Predicting the in situ rate constant of soil carbon mineralisation from laboratory-based measurements in tropical soils under contrasting tillage management systems

Predicting soil organic carbon (SOC) mineralisation in the field is crucial to assessing the impact of changes in land use and tillage practices. Although soil data from long-term field experiments are essential to calibrate model parameters for SOC mineralisation, these are frequently lacking regarding some parts of the tropics. The aim of this study was to develop and test an indicator for the in situ SOC mineralisation rate constant using data obtained during soil incubation in the laboratory. Sixty-nine plots corresponding to four soil types (andosol, nitisol, ferralsol and vertisol) under six crops (banana, sugarcane, vegetables, yam, melon and pineapple) involved in 12 tropical cropping systems were analysed. Soil sampling and laboratory incubation procedure were designed to reflect the long-term impact of cropping systems on SOC dynamics. Data from long-term experiments were obtained from a previous study performed on the same cropping systems in Guadeloupe (Caribbean). While SOC contents and stocks were only controlled by soil type, mineralised SOC in the laboratory (Cmin) was controlled to the same degree by both soil type and crop. Moreover, the Cmin/SOC ratio, which is an indicator of the more active SOC fraction, was only controlled by the crop. Although Cmin and Cmin/SOC were not affected by recent C inputs from crop residues, they were negatively correlated with the rate constant of SOC mineralisation observed in the field (kfield). These results indicate that differences between the cropping systems (i.e. perennial vs. annual crops) concerning the management of soil tillage markedly affected depletion of the mineralisable SOC fraction. Overall, the results showed that Cmin measured under regulated laboratory conditions could be helpful to estimate kfield. This is important in tropical regions in order to anticipate the effects of changes in land use and tillage management before changes in SOC stocks become noticeable in the field.