Carbon in hillsides soil: factors that must be considered to determine its change over time

Factors that intervene in the reproducibility of soil organic carbon (SOC) measurements must he considered to monitor changes in the ecosystem overall C over time. Aside from this purely analytical aspect, in mountainous regions position on the hillside can determine a specific pattern in the spatial variation of SOC contents. The objective of this study was to analyze some factors that must he considered in determining changes in SOC in hillside land in the Sierra Norte of Oaxaca. SOC measurements were taken in samples collected in experimental plots using a measurement procedure developed specifically for that purpose. The factors that most affected determinations of SOC changes occurring in the soil were measurement of bulk density (Db) and the diligence with which organic residues were eliminated from the sample. There were no significant differences in reproducibility in analytical laboratory measurements of SOC among the different measurement times in the same samples. Nor were there differences in accumulated SOC in the upper or lower part of the slope of a geo-referenced micro-site. Therefore, in conducting studies of changes in SOC in hillside land, it is necessary to standardize elimination of organic residues of the sample before analysis as well the determination of Db for high reproducibility in successive periods of observation.