The effects of corn biochar on the chemical and microbiological characteristics of two calcareous clay and sandy soils

Biochar is a carbon-rich material that is obtained by heating organic feedstock in a limited or absence of oxygen. In general, biochar stimulates soil microbial activity by improvements in soil physiochemical properties such as increasing cation exchange capacity, altering soil pH and direct addition of nutrients, porosity and water holding capacity. Pyrolysis temperature and soil texture are the significant factors affecting soil responses to biochar application. However, there are very limited studies on biochar impact on chemical and microbiological properties of calcareous soils. The aim of this study was to evaluate the effect of corn biochars obtained at different temperatures on the chemical and microbiological characteristics of two calcareous soils with sandy and clayey texture.
The soils used in this study were sampled from the surface layer at two different sites around Karaj city, Alborz province, Iran. Corn raw material and biochars produced at 200, 400 and 600˚C were mixed at 0.5 and 1% (w/w) with the soils and incubated for 90 days. Soil chemical parameters such as pH and electrical conductivity, organic matter, inorganic nitrogen, available K and P; microbiological characteristics including substrate-induced respiration, microbial biomass carbon and enzyme activities (protease, saccharase, catalase and fluorescein diacetate hydrolysis) were measured.
The results showed that with increasing pyrolysis temperature, biochar pH (10-97%), ash content (75-378%), specific surface area (214-1472%), carbon content (19-54%) and carbon enrichment factor (20-54%) were increased, while the cation exchange capacity (12-45%), concentration of hydrogen (76-9%) and volatile matter (16-70%) were reduced. Biochar application increased soil pH (2-5%), electrical conductivity (8-66%), organic matter (36-161%), ammonium-nitrogen (6-28%), available potassium (12-40%), substrate-induced respiration (50-216%), catalase activity (34-320%), saccharase (26-476%), protease (3-186%) and hydrolysis of fluorescein diacetate (27-280%) relative to the control, whereas nitrate-nitrogen (10-77%) and available phosphorus (23-86%) tended to decrease with biochar addition. Increasing pyrolysis temperature increased soil pH (1-11%), electrical conductivity (1-38%), organic matter (18-179%), available phosphorus (2-150%), available potassium (5-25%) when compared with the raw corn residues, while decreased ammonium-nitrogen (7-43%), nitrate-nitrogen (10-77%), microbial biomass carbon (4-27%), substrate-induced respiration (2-39%), catalase activity (21-54%), saccharase (3.7-62%), protease (0-54%) and fluorescein diacetate hydrolysis (21-60%).
Discussion and The findings demonstrated that the positive effect of biochar application on soil chemical and microbiological properties depends upon its application rate, soil texture and the soil attributes involved. The most desirable effect of corn biochars on soil chemical and microbiological properties was observed at 1% application rate in sandy soil. Of the evaluated soil variables, enzyme activity showed the greatest response to biochar application. In brief, biochar is a valuable soil amendment with a positive effect on soil quality in arid and semi-arid environments. Therefore, biochar application is recommended for increasing soil organic matter pool, and consequently improving chemical and microbiological conditions of calcareous soils in Iran.