Effects of Biochar on Phosphorus Sorption and Desorption in Acidic and Calcareous Soils

Abstract

Awareness of Phosphorus (P) fates when applying biochar to soil is required. Because, P retention and releasing mechanisms provide vital indication for the effective management of P to boost crop production and sustain soil. This study was conducted to evaluate the effects of coffee husk biochar (CHB) produced at two temperatures (350 and 500⁰C) and applied at a rates of (0, 5, 10 and 15t/ha) on phosphorus sorption and desorption in two soils with different P sorption capacities Fe and Al dominated strongly acid (pH=5.08) and Ca dominated alkaline calcareous soil (pH=7.85). Composite air dried, ground and sieved (2mm) soil samples were mixed with biochar and a 2 months incubation experiment was conducted at ambient temperature. In addition, P sorption characteristics of soils amended with biochar and in combination with and without mineral KH₂PO₄ fertilizer were determined. The results showed significant effects (p<0.05) on selected soil chemical properties by increasing soil pH and reduced exchangeable acidity, exchangeable aluminum, and exchangeable iron in a way that increased the availability of P from 4.52 to 23.21mg/kg (83%) in acidic soil after 2months of incubation and when CHB500⁰C was applied at a rate of 15t/ha and from 8.2 to 27.4mg/kg (70%) in calcareous soil when CHB350⁰C was applied at a rate of 15t/ha. Application of highly alkaline biochars to calcareous soil significantly increased the sorption of P and decreased the availability of P by higher biochar application rates. We concluded that CHB500⁰C and applied at 15t/ha is promising to potentially increase soil P availability in acidic soil and decreased in calcareous soil but, increased in calcareous soil when CHB350 and applied at 15t/ha. Moreover, further researches at field scale are needed to evaluate the effect of biochar on availability and fates of phosphorous in acidic and calcareous soil.

Keywords: desorption, sorption, acidic soil, calcareous soil