis. The N content for the
poultry litter was determined by digesting 0.5 g samples using the Kjeldahl wet digestion method (Bremner and Mulvaney, 1982), followed by N analysis
using the Kjeltec 1026 N Analyzer (Kjeltec, Sweden).
The amounts of poultry litter to supply 100 and
200 kg N haÿ1 were calculated each year based on
the N percent of the poultry litter and a 60% adjustment factor to compensate for N availability from
poultry litter (Castellanos and Pratt, 1981; Keeling
et al., 1995). The residual effect of poultry litter in the
second year varies with environmental conditions and
was not measured. The poultry litter was broadcasted
by hand and incorporated to a depth of 5±8 cm by preplant cultivation in the conventional and mulch-till
systems. In the no-till system, the poultry litter was
surface applied. The ammonium nitrate and poultry
E.Z. Nyakatawa et al. / Soil & Tillage Research 57 (2001) 213±224
litter were applied to the plots 1 day before cotton
planting. The experimental plots received a blanket
application of 336 kg haÿ1 of a 0±20±20 fertilizer to
nullify the effects of P and K applied through poultry
litter.
2.2. Winter rye cover crop establishment and cotton
planting
A no-till planter was used to seed the winter rye
cover crop, var. Oklon on 4 December 1996 in the ®rst
year, which was killed with Roundup herbicide on 8
April 1997. In the second year, the winter rye cover
crop was seeded on 24 November 1997 and was killed
the same way on 28 February 1998. A herbicide
mixture of Prowl (pendimethalin) at 2.3 l haÿ1,
Cotoran (¯uometuron) at 3.5 l haÿ1, and Gramoxone
extra (paraquat) at 1.7 l haÿ1 was applied to all plots
before planting cotton, var. Deltapine NuCotn 33B, on
8 May 1997 and 5 May 1998. All plots received
5.6 kg haÿ1 of Temik (aldicarb) prior to planting,
for the control of thrips. No major weed problems
were observed in the cotton plots. The major insect
pests observed in cotton were aphids (Aphis spp.) and
bollworms (Heliothis spp.). Aphids were controlled by
spraying Bidrin (dicrotophos) at 0.4 kg haÿ1, whereas
bollworms were controlled with Karate (cypermethrin) at 44 ml haÿ1.
2.3. Description of the RUSLE computer model
RUSLE incorporates four physical parameters associated with erosion by water: rainfall erosivity, soil
erodibility, topography, and land-use management.
The model calculates the average annual soil erosion
on ®eld plots from the equation A RKLSCP, where
A is the predicted long-term average of annual sheet
and rill soil loss from a de®ned slope (t haÿ1 yrÿ1), R
the rainfall-runoff erosivity factor [(hundreds of fttons) in. acreÿ1 hÿ1 yrÿ1], K the soil erodibility factor
as measured under unit plot conditions [tons acreÿ1
(hundreds of ft-tons acreÿ1 in. hÿ1)ÿ1], LS the erosion
impact of the slope length (L) and steepness (S) on
erosion in comparison to unit plot conditions (dimensionless), C the erosion impact of cover and management schemes on erosion in comparison to unit plot
conditions (dimensionless), and P the erosion impact
of conservation support practices (e.g. contour tillage,
215
strip cropping, terraces, and drainage) on erosion in
comparison to unit plot conditions (dimensionless).
Among the RUSLE factors, R, K, and LS are nature
dependent or intrinsic to the landscape. They do not
change when soil conservation practices are applied.
Also, installing support practices that reduce the
P-value requires considerable monetary costs. Therefore, only C is the factor that can be managed with
reasonable planning and minimal costs to in¯uence
the soil losses in a given ®eld. The RUSLE model
consists of three main databases: climate, crop, and
soil databases. In this study, the calculations of soil
erosion estimates were done by plot for each year,
using RUSLE Ver. 1.06 computer program (RUSLE
Users' Guide, 1993).
2.3.1. Climate database
The climate database contains information on
monthly temperature and precipitation. The rainfall
erosivity (R) factor is the product of the storm energy
(E) and its maximum 30 min intensity (I30) for storms
of at least 0.5 in. (15 mm). This product, called an
EI30-value, is directly proportional to the product of
the storm amount and I30 for storms of intensities of at
least 0.5 in. hÿ1 (Renard et al., 1993). The R-value for
a given site is the average of EI30-values summed for
each year for a 22-yr period. The values for EI30 for
10-yr periods have been computed and entered into the
city database utility ®le for each location and have
been used to draw maps which show R-values for
different locations.
2.3.2. Crop database
The crop database contains information on crop
growth curves, crop residue and yield relationships,
and crop residue characteristics. This database
includes the vegetation database utility and the ®eld
operations database utility ®les. The important parameters in the development of the C-factor are the
impacts of prior land use (PLU), which have a strong
impact on soil aggregation and aggregate stability, as
well as physically inhibiting the formation of rills; the
vegetative canopy cover (CC), which intercepts raindrops and reduces their impact energies; the surface
cover (SC), which slows runoff and reduces raindrop
impact and ¯ow; the surface roughness (SR), which
slows runoff and causes local deposition of transport
sediment; and the soil moisture (SM) which effects the
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E.Z. Nyakatawa et al. / Soil & Tillage Research 57 (2001) 213±224
rainfall in®ltration rate. Each of these parameters is
assigned a subfactor value, and these are multiplied
together to yield a soil-loss ratio (SLR), thus
SLR PLU CC SC SR SM. Each of these SLR values
is then weighted by the fraction of rainfall and runoff
erosivity (EI) associated with the corresponding time
period of the cover and management, and these
weighted values are combined into an overall C-factor
value (Renard et al., 1993). The ®eld operations
database utility ®le contains information on how ®eld
operations such as tillage, planting, fertilizer application, and harvesting operations affect soil, vegetation,
and residue.
2.3.3. Soil database
The soil database contains soil survey and soil
characterization data. It holds information on the soil
erodibility (K) factor, the slope length (L) and steepness (S), which comprise the LS-factors. The K-factor
represents the susceptibility of a soil to erode and the
amount and rate of runoff, as measured under the
standard unit plot condition. The unit plot condition is
a continuously cultivated fallow plot, 72.6 ft (22.1 m)
long with a slope of 9%. The soil erodibility nomograph (Renard et al., 1993) calculates K-values based
on soil texture, structure, permeability, and percent
organic matter. The slope length (L) factor computes
the effect of slope length on erosion, while the slope
steepness (S) factor computes the effect of slope
steepness on erosion. The values for L and S under
the unit plot conditions equal 1, hence values for L and
S for any given location are relative to the unit plot
conditions.
2.4. Cover management (C) factor data collection
Most of the information required for predicting soil
erosion using RUSLE, such as rainfall and soil data
can be obtained from published records. The exception is the C-factor which varies with season and
production system. Conservation tillage such as notill and mulch-till affect the C-factor by reducing soil
degradation, reducing runoff, and increasing in®ltration and soil organic matter, which in turn reduce soil
erosion. Crop data collected for the RUSLE C-factor
calculation in this study included winter rye biomass,
surface residue cover (SRC) after cotton planting,
cotton CC, effective fall height (FH) from the cotton
canopy, and cotton surface root mass. SRC was measured in all plots using the camline transect method
(Renard et al., 1993; Reddy et al., 1994) immediately
after cotton planting. CC was determined by measuring the width of the crop canopy of each row from the
four central rows on each plot using a ruler and
expressing the ®gure as a percentage of the row width.
Effective FH is the distance a raindrop falls after
striking the crop canopy. This was calculated from
the equation:
FH 12 TH ÿ BH BH
(1)
where TH and BH are the top and bottom heights of
the cotton canopy, respectively.
