Soil Water, Plant Growth, and Yield of Strip‐Intercropped Corn

Abstract

Strip‐intercropping soybean ( Medicago sativa L.) with corn ( Zea mays L.) decreases yields in soybean border rows. Separating corn and soybean with a small grain strip could decrease competition for soybean and improve overall yield. This study was conducted to determine the effect of a small grain strip on corn and soybean performance and on soil water content in the corn strip. Corn and soybean were strip‐intercropped (rows running north‐south) with oat ( Avena sativa L.) in 1991 and barley ( Hordeum vulgare L. emend. Lam.) in 1992 on a ridge‐tilled Dalhousie silt loam (fine, mixed, mesic Typic Endoaquoll) in Nepean, Ontario. Both years, plant height varied among corn rows. In 1992, plant development was faster and grain moisture at harvest was lower in corn border rows than in non‐border rows. In 1991 and 1992, soil water was depleted earlier in the corn and small grain interrow than in the corn and soybean interrow. In 1991, a hot and dry growing season, yield of the corn row next to small grain was 20% lower than that of other corn rows. In 1992, a wet and cool growing season, both corn border rows yielded yielded 26% more than nonborder rows, partly due to increased number of ears per plant. Both years, soybean yield in the row bordering small grain was similar to that of nonborder rows but yield in the row bordering corn was 18% lower than that of nonborder rows. Including a small grain in corn and soybean strip‐cropping can be beneficial if soil moisture is not limiting. Research Question Farmers who plant corn using strip‐intercropping with soybean often attribute high yields in the corn border rows to improved light interception. They also attribute low soybean yields in rows next to corn to light competition from the corn plants. Thus, some farmers have thought of including a small grain crop in the soybean‐corn strip intercropping system to improve light conditions for soybean. During dry growing seasons, however, competition for water from the early‐developing small grain may affect corn, which has a high demand for water later in the season. This study was undertaken to determine the effect of strip‐intercropping corn with soybean and a small grain cereal on (i) corn row and interrow water content, (ii) corn height and development, and (iii) corn, soybean, and small grain yield. Literature Summary Scientific literature has consistently documented soybean yield decreases and corn yield increases in corn‐soybean strip‐intercropping systems in North America, although the extent of the yield increases or decreases can be variable. Sometimes, corn yield increases can be observed only on very narrow strips of less than three rows. In addition, the optimal strip width for corn at a specific location can vary annually, indicating that strip‐intercropping performance can be affected by weather conditions. An experiment in eastern Nebraska comparing strip‐intercropping of corn and soybean under dryland and irrigated conditions demonstrated that soil water availability is important in achieving high corn yields. Study Description The study consisted of a soybean, corn, and oat strip‐intercropping experiment in 1991 and of a soybean, corn, and barley strip‐intercropping experiment in 1992. The rows were oriented in the north‐south direction with the small grain cereal strip located east of the corn strip and west of the soybean strip. Each crop was planted in a 15‐ft wide strip allowing for six rows of corn or six rows of soybean per strip. Soil type and tillage: Dalhousie silt loam previously planted to ridge‐tilled corn Growing season moisture: 4.9 in. in 1991 and 11.1 in. in 1992 Oat cultivar and planting rate: Ultima planted in 80 lb/acre Barley cultivar and planting rate: Leger planted at 80 lb/acre Soybean cultivar and planting rate: OAC Bravor or PS42 planted at 162 000 seeds/acre Corn hybrid and planting rate: Pioneer 3902 planted at 28 300 seeds/acre for all rows. Applied Questions Were soybean yields higher in the row next to the small grain strip than in the row next to the corn strip? Soybean yield was 18% higher in 1991 and 19% higher in 1992 in the row next to small grain than in the row next to corn. The difference is consistent in the 2 yr despite the fact that 1991 and 1992 were opposite extremes in weather for northern soybean growing areas. Including a small grain strip east of the corn strip and west of the soybean strip was beneficial for soybean yield. Were plant growth conditions and grain yield in the corn row next to the small grain strip similar to those in the corn row next to the soybean strip? In both years, there were differences in plant developmental rates and final height among rows in the corn strip, including differences between the two border rows. In both years, soil water content was lower in the interrow next to the small grain strip and higher in the interrow next to the soybean strip. Grain yield was 20% lower in the row next to small grain than in all other rows in the dry year. Grain yield was 26% higher in both border rows than in nonborder rows in the wet year. Thus, the environment of the plants at the two border rows was different. These differences had deleterious consequences on corn grain yield in the dry year. Since corn yields are important for net returns, it is not recommended to include small grain cereals in a corn and soybean strip‐cropping system in areas where prolonged dry periods occur regularly.

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