Labile C as an indicator of the impact of trash removal on soil health in the sugarcane production system

摘要

The use of sugarcane harvest residues (trash) for alternative uses such as energy cogeneration or second-generation ethanol production has generated uncertainty about the impact of the removal of waste on soil health. In order to study the impact of this practice in the long term, an experiment was established in 1999 at the CENICANA experimental station in Colombia. Ten years after the experiment was initiated, organic matter was assessed as a possible indicator of the impact of different trash management options. However, as it was difficult to detect significant changes in its concentration, it was decided to investigate labile C as an alternative impact indicator. Although labile C generally represents less than 5% of the total C of the soil, it has been reported in different studies that this fraction is very sensitive to agronomic practices. The trial was divided into three zones: total remove of residue, double amount of residue, and regular amount of residue. In every year, the cane was harvested without burning. Undisturbed soil cores were collected at four soil depths (0-2,10-12,20-22 and 40-42 cm) from 54 plots (18 in each area). Soil OM by the Walkley and Black methodology and labile C by permanganate-oxidizable carbon methodology (POXC) were determined for each core. The resulting dataset was mapped to show the spatial distribution of labile C and OM over the entire residue-management study site. This was then compared to maps showing the spatial distribution of soil texture. Residue management clearly affected the spatial distribution of labile C. Where the residue was totally removed, the labile C content decreased in the 0-2, and 10-12 cm depths. The highest labile C was observed in the zone with the double amount of residue and at each of the sampling depths. The labile C content in the zone with regular amount of residues was intermediate to the other two zones. Soil texture was also found to affect labile C and soil OM. This suggested that the labile C under trash-management options is affected by the interaction of harvest-residue management and soil texture. The results of this study show that labile C (POXC) is a promising methodology for quantifying the effect of different management practices on the labile C pool that is comprised of rapidly cycling organic material. In contrast, most of the OM pool is composed mainly of organic forms that decompose slowly. This tool may help to identify sites where it is possible to extract harvest residues for electricity cogeneration, or in future, to produce second-generation ethanol without risk of negative effects on the OM/soil health. The next step is to investigate the use of labile C in combination with mineralizable C to predict if a site has an ability to either accumulate/stabilize or mineralize SOC.