All urban agriculture projects, whether commercial, nonprofit, or community-based, will be well served by growing the most productive crops possible. In the case of plant-based agriculture, this means providing the best possible growing environment, including the correct quantities of nutrients and water. Except in cases of hydroponic production, soil quality and fertility is the key determinant of whether plants will get the correct nutrients and an appropriate amount of water.
Soil Fertility
Soil fertility is the ability of a soil to provide the nutrients necessary for plant growth. Soil fertility can vary depending on the inherent type of soil, the way in which that soil has been used in the past, and any amendments, such as fertilizers that have been added to the soil.
If you are interested in learning about soil fertility and composition in greater depth, this guide titled Soil Fertility Basics from North Carolina State University is a great start.
The Urban Nutrient Management Handbook from collaboration in Virginia provides a comprehensive soil science overview with an urban-specific perspective. The focus is on turf grass rather than food crops but this publication is a great resource for those who want to dig deeper into the science of soil and water systems. A second good resource for foundational soil science concepts is the Concepts of Basic Soil Science chapter published by Virginia Cooperative Extension.
How to Take a Soil Sample
Periodic soil testing, or sampling, gives you information about the nutrient and organic matter content of your soil and can help you make informed fertilization and management decisions. UW Extension county agent Ann Weid describes the reasons and process for soil testing in her article Why Test Soil.
Soil sampling is critical whenever you are growing on a new parcel of land and should be repeated every 1-3 years. Soil sampling will provide you with detailed information about the nutrients in your soil and help you make informed decisions about what fertilizer to apply (including compost.) If you skip soil sampling, you risk growing plants with insufficient soil fertility, which will result in poor production, or over-applying fertilizer, which can have negative impacts on soil pH as well as harmful environmental impacts. Fortunately, soil sampling is easy! Here are a couple of resources to walk you through the process:
- A video from the University of Minnesota: https://www.youtube.com/watch?v=MhSfvTcsvSk
- A 3-page overview of the why’s and how’s of soil sampling in Sampling Soils for Testing out of the University of Wisconsin Extension
Since the minerals in soil vary from place to place, it’s best to have your soil tested by a lab in your home state if possible. Soil testing labs can be found easily in most states by doing an Internet search for “soil testing [insert your state]”
Reading a Soil Test Report
Now that you’ve had your soil tested and you’ve been sent a report, what do you do with it? Understanding Your Soil Analysis from the University of Wisconsin explains the information commonly found in basic soils tests.
Addressing Issues in Fertility
Chances are that your soil test report indicated that your soil needs some additional nutrients. The way in which you apply those nutrients will depend upon how you manage your farm. The report will often include recommendations for non-organic fertilizers and amendments. These can be followed directly if those recommendations fit within your farming system. Many urban growers use organic methods, though. Organic fertilizers will have nutrients that occur in different percentages than those included in the conventional recommendations on the soil report. Organic amendments may also have several nutrients in a single product. Organic growers will have a bit of extra work to do in converting the recommendations given by the soil report to your preferred soil amendments.
How to Convert an Inorganic Fertilizer Recommendation to an Organic One from the University of Georgia Extension provides a great explanation of the roles of different nutrients in organic systems followed by concrete amendment calculation examples, including how to calculate the amount of compost when used as a fertilizer.
Compost
Composting represents not only a way to add beneficial organic matter to your soil, but also to divert organic waste out of landfills. The process of composting takes raw organic waste materials and turns it into biologically stable soil amendments. If you are interested in learning the benefits of composting, or how to start composting yourself, see The Art and Science of Composting published by the Center for Integrated Agricultural Systems (CIAS) at the University of Wisconsin Madison. This publication outlines things like the composting process, how to choose a composting system that is right for your operation, and information on permits and regulations relating to compost.
Soil Safety
Urban farms must be particularly mindful of the risk of growing food in contaminated soils. Some choose to use raised beds or other means of avoiding the original soil entirely. Alternatively, you can test your soil for heavy metals and other common urban contaminants. The Johns Hopkins Center for a Livable Future has a publication titled Soil Safety Resource Guide for Urban Food Growers that offers a basic overview of common garden soil contamination issues, possible solutions to approaches to deal with contamination, and a reference list of related resources.
Citations
Cooperband, Leslie. 2002. The Art and Science of Composting: A Resource for Farmers and Compost Producers. The Center for Integrated Agricultural Systems
Daniels, W. Lee and Kathryn C. Haering. 2006. Chapter Three: Concepts of Basic Soil Science out of The Mid-Atlantic Nutrient Management Handbook. Mid-Atlantic Water Program
Gaskin, Julia, David Kissel, Glen Harris, and George Boyhan. 2014. How to Convert an Inorganic Fertilizer Recommendation into an Organic One. UGA Extension
Goatley, Micheal Jr. and Kevin Hensler. 2011. Urban Nutrient Management Handbook. Virginia Cooperative Extension
Hodges, Steven. 2010. Soil Fertility Basics: NC Certified Crop Advisor Training. North Carolina State University Soil Science Extension
John Hopkins Center for a Livable Future. 2014. Soil Safety Resource Guide for Urban Food Growers. The John Hopkins Center for a Livable Future
Peters, John B. and Carrie Laboski. 2013. Sampling Soils for Testing. University of Wisconsin Cooperative Extension
University of Wisconsin-Madison Soil and Forage Analysis Laboratory. Understanding Your Soil Analysis. Available Online.
Wied, Ann. 2014. Why Test Soil? University of Wisconsin Extension Master Gardener Program