Long-term crop rotations affect soybean yield, seed weight, and soil chemical properties

Crop rotation is an important management practice in the production of soybean (Glycine max (L.) Merr.). For the eastern Great Plains, more information is needed to determine whether current crop rotations are sustainable for soybean production over a long-term period. A field study was conducted in southeastern Kansas from 1979 to 1998 on a Parsons silt loam soil (fine, mixed, thermic, Mollic Albaqualf) to evaluate long-term effects of crop rotation on soybean yield, seed weight, and soil chemical properties. Treatments consisted of three 2-years rotations and one monoculture system: (1) W-S/S (winter wheat (Triticum aestivum L.)-soybean doublecrop)/full-season soybean; (2) W-Fal/S = (winter wheat-summer fallow)/full-season soybean; (3) GS/S = grain sorghum (Sorghum bicolor (L.) Moench)/soybean; (4) S/S = continuous soybean. Full-season soybean yields were compared across all treatments in even-numbered years. On average, crop rotation increased soybean yields 16% compared to monoculture soybean. Full-season soybean yields averaged 1.91 Mg ha(-1) following wheat-double-cropped soybean, 2.09 Mg ha(-1) following wheat-summer fallow, 1.99 Mg ha(-1) following grain sorghum, and 1.68 Mg ha(-1) following soybean. Soybean seed weights were also significantly greater in most years when grown in rotation compared to monoculture soybean. Crop rotation increased total soil C and total soil N concentrations by 25% in the upper soil profile compared to monoculture soybean. Differences in soil values among crop rotations were directly proportional to the total quantity of above-ground crop residues produced. On average, W-S/S, W-Fal/S, and GS/S rotations produced more than 8 Mg ha(-1) of above-ground crop residues for each 2-years cropping cycle compared with only 3 Mg ha(-1) for S/S. In the short-term. benefit of crop rotation was increased soybean yield, which would likely increase soybean profitability. In the long-term, rotations with high residue-producing crops, such as wheat and grain sorghum, significantly increase total soil C and N concentrations over time, which may further improve soil productivity. (C) 2003 Elsevier Science B.V. All fights reserved.