Mineralização da palhada de cana-de-açúcar: efeito da incorporação, da adição de nitrogênio e da temperatura

Abstract

Brazil is expanding sugar cane cultivation with mechanized harvesting, mainly in the Southeast, resulting in the deposition of large amount of straw dry mass on the soil. Such trash cannot be eliminated with prescribed fire, not even as a facilitator of manual sugar cane harvest, according to the decree 11.241, 20004. The relation of straw with soil and the identification of different carbon © additions with C-CO2 (carbon dioxide) emission has raised questions about the role of soil C and the importance of agriculture on the emission of greenhouse effect gases. Therefore, this study determined the addition of carbon and C-CO2 emission in soil incubated with sugarcane trash (surface or incorporated management) and nitrogen fertilization (0 Kg N ha-1 or 120 Kg N ha-1) in different temperatures (20, 25 or 30° C). It was observed that incorporated trash and N addition to soil resulted in greater mineralization rates of COT, respectively 12.24 and 2.14% in relation to non incorporated and with no N added trash management. However, no differences were observed between COT and C from humine fraction (CHU) after 79 days of soil incubation. Emission of C-CO2 peaked in the first four days of incubation for surface trash management, with 5.45, 10.82, 14.00, 11.92 μg mol C-CO2 soil m-2 s-1 and incorporated with 11.20, 14.47, 15.98, 14.74 C-CO2 m-2 s-1, with subsequent decrease in emission until becoming stable after 40 days of incubation. Also, there was an increase of soil N by 6.89% after trash incorporation, in comparison to surface management. Greater additions of total N, were obtained for sugarcane trash, especially after incorporation coupled to nitrogen fertilization. There was no effect of treatments on carbon contents in soil microbial biomass (C-BMS), labile carbon (Clabile), calcium (Ca+2), magnesium (Mg+2) and phosphorus (P).