Soil organic and organomineral fractions as indicators of the effects of land management in conventional and organic sugar cane systems

Abstract

Brazilian sugar cane production has undergone changes in residue management. To better understand the dynamics of soil C and N in soil organic matter (SOM) fractions resulting from sugar cane management practices, we determined: the effects of different sugar cane management on the C and N content of SOM fractions; the effects of crop management, soil texture, depth and different organic matter additions on changes in 13C/12C and 15N/14N isotope composition; and the amount of SOC derived from different sources. Physical fractionation of SOM was performed for soils cultivated under four sugar cane managements, namely straw burning(SB), green cane (GC) and organic systems consisting of sugar cane grown under GC harvesting with high inputs of organic residues for 4 and 12 years (O-4 and O-12 respectively), as well as from a native vegetation (NV) area (Goianésia, Brazil). Ultrasonic dispersion of soil samples from 0–5, 5–10, 10–20 and 90–100-cm depths resulted in three organomineral fractions (<53, 75–53 and 2000–75µm) and one organic fraction denoted as light fraction (2000–75µm). C and N concentrations, 13C and 15N natural abundance and the proportion of C derived from C4 sugar cane plant residues (C-C4) were determined for each fraction. The C management index (CMI), derived from the total C pool and C lability, is useful in evaluating the capacity of management systems to improve soil quality and was calculated using the NV as the reference. Highest C and N concentrations were found for O-12 and O-4, mainly for the <53-µm organomineral fraction at 0–5cm depth. The 13C and C-C4 values indicated a greater accumulation of C-C4 in SOM fractions in organic compared with burned and unburned systems. GC combined with organic management is a strategy for long-term storage of total C and N in the SOM fraction associated with <53-µm fraction and light fraction. In addition, the highest CMI and its positive relationship with C-C4 in O-12 suggest the role of this system to foster soil quality improvement. The results allow infer regarding the potential of management practices on C accumulation in SOM fractions, which, in turn, can be used as indicators of the effects of land management.

Acacia Changes Microbial Indicators and Increases C and N in Soil Organic Fractions in Intercropped Eucalyptus Plantations

“…To evaluate the influence of microbial indicators on the dynamics of C and N, soil OM was physically fractionated from a soil air-dried mass (20 g) using the granulometric method (Brandani et al, 2017 ). This process, separates organic (OF) (2,000–75 μm), organic-mineral 1 (OMinF1) (2,000–75 μm), organic-mineral 2 (OMinF2) (75–53 μm) and organic-mineral 3 (OMinF3) (<53 μm) fractions.…”

“…C and N concentrations in each OM fraction were determined by dry combustion with an elemental analyzer (LECO®) (Nelson and Sommers, 1982 ; Christensen, 2001 ; Signor et al, 2014 ). TOC and Total-N contents in soil OM fractions were obtained by multiplying C and N concentrations of each fraction by their corresponding mass (Brandani et al, 2017 ).…”

Multi-Analytical Interactions in Support of Sugarcane Agroecosystems Sustainability in Tropical Soils

“…Although it represents a small proportion of total soil mass, it contains a significant part of the total soil C and N, so that its evaluation can provide an early indication of changes in land use and soil management [107]. Brandani et al [108] verified that burnt harvest combined with organic management was a strategy for long-term storage of total C and N in the light organic fraction, which were related to the quality (diversity) and quantity (frequency) of organic residue addition [107].…”

Peer Review #2 of "Vinasse application and cessation of burning in sugarcane management can have positive impact on soil carbon stocks (v0.1)"

“…Evaluating the C content of different particle-size fractions can therefore improve our understanding of the mechanisms by which the soil C stabilisation occurs, as well as the sensitivity of SOM content in response to management practice (Brandani et al 2016). Recent studies appraising different sugarcane management practices have reported changes in C measured in different soil fractions (Brandani et al 2016;Lisboa et al 2009;Signor et al 2014). Brandani et al (2016) highlighted that the cessation of burning combined with organic fertiliser inputs is able to accumulate soil C in at least three SOM fractions (< 53 μm; 75-53 μm and 2000-75 μm).…”

“…Recent studies appraising different sugarcane management practices have reported changes in C measured in different soil fractions (Brandani et al 2016;Lisboa et al 2009;Signor et al 2014). Brandani et al (2016) highlighted that the cessation of burning combined with organic fertiliser inputs is able to accumulate soil C in at least three SOM fractions (< 53 μm; 75-53 μm and 2000-75 μm). Additionally, Signor et al (2014) showed that cessation of burning can also lead to increased soil C stocks particularly in organo-mineral complexes that typically have a higher mean residence time in the soil than particulate organic matter.…”