Surface applying urea‐containing N fertilizers may result in greater N losses by volatilization of NH 3 as urea hydrolyses than nonurea containing materials. The objective of this study was to evaluate the N efficiency of urea‐ammonium nitrate (UAN), urea and urea‐urea phosphate (UUP) at 56, 112, 168, and 224 kg ha −1 N rates applied broadcast, surface banded, and injected for no‐till corn ( Zea mays L.). Yield, ear‐leaf N concentration, and N uptake were used to estimate N availability. Broadcast ammonium nitrate (AN) and injected anhydrous ammonia (AA) were used as controls for evaluating N efficiency of urea‐containing N sources and their application methods. The method of applying the urea‐containing N sources has a significant effect on apparent N fertilizer availability. Injecting UAN and urea resulted in significantly higher yield, leaf N concentration, and N uptake when compared with broadcast and surface band application methods. Surface banding UAN at 168 and 224 kg ha −1 resulted in higher yields than urea or UUP. Yield, leaf N concentration and N uptake differences among the three urea‐containing N sources were not observed when broadcast applied. Broadcasting AN at 168 and 224 kg ha −1 resulted in higher yields than UAN, urea or UUP. Injecting the N sources resulted in higher yields when compared with broadcasting AN.
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Howard et al. (1989) studied this question.