Technical manual for “Crop water requirements and irrigation scheduling”
George, Biju Alummoottil
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In arid climates where fresh water resources are scarce, proper water management to maximize water use efficiency is vital to meet increasing demands and to protect diminishing resources. With irrigated agriculture being the largest consumer of water, it requires special attention. As Larson 1981 states it: “As long as water was thought to be abundant and energy was cheap, the approach to irrigation was to apply plenty of water. Little attention was paid to how much water was applied or how efficiently it was applied. This situation prompted researchers to develop techniques that irrigators could use to avoid over irrigation, thus reducing water use, energy consumption, and irrigation costs. The techniques that were designed to avoid excess water use are called irrigation scheduling. Irrigation scheduling is defined as applying the right amount of water at the right time. The goal of irrigation scheduling is to meet the full water requirement of the crop such that water stress is avoided and maximum yields are obtained." An article in The National (UAE) in July 2014 reported about findings of a joint research by the Environment Agency Abu Dhabi (Ead) and New Zealand. Preliminary results showed that most farmers in the UAE over-irrigate, to an extent that some farmers apply 2.5 times the amount suggested by the UN Food and Agriculture Organization for irrigation of date palms, thinking that the trees will be in good condition if they receive more water. It should be noted, that in the contrary, over-irrigation can have negative impacts on the plants and on the environment through leaching of nutrients away from the root zone and into the aquifer and reducing the oxygen level in the soil below optimal values for plant growth, and may lead to root rot and fungal infections. On the other hand, some farmers under-irrigate, which may lead to plant stress, yield reduction and unavailability of applied fertilizers to plant roots. Irrigation scheduling aims at applying just the right amount of irrigation water for plant growth. Irrigation scheduling consists of two components; the first is to determine the crop water requirements, while the second is to estimate the right time to supply the water to plants.