Water requirement of irrigated and rainfed crops

Abstract

Irrigated agriculture has been showing considerable levels of evolution over the last few years, in addition to showing a relevant option for food production. Alternative methods and technologies have been developed for the rational use of water in the field to be used also by small producers, with the aim of increasing productivity in the crops worldwide. It is known that for the proper management of irrigation it is necessary to determine the reference evapotranspiration, ETo. Evapotranspiration consists of a combined process of heat transfer and mass, in the form of vapor, from a vegetated surface to the atmosphere, covering the direct evaporation of soil and plant surfaces and the transpiration of plants. Considering this concept, soon there were difficulties in its use, checking the need for standardization. The ETo is defined as evapotranspiration of a hypothetical crop covering the whole soil, in active growth, without water or nutritional restriction, with a mean height of 0.12m, surface resistance of 70sm-1 and albedo of 0.23. The ETo can be calculated using direct methods: drainage lysimeters, mechanical / electronic weighing, and flotation, field experimental plots method, soil moisture control, "Input - Output" method. Among the various methods for estimating ETo are FAO-24 Radiation, Priestley-Taylor, FAO-24 Blaney-Criddle, Hargreaves-Samani, Camargo-71 and FAO Penman Monteith, standard method considered by FAO. The determination of ETo is a complex nonlinear process, depending on the interaction of several climatological variables, such as air temperature, humidity, wind speed, radiation, as well as the growth stage of the crop. For this reason, several studies with crops of great commercial value, such as corn, tomato, sugarcane, soybean, wheat and cotton, have been developed applying the different methods to determine the ETo, considering different situations.