I often get calls saying, “I am ready to plant, what fertilizer should I use?” That’s an excellent question, but I can’t answer it very well without additional information. I have seen hundreds of soil test reports and it is clear that that gardens are extremely variable in mineral content. Without a soil test report, adding fertilizer is just a guess. Even with a soil test in hand, my recommendation is always, “go slow when adding fertilizers.” This also applies to the use of compost.
The easiest soils to adjust are those where the original mineral contents are slightly low. This is likely to be the case with our native prairie/pasture soils that have not been fertilized. The hardest, and sometimes nearly impossible adjustments, are those soils where the gardener has added excessive amounts of compost and/or certain minerals.
The goal in gardening is to slowly raise the soil organic matter to about 5 percent, and get all of the minerals to an acceptable level. Once you get to that level, high quality compost may be all you need to add to your garden. Your compost quality will only be as good as the material from which it is derived.
Organic fertilizers are available in the area (Nitron Industries and others) and you have options for what to use for the various elements needed for good plant growth and production. Here are some fertilizer recommendations for nitrogen-N, phosphorus-P, potassium-K, calcium-Ca, and boron-B. The percent of the mineral in the fertilizer may vary with source of material. It will specify the amount on the bag. Unless
specified otherwise, the ratios indicate the percent N, P and K in the fertilizer.
Nitrogen: Use alfalfa meal (3-1-2), fish meal (10-2-2), or feather meal (14-0-0).
Phosphorus: Use soft rock phosphate (0-5-0). The 5% is available the first year, and more each year, up to 22%. Soft rock phosphate also contains calcium.
Potassium: Use greensand (0-1-5) or kelp (1-0-8). Many local soils have a near-adequate amount of K.
Calcium: Use high quality calcium carbonate or lime (0-0-0-38 percent Ca). Most local soils will need additional Ca.
Boron: Use Borax, which is 10% boron. Remember this mineral is involved in the plant’s ability to use calcium. For local soils that test zero for boron, add 4 Tablespoons of Borax per 100 square feet.
The advantages of these fertilizers are: (1) they are slow release and provide long-lasting nutrition for good plant growth; (2) they are not detrimental to soil microorganisms, as is the case with some high-salt fertilizers; and (3) they are mostly single element fertilizers, which can be tailored to the specific needs defined by the soil test.
For those wanting information describing how organic systems build soils, check out the recent March 2011 USDA Organic Farming Systems Research Conference. Evidence from long-term studies shows the values of the organic approach for the health of the soil, the plant and the consumers.