Rice is one of the most important food crops in the world, and staple for more than half of the global population. Looming water crisis, water-intensive nature of rice cultivation and escalating labour costs drive the search for alternative management methods to increase water productivity in rice cultivation. Direct seeded rice (DSR) has received much attention because of its low-input demand. It involves sowing pre-germinated seed into a puddled soil surface (wet seeding), standing water (water seeding) or dry seeding into a prepared seedbed (dry seeding). In Europe, Australia and the United States, DSR is highly mechanised. The development of early-maturing varieties and improved nutrient management techniques along with increased availability of chemical weed control methods has encouraged many farmers in the Philippines, Malaysia, Thailand and India to switch from transplanted to DSR culture. This shift should substantially reduce crop water requirements, soil organic-matter turnover, nutrient relations, carbon sequestering, weed biota and greenhouse-gas emissions. Still, weed infestation can cause large yield losses in DSR. In addition, recent incidences of blast disease, crop lodging, impaired kernel quality and stagnant yields across the years are major challenges in this regard. In this review, we discuss the experiences, potential advantages and problems associated with DSR, and suggest likely future patterns of changes in rice cultivation.

Rice direct seeding: Experiences, challenges and opportunities

Sub-Saharan Africa (SSA) faces multiple problems. The main one is improving the lives of the 30% of its population that suffers from extreme poverty and food insecurity. As more than 70% of the population lives off farming and related activities, agricultural development will have to play a major role in improving this situation. Fortunately, Africa has an abundant supply of natural resources that can support a huge expansion in food, specifically rice production. Because of strong demand, rice area expansion in SSA is larger than for any other crop. Total milled rice production increased from 2.2 million Mg in 1961 to 9.1 million Mg in 2004. Rice imports into SSA also increased from 0.5 million Mg of milled rice in 1961 to 6.0 million Mg in 2003 and SSA currently accounts for 25% of global rice imports, at a cost of more than US$1.5 billion per year. Therefore, many African governments accord high priority to developing their local rice sector as an important component of national food security, economic growth, and poverty alleviation. The abundant supply of agroclimatically suitable wetlands (~239 million ha) and water resources can support a large expansion in rice area and productivity. Currently, less than 5% of the potentially suitable wetlands are planted with rice because of various constraints. Expansion and intensification of rice cultivation in SSA will not compete with other crops in terms of land and water resources because, during the rainy season, only rice can be grown on low-lying wetlands, including inland valleys. In addition, the labor-intensive nature of rice cultivation will provide additional sources of work and income to the rural poor, especially women. Should labor shortages become acute, however, appropriate mechanization can be considered. Small farmers want to earn money from rice farming, but lack modern inputs and capital to fully exploit their rice lands as these items are limited or not available. This is where an innovative public–private partnership is desirable to support the intensification of rice farming. Rice is cultivated in four ecosystems of SSA: dryland (38% of the cultivated rice area), rainfed wetland (33%), deepwater and mangrove swamps (9%), and irrigated wetland (20%). Many abiotic stresses (drought, flood, and variable rainfall; extreme temperatures; salinity; acidity/alkalinity and poor soils, soil erosion, and high P fixation) and biotic constraints [weeds, blast, Rice yellow mottle virus (RYMV), and African rice gall midge (AfRGM)] limit rice production on the continent. The changing climate is expected to further aggravate the abiotic constraints and reduce rice yields in all ecosystems. Rice production is also restricted by many technical, management, socioeconomic, health, and policy constraints. The constraints to irrigated wetland rice in the Sahel of SSA are similar to those faced by Asian farmers in the 1960s; therefore, well-tested irrigated rice technologies from Asia and elsewhere are being introduced and adapted to local conditions to obtain fast returns on investment. For rice in irrigated wetlands in the humid and moist savanna zones, rainfed wetlands, and drylands, locally developed NERICA (new rice for Africa) varieties and production technologies are being tested in target environments. The progenies of Oryza glaberrima and O. sativa subspecies indica are better adapted to rainfed and irrigated wetlands, while those of O. glaberrima and O. sativa subspecies japonica are more suited to rainfed drylands. In addition, research is ongoing to tackle SSA-specific problems such as RYMV and AfRGM and to develop efficient crop management technologies. Currently available best management practices (integrated crop management options) for different rice ecosystems are shown in Table XV. Additional support through the provision of technical advice through revamped national RD a supply of good-quality seed and other inputs, including farm credit; and enabling policy are needed for profitable and sustainable intensification of rice cultivation in SSA. It is also critical to organize preventive health measures for farmers against wetland-related diseases (malaria, bilharzia, and so on), protect certain natural wetlands (e.g., with bird sanctuaries), preserve mangrove forests in strategic coastal belts and rich peats in inlands, and use chemical inputs efficiently to minimize pollution and maintain environmental quality while intensifying rice production. Anticipatory research is needed to tackle the impacts of changing climate on rice farming and the environment. Modern information and communication technologies (ICTs) can be exploited to reach out to farmers in remote areas and to deploy technologies effectively. In addition, the development of innovative private–public partnerships and the organization of farmers into user-groups will enhance the training, farmer education, and technology adoption required for intensive commercial rice farming.

