Procedures for estimating gross irrigation water requirement from crop water requirement.

Abstract

The goal of irrigation is to supply sufficient water for crop growth to all areas within a field. Therefore, the uniformity of application of irrigation water is of great importance. The objectives of this study were to quantify the performance of irrigation systems under field conditions using standard evaluation techniques and to investigate the use of spatial statistics to characterise the spatial variability of application. The main objective was to develop techniques to estimate gross irrigation water requirement that incorporates the uniformity of application. Different practitioners have given different definitions to the criteria used to evaluate the performance of an irrigation system. A literature review was conducted to determine the current definitions used and the factors that affect these performance criteria. The theory and application of spatial statistics was investigated in order to charaterise spatial distribution of irrigation water. The spatial distribution of irrigation water under centre pivots was determined using field measurements. A number of centre pivot, sprinkler, floppy, drip and micro-irrigation systems were evaluated using standard techniques. The results from the evaluation of spatial data show that this approach is useful to determine a map of the distribution of applied irrigation water. Due to the smoothing characteristic of the spatial statistical method employed, the maps have a uniformity that is greater than in reality. The results from the standard evaluation techniques show that quick and representative results for the performance of an irrigation system can be obtained. The distribution uniformity has an affect on the efficiency of a system and should therefore be included in the calculation of the gross irrigation water requirement. The methods for these calculations are discussed. Further research needs to be conducted to determine actual distribution uniformities and application efficiencies for irrigation systems under various field conditions. This will provide useful standards to include in the calculation of gross irrigation water requirements.