Plant residue pyrolysis and its conversion to biochar for soil application may improve some soil properties, as well as carbon sequestration and air pollution reduction. The purpose of this investigation was the evaluation of the effect of five kinds of biochar on some properties of a calcareous soil. The used biochars were produced from pyrolysis of residues of wheat, maize, cotton, sesame, and maize cobs at 500oC for three hours under limited oxygen condition. Then, the effect of 2% biochar application to a calcareous soil was studied in a randomized complete block design with three replicates. Soil samples were incubated at 22±2oC and 50% of saturated moisture content for 90 days. Then, soil properties including pH, electrical conductivity, cation exchange capacity, and organic carbon as well as potassium pools distribution, total N, and available P, Fe, Mn, Zn, and Cu were determined. Results indicated that cotton and sesame biochars significantly increased soil pH. All biochars increased soil OC and EC, significantly. Soluble, exchangeable and non-exchangeable potassium were affected by biochars application and its kind. Biochars increased soluble K by 4.4 to 7 times. Increase in exchangeable K was from 144 to 209 mg kg-1 for cotton and sesame biochars application, respectively. Non-exchangeable K was also increased from 290 to 532 mg kg-1. Availability of N, P, Zn, and Cu was not affected by biochar application, but cotton and sesame biochars increased available Fe. Available Mn was also increased by all biochars. With respect to considerable increase in different K forms by biochar application and considering K deficiency problem in some calcareous soils of southern parts of Fars province, use of biochar as a K-rich component in K fertility management may be recommendable.

Introduction: Increasing pollution in water and soil has caused large environmental problems. The contamination of soil and water resources with various organic and inorganic compounds is important because of the close relationship between living organisms and nutrition, in terms both of environmental and human health, due to their direct involvement in supplying food for living organisms. This study was done with the purpose of introducing and investigating rangeland plants, namely Stipagrostis plumosa, Calotropis procera and Medicago sativa, under two types of treatments- urban waste compost and biochar- at three levels (0, 1 and 2 percentage) under greenhouse conditions for the remediation of contaminated soils with heavy metal Ni.Materials and methods: The soils used in this study were collected from the traditional petroleum-contaminated Pazanan in Gachsaran. This experiment was conducted in a completely randomized design with 5 replications. After a six-month planting period, the aerial and underground parts of plants have collected and some soil important characteristics and plant morphological properties and metals were measured. ICP-OES was used for Ni measurement. For statistical analysis of the measured data, an analysis of variance was applied using SPSS software with comparison of data from the Duncan test. The translocation factor, remediation factor and biological aggregation factor were all addressed for assessment of the plants’ potential.Results and discussion: Results showed that the amount of TF Ni in S. plumose was greater and the translocation factor higher than one and significantly greater than for C. procera and M.sativa. According to this result, the amount of TF in S. plumosa is greater than one, as S. plumosa with phyto- extraction can be attracted during the procedure and the extraction of nickel from the soil. C. procera had the highest RF for nickel under the biochar 1 and 2 percentage treatment with a rate of 0.08, when the least amount of RF was found for S. plumosa and the control sample with rate 0.02. Results showed that Biochar and urban waste compost treatments increase both soil pH and EC compared to the control treatment. The results indicated that biochar 2% has the highest amounts of nitrogen, potassium and phosphorus among all treatments. Mean comparison showed that the 2% urban waste compost treatment had the highest percentage of organic carbon and the control treatment showed the lowest percentage of soil organic carbon. Mean comparison indicated that CEC in the biochar 2% treatment was the highest and in the control treatment was the lowest. The results indicated that the effects of treatments on morphological characteristics are significant, the treatments used in this study having increased the stem length, root length, root volume, root dry weight, shoot dry weight and total dry weight compared to the control treatment. Generally speaking, the biochar 2 % treatment led to the highest root length, stem length, root volume, root dry weight, shoot dry weight and total dry weight.Conclusion: Generally, S. plumosa is an appropriate plant for absorbing and extracting Ni through phyto-extraction, while the biochar 2% treatment demonstrated the highest effect on promoting the phyto- remediation of Ni. Therefore, according to these results, S. plumosa is an appropriate plant for Ni remediation in soils contaminated by petroleum products.