Bone Meal and Other Natural Additives
Bone meal is an excellent source of phosphorus, essential to plant growth, and also of calcium. This phosphorus is water-insoluble in neutral or alkaline soil, can precipitate out quickly, and therefore should be mixed into the growing medium, where plant roots have direct access.
The same applies to rock phosphate, which though cheaper must be used more frequently, may be harder to get, and may also contain significant amounts of uranium. Superphosphate will not contain radioactive material, and may be used; it is also rich in sulfur and calcium.
Blood meal is an excellent source of nitrogen, as are fish meal and hoof meal. Wood ashes and potash (potassium) sulphate raise soil potassium levels. Wood ashes also raise the soil pH, for more alkaline soil, and potash lowers it, for a more acidic soil. Use both with caution, if at all.
Ground or crushed dolomitic limestone may also be used to raise a soil's pH. Mix in very thoroughly. Note that quicklime (burned lime) and slaked lime should NEVER be used.
Do not use too much of any of the above additives: too strong a concentration of the active ingredients will adversely affect plant growth. Use no more than two or three pounds per 100 square feet, about one kilogram per 10 square meters, once per year. Add no more than a handful to the compost pile.
Have your soil tested, or test it yourself. Kits are cheap and readily available, and should guide what you add, and how much. This applies especially to calcium and magnesium compounds: adding calcium lowers magnesium levels, and vice versa. Note also that if used in sulphate form, these will render the soil more acidic.
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