Grassland forage legumes and drought mitigation – sheep wool application improved soil water availability and enhanced drought–stress responses

Background Sheep wool may reduce drought stress in grasslands when used as a soil amendment. Two experiments were conducted to explore if: (i) water absorbed by wool would be biologically ‘active’ and therefore available to plants, using a novel method of measuring water activity ( a w ); and, (ii) adding wool to compost would delay water stress in forage legumes and support plant growth. Experiment 1 determined a w of wool pellets and potting mixtures of 0%, 7%, 14% w/w wool in compost (no plants). Experiment 2 parts a and b used these potting media mixtures to assess a w on droughted and watered red clover and lucerne over 2 weeks, respectively. Results In Experiment 1, wool pellets dry matter content was 915 g kg −1 and a w < 0.473, indicating very low a w . Addition of ≥ 30% w/w water to wool pellets, or mixing pellets with compost, increased a w to > 0.900, confirming high water availability. In Experiment 2, under drought, wool incrementally delayed water stress by ≥ 5 days, compared to compost. Effects of water stress on red clover and lucerne differed, with watering regime having greater influence than wool addition. The 14% wool treatment improved leaf water content of red clover. Wool addition reduced lucerne root weight, length and surface area ( P < 0.05). Conclusion Wool increased water retention in potting media, and the water was chemically available. Wool addition delayed drought–stress responses for red clover and altered the roots of lucerne. Further studies are needed under field conditions to understand the potential of wool on drought mitigation.