The specific procedure or equationused depends on the availability of specific climatic data needed for thatprocess and the desirable intensity level of managing irrigation water.Ĭhapter 2 describes the processes that affect water use requirements for acrop, field, farm, group of farms, or project level evaluation. It provides nationwide acceptable proce-dures to determine crop water needs. This chapter of the SCS National Engineering Handbook (NEH)provides that current technology. Field evaluations and ground truthing mustalways be used to further refine the estimates used for planning irrigationsystems.

Support for many of the estimatedvalues included in this chapter come from field research and many fieldevaluations over many years.

Todays management of irrigation water requires using the best estimatethat current technology can provide for the determination of crop water useand field irrigation water requirements. The impor-tance of irrigated crops is extremely vital to the public's subsistence. Compe-tition for a limited water supply for other uses by the public require the irriga-tion water user to provide much closer control than ever before. The complete management of irrigationwater by the user is a necessary activity in our existence as a society. Supplemental irrigation is also vital to produce acceptablequality and yield of crops on croplands in semi-arid and subhumid climatesduring seasonal droughty periods. Irrigation is vital to produce acceptable quality and yield of crops on aridclimate croplands.

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