Abstract
The study of labile carbon fractions (LCF) provides an understanding of the behavior of soil organic matter (SOM) under different soil management systems and cover crops. The aim of this study was to assess the effect of different soil management systems with respect to tillage, cover crop and phosphate fertilization on the amount of the LCF of SOM. Treatments consisted of conventional tillage (CT) and no-tillage (NT) with millet as the cover crop and a no-tillage system with velvet bean at two phosphorus dosages. Soil samples were collected and analyzed for organic carbon (OC), C oxidizable by KMnO4 (C-KMnO4), particulate OC (POC), microbial biomass carbon and light SOM in the 0.0-0.05, 0.05-0.10 and 0.10-0.20 m soil layers. The Carbon Management Index (CMI) was calculated to evaluate the impacts of soil management treatments on the quality of the SOM. The different LCFs are sensitive to different soil management systems, and there are significant correlations between them. C-KMnO4 is considered the best indicator of OC carbon lability. In the soil surface layers, the CT reduced the carbon content in all of the labile fractions of the SOM. The use of phosphorus led to the accumulation of OC and carbon in the different soil fractions regardless of the tillage system or cover crop. The application of phosphate fertilizer improved the ability of the NTsystem to promote soil quality, as assessed by the CMI.
Highlights
The formation of soil organic matter (SOM) is very complex (Haynes, 2005)
A similar finding was obtained by Rangel et al (2008) that reported a decrease in the organic carbon (OC) level at the 0.0-0.10 m depth compared to the natural system for all systems of soil uses and managements
The labile fractions were found to be sensitive to soil management practices, and the lowest levels of these parameters were observed under a conventional tillage system
Summary
The formation of soil organic matter (SOM) is very complex (Haynes, 2005) This complexity makes it difficult to understand SOM dynamics when the soil is subjected to different management systems. The fractions of labile SOM have high rates of decomposition and short residence times in the soil (Haynes, 2005). Because of this rapid cycling, the labile SOM is a more sensitive fraction for evaluating changes caused by agricultural practices (Vieira et al, 2007; Campos et al, 2011) than the total carbon (TC) (Figueiredo et al, 2013; Quanying et al, 2014). The nature and dynamics of the SOM and P are associated and can be a basis for predicting the modifications that land-use changes can have on soil quality (Aguiar et al, 2013)
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