Carbon and nitrogen stocks and greenhouse gases emissions from sugarcane areas in the Piracicaba region

Author(s)

Diana Signor

• Document type: Master's Dissertation
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2010-06-15

Examining board members

Carlos Eduardo Pellegrino Cerri; Luis Reynaldo Ferracciú Alleoni; Newton La Scala Junior

• Advisor: Carlos Eduardo Pellegrino Cerri

Abstract

Concentrations of greenhouse gases (GHG), such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), have increased since Industrial Revolution and the agricultural sector significantly contributes to the mentioned increase. Soils are important sinks of carbon (C) and nitrogen (N) and management practices could release part of these pools to the atmosphere and contribute to the increase of GHG concentrations in the atmosphere. However, some management practices promote increase in soil C and N stocks and are very important in mitigating global warming. No burning sugarcane harvest system is a practice that increases straw deposition at the soil surface and affects soil C and N stocks, while nitrogen fertilization could influence CO2 and N2O emissions from soils. The first part of this work compared C and N stocks and microbial biomass C content in sugarcane areas harvested with and without straw burning. In the 0-10 cm and 10-20 cm layers, C and N stocks were higher under no-burning system. In 0-30 cm layer, C stocks represented 60 and 53 % and N stocks accounted for 55 and 50 % of the total stocks accumulated in 0-100 cm depth, for areas under no-burning and burning systems, respectively. Due to no-burning adoption, soil C accumulation rate was 0.7 Mg ha-1 year-1, while N presented losses of 0.25 Mg ha-1 year-1. Carbon content in the microbial biomass for the 0-20 cm depth varied from 184.20 to 349.27 mg kg-1 at no-burning areas and from 198.85 to 291.77 mg kg-1 at burning sites. The period of time under no-burning favored an increase in the soil microbial C. The second part of this work consisted in the evaluation of GHG emissions from nitrogen fertilization under sugarcane cultivation. Three experiments were carried out, where the effects of two mineral N sources were compared: urea and ammonium nitrate. At laboratory conditions, the rates of 60, 80 and 120 kg ha-1 N were evaluated. Influences of sources and rates of N addition to the N2O emissions were observed and the greater emissions were associated with urea. At the field conditions, testing rates of 60, 90, 120 and 180 kg ha-1 of N, showed greater emissions for ammonium nitrate at the bigger rates. A third experiment, carried out under field conditions, evaluated the influences of the same N sources and addition rates in the CO2 emissions. Alterations in the emissions were observed only in plots that received urea, despite the large data dispersion, which compromises the regression adjustment. (AU)