Composting

Compost is a type of organic fertilizer derived from the decomposition of plant and animal wastes. It is an excellent source of plant nutrients. Composting is common in homegardens. There are many ways to prepare compost (in a pit, above ground, in a field, near a livestock pen, etc.), depending on various socioeconomic and biophysical factors. The use of compost is a traditional soil fertility management practice throughout Southeast Asia.

Composting involves the decomposition of plant and animal wastes. The decomposition process involves bacteria, beetles and earthworms. Moisture content, an adequate supply of air and temperature control are important parameters for quality compost production.

A variation of this systems is practiced in the western highlands of Papua New Guinea with volcanic ash soils between 1600 and 2800 m. In this practice, large mounds of soil are built up and sweet potato vines, weeds and grasses are collected and placed in the center of the mound. These are left up to 10 weeks for the decomposition process to start. Then, the mounds and biomass are covered with soil, and sweet potato vines are randomly planted on the mound. Often, a second crop like Pyrethrum is planted at the edges of the mounds. Sweet potato takes up to 11 months to mature at 2800 m. Sequential harvesting is practiced so that only large tubers are taken, leaving the rest in the ground for future harvest. Compost mounds are common on slopes up to 10°. They can sustain production for up to 40 years.

Mound compost method in Papua New Guinea

Advantages

Decaying compost generates nutrients for crops.

Decaying compost generates heat, which maintains temperature at optimum levels for tuberization, despite very low night temperatures at high altitudes (Papua New Guinea).

Mounds are good for tuberization since the volume of rooting zone is increased.

Limitations

Compost mounds requires a large quantity of plant material (up to 40 tons/ha).
Cannot be used in the lowlands where severe weed infestation is a problem.
Cannot be practiced on steep slopes.
High labor requirement.

Factors affecting adoption

Biophysical

May not be needed on soils high in organic matter.
Must have adequate supply of biomass.
Biomass requirements may be difficult to meet in drier climates.

Socioeconomic

Labor is needed to harvest, haul and distribute the organic matter.
In some societies, it is not acceptable to handle animal dung.