6 Conclusions and Recommendations
From this study a number of conclusions can be drawn about the practicality and suitability of the proposed set of indicators of sustainable irrigated agriculture.
- The greatest difficulty encountered was measuring water flows. None of the six farms chosen had systems amenable to installation of a single flow meter. To record flow continuously, as originally intended would have required a combination of multiple flow meters and/or extensive alterations to head-works structures. This is potentially a major limitation to evaluating irrigation indicators on a large number of farms where water meters are not already present.
- Estimates of total seasonal water consumption were based on area, application depth, and number of applications. The accuracy of these estimates depends largely on the estimation of application depth. In this study no tests were performed to verify application depths, although this would improve the reliability of the calculated indicators.
- Despite the problems mentioned above, the production and water use indicators proved to be the easiest to evaluate. These also appeared to stimulate the greatest interest amongst the farmers.
- With the limited number of dairy farms, and two recent conversions in the sample, it was not possible to collect meaningful financial information. The financial information from the arable crops was potentially more useful as this gives the farmer some measure of the financial implications of water management strategies during times of water constraint. This is an area that requires more development.
- The ease of determination and meaningfulness of the environmental indicators varied.
- Interpretation of the fertiliser and agri-chemical application rate data should be approached with caution as is does not contain information about timing and amount of individual applications.
- Determining the soil indicators was relatively easy, but expensive, using the standard laboratory techniques. The soil quality monitoring systems developed by Crop & Food and Lincoln may well prove to be useful in reducing the cost of obtaining this information. At this point some doubt must be raised about the relevance of the soil indicators to sustainable irrigation. While there are know links between soil physical and chemical properties and water holding capacity and application rates and soil structure, the indicator data collected here requires more specialist interpretation to be more meaningful.
- The indicators requiring daily measurement of water flows could not be determined in this project, nor is it felt that this would be feasible on most farms. An attempt was made to estimate the extent of over-irrigation by introducing alternative indicators, the ratio of water applied to potential and actual water demand, D/ET and D/ET* respectively. This showed that the systems considered were all operated close to the design condition regardless of the weather. This confirmed the findings of the earlier survey of farmer perceptions of and use of water management techniques, which showed that very few irrigators could or would control water application based on monitored soil moisture requirements. However, due to the seasonal integration used, these indicators are unable to show the 'fine detail' of the fate of water during each irrigation application. This can only be achieved using continuous soil moisture monitoring.
- The D/ET and D/ET* indicators are easy for farmers to calculate but they may still mask poor irrigation practices. It is possible to apply the correct amount of water on a seasonal basis but still be over-watering with each irrigation if the depth of application exceeds the available water storage capacity of the soil.
- More accurate determination of soil water holding capacity would have been beneficial in determining the potential for over-watering. The method of comparing neutron probe and quick-draw tensiometer readings can provide a useful indication provided that all equipment is accurately calibrated and sufficient data is collected, as wide scattering of data is often encountered with this technique. For more accurate determination of water holding capacity a laboratory pressure plate method should be used.
- The audits proved to be useful in the analysis of the irrigation systems considered. On farm 2A the audit highlighted several problems including poor matching of pumps and, in places, high pipe velocities and hence high head losses. These factors combined would indicate that there is potential to reduce the cost of irrigation on this property by replacement of existing pumps and pipes. However, the capital cost of achieving this would need to be evaluated to ensure a desirable rate of return on investment.
- The audit on farm 3A showed that the current bore limits the system capacity and hence the flexibility of operation. While increasing the number of siderolls in operation would make the system slightly more flexible this would require greater labour input.
- In general it is easier to measure, determine, compare and interpret technical and economic indicators than environmental indicators. The former relate to short-term farm goals that are usually well articulated by farmers, while the latter relate to longer-term goals that are somewhat 'fuzzy' in nature and not well communicated by farmers. There is a perceived danger that this will result in future research concentrating on technical and economic factors rather than environmental factors.
From these field trials a number of recommendations emerge.
- There is a need for low cost accurate flow metering to be available if the indicators are to be calculated accurately.
- Indicator data should not be used for inter-farm or inter-system comparison but rather as a measure which each farmer and irrigation scheme operator can use within their own 'Plan-Do-Check-Act' cycle of improving sustainable management.
- Data should be collected from a wide range of farms to produce statistically reliable estimates of the range of each indicator and this information should be made available for irrigators as benchmarks to help identify areas for improvement.
- There is a need for more research on the relationship between soil indicators and sustainability of irrigation practices.
- There is a need to develop a methodology to aggregate indictors for arable and mixed farms if a meaningful value is required at the whole farm level.
- There is a need to 'tie together' the various sustainable agricultural indicator projects to arrive at an overall suite of indicators that includes all factors relevant to the decision making processes on a farm including economic, physical and environmental factors.
Contact for Enquiries
MAF Information Services
Pastoral House
25 The Terrace
PO Box 2526
Wellington, NEW ZEALAND
Fax: +64 4 894 0721
Contact this person
