Carbon and nitrogen accumulation in soils under conservation agriculture practices decreases with nitrogen application rates

Abstract

In intensively managed agricultural systems, fertilizer management has great impact on the size and activity of microbial functional communities. However, the effects are not clear due to the variability of soil type, climate and cropping diversity. We have investigated microbial biomass and enzyme activities in soils under seven consecutive years of strip (ST) and conventional tillage (CT), high (HR) and low (LR) levels of residue addition, and three N fertilization rates in a wheat (Triticum aestivum)-mung bean (Vigna radiata)- rice (Oryza sativa) crop rotation. Nitrogen rates of each crop were in agree to the recommended dose (RD) or 60% RD or 140% RD. The interaction effects of tillage, residue retention and N rates showed higher potential for lower N rate (60RD) in ST with HR sequestering more carbon. Likewise, the highest total N content was found at 60RD in ST, with HR being higher than 140RD but similar to 100RD. Increased N application rates above recommended dose reduced the MBC content and dehydrogenase and β-glucosidase activities but it enhanced urease activity. Negative relationships between N application rates and MBC, dehydrogenase and β-glucosidase and positive relationship with urease activities suggest that higher N application suppresses C and N buildup in soils.