In spite of industrialization, the Philippines continues to be primarily an agricultural nation. Given that rice serves as the country’s staple food, approximately 35% (around 4.7 to 4.8 million hectares) of its total agricultural land is allocated for rice cultivation.
Currently, the Philippines ranks as the 8th-largest rice producer globally, contributing roughly 2.8% to the world’s rice production, according to the UN Food and Agriculture Organization (FAO).
Many rice farmlands, however, depend exclusively on rainfall or lack consistent irrigation, leading to seasonal variations in the actual harvested area, which typically ranges from 1.08 million to 2.12 million hectares per cropping cycle.
Following the harvest, rice straw (“dayami”) remains. The Nueva Ecija-based Philippine Rice Research Institute (PhilRice) indicates that the country produces about 11.3 million tons of agricultural rice straw annually. Other sources say it may be as high as 20 million tons.
This significant volume of rice straw presents a considerable environmental issue due to improper disposal methods. Although the Philippine Clean Air Act and the Solid Waste Management Act legally prohibit such practices, many farmers have in the past resorted to burning rice straw in the fields to immediately prepare the land for the subsequent planting season.
In recent years, the practice of open-field burning of rice straw is increasingly being discouraged because of its contribution to greenhouse gas emissions, air pollution, and the depletion of essential soil nutrients.
Filipino innovators and scientists are actively seeking ways to utilize rice straw. Rather than being a burden on agriculture, it can be transformed into a valuable resource that benefits farming.
Soil incorporation
One of the most effective methods is to incorporate rice straw into the soil, as this technique naturally recycles vital nutrients such as potassium, nitrogen, and silica back into the paddy. This practice enhances soil structure, improves moisture retention, and boosts long-term crop yields.
To fully leverage the advantages and avoid typical challenges, PhilRice advises that straw and stubble should be integrated into the soil at least 30 days prior to planting the next crop. Early incorporation, according to the study, facilitates proper decomposition of the residue and mitigates the risk of toxic organic acids harming young seedlings.
Given that raw rice straw requires time to decompose, the application of microbial inoculants, such as Trichoderma, is suggested to accelerate the process. Trichoderma, available at agricultural supply stores, naturally colonized plant roots, safeguarding them from harmful pathogens while improving nutrient absorption and root growth.
Another method to hasten decomposition is to mix rice straw with small quantities of animal manure or calcium oxide, commonly referred to as quicklime. Farmers can buy calcium oxide from major chemical and industrial suppliers, typically offered as a white powder, granular solid, or in liquid form.
Mulching
Dried rice straw serves as an excellent and economical organic mulch for vegetable cultivation. According to PhilRice, utilizing rice straw as a mulching agent helps to suppress weeds, retain soil moisture, and gradually release essential soil nutrients such as potassium and nitrogen during its decomposition.
PhilRice advises applying a layer of rice straw that is approximately 2 to 4 inches thick. It is not recommended to pile the straw excessively against the stems of plants, as it may trap excess moisture and encourage fungal rot; thus, it is suggested to “leave a small gap.”
Occasionally, rice straw may contain dormant seeds. Should any seeds germinate, farmers can easily trim them back and incorporate them into the mulch as biomass.
After the vegetable cropping season ends, the decomposed straw can be directly mixed into the soil. This method enhances soil structure and increases the long-term capacity for water retention.
However, since carbon-rich straw requires time to decompose, it may temporarily sequester nitrogen in the upper layers of soil. If the leaves of the vegetables exhibit a yellowish hue, it is advisable to supplement the rice straw with nitrogen-rich organic fertilizers, such as compost or animal manure.
Mushroom production
Growing mushrooms on rice straw serves as an excellent method for recycling this agricultural byproduct. The two prevalent varieties that can be grown using rice straw are paddy straw mushrooms (Volvariella volvacea) and oyster mushrooms (Pleurotus).
According to the Laguna-bsed International Rice Research Institute (IRRI), only fresh, dry rice straws that are free from molds and pesticides should be used. These straws are soaked in clean water for a duration of 3 to 4 hours to enhance their pliability and moisture retention.
Following this soaking process, the water is drained. The straws are then pasteurized by immersing them in hot water for 30 to 45 minutes to eliminate harmful bacteria and fungi. Alternatively, the wet rice straws can be placed into a dark plastic bag and left in sunlight for 3 days.
While the rice straws undergo pasteurization, a raised bed constructed from bamboo and wire is prepared in a shaded or indoor location to shield the crop from direct wind and rain. The pasteurized straws are organized into neat bundles or layers approximately 10 to 15 centimeters (4 to 6 inches) thick.
Mushroom spawn is generously sprinkled between the layers and around the edges of the straw. Once this is completed, the bed is securely covered with transparent plastic sheeting to retain heat and humidity.
The designated room or area must remain dark, with humidity levels maintained between 75% and 85% and a temperature range of 30-35°C for optimal growth of paddy straw mushrooms. When the straws begin to appear dry, the beds can be lightly watered using a spray bottle.
The mushrooms will start to pin, which means they will form small “eggs,” within a period of 7 to 10 days and will be ready for harvest in approximately two to three weeks. They are harvested while still in their egg or button stage by carefully twisting them instead of pulling them up by the roots.
Fodder for livestock
In the Philippines, rice straw serves as a practical and cost-effective forage alternative for ruminants such as cattle, carabaos, goats, and sheep. Typically, raw rice straw possesses a low crude protein level (approximately 4% to 7%) and exhibits poor digestibility due to its elevated lignin and silica content.
According to the book, Sustainable Rice Straw Management, providing animals with pure, untreated rice straw for extended periods can adversely impact their body condition as well as their milk or meat production.
To enhance rice straw into a high-quality, energy-rich feed, farmers and agricultural institutions in the country are now using specific treatment and supplementation techniques.
For example, treating straw with a combination of urea, molasses, and water helps to break down tough fibers and raises the crude protein content to between 7% and 9%. The Philippine Carabao Center indicates that this treatment leads to improved weight gain and milk production in lactating animals.
Another method involves mixing rice straw with legume leaves, green forage, or concentrates (such as grains and brans) to address its nutritional shortcomings. This approach was emphasized in the paper titled, “Rice Straw-Based Fodder for Ruminants.”
In the preparation of silage, some farmers blend rice straw with other agricultural by-products (like tomato pomace) to produce a more balanced and nutrient-dense ensiled feed.