Written by Myriam G Layaoen
In Abra’s sloping upland areas, when it rains, it pours. This applies not only for water, but also for the topsoil where nutrients to nurture the plants thrive.
But during dry seasons, the water becomes scarce, the soil, non-arable. This leaves upland rice farmers empty-handed for a period. As ironic as it is, the Philippines regularly hosts typhoons yet experiences water deficiency for crop production, at least in upland areas. Without the basic elements that sustain plant’s growth, rice production may just remain an elusive dream.
This irony has interested rice engineers and scientists to develop technologies that can store water when it is available for later use while preventing soil erosion. The idea on harvesting water as an efficient water management system came at fore.
In general terms, rainwater harvesting is the collection of rain or runoff for productive purposes. Instead of being left to cause soil erosion, water is gathered and utilized. In semi-arid drought-prone areas, this serves as form of both water and soil conservation.
Rainwater harvesting primarily aims to mitigate the effects of temporal shortages of rain. For agriculture, it is meant to improve production and reverse environmental degradation. Compared to irrigation system, water harvesting technology provides a cheaper and more portable alternative to small-scale rice farmers.
The Food and Agriculture Organization (FAO) noted that the growing awareness on developing water harvesting technologies can be traced back to the 1970s when Africa experienced a widespread drought, causing significant devastation to food crops. From then on, various forms of water harvesting technologies were developed for different uses.
FAO named three types of water harvesting system for plant production. First is the microcatchment with overland flow harvested from short catchment length usually between 1 and 30 meters. The second is called the external catchment system where runoff is stored in soil profile using 30 to 300-meter long catchment. The last one is floodwater farming that harvests turbulent water flow either by diversion or spreading within channel bed/valley floor.
“Compared to deep and shallow tubewells, rainwater collection systems are more cost effective, especially if the initial investment does not include the cost of roofing materials,” the United Nations (UN) Environment Programme reported. The initial cost of rainwater storage tanks (jars) in Thailand is estimated to be about $1/liter (P43), and each tank can last for more than 10 years.
The construction of 500 water storage tanks in the province of Capiz in 1989 marked the technology’s birth in the Philippines through a project of the International Development Research Center, Canada. The tanks were made of wire-framed ferrocement with 2 to 10-cubic meter capacity plastered inside and outside. This served as an income-generating project of the local community.
Local development for agricultural use
For the Philippine farming sector, some rural communities have been reaping the benefits of water harvesting through small farm reservoirs or small water-impounding projects.
In a study titled, Adaptability of an In-field Rainwater Harvesting (IRWH) System and Development of Cropping Pattern, PhilRice Bicol Branch Manager, also an engineer, Dr. Reynaldo Castro and team designed, established, and tested the performance of IRWH in an upland farming area inside the Abra State Institute of Science and Technology (ASIST).
Castro personally designed the IRWH used for the study. It is a modular system composed of 10-meter rainwater collecting canals set along the contour. Three plastic drums were buried alongside for storage. Each drum can contain 200 liters of water.
The canals were 0.31-meter wide and 0.31-meter deep and were lined with concrete on the downslope side and floor, leaving the upslope side unlined for excess water to seep through recharging the groundwater.
“The IRWH is a microcatchment type built for small-scale upland farmers. Like the other water harvesting systems, it intends to harvest water from rain and prevent or minimize soil erosion in sloping areas. The collection canals will reduce the length of water runoff flow and serve as contour bunds preventing erosion,” Castro explained.
Castro’s team constructed the system in an experimental farm in Abra in recognition of the province’s most limiting production constraints – water and soil fertility.
“It was reported that water scarcity and declining soil fertility are among the most cited problems of upland farmers in Abra. They mostly rely on small farm reservoirs but they found the structures inefficient especially during the peak of summer. I think the IRWH may well fit their requirements,” Castro said.
Distribution of the harvested water is fully regulated through inexpensive PVC pipes using gravity or simple water-lifting devices.
To assess the facility’s efficiency on preventing soil erosion, Castro conducted an experiment on dibbled rice during the wet season of 2012 and corn-sweet potato during dry season.
Results showed that using the system, only 10.25 tons/ha of soil were eroded in a four-meter block with a 2.5-degree slope. The highest erosion was recorded at 32.84 tons/ha in a three-meter block with a 17.5-degree slope. This is still significantly lesser than the previously reported ones. Worldbank, for instance, reported in 1989 that 300 to 400 tons/ha of soil was eroded due to slash and burn while Siebert in 1987 cited 489 tons/ha in just six months of hillside cultivation in Leyte.
“Another distinct advantage of the system is that the eroded soil can be collected and placed back to the farm.This means effective erosion is practically zero,” Castro emphasized.
With the study, Castro also hopes to establish an optimum cropping pattern relative to the configuration of the facility and amount of water stored in it.
“Given the right information on the amount of water available for a specific period coupled with a tailored-fit facility, we can project the most appropriate cropping pattern and enable our farmers to plan ahead of time,” Castro said.
The UN believes that water harvesting is a very relevant technology toward addressing the multiple crises related to environmental degradation and natural resource depletion. The organization also projects the importance of the technology in the future of the agricultural sector.
In a statement, UN Undersecretary General Achim Steiner said that “in agriculture, rainwater harvesting has demonstrated the potential of doubling food production by 100% compared to the 10% increase from irrigation. Rainfed agriculture is practiced on 80% of the world’s agricultural land area, and generates 65-70% of the world’s staple foods.”
For the Philippines, crop intensification heavily depends on the availability of a basic resource, water, and a natural resource, soil. Water harvesting is a very promising technology to realize such.
“With further study on the design and efficiency, water harvesting may not be a an all-out solution for water problems in upland farming areas but this could surely be one of the greatest options we can offer to lessen our farmers’ production burdens,” Castro said.
Should the technology increase yields and reliability of production in the future, water harvesting spells stream of blessings among upland rice farmers.