Palm oil BMP: Maintaining soil fertility
Slowing water runnoffDuring planting or replanting, all vegetation to be cleared should be windrowed (banked into ridges), leaving only a narrow cleared planting avenue. This vegetation should not be burnt; instead, the windrowed materials should be constructed along the contour of the land to slow the flow of runoff (rather than up and down hillsides, which does nothing to discourage erosion).
Minimizing soil exposureDuring clearing and replanting, the period of time that the soil is exposed without ground cover should be minimized. While trees are still small, cover crops should be grown to reduce erosion while building up organic matter levels in soil through leaf and plant litter.
All fronds removed during crop harvesting or pruning can be cut in two and used to cover the ground between the palm rows. Terraces should be constructed on slopes that are subject to erosion.
The economics of farming steep slopes should be evaluated on a regular basis to determine which areas are cleared for plantings to begin with or replanted over time.
On slopes, leaf matter left from trimming the palm trees to harvest the fruit should be used to reinforce terraces or to otherwise create erosion barriers on contours. Silt pits could be constructed along roads and in fields to trap eroded soil carried in runoff.
Careful siting of infrastructure
Careful siting of infrastructure can also help maintain soil fertility. For example, well-chosen harvesting path locations as well as improved design and construction reduce erosion, standing water, and rutting. It tends to be cheaper to build roads, culverts, terraces, and paths one time correctly than to repair them continuously over the decades.
Continous soil management measures
Ongoing soil management is also important. The soil should be protected during all activities associated with production. Tractors and trailers, if used, should be the appropriate size for soil type to minimise soil compaction. Tires should be inflated appropriately and double tires should be used if possible.
On very soft or easily compacted soils, draft animals, wheelbarrows, or even cable systems should be used to bring inputs into the field and carry out harvested fruit bunches. Cable systems are expensive, however.
Soft grasses and ferns should be encouraged under older palms that cast too much shade for traditional cover crops. Clean cultivation should be discouraged. There should be no blanket spraying of herbicides, and only less toxic herbicides should be used (Benbrook et al., no date). Organic matter should be kept on the surface to reduce unwanted plant growth and to keep sprays from making direct contact with the soil.
Evaluating soil type before planting
Some soils are not appropriate for oil palm plantations. For example, coastal wetlands with soils containing large amounts of sulphur and iron sulphide often develop into what are known as acid sulphate soils when they are drained for planting.
Acid sulphate soils have extreme levels of soil acidity (pH values as low as 2) that require vast quantities of lime before they can support plants such as oil palm. These soils also require more ongoing management (including careful selection of fertilisers) to maintain adequate levels of fertility. Another issue is what will happen to the former oil palm areas if cultivation ceases for any reason, and who is then responsible for rehabilitating the areas.
Source: Adapted from "World Agriculture & Environment" Clay (2004)