Ammonia Volatilization and Nitrogen Utilization from Sulfur‐coated Ureas and Conventional Nitrogen Fertilizers

Ammonia volatilization was measured on acid and calcareous soils receiving sulfur‐coated ureas (SCU) and highly soluble N fertilizers. Surface and mixed applications of SCU‐30 (30% dissolution rate), SCU‐20 (20% dissolution rate), uncoated (NH 2 ) 2 CO, NH 4 NO 3 , and (NH 4 ) 2 SO 4 were made with and without lime to a fallowed acid fine sand. Without lime, top dressed NH 4 NO 3 , SCU‐20, SCU‐30, and (NH 4 ) 2 SO 4 lost < 1% while (NH 2 ) 2 CO lost 18.5% of added N in 14 days. Topdressing lime with N caused more NH 3 loss from (NH 4 ) 2 SO 4 than from (NH 2 ) 2 CO during the intial 48 hours. However, accumulative losses for 14 days were 51.5, 22.5, 9.0, and 1.7% from (NH 2 ) 2 CO, (NH 4 ) 2 SO 4 , SCU‐30, and SCU‐20, respectively. Incorporating the lime with the soil prior to N addition reduced NH 3 loss > 50% as compared to surface application, but mixing N with the limed acid soil did not reduce NH 3 ‐N losses. Mixing SCU with the soil appeared to increase release rate of N over topdressing, but this effect was not detected in plant response. Nitrogen uptake by corn ( Zea mays L.) on the acid soil substantiated some of the conclusions regarding measured NH 3 ‐N losses. Ammonia losses from N mixed with the finer textured calcareous clay loam were generally insignificant. Surface applied (NH 2 ) 2 CO and (NH 4 ) 2 SO 4 lost significant amounts of NH 3 ‐N, while losses from SCU and NH 4 NO 3 were negligible.