Long, R.J., Brown, R.N., & Amador, J.A. 2017. Growing Food with Garbage: Effects of Six Waste Amendments on Soil and Vegetable Crops. HortScience 52(6): 896-904. doi: 10.21273/HORTSCI11354-16
Much of the organic-rich waste (e.g. food scraps, yard waste) that ends up in landfills could be put to better use, like building soil fertility for crops. A recent study suggests that crops grown in soils that have been amended with a variety of landfill-destined organic waste products produce comparable yields to plants grown with conventional synthetic fertilizers.
Thinking about waste
Landfills are filling up at alarming rates across the US, raising concerns about the limited number of sites suitable for developing and managing waste in the future. In 2014, the US Department of Agriculture (USDA) released a report, stating that in 2010, 31% of the food available to consumers went uneaten, and the vast majority of that food ended up in landfills (read the full report here). The US Environmental Protection Agency (EPA) estimates that over 21% of material entering landfills is wasted food. In light of this, the EPA has set an ambitious goal to curb food wastes entering landfills by 50% by 2030 (read more at the EPA’s website about Sustainable Food Management). One way to reduce the amount of food entering the landfill is to make sure that edible food gets distributed to those in need. Food that is not fit for human consumption can be diverted as animal feeds, or used to build soil quality and fertility for crops.
The difference between synthetic fertilizers and soil amendments
Applying food wastes to agricultural soils is a great way to re-purpose inedible foods scraps that normally are added to landfills. However, conventional agriculture relies mainly on synthetic or inorganic fertilizers (think industrial Miracle Grow) to improve crop yields. Synthetic fertilizers are popular because they are predictable: they released a specific amount of nutrients over a particular time frame. However, the industrial processes required to produce inorganic fertilizer are incredibly energy-intensive (and expensive!). Another draw-back of using synthetic inorganic fertilizers is that they do not add carbon, and do little to improve soil health (see this post to learn more about more environmentally friendly fertilizers).
An alternative to synthetic fertilizers to use organic matter-rich soil amendments. These materials stem from decomposing organic matter (e.g. food scraps, plant leaves and trimmings or animal manure), and contain both nutrients and carbon – which is why they are referred to as “amendments”, rather than “fertilizers”. Organic matter-rich soil amendments are added to soil, in order to provide nutrients for plant growth (like synthetic fertilizer), but also to add carbon to soils which helps build organic matter. Building soil organic matter is important for soil health, but also allows soils to function as a carbon sink – reducing the amount of carbon dioxide in our atmosphere (read more about soils and carbon in this post). However, organic-rich soil amendments do not release nutrients to crops as quickly or steadily as synthetic fertilizers do, and thus their behavior can be a little unpredictable for farmers. However, this trade-off is worth it in the end, because soils with higher organic matter are healthier, and crops grown in healthy soils are more resilient to pests, disease and drought. As consumers and farmers are becoming more interested in environmentally sound farming practices, the use of organic-rich soil amendments (e.g. compost or animal manure – see table) is increasing.
New sources of organic-rich soil amendments
Recently, farmers, researchers and others have become interested in using novel sources of organic waste as soil amendments, including wastes from industrial and municipal sources (e.g. food scraps from restaurants, or domestic food waste destined for the landfill). These new sources of organic waste are interesting for a variety of reasons, including low cost and ready availability, mitigating accumulations in landfills, and repurposing waste (one man’s trash is another man’s treasure!). However, the use of organic wastes from industrial and municipal sources is not hugely popular at the moment, because farmers have questions around the safety of the wastes (especially concerning heavy metal content), and whether using these organic waste products as soil amendments will actually help plants grow and produce yields comparable to plants fertilized with synthetic products. Though past research efforts have shown mixed results on the fertility and yield outcomes of crops fertilized with organic wastes, a recent research study by R. J. Long et al. (2017) suggests that organic wastes can compete with synthetic fertilizers when used as soil amendments for a variety of crops, including sweet corn, potatoes and squash.
Long et al. found that organic-rich wastes are productive alternative soil amendments, and using them in soil is preferable to disposing of them in landfills. In this study, six different types of organic-rich wastes were compared with an inorganic fertilizer, to determine their effects on soil quality and crop production over two growing seasons. The six types of organic-rich wastes under study were (1) biosolids & yard waste compost, (2) dehydrated restaurant food waste, (3) gelatin manufacturing waste, (4) multisource compost, (5) paper fiber & chicken manure blend and (6) yard waste compost. These six soil amendments, as well as inorganic fertilizer, were applied to different plots of sweet corn, potatoes and butternut squash. In each plot, researchers tested soil health parameters, heavy metal concentrations in both soils and plants (a commonly cited concern related to application of municipal and industrial wastes), and plant tissue concentrations of various macro and micronutrients. Plant growth and crop production (yield) were also measured and compared among all the soil amendment options. Overall, Lang et al. found that none of the soil amendments had negative impacts on soil quality, while some actually improved soil quality. Furthermore, all amendments were found to produce comparable yields to inorganic fertilizers in at least one of the studied crops. The results on which fertilizers produced the best yields in a particular crop where a bit of a mixed bag – each crop seemed to do better with a different waste amendment. Interestingly, none of the amendments increased heavy metal content of either soil or plant tissue, indicating that these wastes are safe for application to food crops. Finally, the scientists conclude that each of the six tested types of organic-rich wastes represents a promising soil amendment – both because they are beneficial for soils and crops, but also because they reduce the volume of material that normally ends up in landfills.
If farmers begin adopting the practice of repurposing landfill-destined organic-rich wastes as soil amendments, our landfill woes might soon become less urgent… These practices would also go a long way towards meeting the EPA’s goal of reducing food waste in landfills by 2030. However, there are other ways we as consumers can mitigate food waste entering landfills, including donating edible food items to local food pantries and changing our shopping habits to prevent excess food purchases from spoiling before we have time to consume them. If you’re interested in more ways to combat our food waste problem in the US, read more at the EPA’s website about Sustainable Food Management!