Nutritional and microbiological effects of vermicompost tea in hydroponic cultivation of maple peas (Pisum sativum var. arvense L.)

Hydroponics receives considerable attentions due to population expansion, soil pollution, and farmland scarcity. However, one significant problem is that its residual effluents are detrimental to the surrounding ecosystem. There is a dire need to find an organic, alternative, biodegradable substrate. Vermicompost tea (VCT) was investigated on its suitability as a hydroponic substrate to provide both nutritional and microbiological benefits. It was found VCT increased the biomass of maple peas (Pisum sativum var. arvense L.), increased stem length, raised the potassium ion content, and promoted the uptake of nitrogen by the roots. Meanwhile, the microorganisms associated with earthworm guts were detected in the maple peas root system, namely the inter-rhizosphere of maple peas, including Enterobacteriaceae, Pseudomonadaceae, and Flavobacteriaceae. The presence of these microorganisms in large number indicated the ability for VCT to retain earthworm intestinal microbes via intestinal tract movement, excreting, and other vital activities. In addition, Rhizobia spp., such as Burkholderiaceae and Rhizobiaceae were also identified in VCT. They are critical for legumes as they can form root or stem nodule symbioses to produce growth hormone, vitamins, nitrogen fixation, and protection against plant stress. These findings are consistent with our chemical analysis that VCT-treated maple peas had increased nitrate and ammonium nitrogen content relative to the control in roots, stems, and leaves, hence increasing maple peas' biomass. The abundance and species of the inter-root bacterial population were found to change during the experimental period, indicating the importance of microbial balance to the growth and nutrient uptake of maple peas.