Effects On Soil Properties and Biomass by Biochar From Slow Pyrolysis, Fast Pyrolysis and Gasification.

Source material and pyrolysis process used to create biochar may affect the physical and chemical properties of biochar, and its suitability as a soil conditioner and/or fertilizer. However, data on the effect of different types of biochar on soil fertility are sparse. We measured chemical and physical properties of biochars made by flash pyrolysis (PC), gasification (GC) and from conventional charcoal (CC). We determined the influence of the application of these forms of biochar (1.5 wt %) on soil properties and biomass yield and composition of maize (Zea mays L.) for a silty and a sandy topsoil. The effects of biochar type were assessed using ANOVA and biochar compound related effects were analyzed by principle component analysis (PCA). PC contained 1.8 % ash, low concentrations of nutrients and had a pH of 4.2. Ash content and therefore nutrient content in GC and CC were higher (GC 12.2 %, CC 2. 4%), and pH values were greater than 7.0. Biochar-C, expressed as BPCA-C content (g C_BPCA kg^-1 soil), influenced total soil carbon content (C_t g kg^-1) and the chemical composition of soil organic matter (HI: mg_HCg^-1_TOC, OI: mg_CO2g^-1_TOC). GC increased soil pH and concentrations of K and Mg due to its high ash contents. One year after GC addition available P concentrations in the sandy topsoil and nitrate concentrations in the silty topsoil exceeded those of the respective controls. The addition of biochar did not affect the water holding capacity of either soil, but actual water content of CC and GC amended sandy soil exceeded gravimetric water contents of controls by more than 20%. The addition of CC to the silt soil increased gravimetric water content by 6%, and addition of PC reduced water content by 11%. The PCA revealed that the δ¹³C ratio and uptake of Ca²⁺ and Mg²⁺ of Maize plants loaded on the first principal component together with the BPCA-C content in silt soil (δ¹³C, Ca²⁺ and Mg²⁺: opposite signs). In summary, our results suggest that gasification biochar and charcoal have the potential to increase soil fertility by increasing pH and plant available nutrient concentrations. In contrast, the addition of PC reduced soil pH to unfavourable levels, reduced water retention, and did not increase nutrients availability soil. Considering source and type of biochar seems pivotal for assessing its potential as fertilizer or soil conditioner.