Correlations between two soil extractants and corn leaf potassium contents from Hungarian field trials

Corn (Zea mays L.) leaf weight, leaf potassium (K) content at the flowering stage, and ammonium lactate (AL)- and neutral normal ammonium acetate (NH4Ac)-extractable K were determined in a network of 27-year-old long-term Hungarian field trials ("OMTK trials") with different K fertilization rates on nine locations representing various agro-ecological and soil conditions of the country. Corn leaf weights at the flowering stage were affected less by soil-extractable K than by the different agro-ecological conditions. Corn K contents, however, were much more affected by K rates than leaf weights. The additional effect of the higher K rate, however, was not significant. Leaf K contents were affected by site also. There was no significant correlation between corn leaf K content and leaf weight. Above 1.5% K leaf content, however, leaf weights did not increase. Corn leaf weight increased together with soil test values up to 150-160 mg kg(-1) soil-extractable K. There was a poor linear correlation between soil-extractable K and leaf weight (r = 0.40**). There was a significant quadratic polynomial correlation between soil-extractable K and leaf K content (R = 0.60***). The lower 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 between NH4Ac- and AL-extractable K (r = 0.91***). Both the AL and NH4Ac methods identied the different soil K levels similarly. As a first attempt, new NH4Ac-extractable K supply categories were established for Hungarian 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.