Root biomass was determined by sampling plants
with their roots intact from 0.5 m2 quadrants from
each plot. Roots were extracted out of the soil by
removing soil from both sides of the row and lifting
the intact plants from the base with a garden fork. The
roots were cut from the shoots, washed in water to
remove soil and placed in separate bags. The shoot and
root samples were oven dried to constant weight at
658C for 72 h before weighing. The cotton crop growth
data were taken in each plot at 15-day intervals.
2.5. Data analysis
Statistical analysis of the data were performed using
the GLM procedures of the Statistical Analysis System. Contrast analysis procedures were used to compare the main effect treatment means for tillage
systems, cropping systems, and N treatments. The
analyses were performed separately for each year.
There were signi®cant tillage cropping system and
tillage nitrogen source interactions for C-factor and
soil erosion estimates.
3. Results and discussion
3.1. Surface residue cover
Percent SRC data taken after cotton seeding for
conventional till, no-till and mulch-till systems under
continuous cotton and cotton±rye sequential cropping
at Belle Mina, AL in 1997 and 1998 are given in
Table 1. Based on the de®nition for conservation
tillage, no-till or mulch-till with cotton±winter rye
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E.Z. Nyakatawa et al. / Soil & Tillage Research 57 (2001) 213±224
Table 1
Surface residue cover in cotton plots immediately after seeding as affected by tillage systems and cotton±winter fallow (CF) and cotton±winter
rye (CR) sequential cropping systems, Belle Mina, AL, 1997 and 1998
Tillage systems (%)a
Conventional till
Cropping systems
CF
CR
S.E.b
CVc (%)
Mulch-till
No-till
1997
1998
1997
1998
1997
1998
1.3 a
20.4 b
1.2 a
19.8 b
6.1 a
64.8 b
5.7 a
51.3 b
16.8 a
99.8 b
12.6 a
100.0 b
9.5
4.8
9.3
4.3
25.3
4.8
21.9
4.3
41.5
4.8
43.7
4.3
a
Means for tillage systems within a column followed by different letters are signi®cantly different at the 1% level.
Standard error of the difference between means.
c
Coef®cient of variation.
b
cropping systems which left at least 30% of the soil
surface covered with residues qualify to be described
as conservation tillage. As SRC approaches 100%, soil
erosion approaches zero (Moldenhauer and Langdale,
1995). With 50% residue cover, soil erosion reduction
is about 83% and with 10% residue cover, soil erosion
is about 30%. Based on the above ®gures, soil erosion
in plots with no-till or mulch-till under cotton±rye
sequential cropping system is expected to be very low.
3.2. Cotton growth parameters used as RUSLE input
data
Cotton FHs, CC, and root biomass as in¯uenced by
tillage systems and N levels at 2-week intervals during
1997 and 1998 growing seasons are presented in
Figs. 2 and 3. Drier weather and higher temperature
in the summer of 1998 (Fig. 1) resulted in a faster rate
of cotton growth development which resulted in 2week earlier maturity in 1998 compared to 1997.
Plants under no-till and mulch-till systems averaged
10 cm taller than those under conventional till system
at each sampling period in both years. As a result, FHs
for cotton plants under no-till and mulch-till were
generally higher than those under conventional till
(Fig. 2). Similar trends were observed with CC, which
was highest between 12 and 14 weeks after planting.
A fast growing canopy is a desirable attribute for
cotton. Since cotton is planted in wide rows, most of
the inter-row spacing is exposed to the direct impact of
rain drops which can result in high soil erosion rates.
Therefore, treatments which enable cotton to rapidly
develop a good CC will most likely result in reduced
soil erosion. Plant height was signi®cantly correlated
to CC, r 0:88 and 0.83 in 1997 and 1998, respectively. Maximum CC for cotton plants under no-till
and mulch-till systems was 7 and 11% higher
(P < 0:05) than that for plants under conventional till
in 1997 and 1998, respectively (Fig. 2).
Cotton root mass in the top 10 cm of the soil at 10±
14 weeks after planting for plants under no-till was 20
and 38% higher than that for plants under mulch-till
and conventional till systems, respectively, in 1997
(Fig. 2). However, in 1998, cotton root mass in the top
10 cm of the soil at 10±14 weeks after planting for
plants under no-till was 15% lower than that for plants
under conventional till or mulch-till systems (Fig. 2).
This can be largely attributed to the drought in the
months of August and September 1998. Roots and
crop residues control soil erosion directly by physically holding soil particles together, providing a carbon source for microbial soil processes that promote
water in®ltration, and providing a mechanical barrier
to water and eroded sediment movement. In addition,
roots and crop residues exude binding agents and serve
as a food source of micro-organisms which increase
soil aggregation and thereby reducing its susceptibility
to erosion.
In both years, cotton growth parameters for plants
which received N in the form of ammonium nitrate or
poultry litter were consistently higher than those for
plants which did not receive N (Fig. 3). Growth
parameters for cotton plants which received
100 kg N haÿ1 in the form of ammonium nitrate were
218
E.Z. Nyakatawa et al. / Soil & Tillage Research 57 (2001) 213±224
Fig. 1. Mean temperature, total monthly rainfall, and cumulative irrigation water applied to cotton plots, Belle Mina, AL, 1996±1998.
higher than those for plants which received
100 kg N haÿ1 in the form of poultry litter. This can
be attributed to the slower availability of N from
poultry litter. However, doubling the N rate to
200 kg N haÿ1 in the form of poultry litter resulted
in signi®cantly higher cotton growth parameters than
all the other N levels (Fig. 3). Improved SM conservation in no-till system was largely responsible for better
plant growth and higher yield parameters in cotton
(Nyakatawa et al., 1998; Nyakatawa and Reddy, 2000).
3.3. Cotton lint yields
In addition to reducing soil erosion, conservation
tillage practices such as no-till and mulch-till may give
higher cotton lint yields compared to conventional
tillage. Cotton lint yield under no-till (1360 kg haÿ1)
was 24 and 18% greater than that under conventional
till (1100 kg haÿ1) and mulch-till (1150 kg haÿ1)
systems, respectively, in 1997 (Table 2). In 1998,
cotton lint yield under no-till system (1440 kg haÿ1)
was 7% greater than that under conventional till
(1350 kg haÿ1). There were no signi®cant yield
increases in mulch-till compared to conventional till.
Poultry litter at 100 kg N haÿ1 gave similar cotton lint
yield to ammonium nitrate, whereas at 200 kg N haÿ1,
lint yields were 23 and 38% greater than those at
100 kg N haÿ1 in the form of ammonium nitrate and
poultry litter, respectively, in 1997; and 12 and 25%
greater than those at 100 kg N haÿ1 in the form of
ammonium nitrate and poultry litter, respectively, in
1998 (Table 2).
E.Z. Nyakatawa et al. / Soil & Tillage Research 57 (2001) 213±224
219
Fig. 2. Cotton growth parameters used in RUSLE model as in¯uenced by conventional till (CT), mulch-till (MT), and no-till (NT) systems,
Belle Mina, AL, 1996±1998 (error bars S:E:).
SM measurements in the top 7 cm of the soil
showed signi®cantly higher volumetric SM content
in no-till plots compared to conventional till plots with
and without winter rye cover cropping and in plots
which received N in the form of poultry litter vs.
ammonium nitrate (Nyakatawa et al., 1998). The
improved SM conservation which resulted in early
seedling emergence, higher seedling vigor, and
better plant growth in no-till system, cotton±winter
rye cropping, and 200 kg N haÿ1 in form of poultry
litter were attributed to the greater lint yield of
cotton.
