PS 33-156 - Using green waste for agricultural production

Background/Question/Methods

Supporting human populations in a sustainable way is a primary challenge for cities and islands, in part, because of the enormous volume of waste that is produced and the lack of fertile land for agriculture. Cities and islands import most food, limiting access to nutritious and locally grown food, creating food deserts, and resulting in poor human health. Waste mulch (WM) is made from biodegradable waste such as woody debris, yard trimmings, and felled trees. WM is one solution for repurposing waste to keep it out of landfills. WM can be high in nitrogen, so it may be a beneficial addition to agricultural and horticultural plantings. In addition, using it as a soil cover may prevent erosion, increase soil moisture, increase organic material in the soil, and suppress weeds. We investigated the use of WM in Barbados and the United States to determine whether it increased soil moisture and nutrients, modulated soil temperature, suppressed weeds, and increased crop survival, yield, and nutrients. We did this by partnering with farmers in these two countries to establish replicated plots of sweet potatoes (Ipomoea batatas) that were planted in bare ground or soil that had been covered with a layer of WM.

Results/Conclusions

The addition of WM as a soil cover for one growing season in sweet potato plantings resulted in relatively consistent results in Barbados and the Washington, DC metropolitan area. Mulch did not improve nutrients in the soil or crop, but mass of weeds was lower and yield of sweet potatoes was higher in mulched plots. Also, plant survival was higher in mulched plots in Barbados, but not the United States. Soil moisture and temperature may also differ, but these results are preliminary. WM has some clear and immediate benefits for growing sweet potatoes. We also expect that nutrients in soils are likely to be enhanced if the soils are particularly nutrient-poor or soil samples are collected after mulch has had a longer time to decompose. Some barriers that may prevent widespread use of WM include its price, availability, and lack of equipment to spread it on fields. However, farmers indicate a willingness to use WM if benefits outweigh costs. Possible next steps include determining benefits of using WM for aboveground crops, the potential amount of waste that could be used in agricultural production, and additional economic and environmental benefits of diverting WM from landfills for use in agricultural production.