Effective management of grassland soils and nutrient resources for enhancing nitrogen efficiency and mitigating emissions

The effects of soil pH and nutrient inputs on grass and crop yields are well understood and famers around the world receive agronomic advice on how to improve the soil fertility on their farms for optimal plant growth. Interactions between nutrients within the soil and when assimilated by plants has also been the subject of much research to date. However, refocusing efforts towards balanced nutrient supply in agricultural soils is now more critical than ever for achieving climate smart and sustainable food production systems. In particular, emissions of nitrogen (N) from agricultural soils need to be minimised in-order to reduce the unintended negative consequences of N in the environment.

Grassland productivity is highly dependent on the supply of plant-available N from the soil. The N loss pathways of primary concern to society are nitrate (NO₃) leaching and emissions of greenhouse gases and ammonia. The effect of soil fertility and fertiliser type on emissions of greenhouse gases such as nitrous oxide (N₂O) after N fertilisation is less well understood. Optimising soil pH and soil test phosphorus has been shown to reduce N₂O emissions associated with N fertiliser application on humid temperate grassland soils where denitrification is the main N₂O source (O’Neill et al., 2020; Žurovec et al., 2021). The role of sulphur and potassium in driving N recovery and by different grassland sward types has been re-evaluated and shown to significantly reduce leaching of fertiliser N sources (O’Neill et al., 2020). New research has shown that N-P-K-S compound fertilisers with higher proportion of ammonium based-N source had lower N₂O emissions compared to compound fertilisers with higher proportion of nitrate based-N source (Gebremichael et al., 2021). Overall, these findings indicate that nutrient based technologies and advice are available for immediate implementation on farms to reduce N emissions from grassland soils.

These fertiliser and nutrient management strategies for increasing the efficiency of N use and reducing N emissions on temperate mineral grassland soils are discussed in this paper, along with how these fit together to improve overall N use efficiency in grassland systems and provide opportunities to tackle the challenges facing agriculture.

Co-authors: P.F. Forrestal, D.J. Krol, G.J. Lanigan, K.G. Richards.