220
E.Z. Nyakatawa et al. / Soil & Tillage Research 57 (2001) 213±224
Fig. 3. Cotton growth parameters used in RUSLE model as in¯uenced by N levels from ammonium nitrate (AN) and poultry litter (PL), Belle
Mina, AL, 1996±1998 (error bars S:E:).
3.4. Cover management (C-factor) and soil erosion
estimates
Higher C-factor values indicate higher soil erosion
loss since the C-factor is a ratio of soil loss in a cover
management sequence to soil loss from the unit plot.
C-factors for cotton±winter rye cover cropping under
conventional till were signi®cantly reduced by 15%
(0.487 vs. 0.423) and 28% (0.525 vs. 0.410) compared
to cotton±winter fallow cropping in 1997 and 1998,
respectively (Table 3). C-factors under conventional
till were about four times greater than those under
no-till, under cotton±winter fallow cropping in 1997
and 1998, respectively (Table 3). However, under
constant for all the treatments. The SRC plays an
important role of slowing surface runoff and protecting soil from the direct impact of raindrops whose
energy breaks the soil particles apart which can
then be carried away by moving water. The reduced
C-factors explain the 15% lower (15.7 vs.
18.0 t haÿ1 yrÿ1) and the 25% lower (15.8 vs.
19.7 t haÿ1 yrÿ1) soil erosion estimates in conventional till in cotton±winter rye cover cropping compared to cotton±winter fallow cropping in 1997 and
1998, respectively (Fig. 4).
In both years, soil erosion rates under mulch-till
cotton±winter rye cropping, C-factors under conventional till were up to seven times greater than those
under no-till both years. The main factor which caused
differences in the C-factor is SRC since most of the
other parameters such as rainfall and soil factors are
222
E.Z. Nyakatawa et al. / Soil & Tillage Research 57 (2001) 213±224
Fig. 4. Soil erosion estimates cotton plots as in¯uenced by conventional till (CT), mulch-till, and no-till systems and cotton±winter fallow
(CF) and cotton±winter rye (CR) cropping systems and N levels from ammonium nitrate (AN) and poultry litter (PL), Belle Mina, AL, 1996±
1998 (BF bare fallow).
reduced soil erosion (McDowell and McGregor, 1984;
Stein et al., 1986; Blevins et al., 1990; Seta et al.,
1993). Without cover cropping, soil erosion estimates
in no-till plots were about one-third of that in conventional till in both years. Similar results were found by
Stevens et al. (1992) who reported that no-till cotton
cropping without cover cropping may reduce soil
erosion by 70% compared to conventional till system.
Surface application of poultry litter at 100 kg N haÿ1
gave signi®cantly lower C-factors compared to control
plots and 100 kg N haÿ1 in the form of ammonium
nitrate under conventional till in both years (Table 3).
Similar results were obtained under no-till. The lower
C-factor values with use of poultry litter indicate that
soil erosion rates were lower than those in plots which
received an equal amount of N but in the form of
ammonium nitrate or those which did not receive any
N. The better erosion control with poultry litter can be
attributed to the fact that when surface applied, the
litter material acts as a residue cover which protects
E.Z. Nyakatawa et al. / Soil & Tillage Research 57 (2001) 213±224
soil from the direct impact of raindrops, slows runoff
water movement, and also increases in®ltration. The
RUSLE model takes into account of this fact in the
calculation of the C-factor.
At each level of N, soil erosion estimates in no-till
plots was below 5 t haÿ1 yrÿ1 compared to over
15 t haÿ1 yrÿ1 under conventional till at 0 or
100 kg N haÿ1 ammonium nitrate levels in both years
(Fig. 4). Plots which received 100 kg N haÿ1 in the
form of poultry litter had 10, 3 and 3 t haÿ1 yrÿ1 less
soil erosion rates under conventional till, no-till and
mulch-till systems, respectively, compared to plots
which received the same amount of N in the form
of ammonium nitrate in 1997. Similar ®gures for 1998
were 9, 2, and 3 t haÿ1 yrÿ1. Doubling the N rate
through poultry litter to 200 kg N haÿ1 under no-till
system gave the lowest soil erosion estimate levels of
less than 2 t haÿ1 yrÿ1 in both years (Fig. 4). Application of N in the form of ammonium nitrate or poultry
litter reduced soil erosion rates due to higher cotton
CC, root biomass, and more cotton residues compared
to control plots (Fig. 3).
The tolerance levels of soil erosion loss for these
Decatur series soils is 11 t haÿ1 yrÿ1 (Reddy et al.,
1994). Results from this study clearly show that
growing cotton under conventional till with or without
a winter rye cover crop using ammonium nitrate
fertilizer at 100 kg N haÿ1 on the Decatur silt loam
soils results in soil erosion rates up to 10 t haÿ1 yrÿ1 in
excess of the tolerance level (Fig. 4). However, using
poultry litter as the N source under conventional till
gave soil erosion estimates 4±5 t haÿ1 yrÿ1 below the
tolerance level (Fig. 4). Soil erosion estimates under
no-till and mulch-till systems were about 50% of the
tolerance level. The reduction in soil erosion rates will
reduce the amount of nutrients and pesticide residues
which end up in surface and ground water resources.
4. Conclusions
Soil erosion estimates under conventional till and
continuous cotton cropping system with the use of
ammonium nitrate fertilizer were similar to that in
weed-free fallow plots, which are about twice the
tolerance levels for northern Alabama. Adoption of
no-till or mulch-till systems with winter rye cover
cropping and poultry litter in the current cotton pro-
223
duction systems can signi®cantly reduce soil erosion
to tolerable levels and thus improve sustainability of
cotton soils in the southeastern USA where erosion
and safe disposal of poultry litter that is being produced in increasing quantities from the bourgeoning
poultry industry are major problems.
References
Abdin, O., Coulman, B.E., Cloutier, D., Faris, M.A., Zhou, X.,
Smith, D.L., 1998. Yield and yield components of corn
interseeded with cover crops. Agron. J. 90, 63±68.
Anon., 1991. Agriculture and Natural Resources Timely Information. Alabama Cooperative Extension Service, Auburn University, Auburn, AL, pp. 1±14.
Blevins, R.L., Frye, W.W., Baldwin, P.L., Robertson, S.D., 1990.
Tillage effects on sediment and soluble nutrient losses from a
Maury silt loam. J. Environ. Qual. 19, 683±686.
Bremner, J.M., Mulvaney, C.S., 1982. Nitrogen-total. In: Page,
A.L., Miller, R.H., Keeney, D.R. (Eds.), Methods of Soil
Analysis. Part 2. Chemical and Microbiological Properties, 2nd
Edition. American Society of Agronomy, Madison, WI,
pp. 595±625.
Brown, S.M., Whitwell, T., Touchton, J.T., Burmester, C.H., 1985.
Conservation tillage for cotton production. Soil Sci. Soc. Am. J.
49, 1256±1260.
Castellanos, J.Z., Pratt, P.F., 1981. Mineralization of manure
nitrogen Ð correlation with laboratory indexes. Soil Sci. Soc.
Am. J. 45, 354±357.
CTIC, 1994. National Crop Residue Management Survey Ð
Executive Summary. Conservation Technology Information
Center, West Lafayette, IN.
Gallaher, R.N., Hawf, L., 1997. Role of conservation tillage in
production of a wholesome food supply. In: Gallaher, R.N.
(Ed.), Proceedings of the 20th Annual Southern Conservation
Tillage for Sustainable Agriculture, University of Florida,
Gainesville, FL, USA, June 24±26, pp. 23±27.
