How can I improve clay soil for vegetable production?
Answer: First, take some time to get the field turned around and build tilth and soil structure. The best way to do this is through the biological activity of soil microorganisms. This, in turn, is accomplished with addition of carbon, or organic matter.
For small-scale plots: The use of a broadfork would be advantageous, even if you use it to work over small plots at a time. After broadforking, the soil can be amended with compost and gypsum (helps loosen clay soils), followed by a cover crop. Do this twice in a growing season in spring and fall, and then the following year if needed. Use the most diverse cover crop mix you can, choosing from the following suggested list:
Summer – Sun hemp, buckwheat, oats, sunflower, pearl millet, cowpeas, radish, turnip, safflower
Fall – Vetch, field peas, red clover, annual rye, annual ryegrass, triticale, oats, barley, kale, plantain
I recommend getting in touch with your local NRCS to obtain cover crop recommendations that do well in your area.
Another thing you could do when you begin to plant food crops is to continue the cover cropping before and after food crops, and you can consider in-place composting between rows, and then alternate rows the following year. All these methods serve to increase organic matter in the soil, which helps soil aggregation.
For large plots: You may need a BCS walk-behind or tractor. You could consider hiring out a tractor a few times a year for field work planting and incorporating cover crops for a few seasons. Follow the same compost, gypsum, and cover crop strategies that were suggested above.
The Soil Health Education and Resource Guide by Green Cover Seeds out of Nebraska is an excellent digest of regenerative agriculture concepts including numerous articles on topics important to farmers interested in building soil health and resilience. I highly recommend this guide as a way to think through the various practices to increase soil and crop productivity.
The NRCS Soil Quality Test Kit describes procedures for 12 on-farm tests, an interpretive section for each test, data recording sheets, and a section on how to build your own kit. This practice can help you monitor progress and identify areas that need improvement.
To learn more about topics related to soil, check out the ATTRA Soils and Compost page.