Temperature and moisture effects on C and N mineralization from surface applied clover residue

A better understanding of the effect of temperature (T) and moisture on soil microbial activity should improve our ability to predict N mineralization from soil organic matter and crop residues. The objective of this study was to evaluate the effects of water potential (psi) and T on C and N mineralization from unamended Cecil loamy sand soil (clayey, kaolinitic, thermic Typic Kanhapludult) and from crimson clover (Trifolium incarnatum L.) residues applied on the soil surface. Cecil soil was packed into acrylic plastic cylinders, adjusted to -5.0, -1.5, -0.03, or -0.003 MPa, treated with clover residues on the surface or left unamended, and incubated at 10, 20, 28, or 35 degrees C for 21 d. Headspace gas samples for CO2 and N2O determinations were taken periodically and NH3 evolved was trapped. Inorganic N in soil and residue extracts was analyzed after 21 d. When psi increased from -5.0 to -0.003 MPa, total CO2 evolved from unamended soil increased linearly with In(-psi), whereas total CO2 evolved from clover residue increased exponentially with psi. In both cases the effect of psi was enhanced as T increased. Two-dimensional (T, psi) equations were developed to describe these effects. Apparent net mineralized N from the clover residue increased with psi until it reached a maximum between -0.5 and -0.03 Mpa.