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

Large volatile losses of NH3 can occur from surface‐applied urea in semi‐arid areas. Our objective was to determine possible absorption of this volatilized N by the crop canopy under field conditions. At two different times during crop growth, 15N‐enriched urea was surface‐applied at rates equivalent 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 removed from the field and analyzed for 15N content. Addition of HC1 during soil air drying was necessary to prevent volatile losses of 15N. Of applied urea‐N, 13% was volatilized over seven days at both application times. Of the urea‐N that was volatilized, 15% was absorbed by wheat at the first application time and 7% was absorbed by wheat at the second application time. Plant 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 significant portion of ammonia volatilized from top‐dressed urea might be captured by plant foliage.