Water is undoubtedly one of the most precious resources. Like all living things, rice needs water. Rice does not only need water for its growth and development but also to be able to produce good yields. There is an estimated 150 million hectares of rice lands worldwide, 50% of which are irrigated, usually with continuous flooding for most of the crop season. In many irrigated areas, rice is grown as a monoculture with two rice crops per year.
However, water from agriculture worldwide is also becoming increasingly scarce. The causes can be diverse and location-specific but include its decreasing physical availability through falling groundwater tables and silting of reservoirs, decreasing quality like chemical pollution and salinization, malfunctioning of irrigation systems, and increased competition from other sectors like urban and industrial users.
It is estimated that by 2025, 15-20 million hectares of irrigated rice will suffer from some degree of water scarcity. Aware of the precarious state water resources are facing and concerned about what its impact will be on rice production systems, IRRI continually explores, develops, and promotes strategies and technologies which farmers could adapt to help them improve their water management and productivity. IRRI is working on five areas which could either be directly or indirectly related to water and rice.
Owing to increasing irrigation costs in addition to water becoming more and more scarce, rice farmers know how extremely crucial it is to make efficient use of water. IRRI has developed a basket of practices and strategies to help farmers reduce water losses from their fields, and make more productive use of water.
In the past 15-20 years, there has been considerable progress in both developing and promoting practical management guidelines to reduce irrigation input in puddled transplanted rice. This includes constructing field channels to convey water to individual fields (or small groups of fields) in canal irrigated areas instead of field to field irrigation, good bund preparation and maintenance, good leveling, tillage before land soaking to help close cracks rapidly, and maintaining a shallow floodwater depth (minimum of about 5 cm.).
Meanwhile, in some regions facing mild water scarcity (where there is still enough water to flood fields regularly although not to keep them continuously flooded), safe alternate wetting and drying or AWD, which allows the soil to dry for a few days between irrigations, has tremendously helped farmers in some areas with limited water to continue rice farming. In some cases, farmers were also able to expand areas where irrigated rice can be grown.
Dry seeded rice with safe AWD is also targeted in areas with mild water scarcity, with the goal of getting the same yields as that of continuously flooded and puddled transplanted rice. Dry seeded rice is sown like wheat into tilled or non-tilled soil and with safe AWD, fields are irrigated frequently to try and avoid water deficit stress although they are also not continuously flooded.
Aerobic rice production is another technology which is also dry seeded but targeted at situations with greater water scarcity (situations where it is no longer possible to grow puddled transplanted rice or frequently irrigated direct-seeded rice because of physical or economic water scarcity). IRRI began developing the System of Aerobic Rice with Chinese partners in 2000.
Crop models are useful in studying the soil-crop-atmosphere system as affected by changing weather and agronomic practices like sowing date of crops, fertilizer application, and scheduling of irrigation. Using well-calibrated and validated crop data and historical weather data, scenarios can be ran showing the likelihood of different outcomes, which can help in making management decisions. Moreover, they can also be used to evaluate and optimize water, fertilizer, and management practices under different agro-soil-climatic environments.
In collaboration with the Wageningen University, IRRI developed a rice growth simulation model called ORYZA2000 for potential, water-limited, or nitrogen-limited conditions. The model has been calibrated and validated for more than 17 varieties covering tropical and temperate high-yielding inbreds, aerobic rice cultivars, and hybrids in different environments of several countries (Philippines, Indonesia, north and south China, Japan, Thailand, Korea, India, Iran).
ORYZA2000 has been mainly used to explore impacts on crop (development, growth, yield); components of water balance and various measures of water productivity; range of management interventions (irrigation, nitrogen application, crop establishment); and environments (climate, soil types, groundwater depth). It has also been used to identify yield gaps, limiting factors behind the yield gaps, and management interventions to close these gaps in both irrigated and rainfed systems.
ORYZA2000 is continuously being developed and improved from crop model to cropping systems model. Moreover, it is also being targeted to accurately estimate rice production under potential and abiotic stress conditions, and to give precise management of water and nitrogen in the future.
A cropping systems model can allow researchers or those in the field to study a total cropping system rather than individual crops in isolation. They can be used to evaluate crop sequence options along with the long-term changes, and then optimize rotation and cropping intensity; tillage; residue retention; and nutrient and water management (for high use efficiency and yield), low environment impacts; and climatic vulnerability. ORYZA2000 model was recently incorporated into the Agricultural Production System Simulator and is being integrated with Decision Support Systems for Agro-technology Transfer to allow simulation of rice-based cropping.
Rice environments also provide a unique – but as yet poorly understood – ecosystem services such as the regulation of water and preservation of aquatic and terrestrial biodiversity. Asides from these services, rice systems also play a central role to the culture and lives of those who eat rice as a staple food and see it as an important source of income and livelihood.
To those who mostly subsist mostly on rice, it affects daily life in a number of ways and the social concept of rice culture gives meaning to rice beyond its role as an item of production and consumption. Many traditional festivals and religious practices are associated with rice cultivation and rice fields are valued for their scenic beauty.
Meanwhile however, flooded rice fields produce more of the greenhouse gas methane but less nitrous oxide. They also contribute very little nitrate pollution of groundwater, and use relatively little to no herbicides. Increasing water scarcity however, is expected to shift rice production to more water-abundant delta areas and lead to less flooded conditions in rice fields as well as the introduction of upland crops that do not require flooding. These changes will have environmental consequences and will affect the traditional ecosystem services of rice landscapes.
Although there is little information on how water scarcity will affect the ecosystem services of rice lands, there is a growing recognition throughout the rice-growing world that a better understanding of the ecosystem services of rice environments is needed.
Coastal environments are said to be home for some 40% of the world's population with people living within 100 km of the sea and these areas continuously face pressure. IRRI focuses on sustainable resource management of coastal lands through integrated land and water management for rice farmers within these areas. Apart from helping them sustainably improve their livelihoods in these environments, IRRI looks at the interaction among rice, fishery, and aquaculture production systems while also suggesting socioeconomic and environmental impact interventions.
Together with the International Water Management Institute (IWMI) and a number of partner institutions, IRRI has helped assess the positive impacts of engineering structures like embankments and polders in Bangladesh built by its government for salinity and flood control. Some of the benefits brought by the collaborative project include high-yielding varieties that could be grown in the rainy season (aman).
In addition, water management options and high-yielding, short-duration varieties for increasing cropping intensity were tested and promoted through the collaborative project. They raised the annual rice yield more than 100% and also almost doubled farmers' benefits compared with traditional practices. It’s been reported that aman-boro rice cropping was adopted by thousands of Bangaldeshi farmers on a large scale.
Also, the Bangladesh Water Development Board used the project water management technology as a cornerstone for its water management strategy in the coastal zones of Bangladesh.
Meanwhile in Vietnam, IRRI developed decision support modeling tools and water and land resource management strategies to accommodate the diversification of rice-based and brackish water aquaculture-based farming systems in its Mekong Delta. Agricultural lands in brackish-water zones are generally said to be less productive compared with those from freshwater zones.
The strategies have greatly helped and contributed to the annual growth of 15.7% in Bac Lieu Province. The tools take into account salinity and acidity dynamics of the delta canal or drainage networks, where there were large areas of acid sulphate soils (an unwanted effect that comes with reclaiming brackish-water intertidal swamps).