Fate of Fertilizer Nitrogen as Affected by Time and Rate of Application on Corn

Abstract

AbstractManagement of fertilizer N on corn (Zea mays L.) can greatly affect the efficiency of N use and the potential for adverse environmental effects. Field studies were conducted on two nonirrigated southern Minnesota soils — a Webster clay loam (fine‐loamy, mixed, mesic Typic Haplaquoll) and a Mt. Carroll silt loam (fine‐silty, mixed, mesic Mollic Hapludalf) — to determine the effect of time and rate of N application on recovery of fertilizer‐derived N (FDN) in corn grain and stover and in the soil. Nitrogen rates of 75 and 150 kg ha‐1 on the Mt. Carroll soil and 100 and 200 kg ha‐1 on the Webster were applied at planting or at the eight‐leaf stage as (NH4)2SO4 to the same plots from 1982 to 1984. Enriched 15N was applied to separate microplots each of the first 2 yr to allow measurement of FDN. Grain yield responded to applied N in 5 of 6 site‐yr, but not to time of application. Uptake of FDN in grain was increased by higher N rate in all cases, but by delayed application in only one site‐year. Total plant FDN recovery ranged from 31 to 60% at the low N rate and from 24 to 45% at the high rate. Both yields and FDN recovery were affected by unusually dry midseason conditions. Fertilizer‐derived N recovery from the soil after harvest ranged from 25 to 56%, with a large proportion at the high N rate in inorganic forms, especially with the late application, which increased the potential for leaching losses. Residual uptake of FDN by grain ranged from 1 to 10% of the initial N rate. The difference method for estimating FDN recovery gave different results from the 15N method, emphasizing the importance of examining both labeled and nonlabeled N pools for complete inter‐pretation of 15N studies.