| Relay intercropping soybean into wheat has great potential in Iowa by allowing two harvests on the same land area in the same year. Wheat is planted in September and soybean is interseeded into the standing wheat in May. This system can be important for Iowa by diversifying production, increasing farm productivity, and reducing soil erosion.;A three year experiment was conducted near Boone, IA, to determine the effect of soybean planting dates and spatial arrangements on wheat and soybean in a relay intercropping system, and its relative agronomic efficiency. The experimental design was a split-plot with the main plots (planting dates) arranged in randomized complete blocks with three replications of each treatment. The soybean planting dates were: pre-heading = PD1, heading = PD2, and post-heading = PD3. Five spatial arrangements (sub-plots) were used: 1W:1S (one wheat row alternated with one soybean row), 2W:1S, 2W:2S, 3W:2S, and 4W:3S.;Wheat yield was reduced on average by 33% with soybean interplanting, and was proportionally lower than the reduction of wheat plant population during implementation of the skip-row pattern (33 to 50%). Relay intercropped soybean produced 73% of the sole crop soybean, indicating skip-row patterns are a good alternative for higher soybean yield. Soybean planting at wheat pre-heading or at heading was the best alternative for this system. Arrangements producing the best soybean yields were not good wheat producers and vice-versa, suggesting that improvements in the yield of one crop will negatively affect the yield of the companion crop in a wheat-soybean relay intercropping system. For soybean oriented producers, 2W:2S, 3W:2S and 4W:3S are good choices due to the high soybean grain yield. Arrangement 1W:1S was intermediate for soybean and wheat yields. A land equivalent ratio (LER) of 1.46, on average, demonstrated the agronomic efficiency of relay intercropping over sole cropping. |
