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© 2003 Plant Management Network.
Accepted for publication 30 September 2003. Published 12 November 2003.

Double-cropping Winter Wheat and Soybean Improves Net Returns in the Eastern Great Plains

Kenneth W. Kelley, Kansas State University Southeast Agricultural Research Center, Parsons, KS 67357

Corresponding author: Kenneth W. Kelley. kkelley@oznet.ksu.edu

Kelley, K. W. 2003. Double-cropping winter wheat and soybean improves net returns in the eastern Great Plains. Online. Crop Management doi:10.1094/CM-2003-1112-01-RS.

Abstract

In the eastern Great Plains, winter wheat (Triticum aestivum L.) and different soybean [Glycine max (L.) Merr.] maturity groups (MG) are grown in various cropping systems to diversify crop production. A 10-year field study was conducted in southeastern Kansas to evaluate effects of multi-cropping systems on grain yield and net economic returns. Cropping systems evaluated were: (i) annual double-cropping of wheat and soybean (MG IV); (ii) four 2-year rotations of wheat-soybean double-cropped followed by full-season soybean the next year, where the same soybean MG (I, III, IV, and V) was grown both years; and (iii) a 3-year rotation of wheat, wheat, and full-season (MG V) soybean. On average, wheat yields ranged from 51 bu/acre following early MG I soybean in the 2-year double-crop rotation to 36 bu/acre following MG IV soybean in the annual double-cropping system. Wheat yield differences were primarily determined by planting date. Full-season (MG V) soybean yields were highest (35 bu/acre) following two years of wheat in the 3-year rotation. Double-crop soybean yields in the annual double-cropping system averaged 26 bu/acre for MG IV. Full-season and double-crop soybean yields in the 2-year double-crop rotation system were significantly greater for traditional MGs (III, IV, and V) than MG I. Net economic returns averaged $101/acre for annual double-cropping, which was $10 to $25/acre higher than 2-year systems with MGs III, IV, and V; whereas, net returns were lowest for the 3-year rotation ($51/acre) and for the 2-year system with MG I soybean ($44/acre).

Introduction

In the eastern Great Plains, winter wheat and soybean are planted in various rotations to diversify cropping systems. Both crops can be planted across a wide range of soil types and planting dates, which makes them well suited for multi-cropping systems. Typical cropping systems for wheat and soybean include annual double-cropping of soybean after wheat (2 crops per year), single-cropping of wheat and full-season soybean with no double-cropping (1 crop per year), and a 2-year rotation of wheat followed by double-crop soybean the same year, with a summer crop, such as soybean, corn (Zea mays L.), or grain sorghum [Sorghum bicolor (L.) Moench] grown in the following year (3 crops in 2 years).

Double-cropping soybean after wheat offers a number of potential advantages over single-cropping systems. Among these are more extensive use of fixed resources, improved cash flow, and increased net returns (1,6,11). However, in single-cropping systems, average yields of both wheat and soybean typically are higher than in double-cropping systems primarily because of more timely planting dates (14,15). In 2-year rotations that include double-cropping, cropping intensity is greater than in single-year cropping systems, which could result in greater net profits (5,16). Economic analyses are important to determine which cropping systems are most profitable. This is especially true where more than one crop is grown per year (6,16).

Soybean maturity is an important consideration in both full-season and double-crop systems. For maximum yield potential, soybean cultivar maturity must be closely matched to the climatic environment. For the mid-latitude region of the eastern Great Plains (35°N to 40°N latitude), cultivars of MGs III, IV, and V are most adapted to the environment, although early maturing (MG I) soybean planted in April or early May offers a viable alternative to traditional MGs (13). In this region, traditional full-season soybean is planted from late May to mid-June, and soybean double-cropped after wheat is planted 2 to 4 weeks after full-season soybean.

Because of differences in soybean maturity and planting dates within the various cropping systems (full-season versus double-crop), soybean matures over an extended period, ranging from mid-August for MG I soybean until late October for MG V.

