Living mulches present tradeoffs between soil nutrient cycling and competition during establishment of tea in an organic production system

Tea (Camellia sinensis) is an emerging crop in Florida and the southeastern United States. The impacts of different production system components, including ground covers are still unknown. In this study, we examined the effect of weed barrier cloth (WBC) ground cover compared to two living mulches, perennial peanut (PPC) and a crimson clover rotation (CCR), on plant performance, soil microbiome, and nitrogen (N) cycling during the establishment phase of tea grown in central Florida. Three years after installation, plants under WBC had significantly higher yields than those with the living mulches. The effect of groundcover on soil microbiome was evaluated via qPCR gene count estimation of N-cycling associated genes, as well as dilution plating to establish count and diversity of culturable soil fungi, bacteria and N fixing bacteria. Soil under PPC had higher concentrations of genes associated with N cycling and P solubilization and higher plate counts of culturable microbes, including N fixing bacteria, compared to soil under WBC. Of the two living mulches, PPC soil had significantly higher counts of ammonia oxidizing genes and cultured fungi and bacteria than CCR soil. The impacts of ground cover on N cycling were further examined through an in vitro soil incubation study and an in situ field study of fertilizer-amended and unamended soil under PPC and WBC. In the in vitro study, after 7 days of incubation, 47.3 % of the supplied N was mineralized in PPC soil compared to 20.2 % in WBC soil. Throughout the 28-day incubation, the PPC treatment showed higher levels of nitrate than WBC. In the in situ microplot column field study, no significant differences were found in the overall amount of N mineralized, but differences in the timing of mineralization were observed: the highest nitrate concentration occurred at day 14 under PPC and day 28 under WBC. During the establishment period of tea, use of WBC may benefit plant growth; however, it may also result in changes in nutrient cycling microbial populations that alter the N mineralization rate of applied fertilizers compared to living mulch cover crops. Results of our study established foundational data on N mineralization from organic fertilizers in field grown tea. The rates of N mineralization from organic N fertilizer and soil microbial diversity under WBC and a legume cover crop estimated in this study will be of value for establishing sustainable tea production systems.