Irrigation frequency and total water application with trickle and furrow systems

Abstract

One of the main attributes of trickle irrigation is that it enables the available water to be utilised as efficiently as possible. This is achieved through the elimination of waste that is an inevitable consequence of normal irrigation practice.The water requirements of crops can be calculated to a reasonable degree of accuracy using formulae that have been developed to relate evapotranspiration to the evaporation from a U.S. Class A pan evaporimeter, with suitable adjustments for the particular crop and the degree of ground cover.The aims of the experiments described in this paper were: 1.(1) to compare the yield of field tomatoes under trickle irrigation and furrow irrigation over a range of irrigation frequencies and amounts that can reasonably be used for both methods;2.(2) to compare the effects of irrigation frequency over a range of irrigation amounts that are typical for each irrigation method;3.(3) to compare the effects of irrigation amounts over a range of irrigation frequencies that are typical for each irrigation method;4.(4) to examine the interaction, if any, between irrigation frequency and amount.The results of the trial showed that there was no difference in yield between trickle irrigation and furrow irrigation over a range of conditions for which they could legitimately be compared. At the same time it should be realized that the results for furrow irrigation on small plots may not adequately represent the normal farm practice for this method, where less efficient watering occurs due to long runs and unavoidable inequalities in water application.For both irrigation methods there was a consistent trend of decreasing yields with increasing irrigation frequency. Where departures from this trend occurred in unusual irrigation conditions (i.e. continuous irrigation and prolonged drought) the effect is explained by physiological causes that relate to the particular conditions. In such cases only, there was an interaction between irrigation frequency and amount.For each irrigation frequency the highest yields were obtained for the optimum amounts as calculated to match the potential evapotranspiration rate. Equal amounts of under-watering and over-watering resulted in approximately the same reductions in yields.The results from the trial indicate that the highest yields and greatest efficiency of water use occur at frequent intervals with an amount of applied water approximately equal to that calculated from simple formulae relating evapotranspiration to measured pan evaporation. Extrapolation of the results of particular trials to other crops, soils and climates should be treated with caution. However, the agreement of the results with those predicted from physiological and empirical data, and the fact that the results from other experiments also agree with such formulae, give cause for confidence in predicting the responses to irrigation timing and amounts over a wide range of conditions.