Use of computers in consumptive water use and irrigation scheduling [FAO irrigation management model - CROPWAT based on field data].

Irrigation scheduling is an essential means to achieve better water management. Most irrigation scheduling techniques are developed for sophisticated management condition, using direct or indirect soil moisture measurements (tensiometers, water budget methods) as a base for timing of irrigations. They require frequent observations and close monitoring and maintenance. Such techniques can often not be applied on a practical scale for small farm holdings and under different socio-economic condition. To achieve a better watering of crops, simple and practical guidelines need to be developed which take into account not only the water use by the crops but also the field irrigation method and water supply system. The FAO irrigation management model tested in a number of FAO field projects allows the development of indicative irrigation schedules from average climatic and agricultural field data, taking into account the specific irrigation management conditions of the irrigated crop. The model allows the assessment of efficiency of prevailing irrigation practices in terms of water efficiency and yield reductions from readily available and obtained field data. An example is given of how to develop improved irrigation practices from readily available field data from a FAO field project in Buner, Pakistan. The calculations carried out by the PC computer-based computer CROPWAT include, in addition to irrigation scheduling, crop water requirements and scheme irrigation supply from basic climatic and crop data.