Keeling, K.A., Hero, D., Rylant, K.E., 1995. Effectiveness of
composted manure for supplying nutrients. In: Proceedings of
the Conference on Fertilizer, Aglime and Pest Management.
Department of Agronomy, University of Wisconsin, Madison,
WI, January 17±18, pp. 77±81.
Kelley, K.R., Mortvedt, J.J., Soileau, J.M., Simmons, K.E., 1992.
Effect of winter cover crops on nitrate leaching. Agronomy
Abstracts. American Society of Agronomy, Madison, WI,
p. 282.
McDowell, L.L., McGregor, K.C., 1984. Plant nutrient losses in
runoff from conservation tillage corn. Soil Till. Res. 4, 79±91.
Moldenhauer, W.C., Langdale, G.W., 1995. Crop residue management to reduce soil erosion and improve soil quality. USDA/
ARS Report No. 39, January 1995, pp. 1±47.
Nyakatawa, E.Z., Reddy, K.C., Sistani, K.R., 1998. Tillage, cover
cropping, and poultry litter effects on cotton seedling
emergence. Agronomy Abstracts. American Society of Agronomy, Madison, WI, p. 274.
224
E.Z. Nyakatawa et al. / Soil & Tillage Research 57 (2001) 213±224
Nyakatawa, E.Z., Reddy, K.C., 2000. Tillage, cover cropping, and
poultry litter effects on cotton: 1. Germination and seedling
growth. Agron. J. 92, 992±999.
Reddy, K.C., Weesies, G.A., Lemunyon, J.L., 1994. Predicting soil
erosion in different cotton production systems with the revised
universal soil loss equation (RUSLE). In: Bushan, L.S., Abrol,
I.P., Rao, M.S. (Eds.), Proceedings of the Eighth International
Soil Conservation Organization Conference on Soil and Water
Conservation: Challenges and Opportunities, Vol. 1, Indian
Association of soil and water conservationsists, Dehradun,
India, December 4±8, pp. 1±11.
Renard, K.G., Foster, G.R., Weesies, G.A., Yoder, D.C., 1993.
Predicting soil erosion by water. A guide to conservation
planning with the universal soil loss equation (RUSLE).
Agricultural Handbook No. 703. US Dept. of Agriculture,
p. 47.
RUSLE Users' Guide, 1993. Revised Universal Soil Loss Equation.
Soil and Water Conservation Society, Ankeny, IA.
Sainju, U.M., Singh, B.P., Whitehead, W.F., 1998. Cover crop root
distribution and its effects on soil nitrogen cycling. Agron. J.
90, 511±518.
Schertz, D.L., Kemper, W.D., 1994. Report on Field Review
of No-till Cotton. USDA/ARS/NRCS/Auburn University/
Alabama A&M University, Huntsville, AL, September
22±23.
Seta, A.K., Blevins, R.L., Frye, W.W., Bal®eld, B.J., 1993.
Reducing soil erosion and agricultural chemical losses with
conservation tillage. J. Environ. Qual. 22, 661±665.
Stein, O.R., Neibling, W.H., Logan, T.J., Moldenhauer, W.C., 1986.
Runoff and soil loss as in¯uenced by tillage residue cover. Soil
Sci. Am. J. 50, 1527±1531.
Stevens, W.E., Johnson, J.R., Varco, J.J., Parkman, J., 1992. Tillage
and winter cover management effects on fruiting and yield of
cotton. J. Prod. Agric. 5, 570±575.
Vyn, T.J., Janovick, K.J., Miller, M.H., Beauchamp, E.G., 1999.
Soil nitrate accumulation and corn response to preceding small
grain fertilization and cover crops. Agron. J. 91, 17±24.
Wischmeier, W.A., Smith, D.A., 1965. Predicting rainfall-erosion
losses from cropland east of the Rocky Mountains: guide for
selection practices for soil and water conservation. Agricultural
Handbook No. 282, US Dept. of Agric. Sci and Edu. Admin.,
Agric. Res., 47 pp.
Wischmeier, W.H., Smith, D.D., 1978. Predicting rainfall erosion
losses: a guide to conservation planning. Agricultural Handbook No. 537. US Dept. of Agric. Sci. and Educ. Admin.,
Agric. Res., 85 pp.
Predicting soil erosion in conservation tillage cotton production
systems using the revised universal soil loss equation (RUSLE)
E.Z. Nyakatawaa, K.C. Reddya,*, J.L. Lemunyonb
a
Department of Plant and Soil Science, Alabama A&M University, PO Box 1208, Normal, AL 35762, USA
b
USDA/NRCS, 510 W Felix St., Building 23, PO Box 6567, Fort Worth, TX 76115, USA
Received 6 March 2000; received in revised form 11 September 2000; accepted 27 September 2000
Abstract
Despite being one of the most pro®table crops for the southeastern USA, cotton (Gossypium hirsutum L.) is considered to
create a greater soil erosion hazard than other annual crops such as corn (Zea mays L.) and soybeans (Glycine max (L.) Merr.).
Reduced tillage systems and cover cropping can reduce soil erosion and leaching of nutrients into ground water. The
objectives of this study, which was conducted in north Alabama from 1996 to 1998, were to assess the impact of no-till and
mulch-till systems with a winter rye (Secale cereale L.) cover crop and poultry litter on soil erosion estimates in cotton plots
using the revised universal soil loss equation (RUSLE). Soil erosion estimates in conventional till plots with or without a
winter rye cover crop and ammonium nitrate fertilizer were double the 11 t haÿ1 yrÿ1 tolerance level for the Decatur series
soils. However, using poultry litter as the N source (100 kg N haÿ1) gave soil erosion estimates about 50% below the tolerance
level under conventional till. Doubling the N rate through poultry litter to 200 kg N haÿ1 under no-till system gave the lowest
soil erosion estimate level. No-till and mulch-till gave erosion estimates which were about 50% of the tolerance level with or
without cover cropping or N fertilization. This study shows that no-till and mulch-till systems with cover cropping and poultry
litter can reduce soil erosion in addition to increasing cotton growth and lint yields, and thus improve sustainability of cotton
soils in the southeastern USA. # 2001 Published by Elsevier Science B.V.
Keywords: Cotton; Cover crop; Mulch-till; No-till; Poultry litter; RUSLE; Soil erosion
1. Introduction
Soil erosion is a major environmental problem in
the US and worldwide. Eroded soils carry nutrients,
pesticides, and other harmful farm chemicals into
rivers, streams, and ground water resources (Gallaher
and Hawf, 1997). Soil erosion has been attributed
to the loss of productivity of soils in the southern
*
Corresponding author. Tel.: 1-256-858-4191;
fax: 1-256-851-5429.
E-mail address: [email protected] (K.C. Reddy).
Piedmont ranging from southern Virginia through
central Alabama which were once some of the most
productive cotton producing areas in the US. According to Brown et al. (1985), cotton yields can decline
by as much as 4% for each centimeter of top soil
loss. Erosion has been suggested as being one of the
major causes of static or declining cotton yields in
some areas in the southeast USA. Unlike gully
erosion which is easily recognized, sheet erosion
often goes unnoticed by the producer while having
a signi®cant impact on crop yields. In Alabama, soil
erosion on crop lands averages about 25 t haÿ1 yrÿ1,
which can potentially decrease cotton yields by
0167-1987/01/$ ± see front matter # 2001 Published by Elsevier Science B.V.
PII: S 0 1 6 7 - 1 9 8 7 ( 0 0 ) 0 0 1 7 8 - 1
214
E.Z. Nyakatawa et al. / Soil & Tillage Research 57 (2001) 213±224
440±670 kg haÿ1, if no remedial actions are taken
(Anon., 1991).
