Data presentation, interpretation, and communication

Abstract

Tillering stage winter wheat (Triticum aestivum L.) shoot weight, shoot K concentrations, acid ammonium‐acetate EDTA‐soluble (LE‐, Lakanen and Erviö, 1971) and neutral ammonium acetate ‐ exchangeable (Wanasuria et al., 1981) soil K were determined in a network of 28‐year‐old National Long‐term Fertilization Trials (NLFT) with different K fertilization rates at eight experimental sites representing various agro‐ecological and soil conditions of Hungary. Both wheat shoot weights and K concentrations were affected less by K levels than by the different agro‐ecological conditions. The effect of K fertilization, however, was also significant, especially on shoot K contents. The additional effect of a higher K rate, however, was not so substantial. There was no significant correlation between winter wheat shoot K. concentrations and shoot weight. Above 3.0 % shoot K concentrations, however, shoot weights did not increase significantly. Wheat shoot weight increased with increasing soil K values, up to about 150 mg/kg soil‐exchangeable K concentration. Correlation between exhangeable soil K and shoot weight was described by a saturation (Mitscherlich) curve (R=0.6***). Correlation between exchangeable soil K and shoot K contents was also described by a saturation (Mitscherlich) equation (R=0.5***). The lower limit of good K supply, indicated by shoot K concentration at tillering stage (3.0 % K) was usually reached when NH4OAc‐ K reached as high as 150 mg/kg. The closest, linear correlation was found between soil‐exchangeable and LE‐soluble K (r=0.8***). LE extractant dissolved 10% less K than NH4OAc‐ extractant at the average of sites and K levels. Both the LE‐ and the neutral ammonium acetate methods indicated the different soil K levels in a similar way. As a first attempt, new NH4OAc‐ extractable K supply categories were established for the Hungarian agro‐ecolgical conditions, for the non‐ K demanding crop group, including winter wheat. Soil and plant K analyses data proved to be useful tools in adapting the results of long‐term field trials for improved fertilizer recommendations.