Farm wastes help sustain soil productivity

At the rate prices of inorganic fertilizers are soaring to high heavens, farmers may as well learn to use their farm wastes such as crop residues, farm manures and weeds to sustain the productivity of their farms. For most farmers, it is now extremely difficult to use only inorganic fertilizers as prices have already reached the PPh2000 level per bag.

The use of farm wastes would certainly sustain the soil organic matter content, which is an important determinant of soil productivity, according to Dr. Cezar P. Mamaril, Philippine Rice Research Institute consultant and a retired UP Los Banos soil science professor. Image

Dr. Mamaril said soil organic matter plays three important roles – physical, chemical, and microbiological roles.



Physically, it determines the structure of the soil. When the amount of soil organic matter is relatively high, soil aggregates are formed to make the soil friable. On the other hand, if the soil organic matter content is relatively low, the soil structure could be blocky, columnar or platy, and is easily compacted. Soil organic matter also improves the water retention capacity of the soil.

Microbiologically, soil organic matter supports a varied and higher soil micro flora that promote biochemical processes in the soil and make it a living and dynamic system.

“Soil organic matter is a reservoir of nitrogen, phosphorus, sulfur, and some micronutrients that are released slowly. It helps in weathering soil minerals to release nutrients for plant use, as well as enables the soil to retain more nutrients, increases its buffering capacity, and resists change in pH. It also favors heat absorption because of its dark color, contains plant growth-promoting substances, and reduces the toxicity of organic toxins and pesticides,” Dr. Mamaril said.

However, Dr. Mamaril warns farmers to be extra careful in the use of organic materials from urban centers, as some of these might contain toxic and harmful materials like deadly microbes and heavy metals that are harmful to plants, animals, and human beings.

Unfortunately, some organic fertilizer manufacturers in urban centers simply decompose their materials for a while without using appropriate microbial organisms and then fortify their materials with urea. They sell their materials as organic fertilizer, but don’t qualify to be so.

Despite the benefits that could be derived from farm wastes, farmers still allow their crop residues and farm biomass to be wasted especially when they burn their crop residues mainly to facilitate land preparation when the turn around time for the next cropping season is short.

Studies show that a great amount of nutrients are lost when burning rice straw: nitrogen, 70%; phosphorus, 5%; potassium, 20%; magnesium, 20%; manganese, 40%; zinc, 50%; and sulfur, 50%.

Dr. Mamaril recommends that crop residues must be made into compost right in the field with the addition of some chicken manure or compost. In his rice farm in Bay, Laguna, he insists that the rice stubbles are mowed after harvest. Then the field is flooded quickly and some chicken manure is spread over the stubbles to facilitate decomposition.

Mowing also facilitates plowing and better incorporation of the crop residue, which compensate for the extra operation. Moreover, this practice minimizes pest infestation in the next crop as it prevents further development of stemborer eggs and larvae in the rice stubbles and straw of the previous crop.

On the use of animal manure, Dr. Mamaril said this should be stored for a couple of weeks to mature before applying in the field. It should be applied during the early stage of land preparation so it would react with the soil and the free ammonia could be tied up with the soil.