Thus, in cropping systems where wheat follows soybean, soybean maturity also directly affects wheat planting date and yield potential. In the Midwest, research has shown that wheat can be planted over an extended period, although numerous studies have shown that a rather narrow planting period often results in optimum grain yield for a particular wheat-growing region (2,7,17). Additional information is needed for the wheat- and soybean-producing region of the eastern Great Plains where various cropping systems and soybean maturity groups are grown. The primary objective of this 10-year study was to compare three cropping systems involving wheat and different soybean MGs (full-season and double-cropped) for effects on grain yields and relative net economic returns.

Field Study with Wheat and Soybean Cropping Systems

Site information. Field studies were conducted from 1989 through 1998 at the Parsons Unit of the Kansas State University Southeast Agricultural Research Center (37°N, 95°W). The soil was a Parsons silt loam (fine, mixed, active, thermic, Mollic Albaqualf) consisting of a shallow topsoil (<12 inch) overlaying a thick "clay-pan" subsoil. Initial soil chemical characteristics at the 0- to 6-inch depth included a pH (1:1 soil/water) near 7.0, organic matter (OM) of 2.8%, Bray-1 phosphorus (P) of 30 lb/acre, and exchangeable potassium (K) (1 M ammonium acetate extract) of 150 lb/acre. Additional soil tests were conducted annually in each cropping system after soybean harvest (data not shown). All soils were analyzed following North Central Region recommended procedures (3).

Cropping systems. Cropping systems consisted of three crop rotations (annual, 2-year, and 3-year) involving winter wheat (W) and different soybean (S) maturity groups (MG). Treatments were initiated in 1988, but data were not collected until 1989. Cropping systems included: [W/S] = annual double-cropping of wheat and soybean (MG IV); [W/S] / S = 2-year rotations of wheat - soybean double-cropped followed by full-season soybean the next year where the same soybean (MG I, III, IV, or V) was used both for the full-season and double-crop soybean planting in each year; and W / W / S = a 3-year rotation of wheat, wheat, and full-season soybean (MG V). All phases of each cropping system were present each year, making a total of 12 treatments. The experimental design was a randomized complete block with three replications. Treatments were in plots measuring 40 ft wide by 50 ft long.

Soybean cultivars. Soybean cultivars selected within the various cropping systems included: Weber 84 (MG I); Flyer (MG III); Stafford (late MG IV); Hutcheson (MG V, full-season); and Essex (MG V, double-crop). Essex, an early MG V cultivar, was planted in MG V double-crop systems to insure the crop would reach physiological maturity before the first killing frost, which averages October 20 for Parsons, KS (38°N latitude). Cultivar selection was based on regional performance in statewide yield trials as well as percentage of land area when the study was established.

Field operations and fertilizer rates. A summary of field operations and fertilizer application rates for each cropping system is shown in Table 1. Fertilizer rates were based on initial soil tests and Kansas State University Extension recommendations.

Table 1. Summary of tillage, fertilizer, herbicide, and planting operations for wheat and soybean cropping systems, Parsons, KS.

* Rate (lbs/acre) of N - P₂0₅ - K₂0.

** Herbicide: preemerge = metolachlor plus metribuzin; postemerge = bentazon plus acifluorfen. Fall fertilizer applied preplant for wheat.

Wheat establishment. Date of wheat planting as well as seeding rate varied with cropping system. When wheat followed wheat or early maturing full-season soybean (MGs I and III), planting date was early to mid-October at a seeding rate of 75 lb/acre. When wheat followed MG IV soybean, planting date ranged from mid- to late October at a seeding rate of 90 lb/acre. However, when wheat followed late maturing full-season soybean (MG V) or when wheat followed double-crop soybean (MG IV), planting typically occurred in late October or early November at a seeding rate of 90 to 120 lb/acre, depending on date of planting. Seeding rate was increased to compensate for probable reduced tiller development with later planting date. An early maturing hard red winter wheat cultivar (Karl or Karl 92) was planted each year with a conventional double-disk drill with a 7-inch row spacing.

