Niall Barlow

Lime application to acidic soils is a common practice in agriculture to increase the soil pH and thereby improve soil nutrient availability. Urease inhibitors such as N‐(n‐butyl) thiophosphoric triamide (NBPT) are widely used to reduce ammonia (NH ₃ ) losses from urea. In Ireland, a substantial proportion of straight nitrogen (N) fertiliser is now applied as urease inhibitor–treated urea. Current guidance is to wait 3 months after liming before applying standard urea, but the use of standard solid urea is now restricted in Ireland and other European countries. For NBPT‐protected urea‐based fertiliser (NBPT‐urea), there is currently no research available to guide advice on the effect of the interval between liming and the application on NH ₃ emissions. As a result, there are uncertainties concerning the interval following lime application that should be recommended before applying NBPT‐urea. This study evaluated whether the interval between lime and NBPT‐urea application influences NH ₃ emissions in a grassland field. The initial soil pH of the site was 5.5; a requirement for 7.5 t ha ⁻¹ of lime was indicated. Lime was applied at four timings: 87, 28, 7, or 0 days before NBPT‐urea application. A NBPT‐urea treatment following no lime was also included as was a no‐lime control. The NH ₃ emissions from NBPT‐urea following liming were similar to those from NBPT‐urea following no liming regardless of the interval between liming and fertiliser application. Under the study conditions, the interval between lime application and NBPT‐urea application did not significantly influence the NH ₃ emissions from NBPT‐urea. We recommend that the current study results are validated by further field studies covering other soil types and ambient conditions.