Modeling the effect of land use and manure management on soil carbon sequestration in tropical mixed crop-livestock systems: A case study in Guadeloupe (Caribbean)

In tropical regions, mixed crop-livestock systems (MCLS) afford opportunities to achieve sustainable agriculture by supplying several ecosystem services, including soil C sequestration. The aim of this study was to assess soil C sequestration in representative tropical (Caribbean) MCLS in the Guadeloupe Archipelago. We designed a modeling approach at the scale of the farm and cropping system, based on a data-driven model of soil organic C (SOC) balance coupled to three databases. The variables included soil properties, manure properties (fresh and stored-composted), and farm characteristics of the eight MCLS. The results indicated that land use (i.e., relative area occupied by perennial crops) was the main factor controlling soil C sequestration at the farm scale and that pasture and sugarcane systems were crucial for maintaining or increasing SOC stocks. Under the current MCLS management, only 16 % of manure production is used to fertilize croplands. This mode of fertilization was found to be ineffective at the farm scale, given that it resulted in low (average + 0.03 % yr −1 ) or negative (up to −0.3 % yr −1 ) soil C sequestration; manure C inputs did not compensate for SOC outputs by mineralization in annual systems. It is estimated that increasing manure use to near 100 % would increase the level of soil C sequestration 3.5-fold (average + 0.11 % yr −1 ) and could compensate for up to 20 % of the reduction in C inputs from crop residues used as animal feed. These effects were 50 % higher for fresh manure than for stored-composted manure because of mass and C losses during storage, which reduced the level of manure C inputs to the soil. Overall, the results indicate that increasing manure use and shortening the storage period through, for example, more frequent split applications would be suitable to boost soil C sequestration and sustainability in tropical MCLS by decreasing soil C losses and increasing C retention in soil. However, trade-offs must be made between managing the frequency of applications, the cost and degree of manual labor required, and optimizing the overall health of the MCLS.