Abstract: Maintaining productivity in agricultural environments requires continuous effort and inputs for farms of all scales. Maintaining productive soils in organic agriculture is highly challenging, as fewer options are available. Organic fields often have lower nutrient availability, including phosphorus and other nutrients relative to conventionally managed soil. To mitigate these concerns, some organic growers have begun to embrace a widely accepted understanding within natural systems; soil microbes are the drivers of soil health and nutrient cycling. Thus, more farmers are interested in managing their soil microbes including arbuscular mycorrhizal (AM) fungi.
We partnered with Juniper Hill Farms in Lawrence, KS to integrate this research in situ with the practices incorporated on working organic farms which included irrigation, weekly nutrient amendments, and pest control. We test how AM fungi influence organic crop growth and nutrient concentrations. All tested AM fungal species were originally isolated from a tallgrass prairie in Lawrence, KS. These AM fungi have been shown to be highly beneficial in native plant restoration but were untested in an agricultural environment.
In hoop-house (high tunnel greenhouse with an earthen floor), we inoculated seedlings of two tomato (Solanum lycopersicum) and five pepper (Capsicum annuum) varieties at transplant with a mixture of AM fungi or a non-inoculated control. Fifteen cm3 of living or sterilized inocula was applied in the planting hole at the time of transplanting. Cumulated across the growing season, we found that total tomato harvest was improved 27% after AM fungal inoculation and this was driven by an increase in harvested tomato number with inoculation. Total pepper harvest was improved 3-12% depending on variety, with the exception being shishito (-9%). In a separate greenhouse trial, we inoculated basil (Ocimum basilicum) and chard (Beta vulgaris) with individually five species of AM fungi, their mixture, and a non-inoculated control. Total harvested mass and leaf concentration of total carbon, nitrogen, phosphorus, potassium, calcium, magnesium, copper, iron, manganese, and zinc were generally dependent on AM fungi inoculation and varied among AM fungal species. AM fungal species that promoted plant growth the most tended to also boost plant micronutrients, where biomass was correlated with total carbon, nitrogen, phosphorus, copper, and manganese in leaf tissues.
This work highlights the importance of AM fungal amendments in organic agriculture and demonstrate that amending organic soils with locally collected fungi can benefit total crop harvest, nutrient and protein content for most of the tested crop varieties.