Soybean establishment. Soybean planting date and row spacing also varied among cropping systems. Full-season MG I soybean was targeted for an early May planting with 7-inch row spacing at a seeding rate of approximately 220,000 seeds per acre; however, in 4 of 10 years, wet conditions delayed planting until late May or June. Other full-season soybean (MGs III, IV, and V) were planted in late May or June in 30-inch rows at a seeding rate of 140,000 seeds per acre. The justification for using different management practices for MG I full-season soybean compared to other full-season MGs was based on previous research conducted in the region. Double-cropped soybean was planted from mid-June to mid-July, depending on date of wheat harvest and soil moisture conditions. In years when soil moisture was too dry following wheat harvest for optimum double-crop soybean emergence, soybean planting was delayed until adequate rainfall occurred to insure satisfactory seed emergence. Moreover, in some years, wet conditions during wheat harvest delayed double-crop soybean planting. All double-cropped soybean, regardless of maturity group, was planted in 30-inch rows at a seeding rate of 140,000 seeds per acre.

Grain harvest. Grain yields were determined by machine harvesting a 5-ft-wide-by-40-ft-long area for soybean or a 6.25-ft-wide-by-40-ft-long area for wheat, both from the center of each plot and adjusting to constant moistures of 12.5% for wheat and 13% for soybean. Wheat plots were harvested in June and soybean plots were harvested at different times in late summer and early fall due to differences in soybean maturity.

Economic budgets. Economic budgets were developed annually for each cropping system. Costs for seed, fertilizer, and herbicide were based on local costs in each year of the study. Interest expense (10%) was calculated on one-half of total seed, fertilizer, and herbicide costs. Costs for tillage, herbicide, and fertilizer applications, planting, and harvest were based on average custom rates for eastern Kansas (9). Fixed costs were based on average cash rental prices for the area (4). Grain prices used in the budget were the average prices for the marketing year. Gross income was calculated each year by multiplying crop yield by harvest grain prices. Incomes above variable and fixed costs for each crop were added to provide total income for each system, then totals were divided by the number of years required to complete a system to provide average yearly income for each system. Net returns represented gross returns minus specified costs, but excluded costs for land, management, and general farm overhead. Government program benefits were excluded in this study. The 2-year cropping system of wheat and full-season soybean (W / S) was not established in this study. However, for sake of economic comparison with the 3-year system of W / W / S, net returns for a 2-year W / S system were calculated. For this calculation, it was assumed that first year wheat yield and full-season soybean (MG V) yield would be nearly the same as in W / W / S.

Data were analyzed by year and across years using the ANOVA procedure of SAS (SAS Institute, Carey, NC) (12) to evaluate treatment effects. Treatment means were compared using Fisher's protected LSD (0.05).

Yields and Economic Returns

A 10-year summary of wheat and soybean (full-season and double-crop) grain yields are shown in Table 2. Grain yields were affected by yearly weather conditions (data not shown); however, the variable weather patterns experienced are common for this region.

Table 2. Average grain yields (bu/acre) of wheat and soybean in different cropping systems from 1989 through 1998, Parsons KS.

* [W/S] indicates wheat and soybean double-cropped in the same year.

** For wheat and soybean, means with the same letter are not significantly different at P = 0.05.

Wheat grain yield. Wheat yields were significantly affected by cropping systems. In the 2-year rotations, wheat yields ranged from 51 bu/acre following MG I soybean to 43 bu/acre following MG V. Wheat yields declined as soybean maturity increased mainly because late maturing soybean delayed wheat planting beyond the optimum date. Similarly, wheat following MG IV soybean in the annual double-cropping system averaged only 36 bu/acre due to delayed planting. In the 3-year rotation, first year wheat following full-season (MG V) soybean yielded 42 bu/acre, which was nearly the same as wheat following two soybean crops (full-season and double-crop, MG V) in the 2-year rotation. However, when wheat followed wheat in the 3-year rotation, yields were similar to wheat following MG III soybean in the 2-year rotation.

