Application of Water-stress Models to estimate the Herbage Dry Matter Yield of a Permanent Grassland Pasture Sward Regrowth

This study proposed the concepts of water availability and the related growth support factor and defined them quantitatively. Based on these concepts, the water-stress-dependent effective temperature and global solar radiation accumulation were defined and used as regression variables in statistical modelling of herbage regrowth dry matter (DM) yield of a permanent grassland pasture sward under varying degrees of water shortage. It was found that the proposed method greatly improved the DM yield model accuracy when the influence of water stress on grass growth was prevalent. An effective model was obtained and is recommended for herbage yield prediction under such water-stress conditions. The recommended model predicted DM yield with a coefficient of determination of 0·92 and a mean square error of 0·21 t ha−1. The model can be used for similar herbage regrowth of 3 weeks and beyond. Evaluation using an independent data set confirmed that the recommended model is robust and accurate. The methodology proposed can also be adapted to modelling the herbage growth of different sward types and different (re)growths under the influence of water stress.