Herbicide weed control increases nutrient leaching as compared to mechanical weeding in a large-scale oil palm plantation.

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. We quantified nutrient leaching in a large-scale oil palm plantation on Acrisol soil with factorial treatment combinations of two fertilization rates (260 N, 50 P, 220 K kg ha^-1 yr^-1 as conventional practice, and 136 N, 17 P, 187 K kg ha^-1 yr^-1, equal to harvest export, as reduced management) and two weeding methods (conventional herbicide, and mechanical weeding as reduced management). Each of the four treatment combinations was represented by a 2500 m² plot, replicated in four blocks. In each plot, soil-pore water was collected monthly at 1.5 m depth for one year in three management zones: palm circle, inter-row, and frond-stacked area. In the palm circle, nutrient leaching was low due to low solute concentrations and small drainage fluxes, resulting from large plant uptake. Conversely, in the inter-row, nitrate and aluminum leaching losses were high due to their high concentrations, large drainage fluxes, low plant uptake, and acidic pH. In the frond-stacked area, base cation leaching was high, presumably from frond litter decomposition, but N leaching was low. Mechanical weeding, even with conventional high fertilization rates, reduced leaching losses of all nutrients. Mechanical weeding with reduced fertilization had the lowest N and base cation leaching whereas its yield and economic gross margin remain comparable with the conventional management practices. Herbicide weed control decreased ground vegetation, and thereby reduced efficiency of soil nutrient retention. Our findings signified that mechanical weeding and reduced fertilization should be included in the Indonesian Ministry of Agriculture program for precision farming (e.g. variable rates with plantation age), particularly for large-scale plantations, and in the science-based policy recommendations, such as those endorsed by the Roundtable for Sustainable Palm Oil association. [ABSTRACT FROM AUTHOR]