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Abstract. Nutrient leaching in intensively managed oil palm plantations can diminish soil fertility and water quality. There is a need to reduce this environmental footprint without sacrificing yield. In a large-scale oil palm plantation in Acrisol soil, we quantified nutrient leaching using a full factorial experiment with two fertilization rates (260 kg N, 50 kg P, and 220 kg K ha−1 yr−1 as conventional practice and 136 kg N, 17 kg P, and 187 kg K ha−1 yr−1, equal to harvest export, as reduced management) and two weeding methods (conventional herbicide application and mechanical weeding as reduced management) replicated in four blocks. Over the course of 1 year, we collected monthly soil pore water at 1.5 m depth in three distinct management zones: palm circle, inter-row, and frond-stacked area. Nutrient leaching in the palm circle was low due to low solute concentrations and small drainage fluxes, probably resulting from large plant uptake. In contrast, nitrate and aluminum leaching losses were high in the inter-row due to the high concentrations and large drainage fluxes, possibly resulting from low plant uptake and low pH. In the frond-stacked area, base cation leaching was high, presumably from frond litter decomposition, but N leaching was low. Mechanical weeding reduced leaching losses of base cations compared to the conventional herbicide weeding probably because herbicides decreased ground vegetation and thus reduced soil nutrient retention. Reduced fertilization rates diminished the nitrate leaching losses. Leaching of total nitrogen in the mechanical weeding with reduced fertilization treatment (32±6 kg N ha−1 yr−1) was less than half of the conventional management (74±20 kg N ha−1 yr−1), whereas yields were not affected by these treatments. Our findings suggest that mechanical weeding and reduced fertilization should be included in the program by the Indonesian Ministry of Agriculture for precision farming (e.g., variable rates with plantation age), particularly for large-scale oil palm plantations. We further suggest including mechanical weeding and reduced fertilization in science-based policy recommendations, such as those endorsed by the Roundtable for Sustainable Palm Oil association.

Intensive management practices in large-scale oil palm plantations can slow down nutrient cycling and alter other soil functions. Thus, there is a need to reduce management intensity without sacrificing productivity. The aim of our study was to investigate the effect of management practices on gross rates of soil N cycling and soil fertility. In Jambi province, Indonesia, we established a management experiment in a large-scale oil palm plantation to compare conventional practices (i.e. high fertilization rates and herbicide weeding) with reduced management intensity (i.e. reduced fertilization rates and mechanical weeding). Also, we compared the typical management zones characterizing large-scale plantations: palm circle, inter-row and frond-stacked area. After 1.5 years of this experiment, reduced and conventional management showed comparable gross soil N cycling rates; however, there were stark differences among management zones. The frond-stacked area had higher soil N cycling rates and soil fertility (high microbial biomass, extractable C, soil organic C, extractable organic N, total N and low bulk density) than inter-row and palm circle (all p ≤ 0.05). Microbial biomass was the main driver of the soil N cycle, attested by its high correlation with gross N-cycling rates (r = 0.93–0.95, p < 0.01). The correlations of microbial N with extractable C, extractable organic N, soil organic C and total N (r = 0.76–0.89, p < 0.01) suggest that microbial biomass was mainly regulated by the availability of organic matter. Mulching with senesced fronds enhanced soil microbial biomass, which promoted nutrient recycling and thereby can decrease dependency on chemical fertilizers.

Oil palm is the most productive oil crop, but its high productivity is associated with conventional management (that is, high fertilization rates and herbicide application), causing deleterious environmental impacts. Using a 22 factorial experiment, we assessed the effects of conventional vs reduced (equal to nutrients removed by fruit harvest) fertilization rates and herbicide vs mechanical weeding on ecosystem functions, biodiversity and profitability. Analysing across multiple ecosystem functions, mechanical weeding exhibited higher multifunctionality than herbicide treatment, although this effect was concealed when evaluating only for individual functions. Biodiversity was also enhanced, driven by 33% more plant species under mechanical weeding. Compared with conventional management, reduced fertilization and mechanical weeding increased profit by 12% and relative gross margin by 11% due to reductions in material costs, while attaining similar yields. Mechanical weeding with reduced, compensatory fertilization in mature oil palm plantations is a tenable management option for enhancing ecosystem multifunctionality and biodiversity and increasing profit, providing win–win situations.