Irrigation frequency for white clover and lucerne on a cracking clay in the Murrumbidgee Valley, New South Wales

Abstract

A field experiment was undertaken to study the effect of irrigation frequency on dry matter production of 2 perennial pasture legumes on a grey cracking clay soil (Ug 5.28). This soil has a higher water-holding capacity than the red-brown earths of most previous Australian studies. One-year-old swards of luceme (Medicago sativa L.) cvv. Maxidor II and Pioneer brand 581 (P581), and white clover (Trifolium repens L.) cvv. Haifa and Irrigation, were flood-irrigated at 75, 100, 150, and 200 mm of cumulative net potential evapotranspiration during 3 irrigation seasons. White clover was more sensitive to water stress than lucerne, with yield reductions at the 2 longer intervals of 13% in the first season, 37% in the second, and 39% in the third. Lucerne showed little effect of irrigation frequency during the first 2 seasons, but yields were substantially reduced (by 27%) at the 2 longer intervals in the third season. The 2 white clover cultivars differed in seasonal production and growth habit, Haifa being more productive and withstanding water stress better than Irrigation in the first season. Production was similar in the second season, but Irrigation was able to maintain a denser sward and outyielded Haifa in the third season. There was little difference between the 2 lucerne cultivars. A combination of higher available soil water content and a considerably deeper effective rooting depth (0.8 m at the 100-mm interval), both of which were strongly influenced by soil type, enabled productivity to be maintained at a longer irrigation interval (100 mm) than reported in other Australian studies. Measurements of leaf relative water content reflected the water stress imposed by the treatment intervals. It is considered that in order to maximise production, an irrigation interval up to 100 mm is appropriate for white clover on this soil type. The optimum frequency for lucerne will depend on the life of the stand desired, balanced against productivity and irrigation costs.