Use Less Water and Still Get Good Harvest
Experts say that from land preparation to the last irrigation, one square meter of rice field that usually yields 0.5 to 0.75 kg of rice uses around 2,000 liters or 10 drums of water. However, when farmers continuously flood their fields, 15 to 20 drums of water are used.
Farmers do not know that continuous flooding and a water level in the field higher than 7 cm results in too much percolation, seepage, and even runoff, experts say. It also causes delayed growth and reduced tillering because the reduced oxygen level in the root zone impedes root development.
Continuous flooding also triggers some yield-reducing factors like too much leaching, soil nutrient imbalance (zinc deficiency), lodging due to weak plant base and anchorage, and global warming due to high methane gas emission. These factors result in lesser and untimely water in fields near the tail-end, high water-use in gravity irrigation systems, and too much water cost in pump irrigation systems.
This is why a farmer who lives near the PhilRice central experiment station in the Science City of Munoz, Nueva Ecija immediately followed the controlled irrigation technique when he learned about it. Farmers serviced by a pump irrigation system in Canarem, Victoria, Tarlac also follow this technique.
The National Irrigation Administration (NIA) has also introduced controlled irrigation in three additional systems servicing 150 farmers. At the Upper Pampanga River Irrigation System, this new technology developed by PhilRice with the collaboration of NIA and International Rice Research Institute (IM) is now being introduced to farmers cultivating about 80,000 hectares.
BENEFITS
In a technology bulletin produced by PhilRice, its experts said controlled irrigation offers the following benefits:
• Reduces water use in rice production by 16 to 35 percent without decreasing grain yield
• Aids in proper seed germination and seedling survival, tillering, and grain uniformity
• Increases the efficiency of the plants in using soil nutrients and applied fertilizers
• Helps in controlling weeds
• Minimizes golden kuhol attack with excellent water level control
• Significantly reduces irrigation cost in pump-irrigated areas
• Stabilizes soil and plant base
• Facilitates farm mechanization, especially harvesting and hauling of harvests
• Reduces farm inputs such as fuel, and labor
• Provides for timely water needs of farms at the tail-end of an irrigation system
Aside from these benefits, field trials conducted by PhilRice in the dry season of 2007 showed that the performance of mini-combine harvester is more efficient in a field where controlled irrigation was followed than in flooded fields. It is because the stable soil condition under controlled irrigation facilitates the operation of machine and makes harvesting faster.
TARGET USERS
Two kinds of farms would benefit much from controlled irrigation.
1. Farms with limited water supply or those with supplemental irrigation such as near tail-end of irrigation system and those using small water impounding systems, small farm reservoir, communal irrigation systems, or pump irrigation system (shallow tube or deep well).
2. Farms near main canals with the following characteristics: unstable plow layer or hard pan that causes difficulty in land preparation, harvesting, and hauling; nutrient imbalances like zinc and sulfur deficiencies; and poor root growth due to accumulation of excessive organic acids from decomposing materials as a result of insufficient soil aeration.
WATER SAVING PRACTICES
A number of management practices before and after planting can help save water and these are the following:
1. Fix farm dikes and ditches before or during the first irrigation or before the onset of the rainy season;
2. Use appropriate planting method based on water availability and ability to control it;
3. Plow immediately after the first irrigation. Do not allow newly irrigated field to stand unplowed for several days;
4. Use just enough irrigation water during land preparation to facilitate soil puddling, organic matter decomposition, and land leveling;
5. Establish and level the field’ very well. There should be uniform distribution in the whole paddy at 2 to 3 cm depth of water;
6. Shorten land preparation: one to two weeks for non-weedy or dry plowed fields; three weeks for fields with fresh rice stubbles; and four weeks for fields with much weeds and stubbles;
7. Apply minimal irrigation water (about 2 to 3 cm) until 30 days after planting to promote better seedling establishment and weed control;
8. When using herbicide during the first month after planting, follow the water management scheme required by the herbicide being used;
9. Apply controlled irrigation techniques by using an observation well. This facilitates the monitoring of water status in the field and helps determine the right timing of irrigation.
HOW TO MAKE, INSTALL, AND USE AN OBSERVATION WELL
1. Make an observation well out of a plastic tube or bamboo measuring 25 cm long with at least 10 cm diameter. When using a bamboo, make sure there is no node within the cut material.
2. Designate one end of the tube as “top”. From the topmost part of the tube, make a circumferential mark at 5 cm and 10 cm and label them with “wet season” and “dry season,” respectively.
3. Use a manual or electric drill with 3 to 5 mm diameter to make holes on the tube every 3 cm horizontally or vertically.
4. Keep a 5 cm distance between holes vertically or horizontally.
5. After planting, select a representative site in your field where the observation well can be installed. An ideal site is located 1 to 2 meters from the paddy dike to facilitate regular observation of the paddy water. For farms with uniform conditions among paddies, only one observation well per hectare is needed. On the other hand, farms with heterogeneous conditions or paddies with different soil texture or elevation need one observation well per category (soil texture or elevation).
6. In the selected site, press the tube vertically against the ground as much as you can and then pull it back completely.
7. Remove the soil inside the tube after lifting it above the ground.
8. Repeat the previous two steps until the marker “wet season” or “dry season” on the tube is exactly levelled against the ground surface.
9. Fix the observation well vertically and check if the label for a given season is levelled against the ground surface.
Using the observation well
1. When irrigating during the wet season, flood the field until the water reaches the topmost portion of the tube. During the dry season, flood the field until water rea6es 5 cm below the ground surface.
2. Irrigate again using a controlled irrigation when water is no longer visible in the observation well .
REMINDERS
1. Start irrigating the field based on the observation well 30 days or four weeks after planting. At this time, seedlings are well established and the primary weed control measures were done already.
2. Start irrigating in the afternoon (3 to 4 pm) to minimize evapo-transpiration losses and to take advantage of cooler irrigation water.
3. During the tillering period, the rice plants and soil are healthy if there is enough oxygen to balance the various physiochemical and biological activities in the rhizosphere, hence do not flood continuously.
4. During flowering, maintain 5 cm depth of standing water in the paddy to avoid the development of unfilled grains due to lack of water.
5. Last irrigation should be one week before harvest for light textured soil and two weeks before harvest for heavy textured soil.
6. Practice shallow rotavation after harvesting. This helps conserve residual moisture and minimizes the development of wide and deep cracks during the dry season fallow.