Estimating nitrogen transfer by foliar 15N-labelling in legume – non-legume associations

Abstract

We examined the basis for estimating the transfer of legume N to companion cereals or grasses in intercropping or pature systems using the foliar ¹⁵N-labelling technique. Published data from three pot experiments were used to illustrate different methods for estimating N transfer. Yield-dependent and yield-independent methods based on measurement of the ¹⁵N enrichment of the whole legume biomass at harvest overestimate N transfer. Estimates of N transfer using a yield-independent method based on the ¹⁵N enrichment of the legume roots at harvest were inconsistent with estimates based on the isotopic composition of the whole plant. We propose a new mathematical concept for estimating the transfer of legume N based on measurement of the ‘mean pool abundance’ of the legume biomass during the period of N transfer.