Influence of Gypsum and Carbon Amendments on Carbon Fractionation in Two Contrasting Soils in Ohio.

Gypsum (a byproduct from the combustion of coal for electrical energy production) and crop residues can improve soil properties, but few studies have focused on their effect to impact various C pools in soil. A greenhouse experiment was conducted to measure the different forms of C (i.e. total C by dry combustion, permanganate oxidizable C (POXC) and inorganic C by Chittick’s apparatus)  in 5 soil layers (0-2, 2-4, 4-10, 10-25 and 25-40 cm) as influenced by glucose as a readily available C source (0 and 5.0 Mg ha^-1), crop residues (0 and 13.4 Mg ha^-1) and gypsum (0 and 26.9 Mg ha^-1) additions to a Wooster silt loam and a Hoytville clay loam. Glucose and residue increased total C significantly (P < 0.10) to a depth of 4 and 25 cm, respectively. Gypsum addition did not affected total C concentrations. Also, no significant effects of treatments on POXC concentrations were observed. Glucose addition resulted in significant increase in calcite level in only the 0-2 cm soil layer. Residue and gypsum addition did not increase inorganic C significantly, except in one soil layer 25-40 cm, where gypsum was also included. This was attributed to the abundant supply of Ca²⁺ leading to formation of inorganic carbonates, a form of soil C sequestration. Addition of C and gypsum to soil can increase C levels in soil provided there is a sufficient increase in CO₂ and Ca concentration within the soil profile. The sequestered C can improve soil quality and provide overall environmental benefits.