Drought, submergence, and salinity management

  • About

  • Drought

  • Submergence

  • Salinity

need for stress-tolerant varietiesFarmers who earn a living from areas that are unfavorable owing to problems of flooding, drought, or salinity oftentimes do not get enough rice for the whole year and are mostly steeped in poverty.

By working with many national partners and through a network called the Consortium for Unfavorable Rice Environments (CURE), IRRI develops, tests, and validates crop management options to help farmers cope with drought, flooding, and salinity.

Using a participatory process, we work with farmers who themselves adapt, test, and validate these management options on their farms, providing feedback to IRRI in regards to what suits them or what needs to be adjusted to suit their local conditions or situations.

Wherever possible, these options go alongside stress-tolerant varieties that IRRI continues to develop in collaboration with different partners.

drought-tolerant rice

Drought stress is considered a major constraint to rice production in rainfed lowlands, which cover almost 30% of the world’s total rice area, threatening the livelihood of many poor farmers along with their families.

Drought is estimated to frequently affect 19-23 million hectares of rice lands. Severe and regular droughts affect South and Southeast Asia’s rainfed lowlands, but regional weather patterns, topography, and soil characteristics cause considerable drought-risk variations within and beyond these regions.

Apart from drought, these environments can also be affected by other stresses like submergence, low soil fertility, other soil constraints, and pests. IRRI sees two main strategies for coping with drought. One is by drought escape. This involves either avoiding drought (such as through adapted cropping calendars or planting short duration varieties) or providing access to additional water resources like irrigation.

The second strategy is to moderate drought by reducing unproductive water losses and thereby ‘saving’ water for productive transpiration. This can either be done by dry direct seeding, by adopting aerobic rice production, or by better water and nutrient management.

Because all nutrients are taken up with water, an insufficient amount of it can reduce the nutrient uptake of rice plants, which in turn limits their root growth. By using some fertilizer, roots grow better and get access to more water in the soil.

However, for farmers to make use of this strategy the risk of crop loss due to drought must also be reduced and this can be done with the help of new drought tolerant varieties, aerobic rice, and direct seeding. Bringing all these elements together and adjusting them to farmer needs is an ongoing task for all IRRI researchers working on drought.

the need for submergence-tolerant rice

Too much water is a main constraint to rice productivity in large areas of rainfed lowland ecosystems, resulting in flooding or submergence, which regularly affects some 15-20 million hectares of rice land in Asia.

Short-term flash floods (for up to 2 weeks) can occur at any stage of plant development, sometimes more than once, causing severe yield losses. In direct-seeded rice, submergence after sowing can substantially reduce the establishment of rice crops owing to high sensitivity of existing rice varieties to flooding during germination. In addition, waterlogging or stagnation of 30 to 50 cm for a few months during the growing season is a serious problem in some rainfed areas, and can substantially reduce productivity.

Modern rice varieties are not adapted to these conditions and this is probably the reason these varieties are not widely adopted in areas prone to flooding. As a result, farmers continue to grow their local varieties even though their yield is low. Rice productivity in these flood-prone areas could be enhanced and sustained by combining tolerant varieties with best management practices.

By introducing rice varieties with shorter duration that are also flood-tolerant, farmers can increase the productivity of their farms since they are able to plant earlier, harvest earlier, and when there is still enough moisture, plant another batch of rice or other crops.

Another way of helping is to increase their cropping system intensity to two or three crops per year. This helps reduce dependence on rice produced during the flood-prone season and can increase production to as much as 200%. Usually changes within one season appear small but when farmers move from one season to multiple seasons, the change in their annual harvest can be enormous.

Farmers can also adopt flexible systems to help make their rice farms not only productive but sustainable at the same time. For example, farmers in areas that have too much water during the wet season can opt to raise freshwater fish or prawn alongside the rice. Farmers living in places where salinity is too high during the dry season can raise shrimps instead, and grow rice during the wet season.

need for drought tolerant rice varieties

Salinity and alkalinity orsodicity (soils with high sodium, carbonate, or bicarbonate) also cause problems for rice farmers in irrigated and rainfed areas. In coastal areas, seawater is brought inland during high tides or salt rises from the shallow saline groundwater during the dry season.

In most coastal areas, salinity is high in both soil and water during the dry season. It then decreases over time after the monsoon rains have started. But the salt comes back during the dry season when most of the fields are left barren. Only when freshwater resources are available, can salt-tolerant, short-maturing crops be grown in these areas.

For wet-season rice, the main problems are encountered at the beginning of the season during crop establishment in the months of June to July when soil salinity is still high.

Because rice is highly sensitive to salt stress in its early growth stage, this poses a major problem to rice farmers because transplanted seedlings may all die and establishing a sufficient crop stand becomes very difficult.

Both salinity and alkalinity are encountered in some inland areas. Salt accumulation in these areas is mostly caused by improper irrigation, where oftentimes, excess water is used without proper drainage. In these areas the challenges are even great where salt stress persists throughout the season. Proper reclamation measures are needed to bring these soils back to productivity. This normally involves enormous investment to amend the soils and involves adding gypsum or other chemicals to free salt from alkaline and sodic soils, followed by proper flushing with freshwater and drainage.

Combining salt-tolerant rice varieties with suitable management strategies are crucial for farmers to combat the unwanted effects of salinity on rice plants. Our field tests show that proper nursery management before transplanting and seedling handling, together with nutrient management can substantially improve crop establishment and early growth in salt-affected areas.

Suitable crop, nutrient, soil and water management practices can considerably enhance and sustain productivity in salt-affected areas when combined with salt tolerant varieties. Our research is still developing, testing, and validating best management strategies under farmers’ field conditions.