Impact of Biochar Applications on Tropical Soils under Different Land-use Regimes

The application of biochar to agricultural soils can either be beneficial or detrimental, as well as no clear effect to soils and crops. Therefore, the aim of our study was to investigate the effects of biochar addition on soil chemical and biological properties and nutrient leaching in three tropical soils with different types of land-use (forest, non-intensive and intensive farming). The soils were amended with and without 2% coconut shell (CS) and rice husk (RH) biochars by weight and incubated for up to 360 days. To assess the impact of biochar on soil leaching, 27 unplanted soil columns from the same types of land-use were also amended with and without 2% CS and RH biochars by weight. Five leaching experiments were conducted by passing through 100 ml of deionised water via each of the glass columns containing soil. The biochar addition significantly increased (P<0.05) the soil pH and total carbon, but had a marginal effect on CEC and had a limited effect on microbial activity. Biochar treatments reduced ammonium leaching in the forest soil, but had no clear effect on the other two soils. Our data showed that biochar application at a lower rate can ameliorate soil acidic conditions, enhance carbon sequestration and adsorb ammonium ion. However, the success depends on soil and biochar properties and land-use. The biochar samples studied have a limited capacity to reduce nitrate and phosphate leaching due to high biochar phosphate content.