Pasture irrigation in the Mackenzie Basin

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Abstract
Yields of 25 species and cultivars were compared under irrigated and dryland management on a soil of the Grampians set. Species were grown as pure standards at 3 fertiliser levels (0, 250, or 800 kg per ha per a superphosphate for legumes plus 0, 115, or 345 kg per ha per a of nitrogen for grasses) with basal sulphur and molybdenum added for all species. Depending on species, herbage was cut and removed under either a 6-week or 4-week cutting interval for 2 or 3 years. Yields from 5 legume treatments exceeded 15 tDM per ha per a under irrigation and 9 exceeded 5 tDM per ha per a under dryland conditions. The legumes were generally the highest yielding, grasses only equalling legume production at high N levels. The productivity rating of the legumes was in the following approximate order: Wairau lucerne (best), Hamua, Pawera and Turoa red clover, alsike clover, Huia and Pitau white clover, and then hybrid, Maku, and G4703 lotus. The yield of a Huia white clover/Ruanui ryegrass mixture was similar to that of white clover alone. Within the grasses, with both superphosphate and N fertiliser added, the ranking was: Kahu timothy (under 6-week cutting cycle as compared with 4-weeks for others), Apanui cocksfoot, Roa tall fescue, Matua and Butts prairie grasses, Ariki ryegrass, Nui, Ruanui, and Manawa ryegrasses, Massey Basyn Yorkshire fog, phalaris, dogstail browntop, and Poa pratensis. The yield ratio of irrigated:dryland averaged 3.4 for legumes,and 2.0 for grasses. In a subsequent experiment several species showed up to 50% increase in annual yield under 6 weeks as compared with a 4 week cutting interval. With irrigation and high fertiliser levels, growth was limited to 220–270 days. Early spring growth was often greater under dryland management. Legumes showed only about one-third increase in yield under high as compared with nil superphosphate levels. Grasses showed an 18-fold response to N up to about 800 kg N per ha per annum.

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