Influência do tipo de manejo (orgânico e convencional) na matéria orgânica de solos cultivados com citrus

Abstract

Organic matter plays an important role as a component of agro-systems to promote agricultural sustainability. The change in the system of cultivation from conventional to organic management has triggered a series of changes in the chemical and physical properties of the soil, especially regarding the availability of nutrients and structuring for the crop. Phosphorus is one of the essential macronutrients less absorbed by plants and the most used in Brazil for fertilization. The objective of this work was to evaluate soil and organic matter (humic substances) extracted from these soils, in the face of organic and conventional management, as well as to evaluate the desorption of phosphorus in these soils. Soil samples were collected at Fazenda São Pedro - Sorocaba / SP and sent to the laboratory. The parameters organic matter, pH and total metals (Ca, Mn, Mg, K, P and Al) were evaluated in the soil samples, besides the extraction and characterization of the humic substances by spectroscopy techniques in the region of UV-vis and fluorescence molecular. As for the phosphorus desorption study, two samples were selected, one with higher (A) and one with lower (B) organic matter content. Regarding the pH parameter, in the conventional management a pH of around 5.7 was observed which indicated the occurrence of acidification of the soil when compared to the organic management with a pH of 6.2. Regarding the organic matter content, samples with organic management had higher levels (11.88 - 26.20%) than conventional management (10.03 - 19.46%). Regarding the total metals Ca, K, and Mg were found according to the soil fertility standard. Regarding the characterization of the humic substances, the results showed that for the ratio E4 / E6 (ratio between absorbances 465 and 665 nm) the time evaluated in this work did not influence the ratio of the samples analyzed. As for fluorescence results, it was observed that, in general, the lowest indices occurred for soils of organic management, and the highest for soils under conventional management, thus showing that the samples submitted to conventional management had higher indices of humification. For the desorption studies it can be observed, in general, that the higher desorption occurred in the samples submitted to conventional management, probably due to the additions of fertilizers. Thus, although the samples submitted to organic management present environmental appeal, the present work shows that there were few differences between the management, which results can be associated to the relatively short time of analysis of 4 years.