Evaluation of nutrient management and mulching strategies for vegetable production on an extensive green roof

Background/Question/Methods

Substrate nutrient and moisture management are two major concerns in green roof agriculture.  These concerns are amplified when using extensive green roof systems for food production.  Currently no recommendations or best management practices exist to guide rooftop farmers in dealing with these issues.  The purpose of this study was to explore three mulching strategies (no mulch, pine bark mulch, and a living Sedum mulch) and three fertilization regimens (25, 50, and 100 g/m² of a 14-14-14 N-P-K slow release fertilizer applied twice during each growing season) over two growing seasons to determine their possible benefits to rooftop vegetable and herb production.  Tomatoes (Solanum lycopersicum), beans (Phaseolus vulgaris), cucumbers (Cucumis sativus), sweet peppers (Capsicum annuum), basil (Ocimum basilicum), and chives (Allium schoenoprasum) were included in this study because of their common use in home gardens. 

Results/Conclusions

Crops performed better in 2010 than 2011 because of more extreme temperature and precipitation variations during 2011.  When there were differences among mulch treatments, pine bark usually resulted in higher productivity than the live Sedum mulch.  Mixed effects of live Sedum mulch on crop production are consistent with previous literature on the use of living mulches in vegetable production. Among fertilizer treatments, 100 g/m² outperformed lower rates in most cases.  Instances of higher performance of lower fertilizer rates were observed, likely because those treatments adequately supplied the crops with phosphorus and potassium.  Further research into more types of mulch and their effects on the green roof microclimate could provide a better understanding of the role that mulching could play in green roof agriculture.  Likewise, more research into various types of fertilizers with different compositions could also help in the development of an efficient and productive nutrient management practice.