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.

INTRODUCTION

The predominant cropping system in the central Great Plains is a winter wheat-fallow 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 Research-Extension 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 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 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 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.
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.

Table 1. Typical cultural practices for conventional tillage in a WSF rotation.

  1. Wheat harvest in late June or early July.
  2. Sweep tillage about mid-July.
  3. Sweep tillage about mid-August.
  4. Sweep tillage in early May and apply NH3 (90 kg N/ha).
  5. Sweep tillage immediately prior to planting in late May.
  6. Sorghum planting in late May or early June and apply starter fertilizer (90 kg/ha of ammonium polyphosphate).
  7. Atrazine (0.84 kg/ha) plus metolachlor (2.24 kg/ha) at sorghum planting.
  8. Sorghum harvest in October.
  9. Sweep tillage in May.
  10. Sweep tillage in June.
  11. Sweep tillage in July and apply NH3 (90 kg N/ha).
  12. Sweep tillage in August.
  13. Sweep tillage in late August or early September.
  14. Wheat planting in September and apply starter fertilizer (90 kg/ha of monoammonium phosphate).
  15. Metsulfuron (4.2 g/ha) plus dicamba (70 g/ha) plus 2,4-D (105 g/ha) in March.

Table 2. Typical cultural practices for reduced tillage in a WSF rotation.

  1. Wheat harvest in late June or early July.
  2. Glyphosate (0.42 kg/ha) and 2,4-D (0.53 kg/ha) about mid-July.
  3. Glyphosate (0.42 kg/ha) and 2,4-D (0.53 kg/ha) plus atrazine (1.4 kg/ha) about mid-August.
  4. Sweep tillage in early May and apply NH3 (112 kg N/ha).
  5. Sweep tillage immediately prior to planting in late May.
  6. Sorghum planting in late May or early June and apply starter fertilizer (90 kg/ha of ammonium polyphosphate).
  7. Atrazine (0.84 kg/ha) plus metolachlor (2.24 kg/ha) at sorghum planting.
  8. Sorghum harvest in October.
  9. Glyphosate (0.42 kg/ha) and 2,4-D (0.53 kg/ha) in May.
  10. Sweep tillage in June.
  11. Sweep tillage in July and apply NH3 (90 kg N/ha).
  12. Sweep tillage in late August or early September.
  13. Wheat planting in September and apply starter fertilizer (90 kg/ha of monoammonium phosphate).
  14. Metsulfuron (4.2 g/ha) plus dicamba (70 g/ha) plus 2,4-D (105 g/ha) in March.

Table 3. Typical cultural practices for no-tillage in a WSF rotation.

  1. Wheat harvest in late June or early July.
  2. Glyphosate (0.42 kg/ha) and 2,4-D (0.53 kg/ha) about mid-July.
  3. Glyphosate (0.42 kg/ha) and 2,4-D (0.53 kg/ha) plus atrazine (1.4 kg/ha) about mid-August.
  4. Fluid N fertilizer in early March (123 kg N/ha).
  5. Glyphosate (0.42 kg/ha) and 2,4-D (0.53 kg/ha) in early May.
  6. Sorghum planting in late May or early June and apply starter fertilizer (90 kg/ha of ammonium polyphosphate).
  7. Glyphosate (0.56 kg/ha) plus atrazine (0.84 kg/ha) plus metolachlor (2.24 kg/ha) at sorghum planting.
  8. Sorghum harvest in October.
  9. Glyphosate (0.42 kg/ha) and 2,4-D (0.53 kg/ha) in May.
  10. Glyphosate (0.42 kg/ha) and 2,4-D (0.53 kg/ha) in June.
  11. Glyphosate (0.42 kg/ha) and 2,4-D (0.53 kg/ha) in July.
  12. Glyphosate (0.42 kg/ha) and 2,4-D (0.53 kg/ha) in late August or early September.
  13. Wheat planting in September and apply starter fertilizer (90 kg/ha of monoammonium phosphate).
  14. Metsulfuron (4.2 g/ha) plus dicamba (70 g/ha) plus 2,4-D (105 g/ha) in March.

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 / 384 / 450 / 516 / 503 / 452 / 485 / 549 / 442 / 404 / 465 / 384
Grain sorghum / 366 / 544 / 549 / 345 / 475 / 163 / 480 / 579 / 518 / 447 / 340
Growing-season
Wheat / 257 / 325 / 401 / 340 / 391 / 279 / 198 / 348 / 424 / 330 / 269
Grain sorghum / 328 / 216 / 252 / 302 / 196 / 500 / 396 / 239 / 302 / 295 / 221