Crop establishment of legumes in rainfed lowland rice-based cropping systems

Poor crop establishment is one of the major limitations to the production of grain legumes after rice (Oryza sativa L.) in rainfed lowland rice-based cropping systems. The success of germination and emergence of mungbean (Vigna radiata (L.) Wilzek), soybean (Glycine max (L.) Merr) and peanut (Arachis hypogaea L.) planted in zero tilled (ZT), zero tilled combined with mulch application (ZTM) and tilled soils (T) were investigated in a crop establishment trial as a function of sowing delay. Sowing delay was used as a surrogate for soil-water content. This experiment was conducted under a rain-shelter to ensure continuous and progressive drying conditions. A dibbling trial using the same legumes was conducted concurrently and subjected to the prevailing climatic conditions. Germination and emergence success rate of the traditional dibbling method was compared to dibbling incorporating depth control and seed cover. Both experiments were conducted towards the end of the 1994 rainy season in a Vertisol soil at Ngale and an Andosol soil at Jambegede, in East Java, Indonesia where the season gradually changes from wet to dry season. Mungbean emergence was 93–94% at Ngale and soybean emergence was 84–95% at Jambegede, both in the presence and absence of rain. Peanut emergence was low (50–69%) at both sites. In all three species at both sites, the percentage of seeds that failed to germinate was greater than seeds that failed to emerge, indicating that germination rather than emergence was limiting. Seed rot caused by fungal attack and poor imbibition associated with poor seed–soil contact (observed as intact seeds) were the main constraints for the success of germination of mungbean, soybean and peanut. The failure to emerge was mainly caused by seedling rot and the failure of hypocotyl and radicle to penetrate the hard soil, observed as a curling of the hypocotyl. Cultivation at Ngale on a Vertisol resulted in excessively cloddy soil, which in turn resulted in a significant decrease in germination and emergence. The application of straw mulch had little effect on the emergence of legumes on this soil. The use of depth control and application of seed–soil cover did not have a significant effect. Hence the traditional dibbling method where depth of planting ranged from 4 to 7 cm without seed cover was found to be appropriate for planting mungbean and soybean. Germination and emergence of peanut was improved with the application of soil cover and the dibbling stick had a spike added to the tip to assist the root to penetrate the hard compacted soil.