Subsoiling combined with winter active Italian ryegrass can reduce nitrous oxide emissions without increasing nitrate leaching: Evidence from lysimeter and field plot trials

Abstract

Subsoiling is a common practice for improving soil structure and has recently been recognised for its potential to reduce nitrous oxide (N₂O) emissions. However, its impact on nitrate (NO₃‾–N) leaching must also be considered if it is to be used as a mitigation strategy. This study investigated N₂O emissions, NO₃‾–N leaching and grass yield in an Italian ryegrass pasture soil with a compacted subsoil layer using a lysimeter study. Additionally, a separate field study examined mineral nitrogen (N) concentration and the abundance of nitrifying and denitrifying genes. Both studies have four treatments, with non-subsoiling (NS), subsoiling (SS), non-subsoiling and urine (NSU), subsoiling and urine (SSU), and the urine treatments were applied at a rate of 700 kg N ha‾¹. The results showed that 6 months after subsoiling, soil macroporosity in all treatments remained elevated at a depth of 0–20 cm (p < 0.01) compared with all non-subsoiling treatments. This created more aerobic conditions, which suppressed N₂O emissions from denitrification by 20.3% (p < 0.05) during 190 days after urine application (NSU vs. SSU). Additionally, subsoiling had no significant effect on NO₃‾–N leaching in the presence of winter-active Italian ryegrass. Molecular analysis of N-cycling microbial communities revealed that subsoiling had no effect on the abundance of amoA gene-carrying microorganisms involved in nitrification but reduced the abundance of nirS denitrifier genes, indicating that subsoiling primarily affected the denitrification process. These findings suggest that subsoiling can effectively reduce N₂O emissions without increasing NO₃‾–N leaching when combined with winter-active ryegrass.