Soil microbial communities under cacao agroforestry and cover crop systems in Peru

Authors: Buyer, Jeffrey; Baligar, Virupax; HE, ZHENLI - University Of Florida; GARDINI, ENRIQUE - Tropical Crop Institute (ICT)

Submitted to: Applied Soil Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/2/2017
Publication Date: 9/26/2017
Citation: Buyer, J.S., Baligar, V.C., He, Z., Gardini, E.A. 2017. Soil microbial communities under cacao agroforestry and cover crop systems in Peru. Applied Soil Ecology. 120:273-280.

Interpretive Summary: Cacao (Theobroma cacao) trees are grown in tropical regions worldwide for chocolate production. Cacao plantations suffer from a variety of fungal diseases as well as soil nutrient loss and poor soil health. We studied the effects of agroforestry management systems and cover cropping on soil microbial communities under cacao in two different replicated field experiments in Peru. Two agroforestry systems, Improved Traditional Agroforestry System (ITAS) and Improved Natural Agroforestry System (INAS), were compared. ITAS was a ‘slash and burn’ system in which all native vegetation was removed prior to replanting with cacao and other trees while INAS used selective removal of uneconomical trees followed by cacao planting. The two systems had different microbial community structures, and the shift in microbial community structure was suggestive of increased carbon availability in the INAS system. In the cover crop experiment, five cover crops and two controls (one with and one without nitrogen fertilization) were compared. Certain cover crops altered the soil microbial biomass of specific microbial groups and the overall microbial community structure. Cover cropping with centro (Centrosema macrocarpum) or perennial peanut (Arachis pintoi) may have increased soil carbon availability, while centro also reduced the soil fungal biomass. Our results indicate that management systems and cover cropping can affect soil microbial community structure, with potential improvements in soil health, in tropical agroforestry systems. This information will be useful to scientists developing cacao management systems.

Technical Abstract: Cacao (Theobroma cacao) trees are grown in tropical regions worldwide for chocolate production. We studied the effects of agroforestry management systems and cover cropping on soil microbial communities under cacao in two different replicated field experiments in Peru. Two agroforestry systems, Improved Traditional Agroforestry System (ITAS) and Improved Natural Agroforestry System (INAS) were compared. ITAS was a ‘slash and burn’ system in which all native vegetation was removed prior to replanting with cacao and other trees while INAS used selective removal of uneconomical trees followed by cacao planting. Soil microbial communities were analyzed by phospholipid fatty acid (PLFA) analysis and terminal restriction fragment length polymorphism (TRFLP) analysis. Soils in the ITAS system had lower biomass of Gram-negative bacteria, and a lower Gram-negative to Gram-positive ratio, than soils in the INAS system. However, soil microbial community structure was predominantly controlled by a large soil pH gradient (three pH units) across this experiment. In the cover crop experiment, five cover crops and two controls (one with and one without nitrogen fertilization) were compared. Certain cover crops altered the soil microbial biomass of specific taxonomic groups and the overall microbial community structure. Arachis pintoi (perennial peanut), Calopogonium mucunoides (calopo), Canavalia ensiformis (jackbean), Centrosema macrocarpum (centro), and one non-leguminous cover crop, Callisia repens (callisia). Cover cropping with centro (Centrosema macrocarpum) or perennial peanut (Arachis pintoi) increased the Gram-negative to Gram-positive ratio, while centro reduced the fungal biomass. Microbial community structure was significantly affected by cover cropping. Our results indicate that management systems and cover cropping can affect soil microbial community structure in tropical agroforestry systems, but the effects of soil edaphic properties must be considered as well.