By Melpha M. Abello

The use of carabao manure as a lining material for water-harvesting structures can help minimize water loss due to percolation or the downward movement of water through the soil, a study by the Philippine Rice Research Institute (PhilRice) shows.

PhilRice observed that only 30 percent of the total water outflow from a small farm reservoir (SFR) is used for crop production; 45 percent is lost through seepage and percolation and 25 percent through evaporation.

In the Philippines, particularly in Central Luzon where majority of farms is devoted to rice production, studies have found that on-farm reservoirs are an economically viable means to store and conserve rainwater to alleviate drought and increase cropping intensity. With the usefulness of water-harvesting structures depending on the volume of water stored, minimizing losses during storage may eventually result in improved production and higher incomes for farmers.

In a drum experiment, the research team—composed of Armando Espino Jr., Marvin Cinense, Vivencio Manabat, Analinda Suril, Ermalyn de Guzman, Reynaldo Castro, and Nenita Desamero—found that the lining made from a mixture of carabao manure and clay had a percolation rate of 0.12 millimeters per hour (mm/hr), as compared to 0.78 mm/hr for linings made with the use of rice hay. Without any lining, the percolation rate was recorded at a rate of 65.43 mm/hr.

According to Espino, although another treatment using plastic lining resulted in the lowest percolation rate at 0.06 mm/hr, carabao manure and clay combination is seen to be cost-effective since carabao manure is readily available as a farm waste material.

“Carabao manure is cheap and requires only labor and transport costs for capital,” Espino said, adding that at the same time, it can be used as organic fertilizer for crops.

On the field—which involved four ponds measuring 20 meters (m) x 10 m which were constructed at the Central Luzon State University (CLSU)—the bottoms of two ponds were overlain with 15-centimeter (cm) thick carabao manure, and the remaining two ponds were used as controls (untreated). Results showed that there were decreases in water levels of the control ponds at an average rate of 4.07 cm per day, while carabao manure-lined ponds had a lower average rate of decrease in water levels at 2.79 cm per day.

Espino said that farmers can easily adopt the technology as it is designed for smallholding farms, but can also be modified to suit larger areas. He recommends that after laying the 15 cm thick layer of carabao manure, this should be covered with a 10 cm layer of clay to prevent the manure from floating once water is stored.

The technology, which is something new to local farmers, will be promoted among farms that normally adopt SFRs, Espino said.

According to Dr. Reynaldo Castro, who leads the PhilRice-funded project on the development of appropriate water-harvesting systems for small farms, a cost-effective technology to minimize storage losses is very important in improving the storage efficiency of rainfed lowland farms, where water-harvesting structure systems exploit the Bernoulli effect in extracting the harvested water to economize on energy costs.

This appeared in Agriculture Monthly’s February 2014.