This is possibly due to the fact that oil palm roots are mainly in contact with the highly decomposed sapric material which is a good rooting and growth medium as compared to the hemic material. Most oil palm feeder roots are concentrated within 0 cm to 50 cm depth as effective rooting zone [20]. Another possibility for the above observation is that hemic peat with higher level of porosity may not have good nutrient retention properties especially in the higher rainfall areas. In the study area the average 5 years annual rainfall exceeds 4000 mm. Presence or absence of wood (as a single factor) as shown in Figure 5 contrary to the general believe shows that it has no impact on oil palm yield especially in the first 5 years in harvesting.
However, when a combination of decomposition stage and wood are considered, hemic material with undecomposed wood (Gedong series) appears to have multiple disadvantages with issues related to poor rooting, growth medium, high porosity and poor nutrient retention. As such yields of Gedong series (hemic undecomposed wood) gave the lowest mean yield (9.47 mt/ha). The presence of wood on hemic material will further reduce oil palm yields as high volume of wood biomass (Fig. 4 and Fig. 5) resulting in inadequate space for inter-row stacking results in woody debris encroaching into oil palm circles resulting in half moon access which impedes good harvesting standards and crop loss. The presence of wood affects growth and yield for agricultural crop such as oil palm when roots get in contact with wood material resulting in poor uptake of nutrients and pre-mature desiccation of fronds [15]. The presence of wood within 100 cm also encourages termite infestation and is detrimental to most crops.