Impact of Conservation Tillage on Crop Production in a Semi-Arid Region
Alan Schlegel and Troy Dumler
Research Agronomist and Agricultural Economist
Southwest Research-Extension Center
Kansas State University
ABSTRACT
The predominant crop in the central Great Plains is winter wheat (Triticum
aestivum L.) grown in a wheat-fallow (WF) system. Although summer crops, such as
grain sorghum [Sorghum bicolor (L.) Moench] grown in a wheat-summer crop-fallow
system are increasing in popularity. Tillage intensity is decreasing with reduced tillage
(RT) and no-tillage (NT) systems being utilized more extensively in intensive cropping
systems. This field study across a 9-yr period quantified the effect of reducing tillage
intensity on wheat and grain sorghum production and profitability. Tillage intensities
were conventional tillage (CT), RT, and NT. Wheat yields increased as tillage intensity
decreased with 2690 kg/ha for CT, 2950 kg/ha for RT, and 3160 kg/ha for NT. Grain
sorghum yields were 60% greater with NT than CT (4950 vs. 3070 kg/ha) while RT
yields were only about 7% less than NT. Production costs for wheat were higher with
NT (about $260/ha) than RT or CT (about $195/ha) primarily because of higher weed
control costs. Production costs for sorghum were 44% greater for NT than CT with RT
being intermediate. Economic returns were greater with RT for both wheat and
sorghum. Returns with NT was similar to RT for sorghum, but was the least profitable
for wheat. Averaged across the rotation, conservation tillage increased profitability with
RT being the most profitable and CT the least profitable tillage system for a WSF
rotation.
1
INTRODUCTION
The predominant cropping system in the central Great Plains is a winter wheatfallow rotation. Low precipitation and high evaporation potential limit yields of dryland
crops; thus, fallow is used to increase soil water storage and enhance yield. Compared
to CT systems, RT or NT systems that maintain surface crop residue cover can reduce
evaporation and enhance infiltration and soil water storage (Norwood et al., 1990;
Norwood, 1999). With increased plant-available water, the fallow period can be
shortened and cropping intensity increased. Intensive cropping systems, such as WSF,
are feasible when used in conjunction with RT and other soil and water conservation
practices. Norwood (1994) reported higher sorghum yields with NT than CT in a WSF
system, but similar wheat yields for NT and CT in WSF systems in southwest Kansas.
In western Kansas, Schlegel (1999) reported 23% greater grain sorghum yields with NT
than RT in a WSF rotation, but similar wheat yields with NT and RT. Unger (1984) also
reported greater sorghum yields with NT than RT or CT in Texas, but no effect of tillage
intensity on seed yield of sunflower (Helianthus annuus L.).
In western Kansas, dryland sorghum acreage increased from 260,000 ha in 1991
to 368,000 ha in 1998, while winter wheat acreage on fallow decreased from 1.31
million ha to 1.20 million ha during the same time period (Kansas Farm Facts, 1992,
1999). Many producers are required to maintain residue cover to meet conservation
compliance requirements of the 1996 Farm Bill. Consequently, adoption of NT
practices might further enhance production in more intensive cropping systems.
In a comprehensive review of economic studies of dryland cropping systems in
the Great Plains, Dhuyvetter et al. (1996) found that increasing cropping intensity and
reducing tillage generally increased producer profitability. Dhuyvetter and Norwood
(1994) and Williams (1988) found that WSF had higher returns than WF and that RT
was more profitable than CT in western Kansas. Peterson et al. (1993) found that a
WCF rotation was more profitable than a WF rotation in northeast Colorado, although
WF was more profitable in southeast Colorado. Thus, these studies support increased
cropping intensity and reduced tillage, but the results are somewhat mixed.
The objectives of this research were to compare and quantify crop production
and profitability of a wheat-sorghum-fallow system as affected by tillage intensity.
MATERIALS AND METHODS
The research was conducted in west central Kansas at the Southwest ResearchExtension Center near Tribune from 1991 through 1999. The soil is a Richfield silt loam
(fine, mortmorillonitic, mesic Aridic Argiustoll). The site area was in native sod until
1989 before being cropped. Average climatic data are 400 mm annual precipitation
(62% from May to August), 11 C mean temperature, and 1.8 m open pan evaporation
(April-September). The predominant cropping system in the region is wheat-fallow.
The tillage intensities evaluated were CT, RT, and NT. The CT system used a sweep
plow (three 1.5 m blades) for all tillage operations. The RT systems utilized a
combination of herbicides and tillage for weed control during fallow, whereas NT relied
solely on herbicides. Typical cultural practices for each tillage system are outlined in
Tables 1-3. Plot size was 15 by 30 m. The experimental design was a randomized
2
complete block with four replications. Both crops and all tillage intensities were present
each year.
