2019 ASHS Annual Conference

Space availability is one of the largest barriers to urban agriculture. One way around this issue that urban farmers in some parts of the world are exploring is moving their farming activities to building rooftops. One method of rooftop farming in use is row agriculture using green roof technology. This often comes with some challenges, as green roof media is typically fast draining and contains limited nutrients. Vegetable crop plants, which typically require more water and more nutrients that the ornamental species typically found on green roofs require irrigation and the use of fertilizers. One nutrient management practice that some rooftop farmers are using is the addition of compost, which could lead to changes over time in the water holding capacity, organic matter content, and weight of green roof media. This practices and its long term implications have not been well studied. Green roof platforms were set up at the Harold R Benson Research and Demonstration Farm to examine how addition of compost effects runoff water quality and green roof media properties. Compost treatments included a no compost control, and the addition of 0.33, 0.66 and 1 kg/m² of compost. Organic fertilizers were used to supply additional nutritional needs to vegetable plants grown in the green roof platforms. All green roof platforms are fitted with gutters and water collections buckets. Water samples were collected every month starting July 2018, weather permitting. Water samples were then analyzed for pH, conductivity, color, turbidity, and nitrate-nitrogen, ammonia-nitrogen, total phosphorus, and potassium content. Water quality results were analyzed in R. Analysis of Variance was performed on all variables with compost treatment and month of sampling as fixed effects. Significant differences between treatment means were analyzed using Tukey HSD with an alpha of 0.05. Preliminary results from 2018 do not show a significant effect of compost treatment on water quality metrics within the green roof platforms. There are however some differences between the green roof platforms and similar platforms filled with topsoil that were managed the same way the no compost controls were in this study. There is however a significant effect of sampling month on some runoff water quality metrics. Runoff water pH, conductivity, color and ammonia-nitrate concentration decrease with time. Nitrate-nitrogen and potassium concentrations were higher lowest in July at the start of the study an in November. Total phosphorus concentrations appear to be decreasing with time.