Soil Science Spotlight:
The Dr. John Doran/ USDA Soil Quality Test Kit Guide, Part 1
by John Beeby, Ecology Action Soil Fertility Advisor
growyoursoil.org

One of the primary functions of the GROW BIOINTENSIVE method is to allow small-scale farmers everywhere to build and maintain soil fertility levels that will allow the farmers to grow a large amount of food and compost materials in a very small area, with greatly reduced resource use, for an indefinite period of time, sustainably.

Soil testing and the application of the correct type and quantity of organic soil amendments at the correct time is a fundamental part of building and maintaining sustainable soil fertility levels. To introduce the topic of soil testing and the reasoning and methodology involved in soil test analysis and making soil amendment recommendations to a wider audience, John Beeby and Ecology Action are creating a series of topics on the subject called “Soil Science Spotlight”, which is posted to growbiointensive.org in the “Protocol” section with new posts added often.

Do you want to learn how to understand and improve a soil even if you don’t have access to a soil laboratory and a professional to interpret the results? Read on!

If you think of soil analysis as being like a 3-legged stool, supported equally by biology, chemistry, and physics, you’ll understand that emphasizing the use of one of the legs over the others prevents a full, “stable” understanding of the state of the soil and what it needs to become healthier and more fertile. Probably since the beginning of agriculture, there would have been some understanding of soil physics. To germinate a seed to grow into a harvestable crop, early farmers would have learned not to plant in extremely crusted over or compacted soil, as the germinated seed would simply die on the soil surface. Later, there was some understanding of the importance of tilth, which could be improved by adding organic matter. Later, our understanding of soil chemistry developed, allowing us to measure soil nutrients and know how to meet the chemical needs of soils and crops. More recently, the importance of soil biology, not only to soil health but also to soil chemistry and physics, is becoming clear. We have developed advanced technology that reveals the incredible diversity of life within the soil and emphasizes how little we know about what all these creatures actually do! It is estimated that we have identified less than 1% of soil bacteria and fungi; of those we have identified, we know very little about the function they serve within the complex soil ecosystem.

Because each soil is unique, to work successfully with it, we must first try to understand all three of its “legs”–the soil’s physical, chemical, and biological attributes. Each soil is unique just as each person is unique. Only by knowing a soil’s strengths and weaknesses can we attempt to improve it. There is no “one-size-fits-all” miracle fertilizer or amendment that is beneficial to all soils. If you don’t understand your soil, you could just as easily harm it as benefit it by adding the wrong amendment.

The USDA Soil Quality Test Kit Guide, developed by Dr. John Doran, is one set of tools that considers a soil’s physical, chemical, and biological properties to give you a wholistic understanding of a soil. Dr. Doran is a famous scientist whose work contributed greatly to our understanding of soils, soil organic matter, and soil health. He was a past president of the Soil Science Society of America, and was awarded many honors, including the Onassis International Prize for the Environment. Dr. Doran’s guide describes how to carry out 12 different tests to develop a comprehensive understanding of a soil’s chemical, physical, and biological status, using simple, affordable equipment. While not a direct substitute for soil laboratory testing (as it does not provide quantifiable levels of soil nutrients), in some ways it goes beyond a standard test by providing critical information on the soil’s quality that affects its health and fertility not available through a soil testing laboratory. The Guide describes the procedures to conduct each test, shows you how to interpret your results to improve your soil, and is available for free, online, in both English and Spanish here.

The Guide describes the following tests: soil respiration, infiltration, bulk density, electrical conductivity, pH, nitrate, aggregate stability, slaking, earthworms, physical observations, and water quality. This Soil Science Spotlight series will be devoted to understanding all the information that can be deduced from each of these tests, as well from the combination of tests. It is particularly the combination of test results that is powerful as it provides quite a thorough understanding of a soil and how to improve it. But to reiterate: while the tests described in the Guide can provide valuable insights into a soil that a soil lab test cannot, and can help farmers who lack access to a soil testing laboratory to understand and improve their soil, it is not a substitute for a soil laboratory test and does not provide quantitative values of available soil nutrients. Please get a soil lab test performed if possible, and be very cautious when using the Guide, making sure you’re not drawing conclusions for which you don’t have enough evidence. In Part 2 of this series, I will provide an overview of the tests in the Guide, and how they can be used to understand your soil..

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