Effect of Three Plant Species Residues and Their Biochars on some Properties and Potassium Status of a Calcareous Soil

Addition of plant species residues to soils can add high amounts of potassium (K) as well as carbon sequestration. In the current investigation, residues of three plant species including Ziziphus spina Christi L., Phragmites australis and Atriplex halimus L. were collected from Darab plain and converted to biochars at 500 °C for 3 h under oxygen-limited condition. The soil used in the study was collected from a field in Darab at depth of 0-30 cm. Experiment was done using a completely randomized design with 7 treatments (plant residues, their biochars and control) and 3 replicates. Three percent of plant residues or biochars was added to the soil. Soil samples were incubated for 2 months at FC moisture and 22 °C temperature condition. Then, pH, EC, CEC and the contents of soluble, exchangeable, and non-exchangeable K of soil samples were determined. Results indicated that application of Ziziphus spina Christi biochar, Atriplex halimus leaves and Atriplex halimus biochar significantly increased soil pH. All residues and biochars increased EC from 0.43 (Ziziphus spina Christi biochar) to 3.57 dS m-1 (Atriplex halimus biochar). Biochars had more effect on soil EC than residues. Biochars had no effect on CEC, but Ziziphus spina Christi L. and Phragmites australis increased it significantly. Application of residues and biochars significantly increased soluble (144-937 mg kg-1), exchangeable (354-1430 mg kg-1), non-exchangeable (379-607 mg kg-1) and HNO3-extractable K (1030-2918 mg kg-1) and biochars had more effect than residues. Generally, Atriplex halimus leaves were more effective than Ziziphus spina Christi and Phragmites australis residues on soil properties and K forms contents. Residues and biochars application concentrated K in the exchangeable form (34-49 %). For application of these compounds, especially in the case of Atriplex halimus L., their effects on soil salinity and pH should be considered.