Nitrogen use efficiency and optimization of nitrogen fertilization in conservation agriculture.

Abstract

Abstract In most agroecosystems, nitrogen (N) is the most important nutrient limiting plant growth. One management strategy that affects N cycling and N use efficiency (NUE) is conservation agriculture (CA), an agricultural system based on minimum tillage, crop residue retention and crop rotation. This review summarizes the current knowledge of N management in CA and identifies research gaps that need to be addressed to optimize N management with the ultimate goal to minimize N losses into the environment and to reduce farmers' input costs. Soil physical, biological and chemical processes in CA are compared with those in conventional systems focusing on their relationship to N cycling in the soil and how they are affected by N fertilizer type, method and number of applications. Based on the little available data, CA has lower NUE rates than conventional systems, which seems largely due to N fertilizer immobilization through crop residues and increased fertilizer rates with CA. Fertilizer use recovery and NUE change with different tillage and residue management, thus the adjustment of N fertilization in CA is inevitable. Finally, the review provides a short overview of methodologies to measure NUE and its components. Available results on the optimization of NUE in CA are inconsistent and studies that cover all three components of CA are scarce. Interactions between components of CA and their effects on crop yield, grain quality, soil and fertilizer parameters are complex and will likely require site-specific management options.