Soil Biological Response to Integration of Cover Crops and Nitrogen Rates in a Conservation Tillage Corn Production System

Abstract

Core Ideas Use of N‐fertilizers decreased AMF populations and P, Ca, and Mg concentrations. Conservation tillage and cover crops increased C, N, and S cycling enzymes. Grass and brassica cover crops increased microbial populations compared to legumes. Agricultural production in the US Mid‐South has relied on frequent tillage and synthetic fertilizers decreasing soil health and system sustainability. Conservation tillage and cover crops can fill a vital role in reducing soil erosion while improving ecosystem functions. Seven cover crop blocks, including four legumes (berseem clover [Trifolium alexandrinum], crimson clover [Trifolium incarnatum L.], winter pea [Pisium sativum L.], and hairy vetch [Vicia villosa Roth], three grass & brassica (cereal rye [Secale cereale], forage radish [Raphanus sativus var. longipinnatus], and a cereal rye–forage radish mix), and one fallow control were established in northeast Louisiana to examine the influence of cover crop and urea fertilizer application rates (0, 235, 268, 302 kg N ha−1) on corn production and soil health under conservation tillage. Soil health indicators were measured each year following corn harvest and cover crop termination. The combination of cover crops and conservation tillage increased C and N enzyme activity over the 2 yr while arylsulfatase increased in the spring following cover crop termination only. Relative abundance of saprophytic fungi tended to be higher in legume plots compared to grass & brassica treatments. Overall, the application of N fertilizer at rates of 235 kg N ha−1 or higher decreased populations of AMF and concentrations of P, K, Ca, and Mg, but increased populations of Gram‐positive bacteria. The use of grass & brassica cover crops promoted K, S, Ca, and Mg availability, and supported greater abundance of total FAMEs and all FAME biomarkers except for saprophytic fungi.