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Com a finalidade de verificar a influência da adubação em cultura de milho sôbre o estado de agregação da terra-roxa (série Chapadão), foram feitas as análises de amostras de solo de um ensaio de adubação conduzido pela Seção de Cereais, a partir de 1963. O ensaio compreendia diversos tratamentos com estêrco, calcário e adubação mineral e fôra instalado em 27 parcelas homogêneas de um solo terra-roxa, da série Chapadão. Os resultados mostraram uma redução considerável do diâmetro médio dos agregados do solo das parcelas cultivadas em relação ao solo não cultivado há anos, que, de 1,25 mm, passou a oscilar normalmente entre 0,50 e 0,79. Um dos fatôres que mais contribuíram para essa quebra de tamanho de agregados foi o preparo intenso do solo. Observou-se uma correlação entre o teor de carbono das amostras e os diâmetros médios dos agregados. A aplicação de estêrco contribuiu para aumentar o tamanho dos agregados, quando não acompanhada de calcário e adubo mineral. Nenhuma correlação foi observada entre o estado de agregação e a produção de milho. A terra-roxa apresenta condições excepcionais de estrutura que permitem até o preparo intenso do solo sem que haja repercussões desfavoráveis sôbre o desenvolvimento dessa planta. The purpose of the present study was to investigate the influence on structural improvement of the "terra-roxa" soil by means of application of barnyard manure, lime and mineral fertilizers. An experiment had been run by the Cereals Section from 1953, at the Central Experiment Station in Campinas, on 27 plots of corn, of terra-roxa soil of the "Chapadão" series. Analyses of soil samples from these 27 plots were made and samples were taken from these cultivated corn plots as well as from plots non cultivated for several years; they were passed through a 7.0 mm sieve and the aggregates separated into the following classes as to their diameters: 7.0 to 4.0mm, 4.0 to 2.0mm, 2.0 to 1.0mm, 1.0 to 0.5 mm, 0.5 to 0.25 mm and less than 0.25 mm. Comparing the results regarding the aggregates of the cultivated plots and non cultivated as well, it was found that in the former a decrease of the mean diameter of the aggregates occurred, same ranging from 1.25 mm to 0.5 or 0.79 mm. There is conclusive evidence of the decrease of their mean diameter, the main factor for this being the intensive tillage of the soil. Further, a correlation between the carbon content and the mean diameter of the aggregates was noted. Application of barnyard manure had as a result the increase of their mean diameter. No correlation was observed between the aggregation and the corn yield. The "terra-roxa" highly structured supports intensive work of the soil with no unfavorable effect on the corn plant development

Estado de agregação da terra-roxa (série chapadão) num ensaio de adubação de milho