CORRELATION BETWEEN SOIL P AND CORN LEAF P CONTENTS IN A NETWORK OF HUNGARIAN LONG-TERM FIELD TRIALS

Abstract

Corn (Zea mays L.) leaf weight, leaf P concentrations at flowering stage, 0.01 M CaCl2-, Olsen-, LE-, and AL-soluble soil P contents were determined in a network of uniformed 27-year-old Hungarian long-term field trials (the so-called National Long-term Field Trials, NLFT) with four P fertilization rates on nine locations, representing various agro-ecological and soil conditions of the country. A 4–5 fold increase in soluble P contents was found in all soil P-tests, while the absolute values of dissolved P varied greatly (CaCl2-P: 0.1–3.7; Olsen-P: 3.7–47.7; and AL-P: 12.8–182.2 mg P kg−1). On the other hand, an average twofold difference occurred among the sites in case of soil P-test methods less dependent of soil properties (CaCl2, Olsen), and a fourfold difference in methods using acid solvents, more dependent of soil reaction status and CaCO3 content. On the average of all soils and all P levels, the amount of P dissolved by the different methods increased in the sequence of CaCl2<Olsen<LE<AL (1.5<20<44<74 mg P kg−1). The different agro-ecological conditions had a greater effect on corn leaf weights at flowering stage than soil-P status. Corn leaf P concentrations, however, were affected by both the P rates and the different sites, resp. There was no significant correlation between Olsen-P values and corn leaf weights. Corn leaf weight, however, increased jointly with soil test values, up to 10–15 mg/kg Olsen-P concentration. There was a weak quadratic correlation between corn leaf P concentrations and leaf weights (r=0.35* *). Above 0.25% leaf P concentrations, leaf weights did not increase any more. On calcareous soils, P-overfertilization could result in Zn deficiency induced by P. There was a moderate, logarithmic correlation between Olsen-P and leaf P contents (r=0.62* * *). The lower limit of good P supply,—indicated by 0.26% leaf P concentration at flowering stage—was usually reached when the Olsen-P value was around 10 mg/kg. Only the CaCl2- and Olsen-methods proved to be independent of soil reaction status. A strong, linear correlation was found between these two methods (r=0.80* * *). The behavior of acid LE- and AL- solvents, however, was different in acid and calcareous soils. Correlation between Olsen- and LE-, as well as between Olsen- and AL-methods could be found separately for acid and calcareous soils. The closeness of correlation within the calcareous soil group and within the acid soil group was similar (r=0.89* * * and 0.90* * * for the calcareous, and r=0.89* * * and 0.94* * * for the acid soils group). Soil and plant P analyses data proved to be useful tools in adapting the results of long-term field trials for improved, environmentally sound fertilizer recommendations.