Effect of irrigation and defoliation on the herbage production and water use efficiency of four temperate pasture species

Abstract

Measurements were made over a 12-month period of the herbage production of both dryland and irrigated monoculture swards of four temperate pasture species under two defoliation regimes. By relating herbage production to the previously reported water use results for these swards, water use efficiencies (WUE) have been computed. Dryland clover produced 2000 kg/ha less herbage than did the dryland grasses, although it used a similar quantity of water. Consequently, the WUE of dryland clover was substantially less than that of the dryland grasses. Under dryland conditions, fescue not only produced more herbage, but also used water more efficiently than did the other species. Similar amounts of irrigation enabled the clover to yield an extra 6000 kg/ha of herbage compared with a mean grass response of 1760 kg/ha. The irrigated clover swards generally used water much more efficiently than the dryland clover swards. In contrast, the grasses generally used water with similar efficiency under both irrigated and dryland conditions. Under both irrigated and dryland conditions the frequently defoliated swards usually outyielded those cut infrequently as well as making more efficient use of water. The response of pastures to irrigation is discussed in terms of the effects of irrigation on the water status of the plants and the availability of nutrients in the rhizosphere.