Response of biochar derives from farm waste on phosphorus sorption and desorption in texturally different soils

The information on changes in phosphorus (P) sorption and desorption characteristics and transformations after biochar application to high P fixing soils is still unclear. In the present study, we evaluated the differential response of biochar derives from five different farm waste viz. Lucaena sp., Albbizia sp., Mangifera indica, Triticum aestivum and Oryza sativa applied at 1 and 3 g kg-1 (w/w) on P sorption and desorption in three texturally different (silt loam, clay loam and sandy loam) soils. The amount of P sorbed by the clay loam was significantly (p<0.05) higher than the silt loam and sandy loam, regardless of added P concentration. The Freundlich isotherms exhibit a better fit (R2 = 0.564-0.996 in silt loam, 0.640-0.993 in clay loam and 0.724-0.993 in sandy loam soil) to P sorption data as compared with the Langmuir isotherm. Biochar application significantly decreased the P desorption maxima and desorption constant. The R2 values ranged from 0.447 to 0.999 in silt loam, 0.438 to 0.996 in clay loam, 0.545 to 0.989 in sandy loam. Lucaena biochar showed highest adsorption maxima, thereby suggesting highest P release, whereas soils treated with Triticum aestivum biochar had the lowest adsorption maxima in both clay loam and sandy loam soil. These results indicated that biochar application can significantly enhance P availability; the extent of which is determined by soil texture and type of biochar. The results of present study highlight that biochar application would help increase soil P availability by enhancing fertilizer-P use efficiency associated with decreased P sorption capacity due to increased flush of available-P in soil colloidal complex.