Ammonia Volatilization from Urea as Influenced by Soil Temperature, Soil Water Content, and Nitrification and Hydrolysis Inhibitors

Abstract

AbstractResidue cover influences temperature and water gradients in the soil profile. Changes in the physical environment of the soil influence NH3 volatilization from urea‐containing fertilizers. Field and laboratory experiments were conducted to investigate the influence of residue‐cover‐induced changes in soil water and temperature on NH3 volatilization as impacted by urea treatment with a nitrification and urease inhibitor. Fertilizer treatments were urea, urea plus dicyandiamide (DCD), urea plus N‐(n‐butyl)thiophosphoric triamide (NBPT), and urea plus NBPT and DCD. Following fertilizer application, the soil was either left bare or covered with corn (Zea mays L.) residue. Every 3 h over a 4‐d period, water potential, soil temperature, CO2 production, and NH3 volatilization were measured. The influence of fertilizer treatments on soil pH was determined in a laboratory incubation experiment conducted over 8 d under controlled environmental conditions. Treatments were similar to the field experiment, with NH3 volatilization, pH, and CO2 production measured daily. The NH3‐volatilization rate in the field was highest 2 d after urea application at a time that corresponded with daily maximum soil temperature and decreasing soil water content. Residue cover reduced NH3 volatilization. Volatilization of NH3 as a result of urea application was not increased when urea was treated with DCD. Ammonia volatilization as a result of urea treatment with NBPT was reduced by 100 times over untreated urea. During an incubation experiment, soil pH increased from 6.5 to 7.2 in the urea‐NBPT, and from 6.5 to 9.0 in the urea and urea‐DCD treatments. Associated with the pH increase in the urea‐NBPT treatment was a reduction in CO2 production when compared with the untreated soil.