One square meter of rice field uses about 2,000 liters – or the equivalent of 10 drums used in Filipino households – of water from soil preparation to last irrigation. But farmers continuously flood their fields with 3,000 liters (15 to 20 drums) to store water and to lessen their field visits. Farmers believe that bringing more water to their fields will give them more yield.
But that is not really how things work, according to Richard Romanillos, science research specialist of Philippine Rice Research Institute (PhilRice) in Los Banos. In fact, farmers can have greater harvests if they use lesser water through controlled irrigation (CI) system.
PhilRice brought CI this year to different parts of the country, in line with the observance of 2013 as National Rice Year. The CI is a water-saving technique that can be used by the farmers for the Palayabangan Rice Challenge. Also called “Alternative Wetting and Drying,” it is a new irrigation strategy that reduces the use of water by as much as 35% and other farm inputs like oil, fuel and labor, without the danger of a decrease in yield.
Provinces visited in July included Laguna, Pampanga, and Nueva Ecija.
A typical irrigation system has different structures and devices for supplying and applying large amounts of water to produce and sustain crops. Farmers create ditches or canals that carry the irrigation water to the field. In dry regions where there is a little chance of rainfall, irrigation takes the place of the rainfall. On the other hand, in areas where there is a frequent but uncertain rainfall, irrigation prevents drought.
One way of applying irrigation water is through flooding, done by covering the field with water several inches high until the ground is soaked. But according to Francis Austero, another science research specialist at PhilRice Los Banos, the amount of water depends on the soil type. Sandy soil, for example, takes up water faster than the clay or loam, which means it needs more water. Farmers, however, keep on flooding their fields no matter what soil type they have because of their belief that their plants need more water to grow.
The United Nations Food and Agriculture (UNFAO) estimated that the average water availability for this year in the Asia-Pacific is 2,970 cubic meters per person. With 70% used for agricultural services, many countries, including Southeast Asia, will experience water shortage by 2025.
The truth behind flooding rice fields
While rice can still grow with its roots submerged in water, it doesn’t grow that well unlike “when its roots are able to get oxygen from direct contact with air,” according to Romanillos. “Ang gusto ng palay natin, yung hindi masyadong nabababad sa tubig,” he added.
Aside from wasting water, continuous flooding can cause delayed plant growth, leaching, lowering zinc levels, and global warming brought on by high amount of methane gas released during water evaporation. Methane is a colorless, odorless, and flammable greenhouse gas released mostly by industrialized sectors, and which absorbs infrared light released by Earth from solar radiation. The absorbed infrared light is sent back to Earth in the form of heat, and too much heat will disrupt climate order.
Rice fields with very dry surfaces look alarming, leading many to believe that plants might die. But according to Austero, this is the right way to plant rice.
The benefits of controlled irrigation
During the first three months when the plant starts growing, the soil must be moist but not necessarily flooded. Water is applied only for weeding. It will then be left to dry to the point of surface cracking to allow oxygen to enter the soil and reach the roots. This is to provide enough oxygen for the flowering stage. Also, drying is recommended because when the field is not flooded, the roots need to grow longer to reach for water. On the other hand, if the field is flooded, the roots will become “lazy” and dependent on water which limits their growth and their ability to get nutrients from the soil.
The “golden kuhol attack” will also be minimized if there will be a little water in the field.
Though rice planting doesn’t require too much water and continuous flooding, Romanillos said that there are certain critical stages of the plant growth where more water is needed.
According to Austero, during the flowering stage when grains start to develop and multiply, a thin layer of water (one to two centimeters high) should be applied and maintained. More water will be needed when the time comes to apply fertilizer so that the fertilizer will dissolve faster. Later, the field should be dried completely 25 days before harvest to get uniform fully-developed rice plants.
To lessen the frequent flooding, CI uses a special device called “observation well,” a plastic tube or bamboo measuring 20 cm long and 10 cm wide. Placed in the field 30 days after soil preparation, it serves as a tool that will tell the farmers if the field needs water or not.
But the use of an observation well is just a guide for farmers who are not familiar with the type of soils they have, according to Austero. Being dependent on this device will help farmers to estimate how much water they will put to their fields, and when to irrigate. After a year of using the tube, the farmers should have learned proper water level management, and able to save water even without the observation well.
The use of the observation well is effective since it promotes saving water, while it can still be saved, Given current global water shortage. Romanillos said now is the perfect time to use CI.
CI, however, is not just about the use of observation well. Austero said that it is “a process and the well is just a part of the process.” There are other water-saving irrigation techniques available to farmers, and CI is just one of them, resulting from several field tests conducted by PhilRice in Nueva Ecija.
CI around the Philippines
PhilRice targets farms with limited water supply and those that produce unhealthy rice crops for the CI project. It has partnered with different agencies, such as the National Irrigation Administration (NIA) and International Rice Research Institute (IRRI), for the awareness campaign and promotion of the CI technology.
Romanillos mentioned that from their field visits, farmers, especially first-time CI users, were very convinced of this technology.
“Yung mga farmers na nakakausap namin, sinasabi nila na ito na lang ang gagamitin nila sa irigasyon dahil mas magaan ang trabaho. Hindi na sila nag-aaway-away at nag-aagawan dahil sa tubig, imbis nagbibigayan na sila,” he said. (Maria Isabel Almenteros)