Potassium Research and Agricultural Production - The International ...

The Relation Between Potassium and Nitrogen
in the Production of Plant Material
Prof. Or. O. Sll!ineck, Director of the 'Institut fUr Pflanzenbau und Pflanzenziichtung
der Hochschule fUr Bodenkultur', Vienna/Austria
Conclusions and Summary
Experiments on the influence of varying levels of nitrogen and potassium on plant growth have been
carried out from 1963 to 1968. Under exact nutritional conditions in changing solution culture
(Kopetz, 5tdneck [1962]) the specific effect of both nutrients on plant growth and nutrient uptake
have been determined. According to the results obtained under conditions of constant ionic nutrient
supply the physiological functions of nitrogen and potassium in the production of plant material
appear to be closely related. Yield increases with increase in N supply, but only in the presence of
adequate potassium. Hence the specific effect of potassium is shown indirectly by its increasing the
efficiency of N utilisation and the utilisation of N in the synthesis of plant material depends principally
upon the potassium supply as He/aJ and MengeJ [J968} and Koch and MengeJ [1970J have
also shown. Potassium also innuences the performance of nitrogen in that increasing K causes a
corresponding increment in N uptake as Nguyen and his co-workers [1973} have also shown. Full
utilisation of nitrogen is realised in nutrient solution culture at aN: K ratio, based on ionic number,
between I :0.8 and I: 1. The plant always takes up fewer potassium than nitrogen ions.
The specific regulatory function exerted by potassium on the effect of nitrogen partly explains the
small differences in yield performance which appear when levels of both nutrients are similarly
increased. This fact leads even today to an insufficient supply of potassium. By taking into account
the reciprocal inter-relationship which shows up in the effects of both nutrients it is necessary, in
practice, to apply a sufficient quantity of potassium when nitrogen applications arc increased. Only
then is the full effect of nitrogen on yield guaranteed.
The one-sided dependence of potassium uptake on that of nitrogen shows the indirect contribution
of this nutrient in the synthesis of plant material. In describing yield formation in mathematical
terms the wholc spectrum of individual nutrient effects and their interactions must be taken into
account.
The various nutrient elements are related one with another in their effects on plant production
- providing more of one nutrient enhances the effects on yield of other nutrients
in a definite manner. For given growth conditions increasing nutrient supply
will only increase growth up to the limit of potential maximum yield. This correlation
between nutrients has been established by exhaustive field and pot experiments with
solid media.
The aim in plant production is to supply the plant with nutrients to meet its needs and
this is hopefully achieved by the proper use of fertilizers. For this purpose it is necessary
to understand fully the precise effects of each nutrient as concerns its role in plar.t
nutrition so as to be able to supply nutrients in the physiologically correct amounts. A
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