Evaluation of potential living cover crops under a banana canopy and their short-term effects on soil microbial activity
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The use of cover crops has been widely promoted as a strategy to enhance soil quality and health. The main objective of this research was to evaluate three common plant species in Puerto Rico (Heterotis rotundifolia, Spagneticola trilobata, Tradescantia zebrina and Geophila repens as reference plant) as potential cover crops for banana (Musa acuminata AAA), and their short-term effects on soil microbial activity. The study was conducted following a randomized complete block design (with four replicates) at the Agricultural Experimental Station of Gurabo. Plant growth analysis was conducted with measures of aboveground biomass (AGB), leaf area index (LAI), relative growth rate (RGR), net assimilation rate (NAR) and crop growth rate (CGR). Soil coverage by plant species, weed biomass and labor time were measured among treatments. In addition, soil organic carbon (SOC), Dehydrogenase (DHA), β-Glucosidase enzyme activity, phospholipid fatty acids (PLFA) among cover crops to determine size and composition of the microbial community and functional groups of soil organic matter with mid-infrared spectroscopy were evaluated. Results showed that AGB of cover crops species after 229 days after planting (DAP) were significantly different from each other, with a dry weight of 367 g m-2 for S. trilobata, 244 g m-2 for H. rotundifolia, and 149 g m-2 for G. repens. After 229 DAP, S. trilobata had a significantly higher LAI and CGR. The LAI and AGB were correlated, suggesting that plant species with higher LAI generated more AGB. After 257 DAP, S. trilobata and H. rotundifolia had the highest soil coverage, with 91 % and 84 % respectively, and control plots without a plant species had the highest average weed biomass with 65 g m-2. Labor time was reduced significantly in plots with cover crops species. After 289 DAP, results showed a significant difference among treatment, where G. repens and control plots reflected higher SOC. Overall enzyme activity (DHA and β-Glucosidase) increased significantly among sampling dates. The plant species with the greatest concentrations of microbial biomass were S. trilobata and G. repens, reflecting the highest trophic levels with the presence of predators (protozoan groups). H. rotundifolia showed the highest value and variance for the stress and community ratio. Soil organic functional groups did not reflect a significant difference among treatments. A non-metric multidimensional scaling analysis showed a positive association of PLFA with aliphatic type-C bonds. This study concluded that S. trilobata and H. rotundifolia were the two species with the highest potential as living cover crops for banana fields, according to their functional growth traits, soil cover and competition with weeds. In addition, living cover crops enhance soil quality, increasing SOC and enzyme activity after 254 DAP. Results of microbial community size and composition indicated S. trilobata and G. repens as suitable cover crops to enhance soil health.