Legume and Cropping Intensity Effects On Soil Quality After Seven Years In a Dryland Wheat Agroecosystem.

Intensifying cropping in dryland wheat agroecosystems may substantially increase sustainability by eliminating summer fallow practices that decrease soil organic matter, result in nitrate leaching, and make soils more vulnerable to erosion. Additionally, intensifying cropping with legumes may dually increase sustainability by decreasing nitrogen (N) fertilizer dependence in N intensive wheat production systems. Legumes have been documented to increase soil quality, and legume N may have benefits that N fertilizer cannot provide. We conducted a set of soil quality assessments examining potential effects of alternative legume and intensified cropping systems on soil quality (0-0.15 m) from an eight-year-old dryland wheat rotation study. We compared four no-till systems: 1) summer fallow-wheat (F-W), 2) continuous wheat (CW), 3) pea-wheat (P-W), and 4) pea green manure-wheat (GM-W). Potentially mineralizable nitrogen (PMN) and carbon (PMC) were assessed through a 112-d aerobic incubation experiment. In addition, a subset of soils was fertilized with urea to observe effects of N fertilizer on soil mineralization dynamics. Substrate-induced microbial biomass C (MB) and wet aggregate stability (WAS) were also measured. Results to date show that soils appear to be variably affected by legumes and cropping intensity. The most intensified systems, CW and P-W, showed increased WAS (P < 0.01), but MB appeared unaffected by treatment. Model results from analyses of PMN, PMC, and fertilization effects on mineralization will be presented.