Disponibilidade hídrica e cinética da liberação de potássio em diferentes substratos para produção de mudas

Abstract

The use of substrates that meets properly water and nutrient requirements contributes to production of plants with better quality. The objective of this study was to determine the characteristic curves of water retention and evaluate the kinetics of potassium release from six substrates for seedling production. The substrates consisted of commercial materials with different ratios of pine bark, manure, sawdust, coconut fiber, vermiculite, rice husk, ash, topsoil, charcoal and peat. Water retention curves were drawn based on the adjustment of volumetric moisture data from water retained under different tension values. For determining the particle size distribution, samples of 100g of substrate were dry in air, placed over a set of sieves and stirred manually for three minutes. The content of water-soluble potassium was determined from the extract obtained by the substrate water ratio 1:5, stirred with horizontal motion for a time range from one to thirty six hours. The results showed that all six substrates have different retention capacity of water and air, as a function mainly of their granulometry. Analyses of potassium release showed that large amounts of potassium can be leached, and the study substrates can present different behaviors concerning the nutrient release.