Direct dry seeded rice production technology and weed management in rice based systems

Abstract

In South Asia, rice-based cropping systems account for more than 50% of the total acreage with rice grown in sequence with rice or upland crops like wheat, maize or legumes. In most areas, rice is traditionally grown by transplanting seedlings into puddled fields (henceforth ‘TPR’). There are strong incentives in many parts of S. Asia to promote alternatives to puddled rice cultivation, including: Optimizing system productivity. Puddling is achieved by intensive tillage under ponded water conditions, which serves to break down soil aggregates, reduce macro-porosity, disperse the clay fraction, and form a dense zone of compaction (i.e. ‘plough pan’) at depth. In addition to facilitating transplanting, puddling serves several functions including weed control and to reduce deep percolation losses of water. Although the soil physical changes from puddling can be favorable for rice cultivation, they can also be very detrimental to the growth of subsequent non-rice crops by causing temporary water logging, poor crop emergence, and restricted root development. Reducing irrigation requirements. Around 30% of the total water (1400-1800 mm) required for rice culture is dedicated to puddling and transplanting. In cases where deep percolating waters are not recovered (e.g. in canal irrigated areas), these constitute true losses from the system. Water availability for agriculture is becoming increasingly scarce because of competition with other economic sectors and from accelerating demands for direct human consumption. Per capita availability of water has declined by 40-60% between 1955 and 1990 in several Asian countries, and in some areas this trend is accelerating. For areas with groundwater-based systems, pumping costs and energy consumption are directly related to the number of irrigations. Hence puddle rice cultivation aggravates the energy crisis in many parts of the Indo Gangetic Plains (IGP) and elsewhere. Reducing labor requirements. Timely transplanting of rice is based on the premise of cheap and readily available labor. Across S. Asia, labor scarcity is no longer a projection, but rather a hard felt reality. Rice production technologies that require less labor are urgently required. Fortunately, alternative establishment practices for rice such as direct seeding into dry, unpuddled soil (henceforth ‘DSR’) are suitable for different production environments in South Asia and may alleviate many of the problems associated with TPR. In South Asia, DSR is already practiced in many medium deep- and deep-water rice ecologies of eastern Gangetic plains of India and Bangladesh; and on terraced and sloping lands in the north-east and Western Himalayan region and the Ghats along west coast of India. The acreage of DSR in India, Pakistan and Bangladesh is 14.2 million hectares (M ha) of the total rice acreage of 55.3 Mha (ca. 26%). Without proper management, however, DSR productivity can be low. Common factors contributing to poor yields include supra-optimal seeding rates (60-100 kg/ha), increased weed competition, insufficient fertilizer use, and lack of improved cultivars selected for good stand establishment with direct seeding.