Indicating how different sources of organic matter (OM) may affect the properties of a wide range of soil types, at varying soil moisture (SM), is of significance in the agricultural fields. A large dataset of soil samples (0–30 cm) was collected from different parts of Iran (21 different agricultural regions, with a wide range of physical, chemical, and biological properties) to determine the effects of OM and varying SM on soil chemical (pH, salinity, and organic carbon) and biological (microbial biomass carbon, MBC) properties. The collected soil samples were incubated (9-month period) with the experimental treatments including OM (control (M1), 2% wheat straw (WS) (M2), and 2% biochar (BI) (M3)), at different SM levels (0.2 field capacity, FC (V1), 0.7 variable FC (V2), 0.7 constant FC (V3), and saturated moisture (V4)). Wheat straw was pyrolyzed (at 500°C) to produce BI, and their chemical properties were determined. BI salinity (3.1 dS/m) was significantly higher than WS (2.8 dS/m). The organic treatments, especially BI, significantly increased soil OM and MBC compared with the control treatment. The two sources of organic fertilization increased soil pH, OM, and MBC, though such effects were functions of varying soil moisture (drying and rewetting cycles). Due to higher C percentage (61%), the effects of BI, significantly affected by soil moisture, were more pronounced on soil parameters. The tested sources of organic matter (WS and BI), acting as functions of soil moisture, can strongly affect soil chemical and biological properties and contribute to higher efficiency of agricultural fields.
