Profitability Plus Environmental Sustainability Equals Modified Relay Intercropping

Crop enterprises constitute about 76 percent of farm commodity sales in the seven county area around Crawford County, Ohio. However, grain farmers have had a relatively low rate of return (3.6 percent) on assets according to Forster and Stout (1993). In two studies, one commissioned by Sandoz Agro (1993) and another by Bruening (1991), the most serious problem facing agriculture is contamination of soil and water by fertilizer and/or pesticide use. In Ohio, herbicides are used on over 98 percent of soybean acres (Ohio Agriculture Statistics Service, 1995).

To address the major issues of farm profitability and environmental sustainability, a double cropping system, Modified Relay Intercropping (MRI), has been studied. MRI is the planting of soybeans into headed wheat from 20 to 35 days prior to wheat harvest. Goals of the MRI system are to produce wheat at a yield level of 90 percent of monoculture wheat and to produce soybeans at yield level of 60 percent of monoculture soybeans.

In the area of environmental protection, MRI offers two advantages. First, the only herbicide used to control weeds in the two crops in one year has been 2,4-D (MCPA in 1995) applied at the labeled rate. The cost for this herbicide has been about $4.00 per acre, compared to an average cost of $29.00/acre for conventional soybean production in Ohio, according to Schnitkey (1995). Thus, not only are weed control costs diminished, but the environment is protected. Since land in the MRI system is in a wheat sod for about 1-1/2 years, soil is protected from erosion.

Wheat and soybean production in 10-inch row spacing has been a favorable combination as long as planting dates are in mid-to- late-June. Tram lines are an essential component of the MRI system.

One of the questions associated with this production system is the effect of wheat nitrogen rate on soybean growth and maturation. Johnson (1987) states that when nitrogen fertilizer is applied to soybeans, usually smaller amounts of symbiotic nitrogen are fixed and nodulation is delayed.

Since soybeans in the MRI system are planted approximately 30 days after the optimum date, it is important for soybeans to grow rapidly to insure crop maturity. To that end, the impact on soybean yield on variable rates of nitrogen applied to wheat has been examined with a replicated study in Crawford County. The objectives of the study were: (a) To measure wheat yield under two nitrogen rates in a MRI system; and (b) To measure soybean yield under two wheat nitrogen rates in an MRI system.

Pioneer 2510 wheat was planted in the fall using a Great Plains 15-foot drill with 10-inch row spacing. A tram line (a blank row to allow tractor and implement wheels to travel without damage to the crop) of 18 inches in 1994 or 20 inches in 1995 was established to facilitate soybean planting in June. The two wheat top dress nitrogen treatments were applied in separate applications about six weeks apart. Soybeans were planted with the same Great Plains drill used to plant wheat in June. Wheat was harvested with a John Deere 6620 combine.

Pioneer 2510 wheat was planted in the fall using a Great Plains 15-foot drill with 10-inch row spacing. A tram line (a blank row to allow tractor and implement wheels to travel without damage to the crop) of 18 inches (1994) or 20 inches (1995) was established to facilitate soybean planting in June. The two wheat top dress nitrogen treatments were applied in separate applications about six weeks apart. Soybeans were planted with the same Great Plains drill used to plant wheat in June. Wheat was harvested with a John Deere 6620 combine.

There was no stastically significant differences between nitrogen rates on wheat yield (see table below). There was a significant difference between wheat nitrogen rates on soybean yield in 1995 only. Spring 1995 growing conditions were very favorable for wheat and the canopy cover of the crop was very dense. The extra nitrogen fertilizer applied on wheat in Treatment 2 further enhanced wheat growth. Thus, the soybean growing environment between the wheat rows was more shaded. The soybean yield effect observed in 1995 can be attributed more to a vigorous wheat plant that shaded the 10-inch soybean row than to nitrogen fertilizer reducing soybean nodulation.

In observing the MRI system in various farm trials since 1991, and in replicated research in 1994 and 1995, it was noted that light, or the lack of it, has a profound effect on soybean growth. Soybeans planted too early in the MRI system become etiolated and grow as a vine because the wheat plant shades the row. Wheat row spacing, weather conditions, and wheat variety have all been observed to influence soybean growth, development, and concomitant yield in a MRI environment. The average production of wheat at 68 bushels per acre and soybeans at 34 bushels per acre in 1994 and 1995 would support MRI as a profitable cropping alternative that also protects the environment.

Sandoz, A., (1993). The 1993 Sandoz national agricultural poll. Washington, D.C.: Author

Bruening, T. (1991). Communicating with farmers about environmental issues. Journal of Applied Communications, 75(1), 34-41.

Forster, L. & Stout, T. (1993). Rates of return to farm assets and other assets, (ESO 2072). Columbus: The Ohio State University, Department of Agricultural Economics and Rural Sociology.

Johnson, J. (1987). Soil fertility and crop nutrition. Beuerlein, J. (Ed.). The Soybean in Ohio (pp. 34-41). Columbus: Ohio State University Extension.

Ohio Agricultural Statistics Service (1995). Pest management practices used on soybeans. Columbus, OH: Author.

Schnitkey, G. (Ed.) (1995). Ohio Crop Enterprise Budgets, Grains-Forages. Columbus: Ohio State University Extension.