Winter wheat ('TAM 107') was planted at 56 kg/ha in September. A John Deere
750 single disc drill with 19-cm row spacing was used most years. Grain sorghum
('Pioneer 8771') was planted at 69,000 seeds/ha in late May or early June in 76-cm
rows with a John Deere 7300 planter. Fluid fertilizer N (28-0-0) was applied prior to
planting of sorghum and in the early spring to growing wheat.
The center of each plot was combine harvested in late June or early July for
wheat and October for grain sorghum. Harvest width was 1.9 m for wheat and 1.5 m for
sorghum. Grain yield was adjusted to 12.5% moisture. Aboveground biomass samples
were taken at harvest, dried, and weighed. Wheat straw and sorghum stover were
calculated as aboveground biomass minus grain yield.
Analysis of variance was performed to evaluate treatment effects on dependent
variables using the GLM routine of SAS (SAS Institute, 1996). Mean separation was by
protected LSD at the 0.05 probability level.
An economic analysis compared the relative costs and returns for each system.
Costs for tillage, herbicide applications, planting, and harvest were based on average
custom rates for western Kansas (Kansas Custom Rates 1999). Seed and herbicide
expenses were based on local costs. For economic comparisons, the assumption was
made that anhydrous ammonia would generally be used in CT and RT systems and
fluid N in NT systems resulting in higher N costs for NT systems ($0.24/kg of N for
anhydrous ammonia compared to $0.40/kg for fluid N). Grain prices used in the budget
were the average prices at harvest from 1991 to 1999 in western Kansas. Gross
income was calculated by multiplying average crop yields by average grain prices.
Government program payments under the 1996 Farm Bill and land costs were not
included, because they have no effect on the relative profitability of the various systems.
RESULTS AND DISCUSSION
Precipitation
Water is the most limiting factor for production of dryland crops in the central
Great Plains, so precipitation during fallow and the growing season greatly influences
grain yield. Fallow and growing-season precipitation varied from year-to-year but was
generally above the 30-yr average (Table 4). Growing-season precipitation for wheat
was above the 30-yr average 7 out of the 9 years (range of 26% below in 1997 to 58%
above in 1999) and averaged 23% above average. Growing-season precipitation for
sorghum averaged 33% above normal and ranged from 11% below in 1995 to 126%
above in 1996. Based on 30-yr average precipitation patterns, growing-season
precipitation is usually about 48 mm greater for wheat than sorghum. Fallow
precipitation was above normal for each crop each year except prior to grain sorghum in
1996, when it was only about 50% of normal. Averaged across years in this study,
fallow precipitation was above normal by 21% for winter wheat and 31% for grain
sorghum.
Grain yields
Wheat yields ranged from about 1000 kg/ha in 1991 to more than 5000 kg/ha in
3
1999 (Fig. 1). In 1993 and 1998, wheat yields were significantly increased by reducing
tillage intensity compared to CT; while, in the other 7 years, yields were similar for all
tillage systems. Averaged across the 9-yr period, wheat yields were 10% greater with
RT and 17% greater with NT compared to CT (2690 kg/ha for CT, 2950 kg/ha for RT,
and 3160 kg/ha for NT). This agrees with previous research at this location where
reducing tillage intensity from CT to RT increased wheat yields by 17% (Norwood et al.,
1990). However, in southwest KS, wheat yields in WSF were only 4% greater with NT
than CT (Norwood, 1994). Jones and Popham (1997) reported similar wheat yields with
NT and RT in a WSF rotation in Texas. Thompson and Whitney (1998) reported lower
wheat yields with NT than RT or CT in WSF in central Kansas. They speculated that
NT yields were lower because of reduced stands, increased weed competition, and
drier soils.
