Most people don’t get them. (Soil tests that is). Gardeners who grow organic have been taught to believe that adding organic material in the form of compost will solve all problems. According to people like Michael Astera and Steve Solomon this is not the case. (There’s a rumor that Michael and Steve are joining up to co-write a book on this subject). You can actually have too much organic material in the soil. However, if necessary minerals are not in the material you use to make compost, compost additions will not add minerals to the soil. Michael Astera gives this explanation:
“Soil is formed from the rocks that break down to make it. In most cases, that means the bedrock beneath your field. For young soils, whatever minerals were in the bedrock are the ones in the topsoil, and in pretty much the same proportion. Sandstone, limestone, granite, or basalt will all form a soil with a different mineral balance, and different types of each one will make different soils.
As soils age over thousands and millions of years, their mineral content changes as minerals are eroded or leached away. River bottom lands are usually the richest soils because they have been formed by all of the rocks and minerals that have leached or eroded from the whole watershed.
Over the past 170 years, some researchers have looked into which soils with which mineral balances grow the most yield, or the most nutritious food (not the same thing). What I work with and recommend is an “ideal” balance of minerals for growing food to feed people and animals. This is pretty much the same mineral balance for any food crop from radishes to pastures to fruit and nut trees.
The only way to know what minerals are in a given soil is to get it tested by a lab, with the right test. The next step is to compare the results against the “ideal”, figure out what’s missing or what is in excess, and then add the missing minerals in such a way that the excess, if any, is dealt with at the same time.
In theory, after you did that, your soil would be as rich and fertile as any soil in the world, and the crops would be as nutritious as any crops ever grown anywhere. From there on, you would just add small amounts of whatever minerals were taken up by the crops or leached away through precipitation and irrigation. For a few years you would need to have the soil tested regularly, but after a while you could probably come up with a good idea of what your particular soil needed on an ongoing basis.”
So what does a soil test look like?
Here’s my most recent test. The “hot garden” is a 400 sq. ft garden I added two seasons ago and has not been amended with minerals. The “old garden” is my original garden plat and has 1360 sq. ft. of planting area. I had a previous soil test and amended the old garden with minerals prescribed by Mr. Astera.
2011 soil tests (link to a pdf file to view)
Each soil test cost $20. Michael Astera’s book explains how to read these and how to compute the minerals necessary. But since my mind does not bend that way I paid his very reasonable consulting fee to get an RX for my garden.
Prescriptions for gardens are given as an amount per 1000 sq. ft.
Here’s what I need to add after harvest this fall:
Amendment Hot Garden Old Garden
Calphos 30 lbs X.4 = 12 lbs 30 lbs x 1.36 = 40.8 lbs
Gypsum 35 lbs x .4 = 14 lbs 30 lbs x 1.36 = 40.8 lbs
Hi-calcium ag lime 0 20 lbs x 1.36 = 27 lbs
Sea Salt 3 lbs x .4 = 1.2lbs 3 lbs x 1.36 = 4 lbs
Borax 4 oz. x .4 = 1.6 oz 8 oz. x 1.36 = 10.88 oz
Epsom Salt 4 lbs x .4 = 1.6 lbs 4 lbs x 1.36 = 5.44 lbs
Copper Sulfate 1.5lbs x .4 = .6 lbs 0
Zinc sulfate 2 lbs x .4 = .8 lbs 2 lbs x 1.36 = 3.5 lbs
Total minerals needed:
Calphos 53 lbs
Gypsum 55 lbs
Ag lime 27 lbs
Sea Salt 5 lbs
Borax 13 oz
Epsom Salt 7 lbs
Copper sulfate .61lbs
Zinc sulfate 3.5lbs
Clearly, this adds a new element to gardening. If you are just growing a couple small beds of lettuce this probably won’t be too important to you. However, if you are seriously working to grow significant amounts of nutritious food, why not try make you plants as nutrient dense as you possibly can?
Understanding the principles of nutrient loss and re-mineralization will also make you a more savvy consumer and give you the basis for asking your local commercial growers some tough questions. Question # 1, do they do soil tests? Question #2, how do their veggies rate on a Brix scale? (More on Brix to come soon).