Translations:Manfred Klett: Von der Agrartechnologie zur Landbaukunst/838/en

The composition of the crop rotation serves the goal of developing a stable or, better still, a positive humus balance, and with it, a positive nitrogen balance. Root and cereal crops contribute less to the latter, but legumes contribute all the more. These live in symbiosis with bacteria in the root zone, the so-called Rhizobia or root-nodule bacteria, and in conjunction with the host plant have the ability to fix nitrogen from the air. The alder (Alnus glutinosa), among others, is also capable of the same; it lives in symbiosis in its root zone with the fungus-related Actinomycetes, which is recognisable by the deep green of its foliage, similar to the legumes. The capacity for nitrogen formation without a direct relationship to higher plants is found in free-living bacteria, such as Azetobacter, which prefer a base-rich, more alkaline soil environment, and Amylobacter, which prefer a more acidic one.