Effects of irrigation timing on seedling establishment and productivity of subterranean clover pastures

Abstract

Pure swards of subterranean clover were irrigated from late summer-autumn 1982 to autumn 1985. The period of irrigation varied, with 3 times of initial irrigation (1 February, 1 March and 1 April) and 2 times of final irrigation (mid October and mid November). Seedling establishment, DM production and herbage quality were measured in grazed swards. In each regenerating year, seedling density increased as the time of initial irrigation was delayed from February (5.2 seedlingddm2) to April (20.5 seedling/ dm2). For any time of initial irrigation, seedling density was increased by up to 100%, in plots which were irrigated until mid November in the previous spring. Dry matter yield was increased by early irrigation, with average yields of 11.1, 10.3 and 9.1 t/ha.year achieved for February, March and April as times of initial irrigation respectively. Continuing irrigation until November increased annual yield by 0.76 to 1.58 t DM/ha. The late spring irrigation treatment gave increased spring growth plus increased growth in the following autumn as a result of increased seedling density. The quality of the feed produced in autumn was lower than that produced in winter (in vitro DMD 68% compared with 75%), but was higher than the published DMD values for paspalum pastures in autumn. Digestibility in spring declined rapidly, from 75% in September to about 50% in early December. The implications of these findings are discussed with respect to the most effective use of irrigation water, the reliability of subterranean clover regeneration and the timing and quality of the feed produced.