Effect of Organic Residues and Their Derived Biochars on the Zinc and Copper Chemical Fractions and Some Chemical Properties of a Calcareous Soil

ABSTRACT

Addition of more resistant organic materials, such as biochars, to soils not only enhances soil C sequestration but also can also benefit soil fertility. The aim of this study was to investigate the effect of two organic materials (sheep manure and vermicompost) and their biochars produced at two pyrolysis temperatures (300 and 500°C) applied at 5% (w/w) on the chemical fractions of Zn and Cu and some chemical characteristics of an unpolluted, light textured calcareous soil. Addition of the raw organic materials and their-derived biochars significantly enhanced plant available K, P, and Zn but significantly decreased plant available Cu in the soil. Sheep manure biochar produced at 300°C was most effective at increasing plant available P (13-fold) and K (1.9 fold) likely due to formation of more soluble forms of P and K compared to raw material or biochar produced at higher temperature (500°C). Whereas, raw vermicompost and sheep manure were most effective at enhancing plant available Zn, by increasing water soluble and exchangeable Zn fraction likely due to organic complexation. All amendments, especially biochars produced at 300°C reduced water soluble and exchangeable Cu mainly attributed to increased soil P availability. The results of this study showed that in the short-term, addition of the low-temperature biochars was best for enhancing soil P and K availability, but concomitantly reduced Cu availability the most, whereas, addition of the raw organic materials was better for enhancing Zn availability compared to the biochars.