Sustainable Soils – Part 1 Soil Basics
In a series of articles that will be written throughout this years growing season, I will try to walk you through the process of converting a non-productive and/or chemical dependent lawn, garden, and/or farm into a safe, sustainable environment that requires less time, money and effort to achieve fantastic results. This month, however, we are going to focus on the basics of soil and help you understand how sustainability starts.
Soil is typically made up of 45% clay, silt, and sand; 25% air; 25% water; and 5% organic matter (if you’re lucky). Understanding your soil profile is the start to achieving sustainability but we are not done yet.
The conventional view of the soil looks at three “independent” factors which make up soil and they are structural, chemical and biological. The emerging view of soil and soil health is looking at the same three factors; however, rather than looking at each component independently, soil health is achieved when all three are working together, not autonomously. Lets consider the three factors independently and then how they should work together.
Soil Structure tells us the size and portion of the particles within a sample, in other words the percentage of sand, silt, and clay found in the soil sample. Understanding soil structure is the start to better understanding the soil’s ability to retain nutrients, its holding capacity for water retention, and its tendency to become compacted. For a quick and easy way to test soil structure, try the ribbon test. Here is a link to the ribbon test instructions, http://backyardorganics.net/faq/
Understanding the chemical make up of soils is the typical benchmark used by most land care providers. This will give you a better understanding of the macro (Nitrogen (N), phosphorus (P), potassium (K)) and micro nutrients found in the soil. Chemical testing will also uncover the “blood count” and “blood pressure” of the soil, in other words the pH of the soil. This pH is a critical factor in determining nutrient availability, especially if the soil is lacking biology, but we’ll get into that in later articles. Depending on the test, a chemical test should also give you the holding capacity of nutrients (C.E.C.), organic matter percentage, and soluble values of macro and micro nutrients, which are the nutrients actually available to the plants. Again, the chemical component to soils is certainly a key factor and one that should be understood but by itself will not achieve a healthy, sustainable soil.
The biological component to a healthy soil is probably the least discussed and perhaps the most influential factor in achieving sustainability. The biological component is made of bacteria, fungi, protozoa and nematodes in addition to a variety of other insects. Why is it important to understand the biological make up of your soil? Because without good soil biology, pH alone will determine nutrient availability to your plants and manual inputs will then be required to retain the appropriate nutrient levels to feed those plants.
Here is a closer look at the microbes found in healthy soils; Bacteria are mostly decomposers which feed on plant exudates and fresh organic matter. They immobilize and retain nutrients in their bodies and are very nitrogen dense. Bacteria have six times the nitrogen than the microbe which feeds on them. Think of them as little bags of fertilizer! Fungi are also decomposers, feeding on more complex organic matter. Fungi thread-like growth habit improves soil texture, transports water, and nutrients, and protects against pathogens. Protozoa, nematodes and other insects are the preditors to bacteria and fungi and the carrier of the value which comes in the form of natural, slow releasing fertilizer. The biological component to soil is the difference between “dirt” and “soil”. Without biology, over time you would simply have sterile “dirt”.
“The nation that destroys its soil, destroys itself”, President Franklin D. Roosevelt.
Soils require a balance between structural, chemical and biological components to be sustainable. If you are lacking one component, your soil will require manual inputs in the form of fertilizers (either organic or chemical based) or mechanical soil manipulation. The greater the balance, the more sustainable the soil.
This article will also appear in the February, 2013 edition of Nature’s Pathways
In the months ahead we will talk more about how soil components should work together and how to build and maintain soil fertility.