The pH of soil is typically controlled by the addition of lime (to increase pH) or sulphur (to decrease pH). Most often, soil pH needs to be increased or the soil needs to be made more basic. Most vegetable plants like a pH around 6.5. Lime is made up of calcium (Ca) and magnesium (Mg) carbonates, with other minor components. Carbonate neutralizes acid, making the soil less acidic (or more basic). What is also important is the Ca/Mg ratio, and this can be managed by the type of lime used.
Testing for organic matter tells simply what percentage of the soil is organic. This is more complicated than measuring inorganics, because different forms of carbon are more or less available, and are available on different time frames. Charcoal is poorly available and takes a long time to break down to an available form. Humic acids are readily available and can be used quickly. Building organic matter in soil is a long term process. Compost and manure are excellent sources of readily available carbon, whereas chipped wood and shredded straw break down slowly.
The microbiological elements of soil require organic matter and minerals. What is critical, however, is that plants need to be growing in the soil for microbiological organisms to thrive. Plants feed microorganisms by putting glucose directly into the soil via their roots. Microorganisms, in turn, make minerals available to plants. This is where cover crops are so important to maintain growth of microorganisms. Even weeds are better than bare soil. Typical soil microorganisms include bacteria, fungi, algae, and protozoa.
I get my soil tests performed at West Virginia University by the Extension Service. I sent them Ziploc bags of dried soil taken from various areas of the garden, and they send me back a soil report, like the one below.
This test contains a great deal of information. First, the soil pH is way too low (too acidic). It was measured at 5.6, and should be 6.3-6.5. Therefore, I need to lime the soil, and the report indicates that I should add 87.4 lbs/1,000 sq. ft. The garden is a little over 2,000 sq. ft., so I used about 200 lbs. of lime. When considering what sort of lime to use, note that the Mg levels are high. Crushed, pelleted limestone contains low levels of Mg relative to Ca, and costs about $3 for a 40 lb. bag.
The report also indicates that I need to add 2 lbs. of N, 4 lbs. of P, and 3 lbs. of K per 1,000 sq. ft. So I spread about 40 lbs. of 10-10-10 fertilizer and supplemented that with super phosphate, potash, and organic nitrogen to give the correct ratio and amounts of N/P/K. Amounts of these various fertilizers have to be calculated based on the weight percentage of each component. The 10-10-10 fertilizer contains 10 lbs. each of nitrogen, phosphorous, and potassium per 100 lbs. of fertilizer. So the 40 lbs. I added contained 4 lbs. of N, P, and K, spread out over 2,000 sq. ft., equals 2 lbs. of each per 1,000 sq. ft.
For organic matter, I use three different supplements: compost, chipped wood, and shredded straw. I chip old logs that have been sitting on the forest floor for many years. They still contain a lot of organic matter, but they also contain lots of good microorganisms. Crude organic matter such as shredded straw serves as a long-term source of carbon and it also helps to physically break up the heavy clay in our soil.
For the first time this year, I am going to supplement the garden soil with beneficial microorganisms that I purchased. The product contains 16 species of mycorrhizal fungi and 14 species of beneficial bacteria to supplement the microbes already in the soil. I'm hoping this will make a significant difference in soil health and hence, yields.
Soil health is a three part symbiosis:
- correct levels of inorganic chemicals and correct pH
- organic matter in various forms
- roots of growing plants to feed microorganisms