Any tillage and planting system that leaves at least
30% of the soil surface covered with crop residues can
be called conservation tillage (CTIC, 1994; Gallaher
and Hawf, 1997). Conservation tillage, crop rotations,
and use of cover crops are acceptable mitigation
techniques to soil erosion on highly erodible sites.
The bene®ts of cover crops include improved soil
structure and tilth, addition of organic matter, reduced
soil erosion, and reduced leaching of nitrates into
water resources (Kelley et al., 1992; Schertz and
Kemper, 1994; Abdin et al., 1998; Sainju et al.,
1998; Vyn et al., 1999). The 1985 Food Security
Act and the 1990 US Federal Farm Bill restrict the
production of cotton under conventional tillage on
highly erodible sites for farmers participating in federal commodity programs such as storage loans and
subsidized prices on grain and cotton.
The revised universal soil loss equation (RUSLE) is
an empirical soil erosion model revised from the
universal soil erosion loss equation (USLE) (Wischmeier and Smith, 1965, 1978; Renard et al., 1993). It
computes the average annual soil erosion estimates
caused by rainfall and its associated overland ¯ow.
Published literature on soil erosion estimates in
reduced tillage cotton production systems, particularly
in combination with poultry litter and winter cover
cropping is lacking. This paper describes soil loss by
erosion estimated by RUSLE under conventional till,
no-till, and mulch-till systems with winter rye cover
cropping, and N from poultry litter from cotton plots
on a Decatur silt loam soil in north Alabama. The
experimental data will be useful for extension workers
and farmers who want to come up with acceptable
production practices in erosion prone areas.
2. Materials and methods
2.1. Site description and treatments
The study was conducted from 1996 to 1998 at the
Alabama Agricultural Experiment Station, Belle
Mina, AL (348410 N, 868520 W). The soil at the study
site is a Decatur silt loam soil (clayey, kaolinitic
thermic, Typic Paleudults). The study site has a slope
of about 1.5%. The treatments consisted of three
tillage systems: conventional tillage, mulch-till and
no-till; two cropping systems: cotton±winter fallow,
i.e. cotton in summer and fallow in winter, and cotton±
winter rye cropping, i.e. cotton in summer and rye
(Secale cereale L.) in winter; three nitrogen levels: 0,
100 and 200 kg N haÿ1; two nitrogen sources: ammonium nitrate and fresh poultry litter. Ammonium
nitrate was used at one N rate (100 kg N haÿ1) only.
An additional weed-free (bare) fallow treatment was
included. The bare fallow plots were not tilled and
cropped. They were kept weed-free by the use of
Roundup (glyphosate) herbicide. The purpose of these
control plots was to get an estimate of soil loss from
plots without any vegetation canopy and surface residue protection. The experimental design was a randomized complete block design with four replications.
Plot size was 8 m wide and 9 m long which resulted in
eight rows of cotton, 1 m apart.
Conventional tillage included moldboard plowing
to a depth of about 15 cm in November and disking in
April. A ®eld cultivator was used to prepare a smooth
seedbed after disking. Mulch-till included incorporating surface crop residues to a depth of about 5±7 cm
with a ®eld cultivator before planting, without performing any primary tillage. A ®eld cultivator was
used for controlling weeds in the conventional tillage
system, while spot applications of Roundup herbicide
were used to control weeds in the no-till and mulch-till
systems.
The N contents of the poultry litter used in the study
were 27 and 30 g kgÿ1 N in 1997 and 1998, respectively, on dry weight basis. The N content for the
poultry litter was determined by digesting 0.5 g samples using the Kjeldahl wet digestion method (Bremner and Mulvaney, 1982), followed by N analysis
using the Kjeltec 1026 N Analyzer (Kjeltec, Sweden).
The amounts of poultry litter to supply 100 and
200 kg N haÿ1 were calculated each year based on
the N percent of the poultry litter and a 60% adjustment factor to compensate for N availability from
poultry litter (Castellanos and Pratt, 1981; Keeling
et al., 1995). The residual effect of poultry litter in the
second year varies with environmental conditions and
was not measured. The poultry litter was broadcasted
by hand and incorporated to a depth of 5±8 cm by preplant cultivation in the conventional and mulch-till
systems. In the no-till system, the poultry litter was
surface applied. The ammonium nitrate and poultry
E.Z. Nyakatawa et al. / Soil & Tillage Research 57 (2001) 213±224
litter were applied to the plots 1 day before cotton
planting. The experimental plots received a blanket
application of 336 kg haÿ1 of a 0±20±20 fertilizer to
nullify the effects of P and K applied through poultry
litter.
2.2. Winter rye cover crop establishment and cotton
planting
A no-till planter was used to seed the winter rye
cover crop, var. Oklon on 4 December 1996 in the ®rst
year, which was killed with Roundup herbicide on 8
April 1997. In the second year, the winter rye cover
crop was seeded on 24 November 1997 and was killed
the same way on 28 February 1998. A herbicide
mixture of Prowl (pendimethalin) at 2.3 l haÿ1,
Cotoran (¯uometuron) at 3.5 l haÿ1, and Gramoxone
extra (paraquat) at 1.7 l haÿ1 was applied to all plots
before planting cotton, var. Deltapine NuCotn 33B, on
8 May 1997 and 5 May 1998. All plots received
5.6 kg haÿ1 of Temik (aldicarb) prior to planting,
for the control of thrips. No major weed problems
were observed in the cotton plots. The major insect
pests observed in cotton were aphids (Aphis spp.) and
bollworms (Heliothis spp.). Aphids were controlled by
spraying Bidrin (dicrotophos) at 0.4 kg haÿ1, whereas
bollworms were controlled with Karate (cypermethrin) at 44 ml haÿ1.
2.3. Description of the RUSLE computer model
RUSLE incorporates four physical parameters associated with erosion by water: rainfall erosivity, soil
erodibility, topography, and land-use management.
The model calculates the average annual soil erosion
on ®eld plots from the equation A RKLSCP, where
A is the predicted long-term average of annual sheet
and rill soil loss from a de®ned slope (t haÿ1 yrÿ1), R
the rainfall-runoff erosivity factor [(hundreds of fttons) in. acreÿ1 hÿ1 yrÿ1], K the soil erodibility factor
as measured under unit plot conditions [tons acreÿ1
(hundreds of ft-tons acreÿ1 in. hÿ1)ÿ1], LS the erosion
impact of the slope length (L) and steepness (S) on
erosion in comparison to unit plot conditions (dimensionless), C the erosion impact of cover and management schemes on erosion in comparison to unit plot
conditions (dimensionless), and P the erosion impact
of conservation support practices (e.g. contour tillage,
215
strip cropping, terraces, and drainage) on erosion in
comparison to unit plot conditions (dimensionless).
Among the RUSLE factors, R, K, and LS are nature
dependent or intrinsic to the landscape. They do not
change when soil conservation practices are applied.
Also, installing support practices that reduce the
P-value requires considerable monetary costs. Therefore, only C is the factor that can be managed with
reasonable planning and minimal costs to in¯uence
the soil losses in a given ®eld. The RUSLE model
consists of three main databases: climate, crop, and
soil databases. In this study, the calculations of soil
erosion estimates were done by plot for each year,
using RUSLE Ver. 1.06 computer program (RUSLE
Users' Guide, 1993).
