Glomalin and microbial activity affected by cover crops and nitrogen management in sandy soil with cotton cultivation

Abstract

In most sandy soils with low organic matter content, nitrogen fertilizers are often applied to achieve desired crop yields, which may negatively affect microbial activity in the soil. We hypothesize that cover crops can mitigate the negative effects and balance the system via increased supply of carbon. The objective, therefore, was to evaluate the effect of cover crops (fallow, one grass species, two grass species, one grass species and legumes, and a mixture of three cover crops), nitrogen doses (70, 100, and 130 kg ha−1), and nitrogen sources (conventional urea and controlled-release urea) on soil microbial activity, glomalin content, and relationship of these parameters of soil quality with cotton fiber yield. Grass systems increased the soil dry matter supply. The carbon of the microbial biomass was 117% higher in the mixture and soil respiration and the metabolic quotient was 128% and 372% higher in the mixture compared to fallow. Fluorescein diacetate hydrolysis was (averaging two-year data) 60% higher in mixed cover crop systems than with fallow. Carbon from microbial biomass (grass + legume system) and glomalin content (all systems) were lower with the highest dose of N. Controlled-release urea can mitigate the negative effects of high nitrogen doses in environments with low dry matter input (as noted for enzyme β-glucosidase). Microbial biomass carbon, β-glucosidase, and qCO2 were the principal indicators of soil quality and were highly correlated with cotton yield. We recommend the use of a diversity of cover crops, moderate nitrogen doses, and controlled-release urea activate microbial and glomalin activity in sandy soil.