Improving irrigation practice in New Zealand

Abstract

The Canterbury Plains are the major cropping area, and an increasingly important dairying area, in New Zealand. Irrigation is necessary on most of the Plains to achieve high productivity. However, competition for limited water resources means that farmers increasingly have to justify their demands for water. Farmers need to know when to irrigate, how much water to apply, and the yield penalty if the crop is not irrigated. For annual arable crops, we have used the maximum potential soil moisture deficit (MPSMD) model and a large rainshelter to answer these questions. Total or economic yield of nearly all the crops tested decreased linearly as MPSMD increased, regardless of the timing of drought. The slope of the regression line is the yield loss with increasing MPSMD. For ryegrass dairy pastures, which grow throughout the year, the model has been adapted to simulate actual soil moisture changes. As most farmers do not measure pasture production directly, we have developed a model for potential pasture production, and a simple relationship between grass growth restrictions and actual soil moisture deficits, that fits experimental farm data. Farmers can also reduce the amount of water they apply by improving the water application efficiency of their irrigation systems. Protocols had been developed to identify causes of poor performance in the field, and how these may be addressed. This information is being used by farmers to improve their irrigation decisions, and irrigation system performance, and has been included in decision support systems for arable and vegetable farmers, and is being developed for dairy farmers.