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.