The effect of four different pasture species compositions on nitrate leaching losses under high N loading

Nitrate (NO3-) leaching can cause elevated concentrations of NO3--N in water, which can have adverse impacts on water quality and human health. In grazed pasture systems, most of the NO3--N leaching occurs beneath animal urine-N deposits. The objective of this study was to investigate the effect of four different pasture species compositions [perennial ryegrass/white clover (P.ryegrass WC), tall fescue/white clover (T.fescue WC), Italian ryegrass/white clover (It.ryegrass WC) and perennial ryegrass/Italian ryegrass/white clover/red clover/chicory/plantain (Diverse)] on NO3--N leaching losses from animal urine patches, and to examine the relative importance of root system architecture and seasonal activity to reduce NO3--N leaching losses. The results show that NO3--N leaching losses were 24-54% lower beneath It.ryegrass WC than other pasture species. Total dry matter (DM) yield in the season following establishment was 11-58% greater in the It.ryegrass WC pasture, while average winter daily N uptake rate of It.ryegrass WC over the two seasons was on average 58% greater than P.ryegrass WC and T.fescue WC. In the second season, the P.ryegrass WC and T.fescue WC pastures had up to 140 and 82% more roots between 0 and 40cm depth, respectively, than the other pasture species compositions. These results suggest that in grazed pasture systems, high plant winter activity (plant growth/root metabolic activity) is more important than specific root architecture (e.g. deep roots) to reduce NO3--N leaching losses.