Feasibility of stabilised nitrogen fertilisers decreasing greenhouse gas emissions under optimal management in sprinkler irrigated conditions

Stabilised nitrogen (N) fertilisers with nitrification and urease inhibitors have been proposed to abate greenhouse gas (GHG) emissions in agrosystems. Nevertheless, differences in their application and in the management of water and nitrogen rates make it difficult to evaluate their actual utility. The aim of this study was to analyse the possibility for GHG emissions reduction in a 3-year rotation (maize-maize-wheat) by substituting the traditional split-urea application to maize by a single side-dress application of stabilised urea fertiliser. The experiment was performed in 24 drainage lysimeters in two contrasting soil types (Shallow and Deep) under efficient irrigation practices and adjusted N rates under Mediterranean conditions. Nitrous oxide (N₂O) and methane (CH₄) were measured using static closed unvented chambers, and the soil mineral N was monitored through periodic soil samplings. CH₄ emissions were generally negligible with occasional tendency the soil acting as a sink more than as a net source. Direct N₂O emissions during the whole rotation showed lower values when a nitrification inhibitor (3,4-dimethylpyrazole phosphate) was added than with conventional urea (Deep soil: 73% lower, p < 0.05; Shallow soil: 60% lower, ns). Urease inhibitors (N-(n-butyl) thiophosphoric triamide and monocarbamide dihydrogen sulphate) could not abate direct N₂O emissions, and their effect depended on the soil type. However, all stabilised fertilisers mitigated N₂O emissions in Deep soil when scaled by grain yield (average 54%). Indirect N₂O emissions associated with nitrate leaching were not affected by the treatments but contributed more to total N₂O emissions in Shallow soil (12%) than in Deep soil (6%). These results suggest that adequate use of nitrification inhibitors could have environmental benefits without lessening agronomic production.