2.3.1. Climate database
The climate database contains information on
monthly temperature and precipitation. The rainfall
erosivity (R) factor is the product of the storm energy
(E) and its maximum 30 min intensity (I30) for storms
of at least 0.5 in. (15 mm). This product, called an
EI30-value, is directly proportional to the product of
the storm amount and I30 for storms of intensities of at
least 0.5 in. hÿ1 (Renard et al., 1993). The R-value for
a given site is the average of EI30-values summed for
each year for a 22-yr period. The values for EI30 for
10-yr periods have been computed and entered into the
city database utility ®le for each location and have
been used to draw maps which show R-values for
different locations.
2.3.2. Crop database
The crop database contains information on crop
growth curves, crop residue and yield relationships,
and crop residue characteristics. This database
includes the vegetation database utility and the ®eld
operations database utility ®les. The important parameters in the development of the C-factor are the
impacts of prior land use (PLU), which have a strong
impact on soil aggregation and aggregate stability, as
well as physically inhibiting the formation of rills; the
vegetative canopy cover (CC), which intercepts raindrops and reduces their impact energies; the surface
cover (SC), which slows runoff and reduces raindrop
impact and ¯ow; the surface roughness (SR), which
slows runoff and causes local deposition of transport
sediment; and the soil moisture (SM) which effects the
216
E.Z. Nyakatawa et al. / Soil & Tillage Research 57 (2001) 213±224
rainfall in®ltration rate. Each of these parameters is
assigned a subfactor value, and these are multiplied
together to yield a soil-loss ratio (SLR), thus
SLR PLU CC SC SR SM. Each of these SLR values
is then weighted by the fraction of rainfall and runoff
erosivity (EI) associated with the corresponding time
period of the cover and management, and these
weighted values are combined into an overall C-factor
value (Renard et al., 1993). The ®eld operations
database utility ®le contains information on how ®eld
operations such as tillage, planting, fertilizer application, and harvesting operations affect soil, vegetation,
and residue.
2.3.3. Soil database
The soil database contains soil survey and soil
characterization data. It holds information on the soil
erodibility (K) factor, the slope length (L) and steepness (S), which comprise the LS-factors. The K-factor
represents the susceptibility of a soil to erode and the
amount and rate of runoff, as measured under the
standard unit plot condition. The unit plot condition is
a continuously cultivated fallow plot, 72.6 ft (22.1 m)
long with a slope of 9%. The soil erodibility nomograph (Renard et al., 1993) calculates K-values based
on soil texture, structure, permeability, and percent
organic matter. The slope length (L) factor computes
the effect of slope length on erosion, while the slope
steepness (S) factor computes the effect of slope
steepness on erosion. The values for L and S under
the unit plot conditions equal 1, hence values for L and
S for any given location are relative to the unit plot
conditions.
2.4. Cover management (C) factor data collection
Most of the information required for predicting soil
erosion using RUSLE, such as rainfall and soil data
can be obtained from published records. The exception is the C-factor which varies with season and
production system. Conservation tillage such as notill and mulch-till affect the C-factor by reducing soil
degradation, reducing runoff, and increasing in®ltration and soil organic matter, which in turn reduce soil
erosion. Crop data collected for the RUSLE C-factor
calculation in this study included winter rye biomass,
surface residue cover (SRC) after cotton planting,
cotton CC, effective fall height (FH) from the cotton
canopy, and cotton surface root mass. SRC was measured in all plots using the camline transect method
(Renard et al., 1993; Reddy et al., 1994) immediately
after cotton planting. CC was determined by measuring the width of the crop canopy of each row from the
four central rows on each plot using a ruler and
expressing the ®gure as a percentage of the row width.
Effective FH is the distance a raindrop falls after
striking the crop canopy. This was calculated from
the equation:
FH 12 TH ÿ BH BH
(1)
where TH and BH are the top and bottom heights of
the cotton canopy, respectively.
Root biomass was determined by sampling plants
with their roots intact from 0.5 m2 quadrants from
each plot. Roots were extracted out of the soil by
removing soil from both sides of the row and lifting
the intact plants from the base with a garden fork. The
roots were cut from the shoots, washed in water to
remove soil and placed in separate bags. The shoot and
root samples were oven dried to constant weight at
658C for 72 h before weighing. The cotton crop growth
data were taken in each plot at 15-day intervals.
2.5. Data analysis
Statistical analysis of the data were performed using
the GLM procedures of the Statistical Analysis System. Contrast analysis procedures were used to compare the main effect treatment means for tillage
systems, cropping systems, and N treatments. The
analyses were performed separately for each year.
There were signi®cant tillage cropping system and
tillage nitrogen source interactions for C-factor and
soil erosion estimates.
3. Results and discussion
3.1. Surface residue cover
Percent SRC data taken after cotton seeding for
conventional till, no-till and mulch-till systems under
continuous cotton and cotton±rye sequential cropping
at Belle Mina, AL in 1997 and 1998 are given in
Table 1. Based on the de®nition for conservation
tillage, no-till or mulch-till with cotton±winter rye
217
E.Z. Nyakatawa et al. / Soil & Tillage Research 57 (2001) 213±224
Table 1
Surface residue cover in cotton plots immediately after seeding as affected by tillage systems and cotton±winter fallow (CF) and cotton±winter
rye (CR) sequential cropping systems, Belle Mina, AL, 1997 and 1998
Tillage systems (%)a
Conventional till
Cropping systems
CF
CR
S.E.b
CVc (%)
Mulch-till
No-till
1997
1998
1997
1998
1997
1998
1.3 a
20.4 b
1.2 a
19.8 b
6.1 a
64.8 b
5.7 a
51.3 b
16.8 a
99.8 b
12.6 a
100.0 b
9.5
4.8
9.3
4.3
25.3
4.8
21.9
4.3
41.5
4.8
43.7
4.3
a
Means for tillage systems within a column followed by different letters are signi®cantly different at the 1% level.
Standard error of the difference between means.
c
Coef®cient of variation.
b
cropping systems which left at least 30% of the soil
surface covered with residues qualify to be described
as conservation tillage. As SRC approaches 100%, soil
erosion approaches zero (Moldenhauer and Langdale,
1995). With 50% residue cover, soil erosion reduction
is about 83% and with 10% residue cover, soil erosion
is about 30%. Based on the above ®gures, soil erosion
in plots with no-till or mulch-till under cotton±rye
sequential cropping system is expected to be very low.
3.2. Cotton growth parameters used as RUSLE input
data
Cotton FHs, CC, and root biomass as in¯uenced by
tillage systems and N levels at 2-week intervals during
1997 and 1998 growing seasons are presented in
Figs. 2 and 3. Drier weather and higher temperature
in the summer of 1998 (Fig. 1) resulted in a faster rate
of cotton growth development which resulted in 2week earlier maturity in 1998 compared to 1997.
Plants under no-till and mulch-till systems averaged
10 cm taller than those under conventional till system
at each sampling period in both years. As a result, FHs
for cotton plants under no-till and mulch-till were
generally higher than those under conventional till
(Fig. 2). Similar trends were observed with CC, which
was highest between 12 and 14 weeks after planting.
A fast growing canopy is a desirable attribute for
cotton. Since cotton is planted in wide rows, most of
the inter-row spacing is exposed to the direct impact of
rain drops which can result in high soil erosion rates.
Therefore, treatments which enable cotton to rapidly
develop a good CC will most likely result in reduced
soil erosion. Plant height was signi®cantly correlated
to CC, r 0:88 and 0.83 in 1997 and 1998, respectively. Maximum CC for cotton plants under no-till
and mulch-till systems was 7 and 11% higher
(P < 0:05) than that for plants under conventional till
in 1997 and 1998, respectively (Fig. 2).
