Soil organic matter and CO2 fluxes in small tropical watersheds under forest and cacao agroforestry

Abstract

Annual estimates of CO2 and dissolved carbon concentrations in the soil profile provide valuable insight into the dynamics of organic matter in soil and the effect of changes to vegetation cover. The aim of this study was to observe the spatial influence of litter decomposition in the first few centimeters of the soil for CO2 fluxes and to describe the processing of soil organic matter throughout the soil profile by comparing three small tropical watersheds. Data were collected biweekly for six months, from December 2015 to May 2016. CO2 was measured using an infrared gas analyzer in fixed chambers and the dissolved carbon of soil solution was analyzed in a TOC analyzer. No differences were found in the total soil CO2 fluxes (control flux treatments) between the three study areas. In both cacao agroforestry systems (managed and unmanaged), total CO2 fluxes were influenced by the decomposition of litter. CO2 emissions in the soil profile of the cacao agroforestry systems were highly variable, compared to the preserved forest, and highly dependent on the soil characteristics attributed to the type of vegetation cover. Although a definite pattern between the temperature and soil moisture was not identified, these parameters showed a strong relationship in controlling the release of CO2 between treatments. The organic and inorganic dissolved carbon patterns in the soil solution of the three areas revealed different responses of soil organic matter processing related to soil characteristics and vegetation. The results confirm the hypothesis that the top of soils (total CO2 fluxes) of both cacao agroforestry systems (managed and unmanaged) emits fluxes of CO2, which do not differ statistically from the preserved forest. However, depending on the soil characteristics, the cacao agroforestry system can result in an accumulation of CO2 and dissolved inorganic carbon in the soil profile that is prone to being transported by hydrological routes to groundwater and stream water.

Tree biomass and carbon stock assessment in different agroforestry system trees

“…Simarouba trees were recorded higher CO2 mitigation over kadamb trees, those were higher CO2 mitigation over litchi trees. Contributions of tree species in CO2 mitigation was well mentioned in the past works of Grote (2009) [17] , Costa et al (2018) [18] and Naik et al (2018) [19] .…”

Litter decomposition of six tree species on indigenous agroforestry farms in south-eastern Ethiopia in relation to litterfall carbon inputs and modelled soil respiration

“…Soil respiration CO 2 effluxes are directly correlated to litterfall fluxes and litter decomposition rates and are driven by the same climatic factors (Raich and Schlesinger 1992;Raich and Tufekcioglu 2000;Bond-Lamberty and Thomson 2010). Field measurements of soil respiration rates from tropical agroforestry systems are few (Bae et al 2013;Costa et al 2018), but reported rates are high and similar to those reported for tropical humid forests (Oertel et al 2016). Heterotrophic respiration, which measures the decomposition of soil organic matter, could be expected to show the most correspondence to litterfall and litter decomposition C fluxes.…”

Carbon Farming: Prospects and Challenges

“…Litter and tree roots constitute the highly sustainable way of formation as well as enhancing the quality of soil organic matter (SOM) in agroforestry ecosystems [51,52]. However, soil fertility is distinct in tropical agroforests, where they tend to have low organic matter due to high porosity and depth [53,54]. According to their availability, the management of diverse plant species allocating nutrients at varying levels, allows for sustainable nutrient management in nutrient-depleted soils [55,56].…”