Effects of Changes in Fallow Length On Soil Organic C Due to Climate Change and Socioeconomic Factors in Potato-Based Cropping Systems in the Bolivian Highlands.

Fallowing land has an important role in soil fertility restoration in potato-based cropped systems in the semi-arid Bolivian Highlands (Altiplano) Region.  However, climate change and changes in migration and market conditions have reduced the use of this traditional practice and possibly increased soil degradation.  The objectives of this research were to assess the effects of cropping and length of fallow on soil total organic carbon (C) and labile soil C fractions among indigenous communities in the Central Altiplano.  The study sites were four communities in the Central Altiplano that were selected to represent communities situated at relatively low and high altitudes in the region.  Soil samples were collected to a 20 cm depth from agricultural fields that represented different stages of the common agricultural rotation practiced in the region and that had different fallow periods.  Soils were analyzed for total organic C, water-soluble C, particulate organic matter C, and potassium permanganate reactive C.  Humic acid from the samples was extracted and analyzed using diffuse reflectance infrared Fourier-transformed (DRIFT) mid-infrared spectroscopy. Results from the permanganate test showed that labile C increased with > 40 yrs fallow and varied among communities.  The peak ratios measured by the DRIFT analysis also showed differences among the soil samples with different fallow histories. The findings of this research will assist in determining if appropriate management practices need to be developed to improve soil organic matter in the region.