Soil drying requirement for mobility of heavy combine harvesters in rice fields

M. Y. Shahrin, K. Ayob and O. Suhaimi

Abstract
Cone index values of 3.0 and 5.0 kg/cm² represent the minimum and ideal soil strength respectively for mobility of heavy combine harvesters in rice fields. Using these values as targets, a study was done to understand the process of soil strength development as induced by natural soil desiccation and lowering of groundwater level. The influence of soil water content on the cone index diminished as the bulk density increased. It is important that soil structure particularly at the hardpan. is preserved to ensure that the bulk density is not reduced. Unless so. intensives oil drying will become necessary for soil strength development A cone index of 3.0 kg/cm² was obtained after 9 days of continuous drying when soil water content was at 0.58 kg/kg and the groundwater level decreased by more than 40 cm. Extended drying to a minimum of 17 days produced a cone index of 5.0 kg/cm² with soil water content at about 0.45 kg/kg and the groundwater level at 65 cm below the soil surface. It is difficult to achieve such rates of soil drying. Therefore, a practical drying strategy has to be adopted.

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