Effect of Biochar, Farmyard Manure and Poultry Manure on Zn Adsorption in Calcareous Alkaline Soil

The effect of Farm Yard Manure (FYM), Press Mud (PM), and Biochar (BC) applied to a fresh soil was evaluated on Zn adsorption potential in calcareous alkaline soils [Piedmont alluvium, silty clay loam, Ustochrept]. The Zn adsorption capacity was determined by adding 50 ml of 0, 5, 10, 20, 40, 60, 120, 240 and 360 mg Zn L^-1 (initially Zn applied, IZnA) to 5 g soil with absence (non-treated) or to soil pretreated with FYM, PM or BC at rate of 10 g kg^-1. The suspension was shaken on horizontal shaker for 20 h continuously to assess the equilibrium Zn concentration (EZnC). The difference between the IZnA and EZnC was assumed to be adsorbed. Results showed that FYM, PM or BC yielded lower EZnC and higher Zn adsorption (x/m) at higher IZnA but at lower IZnA 20 mg Zn L^-1 the reverse was observed. The data in non-treated soils were fit to both Langmuir and Freundlich but in treated soils they were fit only when adsorption values for initial IZnA were disregarded. The adsorption, as indicated by b and K values was higher for BC followed by FYM but MCB and 1/n value that reflects the buffering capacity was higher for FYM than BC or PM. The lower adsorption of Zn at lower IZnA below 20 mg Zn L^-1 and higher for higher IZnA for amended soil over non-treated soil suggesting its contrasting effect at different IZnA levels.