Estimating the Proportion of Nitrogen Remobilization and of Postsilking Nitrogen Uptake Allocated to Maize Kernels by Nitrogen‐15 Labeling

Estimating the proportion of N remobilization and postsilking N uptake allocated to kernels may help to improve N‐use efficiency in maize (Zea mays L.). In this study, we show theoretically and experimentally, that 15 N labeling at the beginning of stem elongation can be used in the field to estimate the proportion of N remobilized from the vegetative parts to the kernels of maize by measuring 15 N distribution only at maturity. In the same way, 15 N labeling at silking allows a determination of the proportion of postsilking N uptake allocated to the kernels by measuring 15 N distribution only at maturity. Two 1‐yr experiments with three and four genotypes and one 2‐yr experiment with testcross progenies from 66 recombinant inbred lines were developed. Nitrogen‐15 labeling during vegetative growth provided an estimate of the proportion of N remobilized with a greater accuracy compared with the “balance” method, which computes the difference between the amount of N present in the stover at silking and the amount of N present in the stover at maturity. The validity of our 15 N method is mainly based on the assumption that less than 15 to 20% of 15 N is taken up after silking. The determination of the proportion of postsilking N uptake allocated to kernels requires assumptions that are more difficult to fulfill. Nitrogen‐15 labeling in the field at the beginning of rapid stem growth appears to be a useful tool for studying the genetic variability of N remobilization using a large number of genotypes.