I often say that the basics of organic gardening are very simple and yet very complex. The basics are simple in the sense of following three interrelated ideas. (1) Increase soil biological activity, water holding capacity, and soil mineral levels by adding compost, using cover crops and mulches, and not using pesticides. (2) Keep the soil well aerated, using raised beds and minimum tillage to develop improved soil structure, which means better tilth or soil workability. (3) Remineralize the soil to a level that is adequate to grow nutrient dense plants, using minimally processed and organic materials. These basic ideas become complex when we address the questions of what kind and how much fertilizer to add.
Every soil is different. This is especially true of garden soils where a lot of different fertilizers have been added. Without a soil (or plant tissue) test, it's impossible to give good advice on how much fertilizer to add. It becomes just a guess, and I prefer to leave the gambling to those going to the casinos. It's like asking your medical Doctor for specific advice based on average health conditions for those in the State. It makes no sense.
In addition to the soil test, before giving advice, I like to know some past history of production and problems. I don't try to "fix" every soil problem in one year. If you are providing conditions to create the biologically healthy soil, some of the other soil conditions (like nutrient levels and pH) will change on their own. Microbes are the plant's digestive system, and the workhorses for creating healthy and productive soils.
There is another element of fertilization refinement when we address the specific crop being grown. You will need more phosphorus for leafy crops than for seed crops. For small gardens, I don't try to fine tune at this level. It seems best to just do a single recommendation for all the vegetables in the garden. I do treat the more acid loving blueberries and strawberries separately. For vegetables, I strive for a soil pH of 6. 4. Blueberries do much better if you can get the pH down to 5.5 or lower.
The Arkansas Soil Test Report is a good place to start for assessing your soils. The tests are free and you will get an analysis for ten different elements, plus soil pH, cation exchange capacity, and base exchange for Ca, Mg, K, and Na. I encourage you to get an understanding of what this all means. Because the Arkansas analyses are very general, I have also been sending soils to another independent laboratory, where they have a lot of experience with making fertilizer recommendations for growing nutrient dense produce. Because the different labs use different nutrient extraction methods, direct comparison between laboratories are not possible. If you are interested in additional information on this subject, please contact me.
Recommended Reading: Teaming with Microbes – A Gardener's Guide to the Soil Food Web, by Jeff Lowenfels and Wayne Lewis, 2006. Available from www.AcresUSA.com. In a clear, straightforward language, the authors describe the activities of the soil organisms, and tell us how to promote healthy soils through the use of compost, mulches, and compost teas. The information can you discover how to create rich, nurturing, living soil – without resorting to harmful synthetic chemicals.