| Abstract | Irrigation to increase crop production in humid areas has great potential. To optimize irrigation scheduling, hence irrigation system, dependable precipitation and potential evapotranspiration based on
long term data analysis must be determined. One of the means useful in obtaining this objective is through a computer program.
A developed model computes the dependable precipitation and potential evapotranspiration at varying degree of risks from more than twenty years of past records. Then irrigation intervals, net irrigation for crop growing season for three crops namely upland rice, sorghum and maize,
for four provinces of Thailand, were computed, by using t he dependable precipitation and evapotranspiration on the basis of expectation of occurrence on four years out of five.
The model needs, field capacity of soil in the region, initial soil
moisture level at the time of planting, available soil water for the crops, crop coefficient s of crops and monthly mean temperature, monthly
mean relative humidity and daily rainfall of long term past records. It computes the daily soil moisture balance for deciding when t o irrigate and how much to irrigate. The model was applied to four provinces of Thailand, namely, Lop Buri, Kanchana Buri, Suphan Buri and Prachin Buri. The ability of the model to predict the irrigation intervals net irrigation requirements per irrigation and total net irrigation requirement for given soil crop combination was stated. |