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

Abstract

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.