During normal soil development, nutrient-rich primary silicates and other minerals are broken down and the plant nutrients in them are released into the soil solution. With increasing intensity of agricultural use there is a corresponding increase in the turnover of substances and energy in the plant rhizosphere and in the rate of decomposition of primary silicates. The plant nutrients released from the primary silicates can be taken fully into consideration in the nutrient balance sheet for the cultivated area. Using this and a balance sheet for the soil it is possible to estimate the supply of both potassium and magnesium over a period of several years. For mixed farms, which cover most of those farmed organically, soil production of nutrients is frequently fully balanced by their net loss through the sale of farm products. The principle of {`}maintenance fertilising{'} does not take into account the soil{'}s own contribution to the nutrient supply and can lead to an over application of fertilisers which is associated with increased nutrient leaching. Through soil erosion and the activity of soil microorganism, a balance between influx and efflux of plant rhizosphere nutrients can occur which guarantees the supply of nutrients for an organic farm even over millennia. The soil reserves of plant nutrients are very many times greater than the currently known reserves in geological deposits. These should be kept for extremely nutrient-poor soils or for soils depleted of soluble nutrients.
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During normal soil development, nutrient-rich primary silicates and other minerals are broken down and the plant nutrients in them are released into the soil solution. With increasing intensity of agricultural use there is a corresponding increase in the turnover of substances and energy in the plant rhizosphere and in the rate of decomposition of primary silicates. The plant nutrients released from the primary silicates can be taken fully into consideration in the nutrient balance sheet for the cultivated area. Using this and a balance sheet for the soil it is possible to estimate the supply of both potassium and magnesium over a period of several years. For mixed farms, which cover most of those farmed organically, soil production of nutrients is frequently fully balanced by their net loss through the sale of farm products. The principle of {`}maintenance fertilising{'} does not take into account the soil{'}s own contribution to the nutrient supply and can lead to an over application of fertilisers which is associated with increased nutrient leaching. Through soil erosion and the activity of soil microorganism, a balance between influx and efflux of plant rhizosphere nutrients can occur which guarantees the supply of nutrients for an organic farm even over millennia. The soil reserves of plant nutrients are very many times greater than the currently known reserves in geological deposits. These should be kept for extremely nutrient-poor soils or for soils depleted of soluble nutrients.
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