Ammonia volatilization from conventional and enhanced-efficiency fertilizers under surface and subsurface placement

Soil physicochemical properties influence the efficacy of strategies for reducing ammonia (NH₃) volatilization from urea-based fertilizers, including fertilizer placement and the use of enhanced efficiency fertilizers (EEFs). Across the US Cotton Belt region, which spans the southern part of the country from Virginia to California and has various soil textures, little is known about how these strategies affect NH₃ volatilization. Studies were conducted as a randomized complete block design using four soils from this region to evaluate the impact of surface and subsurface placement of granular urea and fluid urea ammonium nitrate, as well as EEFs, on NH₃ volatilization. The EEFs were Environmentally Smart Nitrogen, N-(n-butyl)thiophosphoric triamide (NBPT) + Duromide, and nitrapyrin. NH₃ volatilization from surface broadcast urea without EEFs was 38%–62% of applied nitrogen (N) across soils and was greatest on the soil with the highest initial pH. Subsurface urea placement reduced NH₃ loss by 52%–80% compared to surface broadcast, and the greatest reduction was observed on the soil with the highest clay content. When urea was treated with NBPT + Duromide, NH₃ volatilization was reduced by 3%–76% compared to urea without NBPT + Duromide, and the lowest reduction was on the soil with the lowest initial pH. These results provide new insights into N management for some agriculturally relevant soils within the US Cotton Belt, which have previously been less evaluated for NH₃ losses. The findings can be used to tailor fertilizer application methods based on soil characteristics such as clay content and pH to minimize NH₃ volatilization.