RESUMO
The correct evaluation of silicon (Si) availability in different soil types is critical in defining the amount of Si to be supplied to crops. This study was carried out to evaluate two methods and five chemical Si extractants in clayey, sandy-loam, and sandy soils cultivated with sugarcane (Saccharum spp. hybrids). Soluble Si was extracted using two extraction methods (conventional and microwave oven) and five Si extractants (CaCl2, deionized water, KCl, Na-acetate buffer (pH 4.0), and acetic acid). No single method and/or extractant adequately estimated the Si availability in the soils. Conventional extraction with KCl was no more effective than other methods in evaluating Si availability; however, it had less variation in estimating soluble Si between soils with different textural classes. In the clayey and sandy soils, the Na-acetate buffer (pH 4.0) and acetic acid were effective in evaluating the Si availability in the soil regardless of the extraction methods. The extraction with acetic acid using the microwave oven, however, overestimated the Si availability. In the sandy-loam soil, extraction with deionized water using the microwave oven method was more effective in estimating the Si availability in the soil than the other extraction methods.
RESUMO
The aim of this study was to evaluate soil fertility amendment, stalk yield, sugar, bagasse, and trash yield as affected by surface application of dolomitic limestone and gypsum in green sugarcane ratoon. A factorial arrangement of four dolomitic limestone rates (0, 900, 1800, and 3600 kg ha1) and two gypsum rates (0 and 1700 kg ha1) was used in the experiment. The experiment was performed from October 2006 to October 2007, starting in the rainy season after the 2nd ratoon harvest of the variety SP813250 in a commercial green sugarcane plantation of the São Luiz Sugar Mill (47º25'33" W; 21º59'46", 627 m of altitude), located in Pirassununga, state of São Paulo, in southeast Brazil. After 12 months, the experiment was harvested, technological measurements of stalk yield were made, and soil samples were taken and analyzed. Gypsum acts as a subsurface conditioner thus contributing so the benefits of surface limestone application, on soil acidity correction, to reach deeper layers, allowing the development of the root system of plants in greater depth. However, application of gypsum may lead to leaching of Mg and K from the topsoil layers. The higher rates of lime in surface application provided acidity amendment and, consequently, increased soil fertility in the soil profile, and increased sugarcane stalk, sugar, bagasse, and trash yield.
O objetivo do presente estudo foi avaliar a correção da fertilidade do solo e produtividade de colmos, açúcar, bagaço e palhiço a partir da aplicação superficial de calcário dolomítico e gesso em cana soca. O arranjo fatorial foi composto por 4 doses de calcário dolomítico (0, 900, 1800 e 3600 kg ha1) e duas doses de gesso (0 e 1700 kg ha1). O experimento foi realizado no período de outubro de 2006 a outubro de 2007, iniciando-se na estação chuvosa após a colheita da segunda soqueira. A variedade utilizada foi a SP813250 em plantio comercial de cana crua da Usina de São Luiz (47º25'33 "W; 21º59'46", 627 M de altitude), localizado em Pirassununga, estado de São Paulo, no sudeste do Brasil. Após 12 meses, o experimento foi colhido, determinado os parâmetros tecnológicos e amostras de solo foram coletadas e analisadas. O gesso atua como um condicionador subsuperficial contribuindo assim, para que os benefícios da aplicação superficial de calcário na correção da acidez do solo, alcancem camadas mais profundas e, portanto, permitindo o desenvolvimento do sistema radicular das plantas em maior profundidade. No entanto, a aplicação de gesso pode proporcionar lixiviação de Mg e K das camadas superficiais. As maiores doses de calcário aplicadas superficialmente propiciaram correção da acidez do solo e consequente incremento na fertilidade do solo, produtividade de colmos, açúcar, bagaço e palhiço da cana.