Cotton root mass in the top 10 cm of the soil at 10±
14 weeks after planting for plants under no-till was 20
and 38% higher than that for plants under mulch-till
and conventional till systems, respectively, in 1997
(Fig. 2). However, in 1998, cotton root mass in the top
10 cm of the soil at 10±14 weeks after planting for
plants under no-till was 15% lower than that for plants
under conventional till or mulch-till systems (Fig. 2).
This can be largely attributed to the drought in the
months of August and September 1998. Roots and
crop residues control soil erosion directly by physically holding soil particles together, providing a carbon source for microbial soil processes that promote
water in®ltration, and providing a mechanical barrier
to water and eroded sediment movement. In addition,
roots and crop residues exude binding agents and serve
as a food source of micro-organisms which increase
soil aggregation and thereby reducing its susceptibility
to erosion.
In both years, cotton growth parameters for plants
which received N in the form of ammonium nitrate or
poultry litter were consistently higher than those for
plants which did not receive N (Fig. 3). Growth
parameters for cotton plants which received
100 kg N haÿ1 in the form of ammonium nitrate were
218
E.Z. Nyakatawa et al. / Soil & Tillage Research 57 (2001) 213±224
Fig. 1. Mean temperature, total monthly rainfall, and cumulative irrigation water applied to cotton plots, Belle Mina, AL, 1996±1998.
higher than those for plants which received
100 kg N haÿ1 in the form of poultry litter. This can
be attributed to the slower availability of N from
poultry litter. However, doubling the N rate to
200 kg N haÿ1 in the form of poultry litter resulted
in signi®cantly higher cotton growth parameters than
all the other N levels (Fig. 3). Improved SM conservation in no-till system was largely responsible for better
plant growth and higher yield parameters in cotton
(Nyakatawa et al., 1998; Nyakatawa and Reddy, 2000).
3.3. Cotton lint yields
In addition to reducing soil erosion, conservation
tillage practices such as no-till and mulch-till may give
higher cotton lint yields compared to conventional
tillage. Cotton lint yield under no-till (1360 kg haÿ1)
was 24 and 18% greater than that under conventional
till (1100 kg haÿ1) and mulch-till (1150 kg haÿ1)
systems, respectively, in 1997 (Table 2). In 1998,
cotton lint yield under no-till system (1440 kg haÿ1)
was 7% greater than that under conventional till
(1350 kg haÿ1). There were no signi®cant yield
increases in mulch-till compared to conventional till.
Poultry litter at 100 kg N haÿ1 gave similar cotton lint
yield to ammonium nitrate, whereas at 200 kg N haÿ1,
lint yields were 23 and 38% greater than those at
100 kg N haÿ1 in the form of ammonium nitrate and
poultry litter, respectively, in 1997; and 12 and 25%
greater than those at 100 kg N haÿ1 in the form of
ammonium nitrate and poultry litter, respectively, in
1998 (Table 2).
E.Z. Nyakatawa et al. / Soil & Tillage Research 57 (2001) 213±224
219
Fig. 2. Cotton growth parameters used in RUSLE model as in¯uenced by conventional till (CT), mulch-till (MT), and no-till (NT) systems,
Belle Mina, AL, 1996±1998 (error bars S:E:).
SM measurements in the top 7 cm of the soil
showed signi®cantly higher volumetric SM content
in no-till plots compared to conventional till plots with
and without winter rye cover cropping and in plots
which received N in the form of poultry litter vs.
ammonium nitrate (Nyakatawa et al., 1998). The
improved SM conservation which resulted in early
seedling emergence, higher seedling vigor, and
better plant growth in no-till system, cotton±winter
rye cropping, and 200 kg N haÿ1 in form of poultry
litter were attributed to the greater lint yield of
cotton.
220
E.Z. Nyakatawa et al. / Soil & Tillage Research 57 (2001) 213±224
Fig. 3. Cotton growth parameters used in RUSLE model as in¯uenced by N levels from ammonium nitrate (AN) and poultry litter (PL), Belle
Mina, AL, 1996±1998 (error bars S:E:).
3.4. Cover management (C-factor) and soil erosion
estimates
Higher C-factor values indicate higher soil erosion
loss since the C-factor is a ratio of soil loss in a cover
management sequence to soil loss from the unit plot.
C-factors for cotton±winter rye cover cropping under
conventional till were signi®cantly reduced by 15%
(0.487 vs. 0.423) and 28% (0.525 vs. 0.410) compared
to cotton±winter fallow cropping in 1997 and 1998,
respectively (Table 3). C-factors under conventional
till were about four times greater than those under
no-till, under cotton±winter fallow cropping in 1997
and 1998, respectively (Table 3). However, under
constant for all the treatments. The SRC plays an
important role of slowing surface runoff and protecting soil from the direct impact of raindrops whose
energy breaks the soil particles apart which can
then be carried away by moving water. The reduced
C-factors explain the 15% lower (15.7 vs.
18.0 t haÿ1 yrÿ1) and the 25% lower (15.8 vs.
19.7 t haÿ1 yrÿ1) soil erosion estimates in conventional till in cotton±winter rye cover cropping compared to cotton±winter fallow cropping in 1997 and
1998, respectively (Fig. 4).
In both years, soil erosion rates under mulch-till
cotton±winter rye cropping, C-factors under conventional till were up to seven times greater than those
under no-till both years. The main factor which caused
differences in the C-factor is SRC since most of the
other parameters such as rainfall and soil factors are
222
E.Z. Nyakatawa et al. / Soil & Tillage Research 57 (2001) 213±224
Fig. 4. Soil erosion estimates cotton plots as in¯uenced by conventional till (CT), mulch-till, and no-till systems and cotton±winter fallow
(CF) and cotton±winter rye (CR) cropping systems and N levels from ammonium nitrate (AN) and poultry litter (PL), Belle Mina, AL, 1996±
1998 (BF bare fallow).
reduced soil erosion (McDowell and McGregor, 1984;
Stein et al., 1986; Blevins et al., 1990; Seta et al.,
1993). Without cover cropping, soil erosion estimates
in no-till plots were about one-third of that in conventional till in both years. Similar results were found by
Stevens et al. (1992) who reported that no-till cotton
cropping without cover cropping may reduce soil
erosion by 70% compared to conventional till system.
Surface application of poultry litter at 100 kg N haÿ1
gave signi®cantly lower C-factors compared to control
plots and 100 kg N haÿ1 in the form of ammonium
nitrate under conventional till in both years (Table 3).
Similar results were obtained under no-till. The lower
C-factor values with use of poultry litter indicate that
soil erosion rates were lower than those in plots which
received an equal amount of N but in the form of
ammonium nitrate or those which did not receive any
N. The better erosion control with poultry litter can be
attributed to the fact that when surface applied, the
litter material acts as a residue cover which protects
E.Z. Nyakatawa et al. / Soil & Tillage Research 57 (2001) 213±224
soil from the direct impact of raindrops, slows runoff
water movement, and also increases in®ltration. The
RUSLE model takes into account of this fact in the
calculation of the C-factor.
At each level of N, soil erosion estimates in no-till
plots was below 5 t haÿ1 yrÿ1 compared to over
15 t haÿ1 yrÿ1 under conventional till at 0 or
100 kg N haÿ1 ammonium nitrate levels in both years
(Fig. 4). Plots which received 100 kg N haÿ1 in the
form of poultry litter had 10, 3 and 3 t haÿ1 yrÿ1 less
soil erosion rates under conventional till, no-till and
mulch-till systems, respectively, compared to plots
which received the same amount of N in the form
of ammonium nitrate in 1997. Similar ®gures for 1998
were 9, 2, and 3 t haÿ1 yrÿ1. Doubling the N rate
through poultry litter to 200 kg N haÿ1 under no-till
system gave the lowest soil erosion estimate levels of
less than 2 t haÿ1 yrÿ1 in both years (Fig. 4). Application of N in the form of ammonium nitrate or poultry
litter reduced soil erosion rates due to higher cotton
CC, root biomass, and more cotton residues compared
to control plots (Fig. 3).
