Research to improve water-use efficiency in rice

 James Quilty, Arvind Kumar, Crisanta Bueno, and Sudhir Yadav   |  

IRRI and its partners will continue to develop water-saving technologies to improve the livelihoods of rice farmers and their communities, particularly in rice-growing regions threatened by water shortages

Rice seedlings emerging from a field using reduced-tillage DSR. (Photo: IRRI)

Rice seedlings emerging from a field using reduced-tillage DSR. (Photo: IRRI)

From its establishment, the International Rice Research Institute (IRRI) has made tremendous efforts to ensure that national institutes across many countries have access to the improved technologies developed at its Zeigler Experiment Station (ZES). IRRI was established before climate change and competition for water resources became widely accepted as significant risks to agricultural production. Therefore, the initial focus of water-use efficiency research at IRRI was on rainfed rice production systems.

Alternate wetting and drying
However, today, one of the most widely recognized water-saving technologies developed and disseminated by IRRI, in collaboration with many partner organizations, is alternate wetting and drying (AWD). This is a simple but effective irrigation scheduling technique that reduces both the water inputs in rice production and greenhouse gas emissions coming from rice fields.
AWD as a water-saving technology combined with improved varieties has been disseminated on a large scale in Bangladesh through collaboration with the Bangladesh Rice Research Institute (BRRI) and with support from donors, including the Asian Development Bank.

This strategy can achieve water savings of 20−25% and can reduce methane emissions by as much as 50%. The water saved through the use of AWD and modern varieties has enabled farmers to plant a third nonrice crop in between two rice crops, thereby increasing the intensification of the rice-based system and the farmers’ income. Thousands of farmers in Bangladesh have been trained on the proper use of AWD and associated mechanized agricultural operations. Efforts have been made through policy dialogues with authorities of the different organizations to develop a mechanism to provide benefits of water saving to farmers, thereby encouraging AWD adoption by farmers.

A tensiometer monitors soil moisture to determine a precise schedule for irrigation instead of using “turn it on and leave it on” practice. (Photo: IRRI)

A tensiometer monitors soil moisture to determine a precise schedule for irrigation instead of using the “turn it on and leave it on” practice. (Photo: IRRI)

The research behind AWD accelerated rapidly at the beginning of the 21st century, but IRRI continues to make significant efforts to improve the water-use efficiency of rice production beyond AWD. In irrigated lowland rice agro-ecosystems, timely and accurate data on the availability and distribution of water resources within irrigation networks and rice fields can help improve the use of irrigation water.

The water science team at IRRI is undertaking research at the ZES with the aim of developing innovative, affordable, and scalable digital technologies for irrigated rice production. This research aims to provide valuable information on water resources to all governance levels of water management within catchments and irrigation networks. To achieve these aims, IRRI has developed a decision tool called AutoMon (Automatic Monitoring). Along with robust data processing and a user-friendly interface, the tool consists of an affordable and robust device that can wirelessly transmit water depth data from within rice fields, and flow and volume data from within irrigation networks.

The tool has been customized for water governance in the Philippines as AutoMonPH and is an integral part of a larger project funded by the Philippine government called WateRice. The outcomes of this research will be improved irrigation management at field, farm, and catchment scales; improved distribution of water resources across irrigation systems; and more equitable distribution of water.

DSR plot seeding using the Wintersteiger Monoseeder. (Photo: IRRI)

DSR plot seeding using the Wintersteiger Monoseeder. (Photo: IRRI)

Direct seeding of rice
Although innovative solutions are being developed to improve the efficiency of water use in irrigated systems, IRRI is also creating opportunities to improve the resilience and productivity of rainfed rice production systems. Increasing water productivity in drought-prone rainfed systems is crucial to food security and to rice farming communities in many regions of South and Southeast Asia, and Africa. The work of IRRI to improve the productivity of rainfed and drought-prone agro-ecosystems is ensuring that the synergies between the genetic diversity in rice and agronomic practices are optimized.

