Management and Urease Inhibitor Effects on Nitrogen Use Efficiency in No‐Till Corn

No‐till corn (Zea mays L.) production is common in the Mid‐Atlantic region and urea‐ammonium nitrate solution (UAN) and urea are by far the most common N fertilizers used in the region. Because of the potential for ammonia volatilization from these sources when they are surface‐applied to no‐till corn, it is necessary to know how the method and time of application affect the N fertilizer use efficiency (grain yield, N uptake, and ear‐leaf N concentration per pound of N applied) obtained with them. We also wanted to determine if the urease inhibitor amendments ammonium thiosulfate (ATS) and N‐(n‐butyl)thiophosphoric triamide (NBPT) would increase the N fertilizer use efficiency of UAN and urea surface applied to no‐till corn. Field experiments were conducted for 3 yr in central Pennsylvania on well‐drained silt loam soils. There were three N rates, 50, 100, and 150 lb N/acre. Averaged over the 3 yr and three rates, broadcast urea and sprayed UAN at plantinggenerally produced significantly lower N fertilizer use efficiency than at‐plant dribbled UAN and broadcast ammonium nitrate, and sidedress applications of dribbled or injected UAN. Nitrogen fertilizer use efficiency of UAN applied to no‐till corn was in the order: at‐plant spray < at‐plant band < sidedress band < sidedress inject. Amending UAN with ATS had no significant effect on N fertilizer use efficiency of sprayed UAN and only a slight effect on banded UAN. Amending UAN with the urease inhibitor NBPT produced significantly greater N fertilizer use efficiency with the sprayed UAN. Amending urea with 0.5% NBPT also significantly increased the N fertilizer use efficiency of unincorporated broadcast and banded urea. Research Question No‐till corn production and the use of urea‐containing fertilizers (urea‐ammonium nitrate solution [UAN] and urea) are very common in the Mid‐Atlantic area. We know that up to 30°/o of the N in broadcast urea or sprayed UAN applied to no‐till corn can be lost as volatilized ammonia. The two main objectives of this research were to: (i) determine the efficiency (defined as grain yield and N uptake per pound of fertilizer N applied) of several N fertilizers and methods and times of application; and (ii) determine if using the urease inhibitor amendments ammonium thiosulfate (ATS) and N‐(n‐butyl)thiophosphoric triamide (NBPT) would increase the efficiency of urea and UAN surface‐applied to no‐till corn. Literature Summary We and a number of other researchers have shown that for no‐till corn, dribbled UAN is generally more efficient than sprayed UAN and that fertilizer N applied as a sidedress is more efficient than that applied at planting. While injecting UAN generally produces greater N fertilizer use efficiency than surface‐banded UAN, not all researchers have found this to be true. There has been much interest in using ammonium thiosulfate as an amendment to increase the efficiency of surface‐applied UAN. The effects of ammonium thiosulfate on UAN efficiency have been mixed, however, especially with sprayed UAN. NBPT has generally been shown to be one of the most effective urease inhibitors ever tested in the lab. There have been several published reports of NBPT increasing the efficiency of surface‐applied urea, but very little research has been reported on the effects of NBPT on the efficiency of surface‐applied UAN. Study Description There were four time‐application method combinations of UAN treatments: spray at planting, dribble at planting, dribble at sidedress, and inject at sidedress. There were two urea time‐method combinations: broadcast at planting and banded at sidedress. There was also a treatment of broadcast ammonium nitrate at planting. In addition, spray and dribble UAN treatments were amended with ammonium thiosulfate, and NBPT was added to the spray and dribble UAN and broadcast urea treatments. These treatments were all at three N rates, 50, 100, and 150 lb N/acre. The experiments were carried out in central Pennsylvania for 3 yr on no‐till corn growing in well‐drained silt loam soils. Applied Questions Which fertilizer source and method of surface‐application to no‐till corn at planting produces the most grain yield and N uptake per pound of fertilizer N applied? Dribbled UAN produced equivalent yields and N uptakes to those with ammonium nitrate, indicating that ammonia volatilization losses from dribbled UAN were minimal. Broadcast urea and sprayed UAN produced the least yield and N uptake of any of the source‐method combinations. Which time‐method combination of applying UAN to no‐till corn produces the most grain yield and N uptake per pound of fertilizer N applied? The 3‐yr average results clearly showed that injecting UAN at sidedress produced the most yield and spraying UAN at planting the least, with the dribble at planting and dribble‐sidedress treatments being in between (Fig. ). This confirms other research showing that applying UAN to no‐till corn as a spray at planting can result in a significant loss of N from the fertilizer as volatilized ammonia. Can adding urease inhibitor amendments to urea or UAN surface‐applied to no‐till corn increase the effectiveness of these sources? NBPT was very effective in increasing the N fertilizer use efficiency of broadcast urea. NBPT use also increased grain yield and N uptake with sprayed UAN. Ammonium thiosulfate had no effect on sprayed UAN and only a small effect on dribbled UAN. Thus, amending urea or UAN with NBPT will increase the efficiency of these sources when they are broadcast at planting. This amendment is not available commercially, however. Recommendation For applying UAN—the most common N source in the Mid‐Atlantic region—to no‐till corn, we recommend a sidedress dribble or sidedress injection. At the same N rate, spraying UAN at planting produced significantly lower grain yield than sidedress dribbled or injected UAN or UAN dribbled at planting. Three‐year average no‐till corn grain yield as a function of the method and time of application of UAN.