A major element in growing vegetables sustainably is soil health. We do many things to maintain and improve our soil, such as rotating crops and planting cover crop. To get a detailed picture of what our soil needs, we do an annual soil test. For us, doing a soil test involves taking about two dozen small soil samples randomly throughout the field, mixing them all together in a clean 5 gallon bucket. Next we fill a quart size freezer bag and send it off to the lab, we use Timberleaf Soil Testing, they provide a detailed report with many suggestions on what your soil needs.
We do our soil test in the late fall, this year the results showed us our soil has a great amount of organic matter, low calcium, and very high magnesium. Since our organic matter is at 5% (the ideal range is 5-6%) the lab does not suggest adding compost this year (last year we added about 50 cubic yards to a 1/2 acre). Calcium is very important to plant growth particularly tomatoes. Our calcium level is 54% it should be closer to 75%. To increase our calcium we have been adding lots oyster shell flour.
We have a surplus of magnesium, our soil contains 30% and it should be around 15%. High magnesium makes the soil particles bond tightly together, meaning we have extremely sticky soil once it gets wet. To help decrease the magnesium we have been adding lots of gypsum. The gypsum binds to the magnesium making it water-soluble and slowly leach away.
Before planting in the field we spread oyster shell flour and gypsum, lightly tilling it in to incorporate the materials into the soil. It is important to be patience, soil does not change over night it is a slow process but a very rewarding one filled with healthy plants and bountiful harvests.