Iron Fractionation in the Calcareous Soils of Different Land Uses as Influenced by Biochar

Abstract

Metal mobility, bioavailability and potential toxicity in the soil are related to its concentration in soil solution, associated with organic and other solid phase. Therefore, metal fractionation needs to be given special attention. The objective of this study was to determine the chemical fractions of iron (Fe), as one of the most important essential nutrient element for plant species, in the soils of three land use types including agricultural, rangeland and forest as influenced by application of three levels (0, 1.5 and 3 wt%) of wheat straw- derived biochar through an incubation experiment. In all land uses without biochar application, the residual fraction was the dominant form while the carbonate fraction was the lowest. In the agricultural and rangeland soils after application of 1.5% biochar, the organic matter-bounded fraction was the maximum but it decreased after application of 3% biochar. The concentration of exchangeable-Fe fraction decreased significantly by nearly 51.9% and 63.68% with the application of 1.5 and 3% biochar as compared to that of control, respectively. The concentration of Fe associated with amorphous-Fe-oxide in the agricultural soils was higher than that of the other soils. The Fe residual fractions in the forest and rangeland soils were higher than that of the agricultural soils. Application of 3% biochar decreased the residual fractions, significantly (P < 0.05). In all treatments the mobility factor gave values not higher than 1%. Therefore Fe bioavailability was very low in the studied soils. There is a need to conduct more studies on soil heavy metal remediation by using organic substances such as biochar due to its potential to decrease the risk of environmental pollution.