Macronutrients content and extraction in zucchini plants in function of potassium top dressing levels

Abstract

Information about content and extraction of nutrients by plants are very important for an adequate fertilization management and they can vary in function of species, fertilization, time of the year, besides other factors. The objective of this research was to study the influence of potassium top dressing levels on macronutrients contents and extraction in shoot and fruits of zucchini, in two cultivation dates: fall (10/03 to 02/06/2010) and spring (04/08 to 03/11/2010) in field conditions, in municipality of São Manuel, SP. The experimental design was randomized blocks, with five treatments (potassium in top dressing levels: 0, 50, 100, 200 and 400 kg of K2O ha-1) and four replications. It was evaluated macronutrients content in the phase of leaf analysis, content and extraction of macronutrients in the end of cycle and macronutrients content in fruits in each weekly harvesting during all cycle. The data were submitted to the variance and to regression analysis. Potassium content in the phase of leaf analysis increased linearly in fall, and calcium decreased in spring in function of potassium levels. Potassium content in shoot at the end of cycle increased and calcium decreased in spring. Potassium content in fruits increased in both dates. Macronutrients (except magnesium) contents in fruits varied, with tendency of decreasing during the cycle. The descending order of the nutrients extracted in plants in fall was K > N > Ca > Mg > P > S and in spring was K > Ca > N > Mg > P > S.