Grain sorghum yields ranged from 1200 kg/ha for CT in 1999 to 8200 kg/ha for
NT in 1998 (Fig. 2). In some years, freezing temperatures in the fall before the sorghum
had fully matured reduced yields. In this region, dry conditions or cool temperatures
during reproductive growth often delay sorghum maturity, which increases the possibility
that fall freezes will adversely affect grain yield. Growing conditions were generally
favorable from 1996 to 1999 with sorghum yields exceeding 6000 kg/ha each year. In
1999, CT sorghum was greatly impacted by hot, dry conditions in August and early
September while RT and NT sorghum was able to withstand these unfavorable
conditions. In 6 out of the 9 years, grain sorghum yields were significantly greater with
RT or NT than CT. The larger increases were in the higher yielding years. For
instance, sorghum yields were almost 3000 kg/ha greater for NT than CT when
averaged across 1996 to 1999. For the 9-yr period, sorghum yields were 49% greater
with RT and 60% greater with NT than CT (3070 kg/ha for CT, 4600 kg/ha for RT, and
4950 kg/ha for NT). This corresponds to earlier research at this location (Norwood et
al., 1990) showing that sorghum yields in WSF were 37% greater with RT than CT
(3260 vs. 2380 kg/ha). Jones and Popham (1997) reported similar sorghum yields
(about 3400 kg/ha) for RT and NT sorghum in a WSF rotation in Texas.
Production costs and economic returns
Production costs were greatest with NT, primarily because of higher weed control
and fertilizer costs with NT. Production costs for wheat were about $195/ha for CT and
RT while costs were about $260/ha or 50% greater with NT (Fig. 3). The cost of weed
control prior to wheat (Fig. 4) was $35/ha greater for NT compared to RT or CT (about
$100/ha for NT compared to $65/ha for RT or CT). Fertilizer costs were greater for NT
because of the use of more expensive fluid N fertilizer in NT ($0.42/kg of N) compared
to less expensive anhydrous ammonia ($0.24/kg of N) in RT and CT.
Grain sorghum production costs (Fig. 5) were 44% greater for NT than CT
($310/ha for NT compared to $215/ha for CT). In contrast to wheat, RT costs were 22%
greater than CT. Again, the higher costs are mostly attributable to higher weed control
(Fig. 6) and fertilizer costs. For sorghum, the rate of N fertilization was also greater with
the conservation tillage systems to correspond to the greater yield levels. For the
economic analysis, assumed N rates were 90 kg/ha for CT, 112 kg/ha for RT, and 123
kg/ha for NT. For NT, the combination of higher N rates and a more expensive N
source (fluid N) caused N fertilizer costs to almost double compared to CT ($81/ha for
4
NT compared to $42/ha for CT).
An economic analysis, excluding government program payments and land costs,
showed that RT was generally the most profitable tillage system, especially for wheat.
In about half of the years, RT produced the greatest net returns (Fig. 7). In 2 years, net
returns were negative for RT and CT was more profitable (or at least produced less
loss). Averaged across 9 years, net returns from wheat were about $150/ha for RT
compared to about $115/ha for CT and NT. The additional cost of NT compared to CT
was offset by the increased yield with NT. The RT system benefited from increased
yield without increased cost compared to CT. This corresponds to previous work at this
location where RT was 40% more profitable ($170/ha vs. $120/ha) than NT for wheat in
a WSF rotation (Schlegel, et al. 1999). In contrast, Norwood and Currie (1998) reported
that CT was more profitable than either RT or NT for wheat in a WSF in southwest
Kansas.
Net returns for grain sorghum were more variable than for wheat, although the
average net returns were similar (Fig. 8). Averaged across the 9-yr period, net returns
from RT sorghum were $160/ha similar to the $150/ha for RT wheat. However, net
returns for RT sorghum ranged from negative returns in 1991, 1992, and 1994 to a
$700/ha profit in 1996. NT was more profitable with sorghum than wheat reflecting the
greater yield benefit from NT for sorghum than wheat. Net returns from NT sorghum
was only slightly less than that of RT ($145/ha for NT compared to $160/ha for RT).
Similar to wheat, the least profitable tillage system was CT at $75/ha or about 50% of
the net returns of RT or NT. In contrast, Norwood and Currie (1998) reported that RT
was the least profitable system compared to CT and NT for sorghum in a WSF rotation
in southwest Kansas.
Averaged across the entire WSF rotation, RT was the most profitable tillage
system (Fig. 9). Total net returns were about $100/ha for RT when averaged across the
entire rotation and total land (sum of wheat, sorghum, and fallow). The least profitable
system was CT with about $65/ha net return. The NT system produced the highest
grain yield but, with the higher costs, net returns were about 17% less than RT.
REFERENCES
Dhuyvetter, K.C., C.R. Thompson, C.A. Norwood, and A.D. Halvorson. 1996.
Economics of dryland cropping systems in the Great Plains: A review. J. Prod. Agric.
9:216-222.
Dhuyvetter, K.C. and C.A. Norwood. 1994. Economic incentives for adopting
alternative dryland cropping systems. p.18-23. In J.L. Havlin (ed.) Proc. Great Plains
Soil Fertility Conf., Vol. 5., Denver, CO. 7-9 Mar. Kansas State Univ., Manhattan, KS.
