Ask Your Soil What it Needs – Get a Scientific Check-In!
Guide to understanding your soil test results
Soil Fertility: The capacity/ability of a soil to supply essential plant nutrients in readily available and balanced forms.
pH: Tells you how acidic or basic your soil is. Nutrients need a certain pH in order to be able to be available to your plants. A pH of 6.5 is the “sweet spot” for plant available nutrients. Nutrients need to be dissolved (or disolvable) in the soil solution for plants to use them. Nutrients get bound up in the soil, making them unavailable to your plants, when pH is too high or low.
EC – Electrical Conductivity: The ability of your soil/water nutrient solution to conduct an electrical charge. The elemental ions that feed your plants, like Ca2+ and NO3–, carry an electrical charge (+ or -). The more ions, or nutrients, there are in the soil solution, the higher the EC.
Humus: These fine organic particles make up the bulk of organic matter. These particles have thoroughly decomposed reaching a point of stability. These organic particles greatly affect soil texture, as well as water and nutrient holding properties of the soil.
CEC – Cation Exchange Capacity: The ability of a soil to hold positively charged nutrients. Calcium (Ca2+), magnesium (Mg2+), sodium (Na+), and potassium (K+), and other trace minerals that are positively charged, are attracted to the negative (-) charge of soil and organic matter (OM) particles. Soils with a lot of clay and or OM have a higher CEC than sandy and/or low OM soils which have a relatively low CEC. Soils with a low CEC often need to be “spoon fed” as the soil has a hard time retaining nutrients. High CEC soils hold more nutrients but are harder to correct when they are out of balance. Microbes, like bacteria and fungi, help turn unavailable elements into a form that can attach to a soil or OM particle, becoming readily available to the plant.
BS – Base Saturation: A measure of nutrients currently IN your soil compared to the amount of nutrients you COULD HAVE in your soil (nutrient holding capacity – how many nutrients COULD be held by your soil IF they were added). (i.e. How “full” is the CEC. Only a % of total exchange sites actually has a nutrient on it.)
Lime Requirement: The optimal pH for plant available nutrients is 6.5, with the general range being between 6-7. Most plants cannot access nutrients at an extremely low pH. It is imperative to maintain an optimal pH or plants will not be able to obtain proper nutrition. The lime requirement is the amount of lime needed to raise the pH of a soil to 6.5. Liming is generally unnecessary if your pH is above 6.5. It is important not to over apply lime because a high pH will also decrease nutrient availability. Another important role that lime plays is to help lower sodium (Na) levels in soil. When calcium (Ca) enters the soils system, it displaces sodium (Na) from the soil exchange sites and allows water to leach sodium (Na) from the soil matrix. Note: ALWAYS lime at a different time than you apply organic or potentially acidic nutrients (manure/compost/humic’s). They will interact with each other rather than acting upon your soil chemistry.
Soluble Salts: In the world of chemistry, salt is more than what seasons our food! Many of these soluble salts are essential plant nutrients. When an acid and a base are combined, they react until they become neutralized. After this reaction, the neutral solution contains equal parts of positively and negatively charged ions. When you feed your soil with fertilizers/amendments you are catalyzing many of these acid/base reactions that create usable food for your plants.
Common soluble salts used by plants:
Ammonium – NH₄+
Calcium – Ca2+
Iron – Fe2+ and Fe3+
Magnesium – Mg2+
Potassium – K+
Sodium – Na+
Nitrate – NO3–
Phosphate – PO43-
Sulfate – SO42-
**These are the forms of soluble salts that are tested in the lab. The fertilizers you buy consist of a percentage (%) of these salts. (ex. sulfate of potash is 50% potash and 17% sulfate.)