Organic fertilizers permitted

Most dynamic factors that affect fruit quality are agronomic practices that can be changed by farmers over relatively short time spans. They are mainly related to fertility management and crop protection and other husbandry interventions and inputs such as pesticides, fertilisers, herbicides, thinning agents and so on. The permitted tools for these activities, however, differ greatly between conventional and organic fruit production. The consequences... 

Current organic farming methods seek to reduce bought-in manures to a minimum, but some fertilizers are allowed as permitted inputs on a restricted basis (Lampkin and Measures, 1999). In general, only fertilizers that release nutrients through an intermediate process, such as chemical weathering or the activity of soil organisms are allowed (Stockdale et ai, 2000). 

Under the organic guidelines, commercial fertilizers and fertilizers produced by the grower can only be used on the basis of soil analyses and in accordance with the needs of the crops. Only then is it possible to calculate the amount still required and apply it in the form of permitted fertilizers. Well-balanced fertilizer application enables the soil to make nutrients available to the fruit trees in a harmonious ratio and in adequate amounts at the right time, and helps to keep the trees in physiological balance. If fruit producers want to apply fertilizers in accordance with requirements, they need to know the nutrient content of their soil before they start fertilizer application. 

The N requirements of fruit trees vary within the growing season and are essentially limited to the months April to July, with a peak in June. Half of the N requirements in spring are met from the tree s own reserves. The provision of N to meet requirements is thus more a matter of timing than of quantity. Only a few N fertilizers, which are mineralized relatively quickly, are permitted in organic farming. This is why the application of N fertilizers needs to be precisely timed. Any competition from companion plants in the row of trees must be controlled in time, e.g. by mechanical tilling, so that mineralization is accelerated and the nitrogen is available for use by the trees. The N supply of an orchard should be optimized by means of N analyses. 

Organic adds which form chelates with Fe or Al apparently release silicic acid from combination with these elements in soil or conversely remove these elements from the surface of the silica, permitting it to dissolve. Uptake of silica is promoted by lowering soil pH (138). Soil can be fertilized with silica solubilized as a complex with ammonium humate, which is analogous to the catecholate complex (139)... 

These may take several years to develop. Cancer of the skin or other organs has a peak incidence about seven years after exposure. The blood can be affected in two ways, either by leukaemia, which is a cancer of the white cells or, less commonly, by a severe anaemia in which the bone marrow fails to produce red cells. Chronic ulceration, loss of hair, cataracts, loss of fingertips, diminished fertility, and mutations may also occur. The maximum permitted doses are indicated in Table 17.1. 

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