Atributos microbiológicos em solos cultivados com cana-de-açúcar (Sacharum spp.) en São Paulo, Brasil

Abstract

The microorganisms are present in great diversity and abundance in the soil. However, the anthropic activities, which result mainly from the inappropriate use and management of the soil, have caused changes in the structure of these communities of organisms. The cultivation of sugarcane, quite intense in the state of São Paulo, was still little studied in relation to possible changes in the soil microbiota, due to factors such as humidity, temperature, straw and nitrogen fertilization. The objective of this study was to evaluate the effects of abiotic factors on the microbiological attributes of soils cultivated with sugarcane (Saccharum spp.). Laboratory tests were carried out under controlled conditions to evaluate the effect of temperature and humidity on the soil microbiota. In addition, two areas of sugarcane ratoon were evaluated in the municipalities of Piracicaba and Jaú, both located in SP, with the following treatments: with or without N (0 and 150 kg ha-1), in the form of nitrate of ammonium in two depths of 0-10 and 10-20 cm. Land sampling was performed to analyze the genetic structure of bacterial communities and soil attributes, such as fertility, carbon and nitrogen from microbial biomass, basal respiration, quantification of specific communities of ammonia bacteria, nitriding agents, nitrates, and soil enzymes. The results were submitted to analysis of variance and test of means and multivariate statistical analysis by principal component analyzes (PCA), non-metric multidimensional scaling analysis (NMDS), similarity analysis (ANOSIM) and simple linear correlation by the test of Pearson, among the soil characteristics. In the experiment under controlled conditions, with different humidity, with or without straw, and with application or nitrogen, soil respiration and qCO2 were influenced by the increase of humidity, especially by 100% humidity in the two soil incubation periods .The nitrogen of the microbial biomass was correlated with the straw, independent of the addition of nitrogen fertilization. The carbon of the microbial biomass was not influenced by the treatments applied in the experiments. The profile of bacterial communities revealed a high correlation between moisture and straw in possible changes in microbial composition, especially in 100% humidity. In the experiment under controlled conditions, with different temperatures, with or without straw, and with or without nitrogen application, soil respiration and C/N ratio were correlated with the absence of straw and influenced by the presence of nitrogen fertilization at the temperature of 20°C. The carbon of the microbial biomass was influenced by the presence of the straw and by the temperature of 30°C. In general, the nitrogen of the microbial biomass was influenced firstly by the presence of the straw and secondarily by the nitrogen fertilization. In the experiments under field conditions, basal respiration was the most sensitive indicator in relation to the change in depth in area 1, while microbial biomass carbon, metabolic quotient and nitrators were not influenced by the application of the treatments in the studied areas. The nitriding agents were correlated to the absence of nitrogen in the depth of 0-10 cm, while the nitrators and the ammoniters were related to the treatment with nitrogen fertilization in the depth of 10- 20 cm independent of the evaluated area.