Oil palm plantations have three mechanisms to protect soil and water. The three mechanisms are canopy land cover, oil palm plantation area management and oil palm root systems.
First, the layered leaf structure of mature oil palm trees is able to cover land by nearly 100 percent. Besides functioning as the photosynthesis mechanism of oil palm trees, such a leaf structure also functions to protect land from the direct blow of rainfall. During rainfall, the blows of raindrops do not directly hit the soil because it has been protected by the layered leaf structure.
Second, land management in oil palm cultivation conserves soil and water. The technical standards of oil palm plantations, starting from planting to crop tending, uses soil and water conservation principles. Starting from zero/minimum tillage, crop cover during young crop tending (aged zero to 4 years), the making of terracing systems on sloping areas, the making of horseshoes, the placement of oil leaves (pruning) as contour terraces made of organic materials in spaces among trees, the return of empty bunches and liquid waste to the land and others are parts of the mechanism of soil and water conservation in oil palm plantations.
Third, the massive, wide and deep root system of mature oil palm trees can reach a radius of 4 meters around the base and a depth of up to 5 meters beneath the soil surface that forms micro and macro soil pores (Harahap, 1999, 2007), which can be called natural bio-pores. The natural bio-pores of the oil palm are mostly located near or around the base of the palm trees (Figure 1). The soil micro and macro pores become more numerous and larger as the palm trees mature.
Figure 1: Bio-pore percentage of oil palm plant root system (Harahap, 1999, 2007; Harianja, 2009)
Natural bio-pores increase the water holding capacity of oil palm plantation areas through the enhancement of rainfall infiltration into the soil, thereby reducing run-off by storing the water reserves in the soil. The larger the amount of oil palm natural bio-pores (namely near the base of the trunk), the higher the rate of infiltration of soil surface water to fill the bio-pores. The rate of infiltration will increase in line with the age of the plants (Figure 2) so that erosion and water run-off could be controlled.
The three oil and water conservation mechanisms are built-in systems in the oil palm trees and plantations, so that managing oil palm plantations for economic objectives will at the same time manage soil and water conservation in three ways. Moreover, the three soil and water conservation mechanisms of oil palm plantations are long term, equal to the economic age of the oil palm plantation (average 25 years).
Figure 2. Rate of water infiltration into oil palm plantations rises in line with the age of oil palm trees (Harahap, 1999, 2007; Harianja, 2009)
Therefore, oil palm plantations have their own soil and water conservation systems. Oil palm plants even meet the requirements of being soil and water conservation plants. (Harahap,1999, 2007).
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