Strip Intercropping of Corn-Soybean in Irrigated and Rainfed Environments

A strip intercropping system of corn (Zea mays L.) and soybean [Glycine Max (L.) Merrill] has the potential to reduce soil erosion and increase the biological and economic efficiencies of a corn-soybean rotational system. The objective of this study was to evaluate grain production in a corn-soybean strip intercropping system under irrigated and rainfed conditions in eastern Nebraska. Corn and soybean were grown in alternating 20 ft. (eight-row) strips in a north-south orientation on a Sharpsburg silty clay loam (fine, smectitic, mesic Typic Argiudolls) at the University of Nebraska Agricultural Research and Development Center near Mead. A full-season corn hybrid was grown in strips in combination with soybean cultivars of different maturity groups. Yields of the two border rows of corn and soybean strips were machine harvested and compared with the middle four rows of each crop strip to determine border effects. Under irrigated conditions, corn yields in the outside two rows increased in 4 of 5 yr. A maximum yield increase of 28 bu/acre occurred in 1986, with a 5-yr average increase of 17 bu/acre (11%) in the corn borders. Under rainfed conditions, corn border row yield increases were less consistent, averaging 5 bu/acre. In 1989, a maximum corn yield increase of 19 bu/acre (23%) was obtained in the rainfed environments. Soybean yields were reduced in the outside two border rows compared with the middle four rows under both rainfed and irrigated environments. Yields from soybean rows adjacent to corn were reduced an average of 6 bu/acre over the 5-yr period. Land Equivalent Ratios (LER = land area needed in monoculture to equal production in one unit area of intercropping) averaged 1.00 and 0.96 for the irrigated and rainfed strip intercropping systems, respectively, suggesting no benefit under either condition for the multi-species systems. Although economics of the system are dependent on corn and soybean prices, results of these experiments indicate strip intercropping systems of corn-soybean show no consistent differences in systems yield or net returns compared with monoculture fields under the same conditions. Strip intercropping will then benefit by reducing erosion on soybean stubble. Research QuestionLimited arable land and potential for high soil erosion in many of our cultivated areas make it essential to seek alternative cropping methods that maintain productivity and economic return. Farmers seeking ways to reduce erosion and meet government program compliance requirements often question how field cropping pattern diversity could contribute to these goals. Strip intercropping of corn-soybean provides one option in which alternating strips are rotated in alternate years to provide in-field diversity and improved residue cover distribution on the farm. We have to learn about the biological efficiency and economics of this system, and find out about the practical management challenges that such a system presents. Literature SummaryResearch in Illinois, Iowa, Indiana, and Minnesota has explored planting alternating strips of different widths of various crops, including corn and soybean. Strips ranged from 12-row alternating patterns to single rows of each crop. With most equipment, it is difficult to manage strips narrower than four rows, and most farmers agree that six or eight rows is a practical minimum strip width. When corn and soybean are planted side by side, there is usually a major increase in corn yields (15 to 40%) in the border row and a substantial reduction in yield (5 to 20%) in the adjacent soybean row. Some research shows an effect of strips on the second and third row from the interface. If the increase in corn yield and income is equal to or greater than the reduction in soybean yield and income from the border area, this practice could hold promise as a practical solution to create greater diversity in the field, change the distribution of crop residues, and reduce soil erosion. Study DescriptionThis study evaluated a corn-soybean strip intercropping system under irrigated and rainfed conditions over 5 yr in eastern Nebraska. Different soybean varieties and row widths were evaluated for their effects on system performance. Gross returns from the intercropping system were compared with those from the two crops grown separately in monoculture. We expect the results to be useful in the western part of the Corn Belt, and it is difficult to extrapolate to areas with different rainfall patterns or to other crop combinations. Applied QuestionsWhat were the corn and soybean yields in the strip system? Consistent with results from other states, our corn yields under irrigation were increased as much as 20% in the average of two border rows next to the soybean. This increase was 10% or less under rainfed conditions. For soybean, the yield reductions in the border rows were 12 to 25%, with greater differences under irrigation than in rainfed conditions. In one trial, there was an effect of soybean variety on corn yields, but no effect of soybean planting row width (7 in. vs. 30 in.) on corn yields. Based on crop yields alone, there was no apparent advantage to plant this diversified system. Were there any special problems found in planting this system? In first setting up the experiments, we had some difficulty in precision planting and creating a uniform interface due to the different planting dates of the two crops. Without special attention, this interface can become a weedy problem area. Weed control within the strips also required additional management compared with monocrops; if available chemicals are not compatible with the two crops, it is essential to spray when there is no wind or preferably to use a hooded sprayer. There are now chemicals on the market that are registered for both crops, and it is possible to plant corn a week late and soybeans a week early to avoid some of the difficulties in planting logistics. We have encountered minimal problems with harvest except when there is lodging of one of the crops and difficulty picking it up along the border area. Weed and other pest management problems would have to be solved for strip intercropping to be successful. Were corn rootworms a problem? In the second and third years of the study, corn rootworms caused damage to plants in the border rows, even though we rotated corn and soybean strips each year. We did not use soil insecticides for rootworm control. It appeared that corn rootworms migrated from the adjacent border rows that were in corn the previous year. Adult corn rootworm beetles may have also laid their eggs in the soybean interface rows the previous year because they were weedy. This problem was alleviated by rotating to a different field where a grain sorghum and soybean strip cropping system was being practiced. Are there potentials for increased yield and income? We measured yields over a 5-yr period by machine harvest. The land equivalent ratios (land needed in monoculture to equal strip cropping yields) were close to one, showing similar system yields in the contrasting cropping patterns. Gross returns of the irrigated corn-soybean strip intercropping system were comparable with corn + soybean monoculture systems at several different corn:soybean price ratios. It appears that this type of system has equal gross returns to the two crops grown in separate fields, thus the strip intercropping pattern could be used to reduce erosion and help a farmer meet government program compliance without loss of income. If weed management and other costs are higher with the strip cropping system, they would have to be offset by the value of erosion control. Are there other ways to improve the system, and could it be used with other crops? Questions about strip orientation often come up in the design of these systems. All of our plantings were in north-south strips, so we did not have this comparison. Studies at Parkland College in Illinois over the course of a decade showed no differences between north-south and east-west strips. Research on windbreak orientation has shown large differences in competition of the trees with crops, and the amount of crop yield reduction depends on windbreak direction. It is possible that different strip orientation could change the results, although application of this system would more appropriately follow contours if the strips were to be used to manage soil erosion. We anticipate that these results would apply to similar systems where a short crop (such as soybean) is combined in alternating strips with a tall crop (corn), although we have no data with which to support this conclusion, and results could be different in areas with higher rainfall.