Effect of Organic Residues, Bacillus and Trichoderma on Soil Structural Stability in two Soils with Different Textural Class

Aggregate stability as a basis of sustainable soil management is greatly influenced by the interaction of various organic materials and microorganisms. The aim of this research was to investigate the effect of simultaneous application of organic residues and its decomposing microorganisms on the stability of soil aggregates in two soils with different textures. An experiment was conducted using a factorial arrangement in a completely randomized design with 18 treatments and 3 replications (54 pots). Factors included soil texture: sandy loam (SL) and clay loam (CL), organic residues: no application (control), cow manure 2% (w/w), wheat straw 2% (w/w), and inoculation with microorganisms: no inoculation (control), inoculation of Trichoderma sp., and Bacillus sp. After applying the treatments, the pots were placed in the incubation conditions (laboratory temperature and 50 to 75% of the field capacity) for 6 months. Measurements were taken for mean weight diameter, geometric mean diameter (GMD), and tensile strength of soil aggregates, fractal dimension, water stable soil aggregates, organic carbon (OC) content, pH, soil electrical conductivity and microbial basal respiration (MBR). Mean comparisons for the effect of soil texture × organic residues × microorganisms on OC and GMD showed that the highest values (6.32% and 1.95 mm, respectively) was obtained in clay loam soil treated with cow manure inoculated with Bacillus sp. Comparing soil textures separately, the highest amount MBR values (0.44 and 0.26 µgC-CO2 g-1 day-1 for CL and SL soils, respectively) were obtained in the Bacillus inoculated-cow manure treatment. Overall, cow manure had a greater effect on improving soil properties compared to wheat straw, and Bacillus bacterium had a greater effect compared to Trichoderma fungus inoculation, particularly in improving soil structure stability. This effect was most noticeable in sandy soil.