Enhanced efficiency fertilisers reduce nitrous oxide emissions and improve fertiliser 15N recovery in a Southern Australian pasture.

Unlabelled Image • Enhanced efficiency fertilisers can be used to reduce N 2 O emissions but their impact on soil N reserves is not well known. • N 2 O emissions were measured from urea and enhanced efficiency fertilisers applied to pastures. • N 2 O emissions, but not emission factors, increased as N application rate increased. • Use of enhanced efficiency fertilisers reduced N 2 O emissions by 22–56%. • Using urease and nitrification inhibitors increased retention of N in soil. The effects of reducing nitrogen (N) rates or using enhanced efficiency fertilisers (EEFs) (i.e. urease and nitrification inhibitors, and controlled release fertilisers) on nitrous oxide (N 2 O) emissions and nitrogen use efficiency (NUE) are not well understood in temperate, rainfed pastures. A field experiment on rainfed ryegrass pasture in southern Australia examined the effect of granular urea N rate (0, 250 and 420 kg N ha−1 over 6 months) and EEF use (at 250 kg N ha−1 with NBPT, DMPP, or polymer coating (PCU)) on N 2 O emissions, NUE and fertiliser N recovery (using 15N techniques). Cumulative net-N 2 O emissions increased with N rate from 308 g N 2 O-N ha−1 (250 kg N ha−1) to 514 g N 2 O-N ha−1 (420 kg N ha−1). Using EEFs reduced N 2 O emissions by 22% (NBPT), 44% (DMPP) and 56% (PCU) compared to urea. The emission factor (EF) (kg net N 2 O-N per kg N applied) was 0.12 for both N rates (250 and 420 kg N ha−1) but reduced with the EEFs to 0.10 (NBPT) and 0.07 (DMPP and PCU) compared to urea. EEF use had no significant impact on biomass or apparent NUE but led to a greater recovery of N in the soil after one month (44.8% (DMPP) and 45.9% (NBPT) compared to urea (33.7%)). Within one month 42% of the N applied as urea (U50) was lost from the plant-soil system, which was reduced with DMPP (32% loss) and NBPT (33% loss). After six months, 52% (U50) to 59% (U84) of the urea N applied was lost. The positive effect of the EEFs on N 2 O emissions, and the increased recovery of N in the soil-plant system with the EEFs over one month indicates they could provide longer term benefits though soil N storage, and could be applied at lower N rates to achieve NUE benefit. [ABSTRACT FROM AUTHOR]