The practice of direct seeding of rice (DSR) into dry soil reduces the need for water in land preparation and allows farmers to plant rice crops before the rains of the wet season arrive. This means that rainfall is used in supporting crop growth rather than in land preparation activities. Planting earlier can also help rice avoid drought that generally occurs late in the wet season in rainfed systems. With this in mind, efforts within the breeding program at IRRI targeting rainfed environments use DSR as the crop establishment method in field trials at the ZES. Embedding this practice in the breeding program helps ensure that both genetics and agronomy work together effectively to achieve the best outcome for farmers.

Mechanized DSR, which can reduce water and labor inputs in rice production, requires the introduction of innovative traits in rice varieties to increase their adaptation to DSR cultivation with minimum water requirements. Developing appropriate traits in modern varieties, including the improved ability of rice to germinate from deeper soil depths with conserved moisture, early vigor, extensive root systems for efficient nutrient uptake under fluctuating soil conditions, lodging resistance, and resistance to nematodes, will improve the capacity of rice to grow under limited water conditions.

Through research conducted at the ZES, quantitative trait loci (QTLs) linking or containing genes that control certain desirable traits have been identified. These include early uniform emergence, early vigor, higher nutrient uptake under soil fluctuations, and lodging and nematode resistance. The marker-assisted breeding experiments conducted at the ZES have successfully introduced many of these traits into elite breeding lines to increase rice adaptation to mechanized DSR.

The sowing depth for DSR can make a significant difference in the performance of a rice crop. In DSR systems, the targeted sowing depth is generally less than 3 cm. This depth aims to ensure that the crop emerges uniformly. Planting rice deeper than 3 cm often causes poor emergence rates and poor uniformity. However, particularly in rainfed systems, the wetting-and-drying cycle of the soil at 3-cm depth can be rapid and extreme. This can make the germinating seed vulnerable to desiccation as the surface layer of the soil dries out after rainfall. Additionally, achieving good rice germination at shallow soil depth requires moisture content at the soil surface that is also sufficient for weed seed germination. Consequently, both rice and weed seeds germinate together, creating an environment in which the emerging rice is immediately competing with weeds for space, moisture, nutrients, and light.

A DSR seedling developed using marker-assisted breeding experiments at the ZES. (Photo: IRRI)

A DSR seedling developed using marker-assisted breeding experiments at the ZES. (Photo: IRRI)

Through the efforts of the rice breeding program at IRRI, sowing depths in DSR systems of 5 cm or more will be an improved option for farmers in the future. Rice varieties capable of emerging from sowing depths as deep as 10 cm are being developed at the ZES as part of the breeding program that targets rainfed environments. Sowing rice at depths of 5 cm or more into a region of the soil profile in which wetting-and-drying cycles are slower than in the top 3 cm helps protect the germinating rice seed from desiccation.

Sowing rice seed into soil moisture below a dry topsoil layer can also provide rice seed with a competitive head start over weeds trying to germinate in the dry soil above. To complement improved seedling vigor, and to ensure system optimization, field experiments on nutrient management and sowing depth, and research on weed control in DSR are ongoing at the ZES.

In February, IRRI and its partners launched the Direct-Seeded Rice Consortium that will explore the process of bringing together a consortium of stakeholders from the public and private sectors that will explore opportunities to maximize the efficiency of DSR, minimize water use, optimize productivity, and ensure the sustainability of rice production systems. At the ZES, the efforts of IRRI and its partners will continue to develop and optimize DSR and other effective water-saving technologies and will create pathways to adoption and impact that can improve the livelihoods of rice farmers and their communities, particularly in rice-growing regions threatened by water shortages.

Dr. Quilty is the head of the ZES, Dr. Kumar leads the rainfed lowland South Asia plant breeding group, Dr. Bueno is an expert in ecophysiology, and Dr. Yadav is a water scientist at IRRI.

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