Vermicomposting separated swine solids is a way to reduce odor and pathogens in a product that can be used off site as a nutrient source and soil amendment. The solid separation system removes a portion of the nutrient and organic loads from the liquid waste stream prior to entering the lagoon system while the vermicomposting process stabilizes the nutrients and organics that are diverted from the lagoon, making it easier to find off-farm uses for the product.
The goal of this project was to demonstrate the usefulness of vermicompost in an agronomic setting. If crop growth can be enhanced without increasing nitrogen or phosphorus runoff pollution, then the vermicompost product can be evaluated further for economic efficiency. In the same manner, if nitrogen or phosphorus pollution can be decreased without reducing crop growth or quality, the product is also in a position for further evaluation.
We grew turnips in small plots with either 0, 10 or 20% vermicompost (by volume) mixed into the top 0.3 m of soil; nitrogen fertilizer was added to half of the plots. The experiment was repeated over four growing periods in two different soil types. Runoff from each plot was measured and analyzed for nutrients, solids, copper and zinc. Plant biomass was harvested at maturity. Both wet and dry weights were determined.
Plant biomass increased with the addition of vermicompost while the volume of runoff decreased. None of the pollution parameters were affected by inorganic fertilizer and only the mass of phosphorus and zinc in the runoff showed an effect of adding vermicompost.
The mass of zinc in runoff decreased but the mass of phosphorus increased because of the degradation activity of microorganisms and earthworms in the vermicomposting process would be expected to break down organic matter and release nutrients. Phosphorus, needed in smaller quantities than nitrogen, would be applied in excess and would end up in soil solution and runoff. Mass of nitrogen in run off was not affected by vermicompost addition, suggesting that the greater biomass growth did not come at the expense of additional nitrogen in runoff.
This project demonstrated the usefulness of using vermicompost in a specific agronomic instance. Turnip growth was enhanced, runoff volume was reduced and pollutants in runoff were generally not greater than control plots of the same soil type. In phosphorus sensitive fields, any addition of manure based products must be used with caution.
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Classen, J.J., J.M. Rice, and R. Sherman, 2007. The Effects of Vermicompost on Field Turnips and Rainfall Runoff. Compost Science and Utilization 15(1): 34-39
By John Classen, Mark Rice and Rhonda Sherman, NC State University
This report was prepared for the 2008 annual meeting of the regional research committee, S-1032 "Animal Manure and Waste Utilization, Treatment and Nuisance Avoidance for a Sustainable Agriculture". This report is not peer-reviewed and the author has sole responsibility for the content.