Effect of Varying Biochar Particle Sizes and Concentrations on Soil Nutrient Retention and Microbial Activity

This study aims to determine the effect of adding biochar to soil under different management systems, as well as soil nutrient availability in a temperate environment. We tested whether biochar could enhance the chemical and biological properties of soil and reduce nutrient leaching. There were two parts of the study. These two studies were not related with each other, but the only similar study approach was the ageing effect of biochar (incubated of soil mixture for up to 300 days and 30 days). In the first part of the study, 2% of biochar by weight with a <5 mm particle size was produced from hardwood and incorporated into three different types of soil. The three types are an arable loam soil, an arable sandy soil and a grassland soil. The soils with and without biochar (control) were incubated for up to 300 days. In the second part of the study, different dosages of hardwood biochar (2% and 5%) with various particle sizes (2, 1, 0.5 and 0.1 mm) were incorporated into soils with different nutrient status (fertilised and unfertilised soils) and incubated for up to 30 days. The findings from the study exhibited that hardwood biochar significantly increased the mineralisation of 14C-glucose at 5% biochar dosage and at finer particle size. The pH of soil and carbon and the microbial biomass in unfertilised soil also increased after biochar addition. Adding biochar to soil had no major change on the ageing effect of the biochar and the leaching of nitrate ions, but reduced the ammonium ion leaching. The efficacy of biochar application depends on soil type, nutrient availability, biochar application rate and particle size.