Walter E. Riedell, USDA-ARS, Brookings, SD and Shannon Osborne, North Central Agricultural Research Laboratory, USDA-ARS, Brookings, SD
Development of crop rotations that support sustainable agriculture depends on understanding complex relationships between soils, crops, and yield. Objectives were to measure how soil chemical and physical attributes as well as maize (Zea mays L.) and soybean [Glycine max (L.) Merr.] stover dry weight, stover mineral concentrations, seed yield, and seed mineral concentrations responded to maize-soybean 2-yr rotation (C-S); maize-soybean-spring wheat (Triticum aestivum L.) 3-yr rotation (C-S-W); maize-soybean-oat/pea (Hordeum vulgare L./Pisum sativum L.) hay 3-yr rotation (C-S-H); and maize-soybean-oat/pea hay underseeded with alfalfa (Medicago sativa L.)-alfalfa-alflafa 5-yr rotation (C-S-H/A-A-A). Rotation treatments under no-till soil management were established in 1997 and maize measurements were made during 2008-2011 while soybean measurements were made during 2009-2010. When compared to C-S rotation, both C-S-W and C-S-H/A-A-A treatments produced greater maize seed yield while seed N concentration was significantly greater only in the 5-yr rotation. Soybean seed yield was about 10% greater in the C-S-H/A-A-A rotation treatment than in the other rotation treatments. Soybean seed protein concentrations were about 3% greater under the C-S-H/A-A-A rotation than under the S-C rotation while the other rotations were intermediate. Because increased maize and soybean grain yield and seed N have also been observed in response to increased N fertilizer application, we speculate that the increased soil N in the C-S-H/A-A-A rotation compared to that seen in the C-S rotation played a role in increasing seed yield and N concentration. Multivariate analysis revealed that alfalfa included in rotation increased soil nitrate-N, reduced soil bulk density, increased grain yield and protein in both maize and soybean phases. Soils, maize and soybean in oat/pea hay in rotation behaved similarly to the C-S rotation in many parameters, but had slightly greater maize yields.