The tolerance levels of soil erosion loss for these
Decatur series soils is 11 t haÿ1 yrÿ1 (Reddy et al.,
1994). Results from this study clearly show that
growing cotton under conventional till with or without
a winter rye cover crop using ammonium nitrate
fertilizer at 100 kg N haÿ1 on the Decatur silt loam
soils results in soil erosion rates up to 10 t haÿ1 yrÿ1 in
excess of the tolerance level (Fig. 4). However, using
poultry litter as the N source under conventional till
gave soil erosion estimates 4±5 t haÿ1 yrÿ1 below the
tolerance level (Fig. 4). Soil erosion estimates under
no-till and mulch-till systems were about 50% of the
tolerance level. The reduction in soil erosion rates will
reduce the amount of nutrients and pesticide residues
which end up in surface and ground water resources.
4. Conclusions
Soil erosion estimates under conventional till and
continuous cotton cropping system with the use of
ammonium nitrate fertilizer were similar to that in
weed-free fallow plots, which are about twice the
tolerance levels for northern Alabama. Adoption of
no-till or mulch-till systems with winter rye cover
cropping and poultry litter in the current cotton pro-
223
duction systems can signi®cantly reduce soil erosion
to tolerable levels and thus improve sustainability of
cotton soils in the southeastern USA where erosion
and safe disposal of poultry litter that is being produced in increasing quantities from the bourgeoning
poultry industry are major problems.
References
Abdin, O., Coulman, B.E., Cloutier, D., Faris, M.A., Zhou, X.,
Smith, D.L., 1998. Yield and yield components of corn
interseeded with cover crops. Agron. J. 90, 63±68.
Anon., 1991. Agriculture and Natural Resources Timely Information. Alabama Cooperative Extension Service, Auburn University, Auburn, AL, pp. 1±14.
Blevins, R.L., Frye, W.W., Baldwin, P.L., Robertson, S.D., 1990.
Tillage effects on sediment and soluble nutrient losses from a
Maury silt loam. J. Environ. Qual. 19, 683±686.
Bremner, J.M., Mulvaney, C.S., 1982. Nitrogen-total. In: Page,
A.L., Miller, R.H., Keeney, D.R. (Eds.), Methods of Soil
Analysis. Part 2. Chemical and Microbiological Properties, 2nd
Edition. American Society of Agronomy, Madison, WI,
pp. 595±625.
Brown, S.M., Whitwell, T., Touchton, J.T., Burmester, C.H., 1985.
Conservation tillage for cotton production. Soil Sci. Soc. Am. J.
49, 1256±1260.
Castellanos, J.Z., Pratt, P.F., 1981. Mineralization of manure
nitrogen Ð correlation with laboratory indexes. Soil Sci. Soc.
Am. J. 45, 354±357.
CTIC, 1994. National Crop Residue Management Survey Ð
Executive Summary. Conservation Technology Information
Center, West Lafayette, IN.
Gallaher, R.N., Hawf, L., 1997. Role of conservation tillage in
production of a wholesome food supply. In: Gallaher, R.N.
(Ed.), Proceedings of the 20th Annual Southern Conservation
Tillage for Sustainable Agriculture, University of Florida,
Gainesville, FL, USA, June 24±26, pp. 23±27.
Keeling, K.A., Hero, D., Rylant, K.E., 1995. Effectiveness of
composted manure for supplying nutrients. In: Proceedings of
the Conference on Fertilizer, Aglime and Pest Management.
Department of Agronomy, University of Wisconsin, Madison,
WI, January 17±18, pp. 77±81.
Kelley, K.R., Mortvedt, J.J., Soileau, J.M., Simmons, K.E., 1992.
Effect of winter cover crops on nitrate leaching. Agronomy
Abstracts. American Society of Agronomy, Madison, WI,
p. 282.
McDowell, L.L., McGregor, K.C., 1984. Plant nutrient losses in
runoff from conservation tillage corn. Soil Till. Res. 4, 79±91.
Moldenhauer, W.C., Langdale, G.W., 1995. Crop residue management to reduce soil erosion and improve soil quality. USDA/
ARS Report No. 39, January 1995, pp. 1±47.
Nyakatawa, E.Z., Reddy, K.C., Sistani, K.R., 1998. Tillage, cover
cropping, and poultry litter effects on cotton seedling
emergence. Agronomy Abstracts. American Society of Agronomy, Madison, WI, p. 274.
224
E.Z. Nyakatawa et al. / Soil & Tillage Research 57 (2001) 213±224
Nyakatawa, E.Z., Reddy, K.C., 2000. Tillage, cover cropping, and
poultry litter effects on cotton: 1. Germination and seedling
growth. Agron. J. 92, 992±999.
Reddy, K.C., Weesies, G.A., Lemunyon, J.L., 1994. Predicting soil
erosion in different cotton production systems with the revised
universal soil loss equation (RUSLE). In: Bushan, L.S., Abrol,
I.P., Rao, M.S. (Eds.), Proceedings of the Eighth International
Soil Conservation Organization Conference on Soil and Water
Conservation: Challenges and Opportunities, Vol. 1, Indian
Association of soil and water conservationsists, Dehradun,
India, December 4±8, pp. 1±11.
Renard, K.G., Foster, G.R., Weesies, G.A., Yoder, D.C., 1993.
Predicting soil erosion by water. A guide to conservation
planning with the universal soil loss equation (RUSLE).
Agricultural Handbook No. 703. US Dept. of Agriculture,
p. 47.
RUSLE Users' Guide, 1993. Revised Universal Soil Loss Equation.
Soil and Water Conservation Society, Ankeny, IA.
Sainju, U.M., Singh, B.P., Whitehead, W.F., 1998. Cover crop root
distribution and its effects on soil nitrogen cycling. Agron. J.
90, 511±518.
Schertz, D.L., Kemper, W.D., 1994. Report on Field Review
of No-till Cotton. USDA/ARS/NRCS/Auburn University/
Alabama A&M University, Huntsville, AL, September
22±23.
Seta, A.K., Blevins, R.L., Frye, W.W., Bal®eld, B.J., 1993.
Reducing soil erosion and agricultural chemical losses with
conservation tillage. J. Environ. Qual. 22, 661±665.
Stein, O.R., Neibling, W.H., Logan, T.J., Moldenhauer, W.C., 1986.
Runoff and soil loss as in¯uenced by tillage residue cover. Soil
Sci. Am. J. 50, 1527±1531.
Stevens, W.E., Johnson, J.R., Varco, J.J., Parkman, J., 1992. Tillage
and winter cover management effects on fruiting and yield of
cotton. J. Prod. Agric. 5, 570±575.
Vyn, T.J., Janovick, K.J., Miller, M.H., Beauchamp, E.G., 1999.
Soil nitrate accumulation and corn response to preceding small
grain fertilization and cover crops. Agron. J. 91, 17±24.
Wischmeier, W.A., Smith, D.A., 1965. Predicting rainfall-erosion
losses from cropland east of the Rocky Mountains: guide for
selection practices for soil and water conservation. Agricultural
Handbook No. 282, US Dept. of Agric. Sci and Edu. Admin.,
Agric. Res., 47 pp.
Wischmeier, W.H., Smith, D.D., 1978. Predicting rainfall erosion
losses: a guide to conservation planning. Agricultural Handbook No. 537. US Dept. of Agric. Sci. and Educ. Admin.,
Agric. Res., 85 pp.