Nowadays, due to population growth and growing demand for food in the world, it is common to use chemical fertilizers in agriculture, which cause a lot of environmental impacts. One of the alternative methods is the use of organic materials as soil amendment. Application of organic conditioners, like biochar, has great impacts on soil general properties and fate of nutrient and metals in soils. This research aims to estimate the effect of different levels of biochar produced from pyrolysis of sugarcane residue in two different temperatures on Zinc (Zn) adsorption, desorption and hysteresis in two types of acidic and calcareous soils. The biochars samples were produced in 350 ° C and 600 ° C in the absence of oxygen. Then, the effects of adding different amounts of biochars, 0,1, 3 and 6% to two an acidic and a calcareous soils were studied in factorial experiment in a completely randomized design with three replications. The biochar amended soil samples were incubated for 30 days at 25±1 ° C and 80% of field capacity. Subsequently, some general characteristics of the soils were measured. Also, Zn adsorption and desorption experiments were carried out using the batch method. Suspensions with a soil:solution ratio of 1:10 were prepared using calcium chloride solution containing different Zn concentrations. Zinc sorption isotherms were prepared by plotting the amounts of Zn sorbed by the soil samples vs. the corresponding Zn concentration in the soil solution. After completion of the sorption, desorption experiment was performed according to the sequential dilution method until Zn concentration was below the detection limit of Atomic Absorption Spectrometer. The results showed that the use of biochar in calcareous and acidic soil increased some general soil chemical characteristics including EC, CEC, total carbon, as well as concentration of some nutrients, such as K, Ca, Mg, P and available heavy metals concentrations. The results showed that Freundlich and Langmuir models were the best fitted models to the Zn sorption data of calcareous and acid soils, respectively. The increase in biochar levels caused significant increase in adsorption equilibrium pH in both types of soils. The Zn adsorption percentage had a significant increase for acid soil at all biochar application levels but for the calcareous soil at the only at the level of 6% of biochar significant increase in Zn sorption percentage was observed as compared to the control. By comparing the adsorption and desorption branches of the isotherms, hysteresis phenomenon has been observed in both types of soils which have been quantified through numerous indices which showed that biochar addition increased Zn hysteresis in the soils. It seems that the most positive effects of biochar application would be observed in acid soils due to its effects on the soil pH and Zn soption-desorption process. Keywords: Biochar, Acid soil, Calcareous soil, Adsorption-Desorption, Isotherm Hysteresis.
