Intensification of field pea production: Impact on soil microbiology

Abstract

The economic and environmental benefits of including grain legumes in crop rotations may tempt farmers to grow them more frequently than recommended, resulting in potential changes to soil chemical, physical, and biological properties. We investigated the effects of increasing the frequency of field pea (Pisum sativum L.) (P) in a wheat (Triticum aestivum L.) (W)-based cropping system on soil microbial biomass C (MBC), β-glucosidase enzyme activity, bacterial diversity, and populations of Rhizobium leguminosarum bv. viceae in the last 3 yr of a 13-yr field study. The treatments consisted of three rotations: P-P, W-P, and W-W-P. Fertilizer N at 5, 20, and 40 kg N ha-1 was applied to pea in P-P and W-P rotations to examine the role of starter N. Soil MBC and diversity were lower in P-P than pea rotated with wheat, presumably due to reduced amounts and diversity of C inputs under P-P. These reductions in soil MBC and diversity probably further reduced field pea growth and grain yields through reduced nutrient cycling. In field pea, β-glucosidase activity increased with increasing N, suggesting that N was limiting the capacity of soil microorganisms to recycle nutrients from organic materials (including crop residues). Populations of soil rhizobia were not affected by treatment. Wheat grown after pea in the 3-yr W-W-P rotation had greater MBC and β-glucosidase activity than that in the W-P rotation, indicating the importance of long rotations. Therefore, pea monoculture reduced soil microbial quality, with adverse effects on nutrient cycling. © 2012 by the American Society of Agronomy.