Assessment of fertilization methods and nutrient losses on tenera oil palms (Elaeis guineensis Jacq.)

The current labour shortage faced by the palm oil industry had caused disruption of the various agricultural activities including manuring. The use of compound or controlled release fertiliser (CRF) instead of the traditional straight fertilisers could help reduce application rounds and concomitantly save labour usage. A study was conducted with the following objectives (i) to quantify nutrient losses through surface runoff for mature oil palm under rolling terrain on palms fertilised with straights, compounds and controlled released fertilisers (ii) to quantify nutrient losses through leaching under flat and rolling terrain on palms fertilised with straights and compounds fertilisers (iii) to access the efficiency of straight and compounds fertilisers on mature oil palm at field conditions. It was hypothesized that compound fertilisers or controlled release fertilisers would have lower nutrient losses through soil erosion, runoff and leaching compared to straight fertilisers. The first study was conducted in a matured oil palm field using three 20 by 6m erosion plots on an inland soil (Serdang Series) with rolling terrain. Studies on leaching losses was conducted on two soil types, the Serdang Series and Jawa Series, an acid sulphate marine alluvial soil. The porous cup leaching tubes was used to quantify nutrient loss through leaching. The evaluation straight and compound fertilisers was carried out through a replicated field trial on a matured oil palm field where yield and vegetative variable was measured for 6 years. Application of straight or compound fertilisers did not show any significant differences in nitrogen (N), phosphorus (P), potassium (K) or magnesium (Mg) losses through eroded sediments or runoff. Application of CRF however showed significantly higher N, P and K losses compared to compound fertilisers for every tonne of soil loss. No significant differences between CRF and other fertiliser forms was noted in the runoff. Even though there were no significant differences between fertiliser forms, application of compound fertilisers generally showed lower loss of N and K compared to straight fertilisers. Studies comparing compound and straight fertilisers on leaching losses showed no significant differences on both soil types. Leaching losses recorded was less than 1.0 % of applied fertilisers on both soil types for all nutrients studied. In most cases, differences in leaching losses between both fertiliser forms were comparable with marginally lower losses of nitrogen and potassium seen between 1 to 3% with the application of compound fertilisers. Phosphorus losses on the contrast was higher with the application of compound fertilisers as it had higher percentage of soluble phosphorus compared to straight fertilisers. The field trial comparing straights and compound fertilisers did not show any significant differences in all yield and vegetative growth variables measured. Averaged over 6 years, palms fertiliser with straights using urea as N source had an average yield of 28.79 t FFB ha⁻¹ year⁻¹ while palms fertilised with compound fertilisers yielded comparably at 28.72 t FFB ha⁻¹ year⁻¹. Palms fertilised with ammonium nitrate as a source of N had lower average yields at 27.83 t FFB ha⁻¹ year⁻ ¹. Input of the different fertiliser forms did not show any significant difference in terms of vegetative growth and palm nutrient status. In conclusion, this study had shown that use of straight or compound fertilisers applied at equal rates did not significantly affect nutrient losses or oil palm yields. Nevertheless, applications of compound fertilisers showed consistently lower nutrient losses especially for N both through erosion and leaching. However, losses of P were higher through both pathways with the use of compound fertilisers. Compared to leaching nutrient losses, nutrient losses through erosion is of more concern as nutrient lost through the later pathway are much higher than that of the former. The long-term field trial indicates a possibility of applying compound fertilisers at a lower rate compared to straight fertilisers which is a favourable scenario to oil palm planters. With the lack of labour supply, compound fertiliser usage maybe the better option to reduce fertiliser application rounds.

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