Composting Invasive Plants in the Rio Grande River

Abstract The purpose of this study was to determine the effect of whole-plant composting on the viability of seeds and other propagules of the invasive plant species waterhyacinth, waterlettuce, hydrilla, and giant reed while producing a valuable compost product. Invasive species were subjected to preliminary germination and growth tests and oven mortality tests to evaluate whether species distribution was via seeds, vegetative propagules, or both, as well as whether the composting process had the potential, through the high temperatures obtained, to kill seeds and other propagules. Germination and growth tests determined the means by which invasive species spread. Oven tests determined the temperatures at which unscarified and scarified seeds and propagules were rendered inviable. Achieving temperatures of at least 57.2 C was necessary within constructed compost piles to effectively kill the plants without the danger of redistribution. In the field, the study successfully developed a large-scale composting operation using invasive plant species as the primary feedstock. Analysis of field-scale composting showed final materials were within satisfactory to ideal levels for samples analyzed by the U.S. Compost Council's Seal of Testing Assurance Program and were, therefore, a valuable compost product. Nomenclature: Giant reed, Arundo donax L. , hydrilla, Hydrilla verticillata (L. f.) Royle, waterhyacinth, Eichhornia crassipes (Mart.) Solms, waterlettuce, Pistia stratiotes L. Management Implications: The ecological impacts of invasive species are primarily due to their rapid growth, clogging waterways as well as outcompeting or completely displacing native species, which can result in the reduction of native population densities, species diversity, and richness (Chilton and Durocher 2009). Many exotic aquatic plants were introduced into the United State through the aquarium trade and through initial uses for erosion control (Chilton and Durocher 2009). However, most invasive aquatic plants are noxious weeds in aquatic environments nationwide (United States Congress 2006). In the past, biological control agents, chemical herbicides, and mechanical removal and harvesting were implemented to manage species in their various environments (Chilton and Durocher 2009). As a waste management system within agriculture, the composting process has been shown to kill plant pathogens and weed seeds if temperatures obtained are high enough and last long enough (Dougherty 1999; Wiese et al. 1998). Compost has also been used by the horticulture industry to decrease plant diseases, to increase plants' nutrient access, and as an effective weed-control agent (Faucette 2003). Some exotic plants have been successfully composted in the past, but the composting of invasive species has not been fully investigated to determine whether all plant seeds and propagules are inactivated during the composting process (Rogers 1983). This study investigated, and results demonstrated, the effectiveness of a large-scale composting operation in successfully rendering invasive plant seeds and propagules of waterhyacinth [Eichhornia crassipes (Mart.) Solms], waterlettuce (Pistia stratiotes L.), hydrilla [Hydrilla verticillata (L. f.) Royle], and giant reed (Arundo donax L.) inviable while producing a valuable compost product for the agricultural and horticultural industries. This strategy can inform composting operation models for other invasive species.