Soil respiration and distribution of aggregates in modified agroforestry systems of coffee and avocados in Huatusco, Veracruz, Mexico

Coffee agroforestry systems (CAFS) in Veracruz, Mexico, are being altered by introduction of avocado trees, which is currently introduced among the coffee. This practice could change the soil organic carbon (SOC) content, soil structure, biological activity, and CO2 emissions. The objective of this work was to evaluate the variation of soil respiration (SR) and aggregate size in modified CAFS with avocados. Three CAFS, an avocado-coffee system (ACS), and an avocado monoculture (AMC) were compared. Three plots were delimited in each system, where soil samples were extracted at three soil depths. Before incubation, soil pH, bulk density (Mg m(-3)), soil organic matter (SOM, %), and SOC (mg C g(-1)) contents were determined. The distribution of soil aggregates was quantified in dry soil and the weighted minimum diameter (WMD) was determined. Incubation allowed to determine the potential CO2 flux generated by SR for 30 days; the residual SOC was determined after incubations, whose difference with the initial SOC allowed to perform a balance of C, calculating a SOC degradation rate constant (Kt). ANOVA (p <0.05) and means comparison with the Tukey's test was performed. In the ACS a lower range average (0.6 a 0.8 mm) of WMD was found at the three soil depths, the lowest SR (150 kg CO2-C ha(-1) h(-1)), a positive balance of SOC, having a negative Kt constant were recorded. Subsequently, the introduction of avocados contributes to the storage of SOC and the reduction of CO2 emissions.