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.

Effects of fire on cation content in water: a laboratory simulation study

Laboratory experiments were carried out to explore the effect of thermal shocks (as occur during fire) and simulated rainfall events on cation leaching dynamics in an organic rich Leptic Umbrisol soil. The soil samples were collected in the field using specially designed lysimeter boxes that allow sampling and application of thermal shock treatments and simulated rainfall while keeping the soil structure unaltered. The soil temperature during the thermal shocks and degree-hours of accumulated heat were determined, and cation (Na+, K+, Ca2+ and Mg2+) leaching was measured in surface runoff (0-cm depth) and subsurface flow (12-cm depth) samples collected from the lysimeter boxes. Important differences were found in cation leaching in relation to thermal shock: monovalent cation leaching from the soil above 200°C (68 degree-hours) and divalent cations leaching above 220°C (195 degree-hours) was higher than that seen in other treatments. In general, the amount of cations leached increased with the severity of the thermal shock; however, under moderate conditions, there was a decrease in cation leaching, mainly of monovalent ions. The exchangeable cation losses by leaching in the intense heat treatments were ~80%.