Jones, O.R. and T.W. Popham. 1997. Cropping and tillage systems for dryland grain
production in the southern High Plains. Agron. J. 89:222-232.
Kansas Custom Rates. 1999. Kansas Agricultural Statistics. Kansas Dept. of
Agriculture and U.S. Dept. of Agriculture, Topeka, KS.
5
Kansas Farm Facts. 1992 and 1999. Kansas Agricultural Statistics. Kansas Dept. of
Agriculture and U.S. Dept. of Agriculture, Topeka, KS.
Norwood, C.A. 1994. Profile water distribution and grain yield as affected by cropping
system and tillage. Agron. J. 86:558-563.
Norwood, C.A. 1999. Water use and yield of dryland row crops as affected by tillage.
Agron. J. 91:108-115.
Norwood, C.A. and R.S. Currie. 1998. An agronomic and economic comparison of the
wheat-corn-fallow and wheat-sorghum-fallow rotations. J. Prod. Agric. 11:67-73.
Norwood, C.A., A.J. Schlegel, D.W. Morishita, and R.E. Gwin. 1990. Cropping system
and tillage effects on available soil water and yield of grain sorghum and winter wheat.
J. Prod. Agric. 3:356-362.
Peterson, G.A., D.G. Westfall, N.E. Toman, and R.L. Anderson. 1993. Sustainable
dryland cropping systems: Economic analysis. USDA-ARS Tech. Bull. TB93-3.
SAS Institute. 1996. SAS user’s guide: Statistics. Version 6.12 ed. SAS Inst., Cary,
NC.
Schlegel, A.J. 1999. Agronomic and economic impact of tillage and rotation on wheat
and sorghum. J. Prod. Agric. 12: (in press).
Thompson, C.A. and D.A. Whitney. 1998. Long-term tillage and nitrogen fertilization in
a west central Great Plains wheat-sorghum-fallow rotation. J. Prod. Agric. 11:353-359.
Unger, P.W. 1984. Tillage and residue effects on wheat, sorghum, and sunflower
grown in rotation. Soil Sci. Soc. Am. J. 885-891.
Williams, J.R. 1988. A stochastic dominance analysis of tillage and crop insurance
practices in a semiarid region. Am. J. Agric. Econ. 70:112-120.
6
Table 1. Typical cultural practices for conventional tillage in a WSF rotation.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Wheat harvest in late June or early July.
Sweep tillage about mid-July.
Sweep tillage about mid-August.
Sweep tillage in early May and apply NH3 (90 kg N/ha).
Sweep tillage immediately prior to planting in late May.
Sorghum planting in late May or early June and apply starter fertilizer (90 kg/ha
of ammonium polyphosphate).
Atrazine (0.84 kg/ha) plus metolachlor (2.24 kg/ha) at sorghum planting.
Sorghum harvest in October.
Sweep tillage in May.
Sweep tillage in June.
Sweep tillage in July and apply NH3 (90 kg N/ha).
Sweep tillage in August.
Sweep tillage in late August or early September.
Wheat planting in September and apply starter fertilizer (90 kg/ha of
monoammonium phosphate).
Metsulfuron (4.2 g/ha) plus dicamba (70 g/ha) plus 2,4-D (105 g/ha) in March.
7
Table 2. Typical cultural practices for reduced tillage in a WSF rotation.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
Wheat harvest in late June or early July.
Glyphosate (0.42 kg/ha) and 2,4-D (0.53 kg/ha) about mid-July.
Glyphosate (0.42 kg/ha) and 2,4-D (0.53 kg/ha) plus atrazine (1.4 kg/ha) about
mid-August.
Sweep tillage in early May and apply NH3 (112 kg N/ha).
Sweep tillage immediately prior to planting in late May.
Sorghum planting in late May or early June and apply starter fertilizer (90 kg/ha
of ammonium polyphosphate).
Atrazine (0.84 kg/ha) plus metolachlor (2.24 kg/ha) at sorghum planting.
Sorghum harvest in October.
Glyphosate (0.42 kg/ha) and 2,4-D (0.53 kg/ha) in May.
Sweep tillage in June.
Sweep tillage in July and apply NH3 (90 kg N/ha).
Sweep tillage in late August or early September.
Wheat planting in September and apply starter fertilizer (90 kg/ha of
monoammonium phosphate).
Metsulfuron (4.2 g/ha) plus dicamba (70 g/ha) plus 2,4-D (105 g/ha) in March.
