Nitrous oxide responses to long-term phosphorus application on pasture soil

Abstract

Nitrous oxide (N₂O) is a greenhouse gas emitted from grazed pasture systems. The influence of phosphorus (P) fertility on these emissions is not understood. This study examined if fertiliser P affected N₂O emissions following nitrate application to soil from the Winchmore long-term P fertiliser trial. We hypothesised increasing P fertility would enhance soil carbon (C) supply and N₂O emissions via denitrification. Using mesocosms, N₂O and CO₂ fluxes were measured over 29 days following KNO3-15N and glucose additions, along with soil chemical and biological variables. Microbial biomass P increased (P < 0.001; R 2 = 98.2%) with increasing Olsen-P. Fertiliser P enhanced net N mineralisation. Cumulative CO₂ fluxes were unaffected by P treatment regardless of KNO₃ addition. Fluxes of N₂O increased one day after KNO₃ addition with higher emissions at 250 kg ha¯¹ of superphosphate. Relatively low N₂O-¹⁵N enrichment indicated minor denitrification contributions to the N₂O flux. Subsequently, glucose addition enhanced N₂O-¹⁵N enrichment and denitrification in the KNO₃ treatment. Following glucose addition, the emission factor increased with P fertiliser. Denitrification derived N₂O emissions will increase with P fertilisation but only if C limitation is overcome.