Yield and water use of a ryegrass/white clover sward under different nitrogen and irrigation regimes

Abstract

We investigated how N availability affected the wateruse efficiency (WUE) of a perennial ryegrass/white clover sward under different soil moisture regimes at Lincoln. Four combinations of ± N fertiliser and ± irrigation (I) were applied to plots rotationally grazed by sheep, and WUE (yield/water used) was measured from August 2011 to May 2013. The +N swards had a higher annual WUE than -N swards (27 vs 19 kg DM/ ha/mm) due to greater yields for the same amount of water used. This was associated with higher N contents in the +N grass herbage. The N response of WUE was consistent across soil moisture regimes and for most of each year. Irrigation did not affect annual WUE because the +I swards yielded more herbage but used more water than the -I swards. The results suggest that high WUE can be achieved by strategic applications of N fertiliser, use of pure legume swards, and through management that encourages clover growth in grass/clover swards. Keywords: dryland, Lolium perenne, Trifolium repens, water-use efficiency