Quantifying Foliar and Soil Uptake of Granular 15N‐Labeled Urea by Corn

Abstract

Core Ideas Foliar uptake of nitrogen from granular urea placed in the corn whorl can be significant over short time periods. Foliar nitrogen applications cannot provide season total corn nitrogen requirements. Nitrogen recovery efficiency of whorl‐applied urea can be as high as 16.6% in the 11 d following application. Corn (Zea mays L.) “green‐up” in the absence of rainfall or irrigation following broadcast applications of urea led to the initiation of this experiment. The objective was to compare corn aboveground‐N (TN) content, fertilizer‐N recovery efficiency (FNRE), and mass of fertilizer‐N recovery (MFNR) of granular urea applied directly into the corn whorl and directly to the soil for 11 d after the V6 stage under greenhouse and field conditions. Nitrogen rates of 0, 56, 112, and 168 kg N ha−1 using 2.5 atom% 15N labeled‐urea were applied to compare N assimilation via foliar or soil pathways. In the greenhouse, FNRE (16.6%) and MFNR (27.8 kg N ha−1) were influenced by the two‐way interaction of N rate and N placement (p < 0.0001) with values being maximized with 168 kg N ha−1 applied directly into the corn whorl at the V6 growth stage. The FNRE and MFNR of soil‐applied N were significantly lower than the whorl applications for all N rates (FNRE) and the two highest N rates (MFNR). Although not statistically compared, the FNRE and MFNR of the field trial were numerically lower than the values observed in the greenhouse. The FNRE of whorl‐applied N in the field trial was not influenced by N rate and averaged 7.1%, whereas the soil‐applied N varied across N rates, but was maximized at 1.9%. Results indicate that foliar uptake of granular urea applied directly into the corn whorl can be substantial over short time periods (<11 d) but not sufficient for season‐total N uptake.