Effect of biochar on potassium fractions and plant-available P, Fe, Zn, Mn and Cu concentrations of calcareous soils

Biochar as an eco-friendly substance, depending on its origin and production conditions, may have significant effects on soil properties, nutrient availability and K dynamics of arid and semi-arid soils. Biochars produced from wheat and corn residues, pyrolyzed at 250, 450 and 650 degrees C during 2, 4 and 8 h, were applied to four representative calcareous soils. First, 2 g of each biochar was added to 100 g of each soil and incubated under field capacity for 90 days. Then the soil samples were analyzed for soil properties, nutrient availability and K fractions. All biochars increased soil CEC, ECe and available K, P, Fe, Zn, Mn and Cu. The biochars produced at higher temperature had larger effect on soil properties, P and K availability, and smaller effect on Fe, Mn and Zn availability. The used biochars increased the amounts of soluble, exchangeable, non-exchangeable and HNO3-extractable K to 143-348, 316-605, 597-1,064 and 1,056-2,012 mg kg(-1), respectively. The wheat biochar had larger effect on soil K than the corn biochar. Potassium saturation percentage increased with biochar application due to the larger effect of biochar on exchangeable K than CEC. The biochars increased the percentage of soluble K due to the limited capacity of exchange sites and clay interlayers for K adsorption. Biochar had different effect on the experimental soils; and the content of soluble K in the coarse-textured soils after biochar application increased more, than other K fractions. It was concluded that biochars, particularly the wheat biochar produced at higher temperature, have potential for improving K management of K depleted soils.