CORRELATIONS BETWEEN 2 SOIL EXTRACTANTS AND CORN LEAF POTASSIUM CONTENTS FROM HUNGARIAN FIELD TRIALS

Corn (Zea mays L.) leaf weight, leaf potassium (K) content at the flow ering stage, and ammonium lactate (AL)- and neutral normal ammonium ac etate (NH4Ac)-extractable K were determined in a network of 27-year-ol d long-term Hungarian field trials (''OMTK trials'') with different K fertilization rates on nine locations representing various agro-ecolog ical and soil conditions of the country. Corn leaf weights at the flow ering stage were affected less by soil-extractable K than by the diffe rent agro-ecological conditions. Corn K contents, however, were much m ore affected by K rates than leaf weights. The additional effect of th e higher K rate, however, was not significant. Leaf K contents were af fected by site also. There was no significant correlation between corn leaf K content and leaf weight. Above 1.5% K leaf content, however, l eaf weights did not increase. Corn leaf weight increased together with soil test values up to 150-160 mg kg(-1) soil-extractable K. There wa s a poor linear correlation between soil-extractable K and leaf weight (r = 0.40*). There was a significant quadratic polynomial correlatio n between soil-extractable K and leaf K content (R = 0.60**). The low er limit of good K supply, indicated by leaf K content at flowering (1 .5% K), was usually reached when the soil-extractable K level reached 150 mg kg(-1). The most significant linear correlation was found betwe en NH4Ac- and AL-extractable K (r = 0.91**). Both the AL and NH4Ac me thods identied the different soil K levels similarly. As a first attem pt, new NH4Ac-extractable K supply categories were established for Hun garian conditions. Soil and plant K analysis data proved to be useful tools in adapting the results from long-term field trials for improved fertilizer recommendations.