Deficiência de ferro em grápia: efeito da adubação fosfatada e potássica

Abstract

Previous studies done with grápia (Apuleia leiocarpa (Vog.) Macbride) showed that the increase in the P fertilization induced visual symptoms of Fe-deficiency in the younger leaves. At cellular level, potassium may contribute to balance charges between the cytoplasm and apoplasm, hence allowing the uptake of iron by plant cells. The aim of this study was to evaluate the effects of phosphorus and potassium fertilization in relation to Fedeficiency in grapia seedlings cultivated in a Paleudalf soil. Twenty seven fertilization treatments were used, represented by the combination of three levels of P (80, 150 e 220 mg P kg-1 of the soil), three levels of K (70, 110 e 150 mg kg-1 of the soil) and three levels of Fe as Fe-EDTA (0, 7,5 e 15 mg Fe kg-1 of soil), under unclimatized greenhouse conditions. The plant growth in number of leaves, number of fallen leaves, height and stem diameter was analyzed monthly. Until 150 days after fertilization (DAF), leaves with visual symptons of Fe deficiency was counted monthly. At 150 DAF δ-Aminolevulinic acid dehydratase activity was determined. Dry matter of leaves, stem, shoot, roots and whole plant, root/shoot dry matter ratio, chemistry features of the soil, as well as P, K, Ca, Mg, Fe, Zn and Cu concentration and content from leaves of grápia were analyzed at 180 DAF. The high availability of P in the soil gave rise to chlorosis in the younger leaves similar to that of Fe deficiency. The P fertilization increased the P/Fe, P/Zn and P/Cu ratios in the leaves, whereas K and Fe fertilization decreased those ratios. Nevertheless, the potassium fertilization did not influence the porphobilinogen formation, a precursor molecule of chlorophyll. Therefore, the increased K availability was not sufficient to resolve the nutritional unbalance induced by phosphorus fertilization on grápia.