The economics of sprinkler irrigation uniformity: A case study of lettuce on the Swan Coastal Plain

[摘要] Executive Summary: The Government of Western Australia has undertaken to develop a statutory water plan for the Gnangara Mound as one of the commitments made under the National Water Initiative. This plan will need to address water allocations to the peri-urban horticultural industry, and may require clawing back of volumetric allocations to address declining groundwater levels. Policies that encourage adoption of water efficient appliances may reduce the impact of reduced allocations, on the irrigation dependent businesses and on the consumers of produce supplied to the metropolitan market. The opportunity for reducing water use in the horticulture industry will depend on the flexibility of current watering regimes and the scope for improving technical water use efficiency. These in turn depend on the relationships between water use and crop yield, and differences in the capital cost and performance of irrigation systems. The economic benefits of more uniform systems depend on the water-yield relationship which affects revenue, and the variable costs of production including irrigation costs and water prices. These must be compared with the capital costs of achieving better uniformity which include for example, the extra materials components associated with closer sprinkler spacing.This report contains an analysis of the economic incentive to adopt more water efficient sprinkler systems using lettuce as a case study. The economic model draws on several Department of Agriculture studies on the performance of sprinkler systems and yield-water relationships for lettuces on the Swan Coastal Plain.Results indicate that growers acting with perfect information regarding the efficiency of their sprinkler systems and the water-yield relationship would, provided they are paid on the basis of yield, have a strong incentive for using water efficiently and for adopting systems with high distribution uniformity. The reason for this is that there is a strong disincentive to over-watering. Farmers lose money by over-watering, due to the leaching of nitrogen at high water application. More efficient sprinkler systems achieve higher economic returns and use less water. Of the systems studied it was shown that twice as much lettuce could be grown with the most efficient system for the same amount of water, and returns would increase by $1,500 to $2,000 per hectare per crop, compared to the least efficient system studied. A possible explanation for low adoption of water efficient appliances is that farmers do not perceive a financial disincentive from over-watering. The study demonstrated that if the farmer believes that there is no yield (or revenue) penalty from over-watering, they will not anticipate any financial gain from adopting more water efficient appliances, particularly if they are making decisions on a short planning horizon. This situation may arise either through lack of information regarding the water-yield relationship, or even where farmers are aware of the effect of over watering on yield, it could arise if they are not paid on the basis of weight. For example, lettuce sales to supermarkets are largely based on the number of heads sold, rather than the head weight of the lettuce. Another significant disincentive to improving irrigation systems is the uncertainty about how long they may be farming due to land use planning changes, with a number of farms likely to be sub0divided for urban development in the short term. The provision of extension information regarding the nature of water productivity for different crops could provide substantial incentive for improving water use efficiency. Where crops are paid on the basis of weight and there is a yield loss at high water application, there are strong gains from adopting more efficient systems. Further research on the nature of water productivity for different crops may be required. The importance of the distribution uniformity measure in determining appropriate water use, economic returns, and the incentive to adopt more efficient systems confirms the need for extension in this area, but further analysis of other cropping systems is required to confirm this. A number of policy options are available for improving the likelihood of adoption of water efficient systems. These include increasing security of tenure over water and land, which will extend the farmers planning horizon and reduce capital costs, and the introduction of water markets. Water markets will increase the incentive for reducing water use in the short term, and will encourage adoption of water efficient sprinkler systems in the longer term. For example, where distribution uniformity is around 55%, the farmer is better off reducing water application by 1.5 ML per crop hectare (20 percent) if the market price is $200 per ML, compared to when there is no market. Water markets will improve incentives for adoption of water efficient practices even when the water-yield relationship plateaus and there is no yield penalty from over-watering.The potential for using capital subsidies to encourage adoption of more water efficient sprinkler systems need to be considered in the context of the other incentives for adoption. For example, if the yield penalty associated with higher water use is shown to exist for other crops, then this information alone should be sufficient to encourage adoption of more efficient sprinkler systems. On the other hand, if the water-yield relationship is shown to plateau at high water application rates then the private incentives for adoption of efficient systems are less pronounced. The introduction of water markets may reverse this incentive without requiring public subsidy of irrigation equipment. However, if there is a concern about the environmental consequences of nitrogen leaching associated with horticultural production on the Gnangara mound, then a number of pollution control alternatives could be considered, including nitrogen or water taxes, mandatory water use efficiency standards, and subsidies to reduce the cost of sprinkler system upgrades.

[发布机构] CSIRO

[学科分类] 地球科学(综合)