Water Requirement of Field Crops Estimated from Total Solar Radiation

Abstract
The proportion of the incident solar energy used in the evapotranspiration process is a measure of the water requirement of plants. It has been found that in Hawaii approximately 60 per cent of the insolation is used in evapotranspiration during a 12-mo period of alfalfa production. Monthly water-requirement estimates were made from the empirical equationwhere W = water requirement in inches per month, and S = solar radiation in calories per square centimeter per month.