Soil is alive. It is more than sand, silt or clay particles. It is even more than rotted organic matter. It is full of bacteria and all kinds of fungi, good and bad. Soil is alive and it needs to be fed.
Some people go to the garden center and buy bags of 5-10-5 fertilizer. The numbers stand for the ratio of nitrogen (N), phosphorous (P), and potassium or potash (K). This kind of fertilizer is soluble and will provide your plants with the three major nutrients that they need. They will not feed the soil. In fact, if only chemical fertilizers are used on soil, the soil will eventually die.
Soil, and our garden plants need more than nitrogen, phosphorous and potassium. They need trace elements like calcium, copper, boron, iron, magnesium, manganese, molybdenum and zinc. Soils that have sufficient organic matter will usually have sufficient trace elements, because only small amounts of these elements are needed for strong plant health. The safest and best way for us gardeners to provide essential trace elements is by regular additions of compost.
If trace element deficiencies are severe enough you can often make a diagnosis of the problem by looking at your plants. For example, yellowing of leaves while veins remain dark green can indicate an iron deficiency.
While all the macro and micro-nutrients might be present in the soil, they need to be made available to the plants. This means the soil cannot be too acid, or too alkaline. When soil is too acid or alkaline those nutrients are locked up. Many gardeners have found that simply by liming their acid soil their plants do better. That is because when the pH is higher those nutrients are available to the plants. Most garden centers sell pH test kits, and while the assumption around here is that our soil is acid, we need to know how acid. We also need to know if it is too alkaline, which can also make nutrients unavailable.
With all those nutrients present and available, what do bacteria and fungi do for the soil?
The fungi are possibly the most important and there are three types. The first type of fungi are the decomposers that digest organic matter and make it usable for plants. They are also important in retaining nutrients in the soil, and storing and recycling carbon in the soil.
Then there are the mutualists, the mycorrhizal fungi, that colonize on plant roots and bring the plant nutrients and even water.
Finally, there are the pathogens and diseases. Verticillium is one of the fungi that can cause problems for the gardener, and the farmer. Fortunately there are now hybrid plants that resist verticillium as well as other fungal diseases.
Soil is complex and if we are going to have healthy plants without depending solely on 5-10-5, we need to feed our soil.
I have not been very scientific about feeding my soil. I spread manure and compost to provide nitrogen and trace elements. I have added greensand to provide potassium. I’ve added rock phosphate to provide phosphorous. Greensand and rock phosphaste (not super phosphate that is soluble and available immediately) break down slowly over time, providing nourishment for a long period.
I have spread lime from time to time, as well as my wood ashes, but I fear my soil may still be more acid than is desirable. Therefore I am going to get a soil test from the UMass Soil Testing Laboratory (http://www.umass.edu/soiltest/list_of_services.htm, For $15 I can get a measure of pH, nutrients and organic content, with recommendations for improving my soil.
To prepare a sample according to their directions I will get 10 or 12 vertical slices (being sure to reach into the root zone) of soil from random areas in my vegetable garden with a clean trowel and put them in a clean container. Mix well. Then take one cup of that mixture and dry it on paper. When dry put it in a zip lock bag. If you send several bags make sure each is identified: veggie garden, front lawn, flower garden, etc. There is a cost for each sample. Send to the Soil Lab with your check and in about two weeks from the time the sample arrives you will have your results.
There are full directions on the UMass website for taking soil samples along with a downloadable form. I will reveal the results of my test when it arrives. Wish me luck.
Tomorrow is Earth Day. Take care of your earth.