Irrigation on the edge: Irrigation effectiveness on the edge of the season, in a context of water resources under increasing pressure and on the edge of low restriction use: Master thesis Irrigation and Water Engineering submitted in partial fulfilment of the degree of Master of Science in International Land and Water Management at Wageningen University, the Netherlands

Abstract

Why was the study undertaken? Water is used by many different users with varying purposes. Agriculture takes up a major share of consumptive water use, mainly in the form of irrigation. Of all water allocated in New Zealand, irrigation encompasses about 77% (Redward, 2002) and Canterbury takes up a 70% share of all irrigated land in New Zealand (Ministry of Agriculture and Forestry, 2004). About 500000 hectares are irrigated in Canterbury, and irrigated farming brings about an enormous increase in revenues, by '1 billion dollars' compared to dryland farming (Redward, 2002). Over the period 2000 to 2010, it is predicted that the national irrigated area is likely to increase by 28%, with about 40% of this increase, equivalent to 60500 hectares, taking place in Canterbury. Although in general it is not foreseen that the demand for irrigation water will exceed the supply over this period, water shortages or water access difficulties are likely to become a serious local problem in certain areas and catchments (Nimmo-Bell & Company Ltd, 2001 ). Environment Canterbury (the regional authority responsible for the protection of Canterbury's natural resources) has recently intensified regulations regarding irrigation water use. This was done in order to guarantee a fair water distribution amongst different user-groups, especially with these future developments in the agricultural sector in mind. With irrigation playing such a dominant role in the national, and especially Canterbury's, water use, more effective irrigation applications could greatly contribute to improving the effectiveness of water use in the region, and open up the resource to other uses. Considering the great expansions in dairy farming and irrigation predicted for the near future, it becomes increasingly attractive to both farmers and regulators to better tune irrigation applications towards crop demand. In this context of increasing pressure on the water resource, regulations regarding water use becoming stricter and irrigation being the main actor in these developments, the idea for this research was developed. Professionals in the Canterbury water sector, connected to both Lincoln University and the private sector, observed that pasture irrigation in Canterbury continues relatively late into the irrigation season, and doubts arose on the necessity or intensity of these irrigation applications on the 'edge' of the season. By investigating the effectiveness of irrigation applications in the autumn 'shoulder' of the season, the possibility is created to tune water applications better towards plant demand and to avoid over-irrigation. The positive outcomes of such a practice would be noticeable in different areas: the environment (reduced water use, water logging and possible drainage or runoff of contaminants); the availability of water to share amongst different users (agriculture, forestry, environment, recreation, drinking water, household water); and reduced expenditures on the farm level, as the daily running costs (mainly electricity) of a centre pivot irrigator in Canterbury are expected to be NZ$250 a day on average (T. Davoren, pers. comm., 2006)