GLEAMS evaluation in potato fields for agricultural nutrient management in central Bolivian highlands

The objective of this study was to assess the suitability of the GLEAMS model as a tool for evaluating fertilization and cropping system practices for potatoes in the Andes of central Bolivia and make recommendations for the continued development of the model as an analysis tool to improve sustainable crop production. Model evaluation was based on comparison with field data taken from three experimental plots for soil total Kjeldahl N, crop production, crop N uptake, and crop P uptake. General trends in model prediction followed expectations, however the predicted crop dry matter production and N uptake were low. The root mean square standard deviation ratio (RSR) and percent bias (PBIAS), respectively, for soil total Kjeldahl N concentration were 7 and -2%. The PBIAS for total crop dry matter production was 39%. The PBIAS for total crop N uptake was 54% and for total crop P uptake was -2%. Evaluation of the various N pathways pointed to low mineralization rates as the key component causing the poor predictions. Since agricultural production in this region of central Bolivia is highly dependent on organic N from soil and applied animal manure, the mineralization processes in GLEAMS must be further evaluated and improved before the model should be applied in this region.