An Urease Inhibitor Effectively Reduces N Losses From Urea Fertilized Mediterranean Agrosystems.

Urea is the cheapest and most commonly used form of inorganic N fertilizer worldwide, accounting for c. 50% of inorganic N use. Nevertheless, the low efficiency of N-urea use by crops represents a threat to environmental quality and public health. It has been estimated that up to 60% of N-urea applied could be lost to the atmosphere via ammonia (NH₃), nitric oxide (NO) and nitrous oxide (N₂O), and to water streams through nitrate (NO₃^-) leaching. Among the proposed mitigation strategies to prevent N losses from urea fertilizing, urease inhibitors have been shown to effectively reduce NH₃ volatilization. Additionally, these compounds have been noticed to decrease the NO and N₂O production rate under certain soil conditions. To evaluate the effectiveness of the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT, trade name Agrotain^®) on mitigating N losses from arable crops under Mediterranean conditions, a set of field experiments were carried out between 2006 and 2011. Ammonia volatilization was measured with a micrometeorological technique in both sunflower and barley crops; losses of NO and N₂O were determined by static chambers in corn and barley; leached NO₃^- was measured in the same crops. Urea and NBPT coated urea (0.14-0.20% w/w) were applied in granular form. The reduction in the hydrolysis rate promoted by the inhibition of urease activity leaded to 42-58% abatement of ammonia volatilization. Additionally, presence of NBPT decreased NO-N and N₂O-N emissions from urea in 74% (i.e. 1.89 kg NO-N ha^-1) and 55% (0.86 kg N₂O-N ha^-1) when nitrification was expected to be the main pathway in the production of these reactive N compounds. Finally, NBPT reduced N losses through NO₃^- leaching in 59% (i.e. 40 kg N ha^-1) in a corn crop.