Full-season and double-crop soybean grain yields. Soybean yields also were significantly influenced by cropping systems. In the 2-year cropping systems, yield of traditional full-season soybean (MGs III, IV, and V) averaged 29 to 32 bu/acre across the 10-year period compared with 25 bu/acre for early maturing MG I. Yield of full-season (MG V) soybean following 2 years of wheat averaged nearly 35 bu/acre, compared to 29 bu/acre for MG V soybean following the 1-year sequence of wheat and double-cropped soybean. It is unclear why this yield response occurred; however, similar yield responses have occurred in other research studies in this region when soybean followed a wheat and summer fallow system (8). The soybean yield increase following 2 years of wheat may be linked to the "rotational" effect, which has been observed in numerous crop rotation studies.

Yield of double-crop soybean averaged 5 to 9 bu/acre less than full-season soybean. In 2-year rotations, double-crop soybean averaged 23 to 25 bu/acre for MGs III, IV, and V; whereas, yield of MG I double-crop soybean averaged only 15 bu/acre. In double-cropping systems, early maturing MG I soybean have limited vegetative development, short stature, and low yield potential in this region of the eastern Great Plains.

Soybean yields in both full-season and double-crop systems varied significantly between years because of weather conditions during the critical reproductive growth stages (data not shown). The most critical reproductive stage for grain development in soybean is from early pod set (R3) to seed-filling (R6) (10), which in southeast Kansas generally occurred from mid-July through mid-August for MG I soybean, early August through early September for MG III, mid-August through mid-September for MG IV, and late August through September for MG V.

Economic Returns. Net annual returns above specified variable and fixed costs varied significantly among cropping systems (Table 3). For the 10-year period, net returns above specified costs averaged $101/acre for the annual wheat and soybean double-crop system. In 2-year rotations, net returns averaged nearly $90/acre for intermediate soybean MGs (III and IV), $75/acre for late maturing (MG V), and $44/acre for early maturing (MG I) soybean systems. Net annual returns in single-cropping systems averaged $51/acre for the 3-year rotation and $54/acre for the simulated 2-year rotation, which indicated that the second year of wheat did not affect net profits differently than only one year of wheat.

Table 3. Net annual returns ($/acre) for different wheat and soybean cropping systems from 1989 through 1998, Parsons, KS.

* Net returns equals gross returns minus variable and fixed costs.

** Standard error of difference in means.

† Means followed by the same letter are not significantly different at P = 0.05.

‡ Simulated rotation using yield data from 3-year rotation.

In this study, fixed costs associated with land rental charges were assessed the same value for each cropping system, although some may argue that cash-rents on double-cropped land should be higher. However, it should be noted that any economic comparisons between full-season and double-crop soybean would need to account for differences in land costs because double-cropping spreads the land cost over two crops, whereas full-season soybean would carry all of the land costs.

Economic evaluations showed that for wheat and soybean multi-cropping systems in the eastern Great Plains, net returns after specified costs were often higher in double-cropping systems (either annual or 2-year) compared to single-cropping of wheat and full-season soybean with no double-cropping. However, the acreage that can be successfully double-cropped is dependent on available machinery, labor, and weather conditions. In addition, harvesting and planting operations for wheat and soybean double-crop systems have to be performed during the same window of opportunity. Thus, there may be a time constraint associated with double-cropping that is not present with single-cropping. However, in recent years, improved equipment technology has made no-till planting of double-crop soybean more feasible than when this study was established. Thus, no-till planting of double-crop soybean has been adopted by many producers in recent years. This requires fewer labor inputs than with conventional disk tillage operations.

In multi-cropping wheat and soybean systems, results also show the importance of selecting the appropriate soybean maturity group for the production environment. In this region, where air temperatures often exceed 95°F for extended periods in July and August, traditional soybean MGs (III, IV, and V), either single-cropped or double-cropped after wheat, often produce higher yields with greater net returns than early maturing MG I soybean systems. However, with environmental conditions fluctuating from year to year, planting varieties that vary in maturity should be considered by growers. Utilizing a range of maturities can reduce the risks associated with weather-related yield reductions and facilitates timely harvest and efficient machinery use.

Acknowledgments

The author expresses appreciation to Michael Dean, Bobby Meyers, and the late Bobbie Hite for their technical assistance during the study. In addition, the Kansas Soybean Commission provided partial funding for this 10-year research study.

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