Organic Soil Amendments

Last summer we hired a heavy equipment operator to clear our field (about 2 acres). The dozer up-rooted huge pine trees and hardwoods, it untangled masses of overgrown wild vines and brambles, and it left a lot of very deep ruts. All of the debris was piled into a mountain in the middle of the field along with all of the topsoil. We were left with bare, hard, red clay. Needless to say, the nutrient content of our soil had us a little concerned.

So, yesterday I performed a home soil test. The kits can be purchased at local farm supply stores or home & garden centers. They show the pH value and macro nutrient values for nitrogen (N), phosphorus (P), and potassium or potash (K) but they don’t show values for trace minerals such as zinc, magnesium, calcium, etc. The test revealed that our pH was 6.0-6.5; this is a somewhat acidic pH value but not too worrisome since most vegetable that we’ll be planting prefer a pH of 6.0-7.0 anyway. The test results showed our N value as medium, P value as low, and K value as low.

Nitrogen is an essential component of protein. The medium Nitrogen (N) value (instead of being a low value) may be a result of all the natural nitrogen fixers we have growing in our area. Redbud trees, Mimosa trees, and Kudzu are all nitrogen fixing legumes; this means that they contain a bacteria that allows them to pull nitrogen from the atmosphere and later introduce it into the soil through their root systems. Locust trees are also leguminous.  Composted cow manure is a reliable source of N but the value is quite low. Phosphorus (P) stimulates plant growth. It is an essential macronutrient that helps the plant convert other nutrients into usable form. Bone meal is a good source of organic phosphorus as is rock phosphates. Apply them to your planting areas according to packaging instructions. Potassium (K) is a very important nutrient for overall plant health. It’s involved in protein synthesis and in the flow of nutrients and water up and down the plant. The ashes of hardwood trees are a good source of organic K.

Our planting beds are 100 square feet (5’x20′). To raise the K value and to bring up the pH a bit we’ll add 7 cups of wood ash to each bed every 6 months or at least once during the main growing season each year. Wood ash is very alkaline so it will raise the pH somewhat but should only be a concern if your pH is over 6.5. To bring up the P value we’ll add 4 cups of bone meal; this will also add a little calcium. To bring up the N we’ll add 4 cubic feet of composted cow manure (Black Kow) but we’ll only add the manure one time as the beds are being set up. In subsequent years we’ll add N to our soils by utilizing our own compost and growing leguminous cover crops such as broad beans and peas. Manures can actually lower the pH thus making a soil quite acidic so be careful using them.

We’re content with our home soil test results as we simply wanted a base-line for setting up our planting beds for the first time. For more accurate soil test results that will also show micro nutrient values contact your County Extensions Office for referal to a testing agency. Or, a local community college’s horticulture department may be able to do the test for you. Remember, there are always natural means of getting soil nutrients where they need to be.