IRRIGATION OF A HIGH COUNTRY MACKENZIE SOIL

Abstract

Pasture production and water use data are presented for a border strip irrigation trial in the Upper Waitaki Basin. Pasture development on the shallow, poorly structured Mackenzie soil was slow and irrigated pasture remained clover dominant for 6 years. With irrigation at 25% awe pasture herbage production over 3 years of this initial development stage averaged 7.2 t DM/ha/yr, 5 times more than improved dryland pasture. Grazing days (12 - 19 month old ewes) provided during the September to April growing season were 960 under dryland conditions and 5940 under irrigation at 25% awe. Of the 3 irrigation treatments (irrigation at 0%, 25%, 50% awe), irrigating at 25% awe was the most efficient giving near-maximum pasture production and the greatest herbage response per irrigation, Mean annual water use efficiency at 25% awe was high (63%) and irrigation water requirement low (470 mm) for such a naturally, highly permeable soil and was probably due to soil compaction by earthmoving machinery during border strip preparation. Keywords: Irrigation, high country, Mackenzie soil