Predicting soil moisture status and suitable field workdays under tropical conditions

A soil moisture model which estimates daily values of moisture content in the top 300 mm of the soil profile is described. The model was developed by computing evapotranspiration, surface run-off and drainage on a daily basis by using soil characteristics and climatological data. Actual field measurements were carried out in Morogoro, Tanzania to observe the variation of soil moisture content for two consecutive farming seasons. Good agreement was obtained between the predicted values and experimental data. The results show that the model can be extended and used to classify soil moisture data and thus enables one to determine the suitable field working days and non-working days once the soil workability criteria is defined. In this study, a day was found to be suitable for field work when the soil moisture content was at or below 95% of field capacity. Using weather data of the past 11 years, the occurrence of suitable field workdays was determined and the average number of days for soil tillage in Morogoro was established.