Abstract
Vegetative soil cover mitigates climatic variability and enhances the balance between mineralization and humification processes. Under aerobic conditions, most of the carbon that enters the soil is labile, but a small fraction (1%) is humified and stable, contributing to the soil carbon reserve; therefore, it is important to assess the carbon content captured after green manure cultivation and decomposition. During two consecutive semesters, July to December 2016 and January to June 2017, green manure plots (<em>Zea mays </em>L., <em>Andropogon sorghum </em>subsp.<em> sudanensis </em>and <em>Crotalaria longirostrata</em>) were cultivated individually, in a consortium or amended with palm oil agro-industrial biosolids in a randomized complete block design with 12 treatments. Once decomposed, the different carbon fractions (organic, oxidizable, non-oxidizable, removable and total) were determined. The results showed high total and organic carbon contents under the sorghum treatment, at 30 and 28 Mg ha<sup>-1</sup>, respectively, followed by those under the fallow + biosolid treatment, at 29.8 Mg ha<sup>-1</sup> and 27.5 Mg ha<sup>-1</sup>, respectively. Despite the short experiment duration and the possible contributions of previous management on recalcitrant carbon soil stocks, these findings suggest the importance of maintaining plant cover and utilizing green manure in the Colombian Caribbean region. Long-term experiments may be conducted to confirm the full potential of cover crops on carbon sequestration under tropical semiarid conditions.
Highlights
Agricultural practices can be a source of carbon dioxide (CO2) to the atmosphere (Lal 2007, 2014), contributing to climate variability when it surpasses plant carbon fixation by photosynthesis. Reicosky (2002) estimated that soil tillage promotes carbon losses between 30% and 50% and results in moisture and biodiversity losses in edaphic systems
Once the green manures were degraded, low average values of EC1:1 (0.73 dS m-1 at 25 oC) and pH (7.8) were observed in the soil, probably due to the production of organic acids resulting from the organic matter (OM) cycling
We found a low association (r ≤ 0.5) between the accumulation of Total SC (TSC) and biomass and dry mass yield, a situation that may be related to the fact that the fraction represented by the plant root system was not measured, which should be the object of a future study
Summary
Agricultural practices can be a source of carbon dioxide (CO2) to the atmosphere (Lal 2007, 2014), contributing to climate variability when it surpasses plant carbon fixation by photosynthesis. Reicosky (2002) estimated that soil tillage promotes carbon losses between 30% and 50% and results in moisture and biodiversity losses in edaphic systems. The adoption of more sustainable agricultural practices, such as cover crops, can increase SC and the retention of soil moisture (Carvajal et al 2014). Biomass added to soil is readily mineralized to CO2 and quickly released into the atmosphere due to the higher turnover rates (Davidson and Janssens 2006). It was demonstrated that the type of cover crop directly affects the soil organic carbon (SOC) mineralization rates under semiarid conditions (Ghimire et al 2017). Exposing semiarid soils to elevated concentrations of CO2 resulted in increases in net ecosystem productivity and carbon storage primarily as a result of direct effects on photosynthesis
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