Temperature Sensitivity of Carbon Release in An Acidic Soil Is Mediated By Lime and Mulch Amendments.

Liming and mulching are common agricultural management practices. However, there is limited knowledge on the temperature sensitivity of carbon (C) release in acidic soils amended with lime and mulch. We conducted laboratory incubation experiments for 96 days at 20° ± 1 and 40 °C ± 1 using an acidic Chromic Luvisol. The experiments consisted of five treatments viz: soil only (S), soil + lime (S + L), soil + mulch (S + M), soil + mulch + lime (S + M + L) and soil + mulch + 2L (S + M + 2L). Mulch was applied at the rate of 0.5% w/w (M) in the form of sugarcane trash and lime was added at two rates, i.e. 0.46 (L) and 0.92 (2L) % w/w using analytical grade calcium carbonate. The proportions of C released from lime (δ¹³C of –8.67‰), mulch (–13.02‰) and soil (–25.2‰) were quantified using their distinct δ¹³C values and a simple linear mixing model. During the 96-day incubation period, in the absence of mulch addition between 64% and 100% of the applied lime C was released as CO₂ at both incubation temperatures.  Furthermore, an increase of 59% lime derived C, 48% mulch derived C, 284 % soil derived C and 170% total C was found when the incubation temperature was increased from 20 °C to 40 °C suggesting that mineralization of native soil C was more sensitive to temperature than the C released from lime dissolution and mulch mineralization. Temperature sensitivity of soil derived C was lower in treatments with mulch and lime addition compared to soil without C amendments. We obtained a Q₁₀value of 2.41 ± 0.06 for the C released by lime dissolution in the acidic soil.                                                                               

Key words: Liming; dissolution; mulch; CO₂ flux; soil carbon; temperature dependence; Q₁₀; acidic soil.