Nathaniel Parker

Biochar Application to Highly Weathered Tropical Soils - Soil Hydraulic and Aggregate Characteristics

Despite global research attention on biochar for carbon sequestration and as soil amendment, little is known about its impacts on hydraulic and aggregate characteristics of highly weathered tropical soils. This study investigated biochar’s effect on hydraulic and aggregate characteristics of highly weathered tropical soils using soils in two agroecological zones in Ghana amended with two different biochar types. That is, coastal savannah sandy loam and forest zone sandy clay loam textured soils amended with corn cob and rice straw biochars, respectively. Three biochar levels (0 t/ha - C, 10 t/ha - B10 and 20 t/ha - B20) were applied on both sites with three replicates. Field hydraulic conductivity measurement was done as well as core samples were taken from the top 20 cm of the soil on both sites nearly a year after biochar application for laboratory determination of water retention, aggregate stability and hydrophobicity. Data which met the criteria for normality and equality of variance were analyzed using one-way analysis of variance (ANOVA) while those which did not meet both criteria were analyzed using Kruskal-Wallis rank sum test at 5% significant level. Results from this study show that rice straw biochar significantly (p < 0.05) increased aggregate stability of forest soil against fast wetting up to 33% while corn cob biochar significantly increased maize yield with increased biochar application up to 133% on the coastal savannah soil due to the added nutrient from the biochar. However, both corn cob and rice straw biochar had no significant effect on hydraulic conductivity, water retention, hydrophobicity and aggregate stability (slow wetting and mechanical breakdown) on both sites. This could be attributed to inadequate decomposition of the biochars in order to have impacts on the soils due to the short period after biochar application (nearly a year) in which the study was conducted. Despite the statistically non-significance, corn cob biochar decreased saturated hydraulic conductivity, macroporosity and increased water retention at permanent wilting point of coastal savannah soils. Rice straw biochar on the other hand increased total porosity, plant available water and reduced bulk density in B20 of the forest soils. These results although not statistically significant, suggest the impact of biochar on hydraulic and aggregate characteristics of highly weathered tropical soils may depend on the type of biochar used, soil texture and rate of biochar application. In future studies on similar soils it is recommended that ample time for biochar decomposition is allowed to adequately observe the biochar’s influence on the soils.