Increasing Rice Production in Sub-Saharan Africa: Challenges and Opportunities

Rice and wheat are the staple foods for almost the entire Asian population and therefore they occupy a premium position among all food commodities. The era of the Green Revolution started during the early 1970s with wheat and rice and since then the rice–wheat cropping system of the Indo-Gangetic Plains has played a significant role in the food security of the region. However, recent years have witnessed a significant slowdown in the yield growth rate of this system and the sustainability of this important cropping system is at risk due to second-generation technology problems and mounting pressure on natural resources. Traditional cultivars and conventional agronomic practices are no longer able to even maintain the gains in productivity achieved during the past few decades. Demand for food is increasing with the increasing population and purchasing power of consumers. The rice–wheat cropping system is labor-, water-, and energy-intensive and it becomes less profitable as these resources become increasingly scarce and the problem is aggravated with deterioration of soil health, the emergence of new weeds, and emerging challenges of climate change. Therefore, a paradigm shift is required for enhancing the system's productivity and sustainability. Resource-conserving technologies involving zero- or minimum-tillage in wheat, dry direct seeding in rice, improved water- and nutrient-use efficiency, innovations in residue management to avoid straw burning, and crop diversification should assist in achieving sustainable productivity and allow farmers to reduce inputs, maximize yields, increase profitability, conserve the natural resource base, and reduce risk due to both environmental and economic factors. A number of technological innovation and diversification options have been suggested to overcome the system's sustainability problems but some of them have not been fully embraced by the farmers as these are expensive, knowledge-intensive, or do not fit into the system and have resulted in some other unforeseen problems. Different concerns and possible strategies needed to sustain the rice–wheat cropping system are discussed in this review on the basis of existing evidence and future challenges.

Productivity and sustainability of the rice-wheat cropping system in the indo-gangetic plains of the Indian subcontinent: Problems, opportunities, and strategies

Increasing the productivity of the rice–wheat (RW) system in north-west India is critical for the food security of India. However, yields are stagnating or declining, and the rate of groundwater use is not sustainable.

Many improved technologies are under development for RW systems, with multiple objectives including increased production, improved soil fertility, greater input use efficiency, reduced environmental pollution, and higher profitability for farmers. There are large reductions in irrigation amount with many of these technologies compared with conventional practice, such as laser land leveling, alternate wetting and drying (AWD) water management in rice, delayed rice transplanting, shorter duration rice varieties, zero till wheat, raised beds, and replacing rice with other crops. However, the nature of the irrigation water savings has seldom been determined. It is often likely to be due to reduced deep drainage, with little effect on evapotranspiration (ET).

Reducing deep drainage has major benefits, including reduced energy consumption to pump groundwater, nutrient loss by leaching, and groundwater pollution. The impacts of alternative technologies on deep drainage (and thus on irrigation water savings) vary greatly depending on site conditions, especially soil permeability, depth to the watertable, and water management. More than 90% of the major RW areas in north-west India are irrigated using groundwater. Here, reducing deep drainage will not “save water” nor reduce the rate of decline of the watertable. In these regions, it is critical that technologies that decrease ET and increase the amount of crop produced per amount of water lost as ET (i.e., crop water productivity, WPET) are implemented. The best technologies for achieving this are delaying rice transplanting and short duration rice varieties. The potential for replacing rice with other crops with lower ET is less clear.

Randhir S. Mehla

Papers

Technology Options for Rice in the Rice–Wheat System in South Asia