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Abstract
Field experiments were conducted at Clemson University in 1975, 1976, 1977, and 1978 to study the accuracy of the heat unit system in predicting maturity date of snap beans. The growing-degree day method was found to be unreliable. Indications were that other environmental factors, in addition to temperature, affected the maturity of this crop. The available soil moisture for each of 10 plantings grown under natural rainfall varied greatly. Because of the unreliability of the heat unit method, it was decided to integrate the available soil moisture parameter into the degree day method. The formula that gave the smallest coefficient of variation was one using the daily heat unit multiplied by a ratio of the available soil moisture to a constant soil moisture value. Predicting the maturity of snap beans was improved by integrating available soil moisture into the heat unit system.