8
Table 3. Typical cultural practices for no-tillage in a WSF rotation.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
Wheat harvest in late June or early July.
Glyphosate (0.42 kg/ha) and 2,4-D (0.53 kg/ha) about mid-July.
Glyphosate (0.42 kg/ha) and 2,4-D (0.53 kg/ha) plus atrazine (1.4 kg/ha) about
mid-August.
Fluid N fertilizer in early March (123 kg N/ha).
Glyphosate (0.42 kg/ha) and 2,4-D (0.53 kg/ha) in early May.
Sorghum planting in late May or early June and apply starter fertilizer (90 kg/ha
of ammonium polyphosphate).
Glyphosate (0.56 kg/ha) plus atrazine (0.84 kg/ha) plus metolachlor (2.24
kg/ha) at sorghum planting.
Sorghum harvest in October.
Glyphosate (0.42 kg/ha) and 2,4-D (0.53 kg/ha) in May.
Glyphosate (0.42 kg/ha) and 2,4-D (0.53 kg/ha) in June.
Glyphosate (0.42 kg/ha) and 2,4-D (0.53 kg/ha) in July.
Glyphosate (0.42 kg/ha) and 2,4-D (0.53 kg/ha) in late August or early
September.
Wheat planting in September and apply starter fertilizer (90 kg/ha of
monoammonium phosphate).
Metsulfuron (4.2 g/ha) plus dicamba (70 g/ha) plus 2,4-D (105 g/ha) in March.
9
Table 4. Precipitation near Tribune, KS during the study period.
Year
Time
period
1991
1992
1993
1994
1995
1996
1997
1998
1999
Mean
30-yr
avg.
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - mm - - - - - - - - - - - - - - - - - - - - - - - - - - - - Fallow period
Wheat
Grain sorghum
384
366
450
544
516
549
503
345
452
475
485
163
549
480
442
579
404
518
465
447
384
340
Growing-season
Wheat
Grain sorghum
257
328
325
216
401
252
340
302
391
196
279
500
198
396
348
239
424
302
330
295
269
221
10
Grain yield, kg/ha
6000
5000
CT
RT
4000
NT
3000
2000
1000
0
1991 1992 1993 1994 1995 1996 1997 1998 1999 Mean
Year
Grain yield, kg/ha
Figure 1. Wheat yields with three tillage intensities in a WSF rotation, Tribune,
KS.
9000
8000
7000
6000
5000
4000
3000
2000
1000
0
CT
RT
NT
1991 1992 1993 1994 1995 1996 1997 1998 1999 Mean
Year
Figure 2. Grain sorghum yield with three tillage intensities in a WSF rotation,
Tribune, KS.
11
300
Cost, $/ha
250
200
CT
RT
NT
150
100
50
0
1991 1992 1993 1994 1995 1996 1997 1998 1999 Mean
Year
Figure 3. Production costs (excluding land and management) for winter wheat in
a WSF rotation as affected by tillage intensity, Tribune, KS.
120
Cost, $/ha
100
80
Herbicide
Tillage
60
40
20
0
CT
RT
Tillage intensity
NT
Figure 4. Herbicide and tillage costs for winter wheat in a WSF rotation, Tribune,
KS.
12
350
Cost, $/ha
300
250
200
CT
RT
150
NT
100
50
0
1991 1992 1993 1994 1995 1996 1997 1998 1999 Mean
Year
Figure 5. Production costs (excluding land and management) for grain sorghum
in a WSF rotation, Tribune, KS.
120
Cost, $/ha
100
80
Herbicide
60
Tillage
40
20
0
CT
RT
NT
Tillage intensity
Figure 6. Herbicide and tillage costs for grain sorghum in a WSF rotation,
Tribune, KS.
13
400
Net return, $/ha
300
200
CT
RT
NT
100
0
-100
-200
1991 1992 1993 1994 1995 1996 1997 1998 1999 Mean
Year
Net return, $/ha
Figure 7. Net returns for winter wheat in a WSF rotation as affected by tillage
intensity, Tribune, KS.
800
700
600
500
400
300
200
100
0
-100
-200
CT
RT
NT
1991 1992 1993 1994 1995 1996 1997 1998 1999 Mean
Year
Figure 8. Net returns for grain sorghum in a WSF rotation as affected by tillage
intensity, Tribune, KS.
14
Net return, $/ha
120
100
Grain Sorghum
Wheat
80
60
40
20
0
CT
RT
NT
Tillage intensity
Figure 9. Net returns for winter wheat and grain sorghum in a WSF rotation (for
total land area including fallow) as affected by tillage, Tribune, KS.
15