Management of Organic and Inorganic Soil Fertility Inputs in Indigenous Agricultural Communities in the Bolivian Highlands.

The Bolivian Altiplano is a mountainous semi-arid region characterized by periodic frost and hail and high drought risk during the growing season.  Due to global climate and socioeconomic changes, the risk of crop failure and food insecurity has increased.  In addition, use of organic and inorganic soil amendments varies among communities and is restricted by several factors, including the relatively high cost of fertilizers.  The objectives of this research were to: 1) develop alternative fertilization practices that would improve long-term soil fertility and increase soil organic matter content to buffer against the effects of climate change and 2) to engage community members in ongoing evaluation of the practices and their potential for adoption.  Field experiments planted to potato were established in 2006 in several communities.  Treatments included a control, sheep and cow manures, compost, peat moss, Biofert (a commercial microbial activator soil amendment), urea and diammonium phosphate and combinations of these different treatments. Soils samples were taken prior to planting, at blooming time and post harvest to assess changes in soil chemical and physical properties due to the treatments. In addition, samples of the organic amendments, and leaf petioles were collected for total N and nitrate analysis.  Mixtures of the animal manures and chemical fertilizers resulted in the highest potato tuber yields with an average of 14 t ha^-1.  Those treatments were also selected by the community farmers at blooming and harvesting time based on relative plant growth and tuber yields and quality.  In some communities, sheep manure resulted in relatively higher soil water content compared to the control and inorganic soil amendments.  Results from the 2007/2008 season with potato and an additional study examining the residual effects of the treatments on the subsequent growth of a local grain crop (i.e., quinoa or barley) will also be presented.