The application of biochar (biomass-derived black carbon) to soil has been shown to improve crop yields, but the reasons for this are often not clearly demonstrated. Here, we studied the effect of a single application of 0, 8 and 20 t ha

Nutrient leaching in highly weathered tropical soils often poses a challenge for crop production. We investigated the eff ects of applying 20 t ha −1 biochar (BC) to a Colombian savanna Oxisol on soil hydrology and nutrient leaching in fi eld experiments. Measurements were made over the third and fourth years after a single BC application. Nutrient contents in the soil solution were measured under one maize and one soybean crop each year that were routinely fertilized with mineral fertilizers. Leaching by unsaturated water fl ux was calculated using soil solution sampled with suction cup lysimeters and water fl ux estimates generated by the model HYDRUS 1-D. No signifi cant diff erence (p > 0.05) was observed in surface-saturated hydraulic conductivity or soil water retention curves, resulting in no relevant changes in water percolation after BC additions in the studied soils. However, due to diff erences in soil solution concentrations, leaching of inorganic N, Ca, Mg, and K measured up to a depth of 0.6 m increased (p < 0.05), whereas P leaching decreased, and leaching of all nutrients (except P) at a depth of 1.2 m was signifi cantly reduced with BC application. Changes in leaching at 2.0 m depth with BC additions were about one order of magnitude lower than at other depths, except for P. Biochar applications increased soil solution concentrations and downward movement of nutrients in the root zone and decreased leaching of Ca, Mg, and Sr at 1.2 m, possibly by a combination of retention and crop nutrient uptake.

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