What is organic and inorganic farming

Sulfur fertilization

Both organic and inorganic sulfur fertilizers are available for fertilization in organic farming. When using organic fertilizers, it must be noted that the sulfur content can vary considerably in some cases. It should also be taken into account that this is not an immediately available supply of sulfur. The necessary mineralization to sulphate depends on various factors and can therefore neither be precisely predicted in terms of time nor quantity. There is a wider range of approved mineral sulphate fertilizers such as potassium sulphate and kieserite. These sulphate fertilizers deliver the sulfur directly in a form that is available to the plants and are therefore immediately effective. When using it, it must be borne in mind that sulphate, like nitrate, is at risk of leaching. Another possibility is the fertilization of elemental sulfur. It must be taken into account that the elemental sulfur must be oxidized to sulfate by a microbial process in order to be available to plants. Similar to organic fertilizers, this means that the timing and available quantity cannot be precisely predicted.

In organic farming, particular attention must be paid to the sulfur supply. With the installation of flue gas desulphurisation systems in the 1980s, the atmospheric inputs have decreased from around 50 kg sulfur / hectare to around 5-10 kg sulfur / hectare. Since fertilization with sulfur has not been customary in practice up to now, it can be assumed that organically farmed areas will gradually become depleted in sulfur. The reduced sulfur input is partially offset by high sulfur withdrawals. Especially the forage legumes, which are important for organic farming, have a very high sulfur requirement with up to 50 kg sulfur / hectare. Studies by the professorship for organic farming at the Justus Liebig University in Giessen have shown that sulfur is already a factor that severely limits yields. With sulfur fertilization, the nitrogen yields of alfalfa and clover grass crops could almost be doubled (see diagram). The sulfur supply thus has an influence on the overall yield of ecological crop rotations via the nitrogen area yields of the fodder legumes. It is therefore particularly worthwhile to keep an eye on the sulfur supply in order to maintain the yield stability of the entire crop rotation.