Die Problematik düngungsbedingter Höchsterträge aus phytochemischer und ernährungsphysiologischer Sicht

The criteria of yield increases is being subjected to a causal examination. Maximum yields — brought about by large nitrogen supply — are being examined with respect to their influence upon disease potential, increase of quality — and non-parasitic defects as well as upon decrease of useful and increase of undesirable compounds. Observations from the world literature as well as our own experiments with vegetables over many years, particularly with spinach serve as evidence. Stimulation of diseases and pests through overnourishment with nitrogen refer particularly to rust, downy mildew, septoria and botrytis organisms as well as to lice and mites. Amongst non-parasitic diseases one has to list a great number of quality defects, a lessening of resistance against mechanical damage at harvest and during transport, a reduction in quantity of commercial grades, flavour losses and above all a decline of keeping in winter storage. Exessive nitrogen supply also results in a decline in content of valuable constituents and increase in biogenic toxicants as well as in plant components to undesirable levels from a technological and nutritional physiological point of view. Fig. 10 summarises these results. The following valuable constituents are particularly affected: dry matter, total sugar, vitamin C, essential oils and potassium, magnesium and phosphoric acid amongst the minerals. Undesirable increase of enzyme activity as well as that of free amino acid content — coupled with a decrease of biological protein value are additional consequences of excess nitrogen fertilizing. Increases of undesirable compounds refer to crude protein (e.g. brewing barley and sugar beet), nitrate nitrogen (spinach) potentially a health hazard to infants (methaemoglobinemia) in case where toxic nitrite is formed in the spinach from nitrate. The removal of watersoluble nitrate from spinach overnourished with nitrogen by prolonged blanching, suggested in some publications, is to be rejected owing to the then unavoidable in part enhanced losses of water soluble compounds of nutritive value, including vitamins and minerals.