Optimising soil P levels reduces N 2 O emissions in grazing systems under different N fertilisation

Résumé fourni par la source

Abstract The effect of long‐term soil phosphorus (P) on in situ nitrous oxide (N 2 O) emissions from temperate grassland soil ecosystems is not well understood. Grasslands typically receive large nitrogen (N) inputs both from animal deposition and fertiliser application, with a large proportion of this N being lost to the environment. Understanding optimum nutrient stoichiometry by applying N fertilisers in a relative balance with P will help to reduce N losses by enabling maximum N‐uptake by plants and microbes. This study investigates the N 2 O response from soils of long‐term high and low P management receiving three forms of applied N at two different rates: a nitrate‐based fertiliser (KNO 3 ) and an ammonium‐based fertiliser ([NH 4 ] 2 SO 4 ) (both at 40 Kg N ha −1 ), and a synthetic urine (750 Kg N ha −1 ). Low soil P significantly increased N 2 O emissions from KNO 3 and (NH 4 ) 2 SO 4 fertilisers by over 50% and numerically increased N 2 O from urine by over 20%, which is suggested to be representative of the lack of significant effect of N fertilisation on N‐uptake observed in the low P soils. There was a significant positive effect of soil P on grass N‐uptake observed in the synthetic urine and KNO 3 treatments, but not in the (NH 4 ) 2 SO 4 treatment. Low P soils had a significantly lower pH than high P soilss and responded differently to applied synthetic urine. There was also a significant effect of P level on potential nitrification which was nearly three times that of low P, but no significant difference between potential denitrification and P level. The results from this study highlight the importance of synergy between relative nutrient applications as a deficiency of one nutrient, such as P in this case, could be detrimental to the system as a whole. Optimising soil P can result in greater N uptake (over 12, 23 and 66% in (NH 4 ) 2 SO 4 , KNO 3 and synthetic urine treatments, respectively) and in reduced emissions by up to 50% representing a win‐win scenario for farmers. Highlights P deficiency in grassland soils causes greater N 2 O emissions. Insufficent soil P inhibits N‐uptake, regardless of rate or form of N. Optimising soil P levels can reduce N 2 O emissions and improve overall NUE.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.