A NONCONVENTIONAL METHOD FOR ESTABLISHING UPLAND CROPS FOLLOWING LOWLAND RICE IN SATURATED SOILS

A novel technique was tested for establishing upland crops in saturate d paddy soils. It is based on the observation that deep planting in we t soil is feasible if the seed holes remain open to maintain an adequa te gaseous exchange pathway to the soil surface. Three field experimen ts were conducted to compare the performance of this 'plunger planter' seeding method against five other methods to establish mungbean (Vign a radiata (L.) Wilzeck) following rainfed rice (Oryza sativa L.). The experiments were conducted on a silty clay Tropaquept during the 1990 and 1991 dry seasons (DS) at the International Rice Research Institute . Planting depths from 2 to 14 cm did not significantly affect seedlin g emergence (which varied from 88-97%) or grain yield. The apparent op timum depth was 6-8 cm. A needle like point attachment to the end of t he plunger increased mungbean stem diameter and facilitated vertical r ooting, but had no significant effect on seedling emergence or yield. Plunger planting (PP) was successful at 50% soil moisture content (g/g ). The other seeding methods could only be employed at a soil moisture content of 34% or less. Grain yields with PP in the 1990 DS (1.3-1.6 t/ha) were significantly greater than with all other methods (yield ra nge of 0.4-0.8 t/ha). In the 1991 DS, yields with PP (2.2 t/ha) exceed ed those with the other methods by 0.4-0.7 t/ha. Seedling emergence, p lant density at harvest, and total dry matter were significantly (P<0. 01) increased with PP in 1990, but not in 1991 (a season of less sever e water stress). The PP method proved to have promising potential as a means of establishing mungbean in saturated soils, gaining time for g ermination and root growth before soil strength becomes prohibitive to root penetration, and enabling greater water use from deep soil layer s. The plunger planter principle is adaptable to mechanical seeding.