Comparison of natural abundance and enriched 15-N methods to quantify nitrogen fertilizer recovery in maize under field conditions

Abstract

Abstract Aims This study aims to compare the ability of natural abundance (NA) and 15N-enrichment (EN) methods to quantify N dynamics in a No-Till legume/non-legume maize crop rotation under field conditions; and deliver precise estimates of fertilizer N recovery across both rotations. Methods A field experiment was established on a Vertisol by sowing a legume (Vicia faba) or non-legume (Triticum aestivum) grain crop. The following maize crop was fertilized using either urea or 15N-enriched (5 atom%) urea, at five rates (0, 62.5, 125, 187.5, and 250 kg N ha− 1) in spatially separated subplots in each field plot. Results The proportional recovery of fertilizer N in grain (%Ndff) showed that EN method provided higher estimates than that determined by NA method, with differences greatest in the wheat-maize rotation. The NA method was better able to quantify residual benefits of fixed N from faba beans in a following maize crop. Unfortunately, different biomass and grain sampling times necessitated by the size of fertilised plots used for each isotopic method confounded comparisons of N derived from fertilizer in crop biomass and grain yields. Conclusion While larger plot sizes able to be used in the cheaper NA method provided better estimates of crop and grain biomass and N content, and enabled quantification of recovery of atmospheric N2-fixed legume N (%Ndfa) in a following maize crop, the EN method was better able to estimate fertilizer N recovery by maize in the field. The reasons for differences in %Ndff between methods and crop histories require further investigation.