SOIL PHYSICAL CONSTRAINTS TO ESTABLISHMENT OF MUNGBEANS (VIGNA-RADIATA L WILCZEK) IN PADDY RICE (ORYZA-SATIVA L) SOILS

In several rice producing countries, production of upland crops, such as mungbeans (Vigna radiata L. Wilczek), is an important means to save foreign exchange on food imports and to exploit the residual soil wat er following paddy rice (Oryza sativa L.) harvest. Since the soil phys ical requirements for establishment and growth of upland crops are dif ferent from those for paddy rice, this study examined (1) soil physica l properties that may limit mungbean emergence in rice soils, and (2) soil management techniques that will alleviate the soil physical const raints to mungbean establishment. Dry soil conditions and high soil re sistance were the major soil physical constraints limiting mungbean se edling emergence in clay soils in a growth chamber experiment. Since s eedzone water content is high after rice harvest, soil strength was vi ewed as the major constraint to mungbean emergence in paddy rice soils . This hypothesis was tested in a field experiment where tillage pract ices (moldboard plow, no-till), planting techniques (inverted-T, dibbl e, furrow), and delays to planting after rice harvest (1-3, 4-5, 7-8, 11-12, or 14-15 days after field drainage) were used to create varying soil strength conditions. The soil was Maahas silty clay (Vertic Trop aquept). Mungbean emergence and soil strength data showed that the max imum emergence corresponded to soil conditions where soil resistance t o seedling emergence was lowest. There were few benefits from tillage on mungbean emergence. Inverted-T and furrow planting performed best i n tilled and no-till plots, respectively, The optimum time for mungbea n planting was from 1 to 8 days after field drainage for no-till, and from 3 to 5 days after field drainage for tilled soils.