Rosane Martinazzo

FÓSFORO MICROBIANO DO SOLO SOB SISTEMA PLANTIO DIRETO EM RESPOSTA À ADIÇÃO DE FOSFATO SOLÚVEL

The phosphorus cycle in the soil is controlled by physicochemical processes, such as adsorption and desorption, and by biological processes, such as immobilization and mineralization. This study was carried out to evaluate the seasonal variation of phosphorus in the soil microbial biomass (Pm) as related to rates and timing of soluble phosphate application. The experiment was carried out in May 2002 on an Oxisol under no-till for seven years, in Ibiruba, in the southern Brazil. Five rates of soluble phosphate (0, 40, 80, 120, and 160 kg ha-1 of P2O5) were applied twice in a Lolium multiflorum/Glicine max cultivation cycle; the first one in the winter at Lolium multiflorum sowing and the second in the summer at Glicine max sowing. Microbial phosphorus and available phosphorus by anion exchange resin were evaluated in the 0-10 cm soil layer 91, 133, 147, 203, and 267 days after Lolium multiflorum sowing. Phosphate application increased microbial phosphorus, more intensely when applied at soybean sowing over the Lolium multiflorum residues. P immobilization in the microbial biomass was temporary and decreased over the course of the crop cycle; these variations were not correlated with variations in P extracted by anion-exchange resin.

MATÉRIA ORGÂNICA EM QUATRO TIPOS DE SOLOS BRASILEIROS: COMPOSIÇÃO QUÍMICA E SORÇÃO DE ATRAZINA

Soil organic matter is the main sorptive soil compartment for atrazine in soils, followed in a minor scale by the inorganic fraction. In this study, the soil organic matter quality and atrazine sorption were investigated in four different soil types. The pedogenic environment affected the humification and therefore the chemical composition of the organic matter. The organic matter contribution to atrazine sorption was larger (60-83%) than that of the inorganic fraction. The organic matter capacity in retaining the herbicide was favoured by a higher decomposition degree and a smaller carboxylic substitution of the aliphatic chains.

Sorção de atrazina e de mesotriona em latossolos e estimativa do potencial de contaminação

Following application herbicides usually reach the soil and undergo several dissipation processes which determine their effects on target organisms and on the environment. This work aimed to evaluate atrazine and mesotrione sorption in Oxisols and estimate their potential impact on the environment. We observed that atrazine sorption was influenced by soil organic matter content and its hydrophobic character. Clay fraction was the main factor influencing mesotrione sorption followed in a lesser extent by soil organic matter content. In contrast to atrazine, mesotrione retention was favored by the higher carboxylic substitution in the aliphatic chains of soil organic matter. Atrazine and mesotrione were considered compounds that are likely to pose an appreciable risk of causing deleterious effects on the environment.

Impacto da queima nos atributos químicos e na composição química da matéria orgânica do solo e na vegetação

The objective of this study was to evaluate the residual effect of periodic burning on soil chemical attributes, composition of soil organic matter, and on vegetation of a Hapludox. Samples from three environments were studied: native pasture under grazing, without burning and shortening (NP); native pasture under grazing and burning (BP); and native forest (NF) adjacent to the pasture area. Soil samples were collected in four layers: 0-5, 0-20, 20-40 and 40-60 cm, in which fertility attributes and contents of C and N were determined, and analyses of Fourier transform infrared spectroscopy (FTIR) were performed. Samples from the above ground vegetation from these environments were analyzed through elemental analyses and FTIR. Pasture burning reduced soil contents of N, Mg and K, and increased Al saturation in soil, in comparison to NP soil. Nutrient contents were smaller in the soil samples under forest, when compared to NP, while C and N contents and Al saturation were greater. The aromatic character of soil organic matter did not differ among the studied environments, and increased with depth in all environments. In comparison to NP, BP vegetation had a lower N content and a greater proportion of Si groups. The forest vegetation contained more N and showed higher aromaticity than the pasture vegetation.