Foliar uptake of volatilized ammonia from surface-applied urea by spring wheat

Large volatile losses of NH3 can occur from surface-applied urea in semiari d areas. Our objective was to determine possible absorption of this volatil ized N by the crop canopy under field conditions. At two different times du ring crop growth, N-15-enriched urea was surface-applied at rates equivalen t to 100 kg N ha(-1) to soil contained in trays placed between two rows of spring wheat. Seven days after application, the soil in the trays was remov ed from the field and analyzed for N-15 content. Addition of HCl during soi l air drying was necessary to prevent volatile losses of N-15. Of applied u rea-N, 13% was volatilized over seven days at both application times. Of th e urea-N that was volatilized, 15% was absorbed by wheat at the first appli cation time and 7% was absorbed by wheat at the second application time. Pl ant absorption of urea N (Y, mg) declined with distance from the source (x, cm) following the equation Y=10.95*10((-0.0142x)). About 90% of absorbed N was within the first three wheat rows. Our findings suggest that a signifi cant portion of ammonia volatilized from top-dressed urea might be captured by plant foliage.