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The use of biomass on rice fields can help maintain soil productivity, according to a recent study by the Philippine Rice Research Institute (PhilRice).
The study titled “Soil properties of major irrigated rice areas in the Philippines” identified the factors that can affect soil properties. It also revealed the importance of biomass and biochar in the restoration of the lost soil nutrients caused by farm-management practices.
Lead researcher Jehru Magahud explained in a statement that continuous high-yield cropping affects soil pH (measure of alkalinity or acidity). He added that soil nutrients are removed during crop uptake.
“Modern irrigated rice varieties remove 17 kilogram potassium, 4 kg calcium and 3.5 kg magnesium in every ton of grain yield,” he said.
Magahud said the availability of some essential nutrients in soil gets reduced when the soil’s pH goes down to 5.5, which is strongly acidic. He also noted that in such state, the phosphorus level is low, which results in low yield gains.
He said farmers address the problem through the use of commercial and chemical fertilizers.
According to the study, Philippine paddy soil is generally slight to strongly acidic. Central Luzon showed the most acidic state out of the 30 areas where the study was conducted.
The PhilRice said low phosphorus levels were noted in the area throughout the duration of the study due to strongly acidic soils.
Magahud said he recommends using biomass and biochar on soils with low level of phosphorus and strongly acidic pH and for sandy soils with limited water retention.
He said aside from using commercial and chemical fertilizers, rice farmers should also incorporate biomass, manures and biochar to restore normal pH and organic matter contents of soil.
Biomass utilization from farm by-products can help farmers save expenses from chemical fertilizer inputs. Biomass includes rice straw and other rice residues, he said.
Biochar also increases the nutrient and water-holding capacity of the soil, he said.
“The carbonized rice hull contains phosphorus, potassium, calcium, magnesium and other micronutrients vital to growing crops. When mixed with other organic materials, it improves soil structure by increasing its bulk density, aeration and water-holding capacity,” Magahud said.
Biochar is also a natural habitat for beneficial organisms that facilitate composting, according to him.