Effect of K on N Utilization by Spring Wheat During Grain Protein Formation

Several researchers reported that high nitrogen rates for cereals require also an ample potassium supply in order to produce maximum grain yields. The physiological relationships between N and K in grain production are not yet completely understood. For this reason experiments have been carried out to study the effect of K on the translocation of N in wheat plants and its incorporation into the grains during the grain filling period. Spring wheat (Triticum aestivum L. cv. ‘Kolibri’) was gown in solution culture at two K levels throughout the growing period and at three N levels during the reproductive stage. Nitrogen was labeled ¹⁵N with the beginning of anthesis. Plants at the higher K rate produced more vegetative dry matter, higher grain yields, fewer unproductive tillers and improved translocation of N from the vegetative plant parts into the grain. Between 87.4 and 89.0~o of the N absorbed during the reproductive stage was present in the grain of plants which had received the higher K supply. In plants grown with the lower K level the percentage ranged from 78.9 to 81.0yo. This improved translocation of nitrogenous compounds from the various plant parts to the grain caused by K resulted mainly in higher contents of prolamin, glutelin, and soluble amino acids in the grain. For the content of albumin and globulin the reverse was true. All four grain protein fractions showed the same degree of N labeling indicating that none of the four protein fractions was preferably supplied by the N absorbed during the reproductive stage. The label of the soluble amino acids in the grain was lower than that of the grain proteins. It is assumed that at the last stage of grain filling a relatively high amount of N from senescing plant parts is exploited for grain filling, thus diluting the N taken up from the nutrient solution. The higher N levels applied during the reproductive stage had a negative rather than a positive effect on grain yield. The additional N increased mainly the content of soluble amino acids, prolamin, and glutelin in the grain.