Abstract
ABSTRACT The permanence of sugarcane straw on the soil surface, in systems without the pre-harvest straw burning practice, directly affects the soil organic matter dynamics. The objective of this work was to evaluate the changes in total organic carbon (TOC), carbon in the light organic matter (CLOM) and particulate organic carbon (POC), and their carbon stocks in a typic Quartzipsamment cultivated for nine years with sugarcane crops, which were conducted without the pre-harvest straw burning practice, in Paraipaba, State of Ceará, Brazil. Disturbed and undisturbed soil samples were collected at depths of 0.0-0.025, 0.025-0.05, 0.05-0.10, 0.10-0.20 and 0.20-0.30 m, in the sugarcane crop area and in an adjacent native forest area, in order to quantify the TOC, CLOM and POC, as well as the carbon stocks accumulated in the layer 0.0-0.30 m related to these fractions (TOCSt, CLOMSt and POCSt). TOC content changes after nine years of sugarcane crops, conducted without pre-harvest straw burning, were found only in the layers 0.10-0.20 and 0.20-0.30 m. The CLOM varied only in the layer 0.025-0.05 m. The POC content changes were more noticeable than the changes in TOC and CMOL. The CLOM of the sugarcane crop area presented high similarity with TOC, which may affect their quantification in studies related to the soil organic matter dynamics. The sugarcane crop increased the TOCSt, POCSt and CLOMSt in the layer 0.0-0.30 m, compared with the adjacent native forest area.
Highlights
The mechanized harvesting system of sugarcane leaves all crop residues on the soil surface, keeping it covered for a long time
The objective of this work was to evaluate the changes in total organic carbon (TOC), carbon in the light organic matter (CLOM) and particulate organic carbon (POC) contents and their carbon stocks, in a typic Quartzipsamment cultivated for nine years with sugarcane crops, which were conducted without the pre-harvest straw burning practice, using an adjacent native forest area as reference, in the semiarid region of the State of Ceará, Brazil
The TOC content in the sugarcane crop area, considering the layer 0.0-0.30 m, was higher than those found in several studies on sugarcane crops in systems with the pre-harvest straw burning practice (BLAIR, 2000; LUCA et al, 2008; PINHEIRO et al, 2010; THORBURN et al, 2012), denoting the beneficial effect of the management system used to the organic matter accumulation in the soil
Summary
The mechanized harvesting system of sugarcane leaves all crop residues on the soil surface, keeping it covered for a long time. Studies show that about 10 Mg ha-1 per year of straw are left on the soil surface, contributing to the improvement of soil fertility (RESENDE et al, 2006; LUCA et al, 2008; SILVA NETO et al, 2013). The permanence of the sugarcane straw on the soil surface provides significant increases in the soil organic matter content (SOM), especially in the more clayey soils (LUCA et al, 2008; CERRI et al, 2011). According to Dick et al (2009), clayey soils tend to have high organic matter stocks than sandy soils, due to its high organomineral interactions and low mineralization rates. Some authors reported that, depending on how long a particular management system was implemented, the TOC is not suitable to detect changes in SOM content depending on land use (LEITE et al, 2003; CONCEIÇÃO et al, 2005; SOUZA et al, 2006). The carbon in the light organic matter (CLOM) and the particulate organic carbon (POC) stand out among these fractions
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