Uptake, Translocation and Utilization of 15N‐Depleted Fertilizer in Irrigated Corn

The objective of this study was to derive a better understanding of the manner in which N serves the nutritional needs of corn ( Zea mays L.) and thereby afford a basis for improved fertilization practices. Measurements of uptake, translocation and utilization of tagged nitrogen (N) fertilizer in irrigated corn as influenced by time and rate of N application were made in a field experiment at the University of Nebraska Field Laboratory. Plant parts of root, crown, foliage, and eventually ear and grain were taken and analyzed for total N, NO 3 ‐ ‐N and isotope ratio at eight growth stages. Application of N at planting resulted in greater vegetative production, but summer sidedressed N effected slightly larger grain production with a higher grain/stover ratio. Isotope ratio analyses revealed significantly greater utilization of fertilizer N in grain production with delayed application due to more active root uptake and translocation of the fertilizer source during the grain filling period. Following harvest, residual mineral N in soil from applied fertilizer was greater with summer sidedressing such that 24% more of the N applied could be accounted for in the crop and soil than with planting time application.