Avaliação da disponibilidade de fósforo em solos de várzea do Estado de Minas Gerais

Abstract

Lowlands have been found to be a very good option for expansion of cultivated area in Brazil, aiming the increase in food production. Due to the easy of irrigation, these areas can be cultivated either under flooding or drying conditions, being more common the rice cultivation under the first circunstance. As the majority of tropical soils, on lowland soils also was found a generalized phosphorus deficiency. There are also difficulties upon this nutrient availability evaluation thirough soil chemical analysis using the nowadays methodology. This work compared four extractors in terms of evaluating phosphorus availability on lowland soils in Minas Gerais State, Brazil. The experiment was conducted in a greenhouse of Soil Science Department at Escola Superior de Agricultura de Lavras . Rice was cultivated under drying and flooding conditions during 54 days in 15 topsoils at 2 P levels (0 and 200 ppm). A totally randomized design was adopted with 3 replications by according to a 15x2x2 scheme. Data including plants dry matter and P absorbed quantity were obtained. The phosphorus was extracted by 4 methods: Bray-1, Mehlich-1, Olsen + EDTA and IER (ion-exchange resin). The rice showed high response to phosphorus application either under drying or flooding conditions, indicating low availability of this element on studied soils. The results also showed an increase in dry matter production and P absorbed amount with flooding for all soils. There was also a decrease in response to P application for the majority of soils, suggesting an increase in this nutrient availability upon flooding. The Olsen + EDTA presented greater extraction capacity followed by IER, Mehlich-1 and Bray-1. These methods had a significant correlation among themselves, with exception of the correlation between Bray-1 and IER. There was variation in the correlations between available P extracted by the utilized methods and the relative production, depending upon the moisture condition utilized during cultivation. The IER was the best extractor in the determination of available P, when correlated with relative production, under flooding as well as drying conditions. There was increase in multiple correlation between relative production and available P, when it is included the organic matter variable, suggesting influence of that parameter upon eficiency of P method for the studied soils.