SOURCE/SINK-RELATIONSHIPS IN PLANTS AS DEPENDING ON AMMONIUM AS "CULTAN", NITRATE OR UREA AS AVAILABLE NITROGEN FERTILIZERS

K. Sommer, H.W. Scherer
The common tenet in mineral N-fertilization that nitrate as compared to ammonium is the more compatible and quicker effective N-form for plants was disproved by the development of the “CULTAN”-system. It was pointed out that the better compatibility and quicker effectiveness of nitrate as compared to ammonium are properties which depend on the kind of N-fertilization. Beyond this it was proved that in case of non-legumes depending on the kind of the available mineral N-fertilizer, between the assimilates producing and the assimilates consuming organs of the plants (the sources and sinks), specific reciprocal actions are existing which may promote the storage of assimilates. In case of nitrogen supply as nitrate broadcasted or urea in deposits there is a joint source within the plants for the synthesis of carbohydrates and organic N-compounds in the extended leaves with a joint sink incline to the growing parts of the shoots and to the roots. In case of the supply of nitrogen according to the “CULTAN”-system there are separated sources for the assimilation of carbohydrates within the shoots and organic N-compounds in the tips of the roots, close to the surface of the “CULTAN”-deposits. Therefore countercurrent sink inclines for the carbohydrates from the shoots to the roots and for the organic N-compounds from the roots to the shoots are existing, which results in fundamental differences according the distribution of assimilates within plants and the intensity of growth of their different organs, i.e. shoots or roots, depending on the supply of nitrogen as nitrate in comparison to “CULTAN”. These differences in the distribution of assimilates depending on the mineral N-fertilizer application have an impact on the synthesis of phytohormones and the specific equilibrium between phytohormones within the plants, and to a large extend regulate growth behavior as well as yield formation. Exceptions in source/sink-relationships in dependence of the nitrogen supply exist in legumes as compared to non-legumes.
Sommer, K. and Scherer, H.W. (2009). SOURCE/SINK-RELATIONSHIPS IN PLANTS AS DEPENDING ON AMMONIUM AS "CULTAN", NITRATE OR UREA AS AVAILABLE NITROGEN FERTILIZERS . Acta Hortic. 835, 65-87
DOI: 10.17660/ActaHortic.2009.835.6
https://doi.org/10.17660/ActaHortic.2009.835.6
CULTAN, N-fertilizers, assimilates, source/sink, carbohydrates, proteins, phytohormones
English