Rapid, Clean, and Sustainable Bioprocessing of Toxic Weeds into Benign Organic Fertilizer

A recent report in this journal from these authors, which shows that vermicomposting transforms a toxic weed such as lantana into a benign organic fertilizer, can be of practical utility only if processes can be developed for rapid, inexpensive, and sustainable vermicomposting of these weeds. This paper describes attempts leading to such a process for the vermicomposting of toxic and allelopathic weeds lantana (Lantana camara), parthenium (Parthenium hysterophorus), and ipomoea (Ipomoea carnea). For it, the ‘high-rate vermicomposting’ concept was employed due to which the weeds could be used for vermicomposting directly in each case without the need for pre-composting or any other form of pretreatment. The manure worm Eisenia fetida, which had been cultured on cowdung as feed and habitat, was slow to adapt to the weed-feed but survived and then began to thrive, in all the three weeds, enabling the weeds’ sustained and efficient vermicomposting throughout the 16 month’s uninterrupted operation of the vermireactors. In all cases the extent of vermicast production per unit time showed a rising trend, indicating that the rate of vermicomposting was set to rise further with time. The vermicomposting was found to accompany a 50 ± 10% loss of organic carbon of each weed with a 50 ± 10% increase in the concentration of total nitrogen as also the weed’s additional mineralization. The combined effect was a significant lowering of the carbon-nitrogen ratio, and enrichment of all major, medium, and trace nutrients in the vermicomposts relative to their parent substrates. The findings establish that sustained, direct, and rapid transformation to organic fertilizers of even toxic and allelopathic weeds can be accomplished with the high-rate vermicomposting paradigm.