Alkaloids from many plants are considered to be used as biological fertilizers in ecological cultivation. This is very important especially in cases when more attention is given to these plants, which play not only a role in production but also in the cyclical maintenance of a field, garden or forest ecosystems614'615'616. Plants containing alkaloids, for example lupines, have the ability to establish complexes with the soil and with the rhizosphere. The excretion of many chemicals from roots to soil occurs in this complex. Plant mediation with the soil environment is the result. The alkaloids play a major role in this plant-soil interaction system.
Alkaloids are used as fertilizers for some crops. Mittex AG in Germany has developed a natural product, Lupinex, which contains quinolizidine alkaloids, minerals and carbohydrates333. Lupinex has more than 9% N, 1% P and 2% K. The raw material for this natural product is a waste received from the lupin alkaloid remowing process, when the edible and non-edible components of food are separated. According to the research data obtained at the University of Hohenheim (Germany), the use of Lupinex increased yields of cereals, legumes, oil plants, tubers and vegetable crops331. Moreover, later research confirmed that the increase in yield have also been observed in sunflowers, soybeans and Chinese cabbage332. Alkaloid extracts of lupin as promoters of yields have also been noted by other authors235 333.
Lupin plants with quinolizidine alkaloids are good examples of alkaloids used in agriculture. As ecology friendly plants, lupines can be used for production of food after processing (especially proteins and oligosaccharides), and by-products containing alkaloids can be used as fertilizers. Moreover, in organic cultivation, alkaloid-rich plant material can be composted and alkaloids in this case serve as nitrogen and carbon sources. In ecological soil management, the maintenance of relations between macro and micronutrients is of great importance, foremost the relation between carbon and nitrogen. According to the field test carried out at the Botanical Gardens (62° 36' N and 29° 43'E) of the University of Joensuu during 1988-1993 on fine, sandy silt soil (21.5% silt, 39.5% fine sand, 10.1% sand, 5.9% clay and 23.0% organic matter) with four different soil preparations, the carbon to nitrogen soil ratio (C:N) was highest when fertilized by alkaloids. Soil 2 was fertilized by a canopy of alkaloid-rich Lupinus mutabilis; the total C:N of the treated alkaloid-rich soils was the highest (5.3) and double in comparison with the control soils (2.4, 2.9)615'616. Moreover, the nitrogen content of soil with alkaloid-rich canopy addition was at the level of 30.6 ± 12.3gL-1 after 1 year, the highest figure in comparison with other soils (Figure 94). The nitrogen content increase and larger changes of SD in Soil 2 were connected with the high alkaloidal content and composting process of the lupin in the soil. Nitrogen content in this soil treated with alkaloid-rich lupin was 20-44% more than in the standard Soils 1 and 4 (without manure) and 5% more than Soil 3, which was treated with grasses growing in the same place with lupine615. The total quinolizidine alkaloid content of the L. mutabilis canopy used in the experiments was 2.1 ± 0.3g100g-1. Besides nitrogen, carbon and microbial carbon content were also relatively high in the soil fertilized by alkaloid-rich lupine615 616.
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