Avaliação agronômica de rocha ígnea extrusiva da Formação Serra Geral como fonte de potássio

Abstract

Agrominerals usage can reduce fertilizer costs as it can utilize regional nutrient sources. Due to the diversity of minerological composition in Brazil, the use of byproducts obtained from rocks processing has been studied for several purposes. On this way, the objective was to evaluate the agronomic efficiency of extrusive igneous rocks from Serra Geral Formation as potassium alternative source. For this purpose, two experiments were carried out in controlled conditions, being the first an incubation experiment conducted in a room with monitored environmental conditions, using 1 dm3 pots containing two soil types: Nitosol and Neosol; two types of agrominerals: dacite in the following particle-size fractions: <0.105 mm, 0.105 to 0.3 mm, 0.3 to 0.84 mm and 0.84 to 2 mm, and andesite-basalt with particle-size of 100% <0.3 mm) and potassium phonolite (EkoSil®) fertilizer as positive control. The aim of this study was to evaluate the particle-size effect of dacite rock and the mixture of dacite and andesite-basalt on soil fertility attributes over time. Four soil samplings were performed during the incubation experiment to characterize the chemical attributes. The second study was a greenhouse experiment carried out using three soil types: Latosol, Neosol and Planosol in pots of 10 dm3, being the treatments composed by the agrominerals: dacite in the particle-size of 100% < 0.105 mm and andesite-basalt in the particle-size of 100% < 0.3 mm), as well as the fertilizers KCl and phonolite in their respective commercial forms. This experiment aimed to evaluate soil nutrient availability from two alternative sources over two agricultural cultivations, as well as their use efficiency regarding the soluble fertilizer commonly used, and the alternative fertilizer already registered as a potassium source. The stem diameter, number of leaves and shoot dry matter of lettuce were evaluated as well as the forage dry matter of ryegrass. After the cultivations, soil samples were collected for its chemical characterization. The different granulometries did not influence on the nutrient release to the soil during the incubation experiment (120 days). Soil type factor predominates over potassium sources for most soil chemical attributes. Generally, in sandy soils, potassium sources of high or low solubility provide more robust responses than in clayey soils.