Effects of Combining Controlled Release Fertilizer and Organic Matter to Nutrient Retention in Green Roof Media

Abstract

Rooftop gardening, a burgeoning sector within agriculture, repurposes existing urban spaces to cultivate plants for consumption, production, and environmental enhancement. This practice offers a sustainable solution for introducing agricultural opportunities to urban communities. As rooftop gardens become increasingly prevalent, research becomes essential to establish best practices for this emerging form of gardening. Currently, rooftop vegetable production faces various challenges, necessitating research into optimal watering regimens, fertility management, disease control, and more. Traditional green roof media (GRM) often suffer from poor water retention and high nutrient losses. Incorporating organic matter (OM) into GRM, alongside controlled-release fertilizer, shows promise in mitigating these challenges and ensuring consistent nutrient supply. To investigate the impact of organic matter on nutrient retention in GRM, we conducted a greenhouse container study. Green roof media, with varying levels of spent mushroom compost (SMC) amendment (2, 4, and 6 cm), were evaluated over two growing cycles (28 days). We measured crop biomass and Zinnia elegans (Zinnia) yield, as well as essential nutrient leachate concentrations, leaching fractions of applied water, and nutrient uptake. Our findings revealed that SMC amendment had no significant effect on crop growth and yield. However, it did lead to reduced leaching of essential nutrients such as phosphorus (P), iron (Fe), and manganese (Mn). Additionally, we observed a notable decrease in water loss through the GRM on average of 12% in 28 days. These results suggest that SMC holds promise as an effective OM source for GRM, offering potential benefits in water and nutrient retention.