Effects of straw mulching, liming, and soil texture on ammonia volatilisation: a study of conventional and enhanced efficiency fertilisers

Context In no-tillage agriculture, maintenance of soil cover combined with liming without incorporation increases nitrogen (N) loss via ammonia (NH3) volatilisation, decreasing the efficiency of nitrogen fertilisers. Aims To quantify N losses by NH3 volatilisation from conventional and enhanced efficiency fertilisers applied to a clayey and a sandy loam soil subjected or not to lime (CaCO3) application and straw mulching. Methods Two laboratory experiments were carried out; one using a clayey soil, and the other using a sandy loam soil. Both experiments followed a 4 × 2 × 2 factorial design with four N sources (urea, urea-NBPT, urea-formaldehyde, and ammonium sulfate), absence and presence of liming, and absence and presence of Brachiaria ruziziensis straw mulching. NH3 volatilisation was measured using closed flasks containing filter paper soaked with sulfuric acid and quantified by titration with sodium hydroxide. Key results NH3 volatilisation was up to 62% of the N applied. Losses due to NH3 volatilisation from both soil types decreased in the following order of treatment: liming + straw mulching > straw mulching only > liming only. Urea-formaldehyde and ammonium sulfate were the most efficient in reducing NH3 emissions. However, when ammonium sulfate was applied to a clayey soil after liming, it resulted in higher NH3 emissions than conventional urea. Conclusions Urea-formaldehyde showed better performance in reducing NH3 losses due to greater stability in the presence of straw or liming. Implications Soils with straw and limestone can lead to large NH3 volatilisation losses if urea conventional is broadcast.