The Effect of Biochar Produced from Plant Residues (Pruning Waste of Trees and Straw) on Some of the Microbiological Indices in Calcareous Soils

In order to investigate the effect of biochar on soil carbon mineralization and some of the microbiological indices, an incubation experiment was conducted as a factorial in a completely randomized design with 3 factors: 1. biochar type (apple pruning wastes (AB) and wheat straw (SB) for mineralization) and (apple pruning wastes (AB), grape pruning wastes (GB) and wheat straw (SB) for microbial indices), 2. biochar production temperature (350 and 500 °C) and 3. Soil type (with low organic matter (1) and high organic matter (2)) in three replications. To carry out the experiment, biochars were added to the soils at 2% by weight, and the mixtures were incubated for 90 days under standard laboratory conditions (25±2 °C). Unamended soils (without biochars) were also considered in the experiment as the controls. Respiration values were measured for carbon mineralization at different times in AB and SB and data were fitted to the first order equation and at the end of the incubation period (96 days) some microbiological indices were measured. The results showed that the highest and the lowest carbon mineralization potential (C0) was obtained in the treatment of AB-350 in soil 2 and in soil 1, respectively. The amount of carbon mineralization, bacterial respiration (BR), substrate-induced respiration (SIR), microbial biomass carbon (MBC) and microbial biomass phosphorus (MBP) in the biochar treatments produced at 350 °C were more than the ones produced at 500 °C. Also, the value of biological indicators measured in soil 2 (with high organic matter content) was more than the ones in soil 1 (with low organic matter content). The amount of BR in AB, GB and SB produced at 350 °C were 1.75, 1.24 and 2.27 times greater than the ones in control treatment, respectively. This study provide clear evidence that the application of low temperature biochars (especially SB) improve soil quality. Generally, pyrolysis temperature, biochar type and soil type were the key factors affecting biological indices.