INTERACTIONS BETWEEN POTASSIUM AND MAGNESIUM CONTENTS IN POTATO

In the years 1987 - 1989 exact field trials with two varieties (Resy - early and Kamyk - late) were established. Total four variants were pe rformed where nitrogen was applied on the same level (120 kg of pure n utrients Per 1 ha), phosphorus was applied on two levels (52.3 and 78. 5 kg of pure nutrients per 1 ha) and potassium was applied also in two doses (132.8 and 199.2 kg of pure nutrients in K per 1 ha) simultaneo usly in combination with lower and higher doses of phosphorus. During vegetation (at the onset of bud formation, at the onset of flowering a nd 21 days after the second sampling) plant samples have been taken. T he plants were split into tops, roots and tubers. Only tubers were tak en in the harvest. All parts of the plant were analyzed for potassium and magnesium contents. Gradual decrease in potassium content appeared during vegetation in various organs of the plant (Tab. 1). In the Res y variety the highest potassium content was found mainly in the second half of the vegetation at an application of the highest potassium rat e. The highest of potassium uptake took place in the stage of the onse t of flowering. Potassium content in the roots was falling during the vegetation, whereby the effect of potassium rate was not apparent in i ncreased potassium content in the roots. Potassium content was falling in tubers of the Resy variety, in all variants, during the vegetation . Potassium uptake by tubers was affected significantly by weight incr ement of tubers, whereby the most significant was the value in the var iant with the highest potassium rate. In comparison of the values of t he Kamyk variety (Tab. II) with the Resy variety it is evident that in the Kamyk variety in all organs of the plants potassium content was f alling during the vegetation. Absolute potassium content values were m uch differentiated among varieties, the trend towards decrease was pre served. Potassium uptake by organs of the Kamyk variety was higher pre vailingly. Magnesium content in foliage was falling in the Resy variet y during the vegetation (Tab. III). Magnesium) content remained in the roots of the plant on approximately the same level. Magnesium content in tubers was ranging in a very small scale and no conclusion about i nfluencing magnesium content in studied variants can be arrived at. Re latively lower reduction in magnesium content was found in the Kamyk v ariety (Tab. IV) than in the Resy variety during the vegetation. The f luctuation of magnesium content in roots of the plant was not consider able also in the Kamyk variety. Magnesium content in tubers was slight ly falling towards the end of vegetation. Magnesium uptake per hectare of area was increasing by tubers of both varieties towards the end of vegetation, this being affected, to a certain degree, by weight incre ment in tubers. It is evident from the assessment of the relation (Tab . V) between potassium and magnesium in rape tubers that potassium con tent was the highest in both varieties in the variant with an increase d potassium rate (variant 3). The highest potassium uptake was also fo und in this variant (in kg of pure nutrients per 1 ha). Potassium upta ke was significantly higher in the Kamyk variety than in the Resy vari ety, this being in association with the highest tuber yield. Magnesium content was not, however, affected by variants, though magnesium cont ent was reduced in the variants 3 and 4 (marked reduction in the Kamyk variety in comparison with the variant I). In evaluation of the mutua l relationship between potassium and magnesium, it follows that potass ium rate is not decisive but the ability of the plant to respond to th is rate. It is necessary to evaluate simultaneously as potassium conte nt and magnesium content in different organs of the plant, as in the a mount of potassium and magnesium taken by the plant per area unit. It follows from the results obtained that the reduction of magnesium cont ent did not appear, however, the changes were manifested in relatively lover uptake of magnesium at an increase of potassium rate. The above -mentioned relations can be applied only to rape tubers. In comparison of e. g. data of the third sampling (i. e. in the phase of 21 days af ter the onset o f flowering), it is evident that the reduction of magn esium uptake was manifested especially in the early variety in the top s, whereas this reduction was found in the late variety only to the fi rst half of the vegetation. It follows from the results obtained that the evaluation of the relation of both cations is of more complex char acter and it is necessary to consider all factors, including an assess ment of the response of the whole plant.