Stocks and quality of organic matter in an inceptisol under long-term sugarcane cultivation

The aim of this study was to evaluate the stocks, and quality of the soil organic matter (SOM) through the use of solid state C-13 nuclear magnetic resonance (C-13 NMR), electronic paramagnetic resonance (EPR) and fluorescence spectroscopy of a fine clay fluventic Eutrichrept after long-term sugarcane cultivation. In one area, sugarcane has been grown for 55 years no field burning before harvest. In another area managed under the traditional system the crop field has been burned before harvest for 35 years; vinasse has been applied on onepart (at a rate of 120 m(3) ha(-1) yr(-1)), but not on another. The increases of 157 and 57% in C stocks of humic acids in the area cultivated without field burning for 55 years were related with the increase in the aromaticity degree as well as lower acidity of the SOM, as shown by C-13 NMR spectroscopy. The serniquinone-type free radical concentration, as observed by EPR, and intensity of fluorescence emission were higher in the humic acid extracted from soils under management system without field burning before harvest. Significant changes in the humification process were observed in the areas with crop trash preservation. However, in areas where sugar-cane fields were burnt at harvest, vinasse application for 35 years resulted in only minor changes in the organic matter quality and C stocks. These data indicate a rapid evolution of the soluble organic matter added to the soil through uinasse application.