Irrigation distribution uniformity analysis on a lateral-move irrigation system

Abstract

Probability distribution functions (PDF) have been used for decades to model the applied water depth by irrigation equipment; however, there are few studies that evaluate the PDF goodness-of-fit to mechanical lateral-move irrigation system water application, especially with oscillating plate sprinklers. The objectives of this study with a lateral-move irrigation system in the field were as follows: (1) to evaluate the normal, uniform, Weibull, gamma and logistic PDFs’ goodness-of-fit to represent the applied water depth ; (2) to evaluate the influence of wind on the coefficient of variation (CV) of the applied water depth; (3) to evaluate the relationship of the distribution coefficient (H), the availability factor (F), the average deficit (Da) and the water storage efficiency (E) as a function of wind speed. Twenty-nine in-field tests were carried out at the Empresa Brasileira de Pesquisa Agropecuaria (Embrapa). The PDFs’ goodness-of-fit to the applied water depths by the irrigation system was based on the Kolmogorov–Smirnov test at a 5% significance level. The normal, uniform, gamma, Weibull and logistic PDFs fitted 21, 8, 19, 26, and 25 of the 29 in-field tests, respectively; however, application of the Weibull PDF is complicated and the normal distribution is suggested instead. The logistic PDF had good fit and warrants further study. In addition, a negative linear relationship (R2 = 0.73) was observed between the wind speed and the coefficient of variation of the applied water depth by the irrigation system, as well as the distribution coefficient (H), the availability factor (F), and water storage efficiency (E), while the average deficit (Da) showed a positive linear relationship with the wind speed.