An increase in population in rural agricultural communities and higher demand for food throughout Bolivia create the need for increased agricultural production. 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 suitability was evaluated through assessment of model representation of observed potato farms and behavior of simulated soil nitrogen (N) and N transformation trends; validation with field data taken from six agricultural sites in central Bolivia for runoff volume, soil total Kjeldahl N concentration, crop production, and crop N uptake; and sensitivity analysis. Validation of model output with observed values was completed both graphically and by determining the root mean square error standard deviation ratio (RSR) and the percent bias (PBIAS). RSR and PBIAS values for runoff volume were 4.0 and 65%, 4.5 and 4%, and 2.7 and 55% for three respective experimental plot repetitions using a calibrated SCS curve number of 90. The RSR and PBIAS, respectively, for soil total Kjeldahl N concentration were 3.0 and -2.2%. The RSR and PBIAS, respectively, for crop dry matter production were 7 and 21%. The RSR and PBIAS, respectively, for crop N uptake were 10 and 21%. The mineralization processes in GLEAMS must be improved before model application to central Bolivia, where agricultural production is highly dependent on mineralization of organic N from soil and applied animal manure. Recommendations for model improvement and development include modification to the process that determines mineralization from the soil potentially mineralizable N pool; validation of the percolation volume and nitrate leaching losses; and improved model representation of banded manure application. / Master of Science / CCRA-2 (Watershed Modeling)

<p>Den snabba utvecklingen och urbaniseringen i stora delar av Kina har ett flertal konsekvenser för miljön. Yangtzedeltats ytvatten är till stor del eutrofierade, delvis p.g.a. diffusa förluster från jordbruket. I denna studie har kväve- och, till viss del, fosforflöden och förluster från två odlingsrutor i ett intensivt odlat grönsaksfält i ett tätortsnära område i Nanjing, med hög tillförsel av organiskt gödsel, undersökts med hjälp av den fältskaliga simuleringsmodellen GLEAMS. GLEAMS parametriserades och kalibrerades mot mätvärden av jordens vatten- och kväveinnehåll. Ett scenario med minskad kvävetillförsel simulerades sedan.</p><p>Simuleringen av vattenhalten i de olika horisonterna var inte utmärkt. Den simulerade mängden mineralkväve i marken var avsevärt lägre än den uppmätta. Detta kan bero på en felaktig simulering av mineraliseringen av organiskt kväve eller en för långsam nedbrytning av gödsel. Det är också möjligt att felen i vattensimuleringarna bidrog till underskattningen av mängden mineralkväve i marken. Simuleringarna på de båda odlingsrutorna gav liknande resultat, förutom att ruta B hade 20% större förluster av N via simulerad erosion och läckage. För fortsatt simulering av alternativa odlingsmetoder bör modellens parametrisering förbättras, särskilt vad avser parametrar kopplade till gödselns mineralisering.</p> / <p>Many parts of China are going through a rapid development and urbanization resulting in various environmental impairities. The Yangtze Delta Region surface water bodies are affected by eutrophication, partly caused by diffuse losses from agriculture. In this study, nitrogen, and to some extent also phosphorus, flows and losses from two plots in an intensively cultivated vegetable field in a peri-urban area of Nanjing, with a high input of organic fertilizer, were analysed by the use of the field-scale simulation model GLEAMS. The GLEAMS model was parameterized and calibrated against measurements of soil water and nitrogen content in two plots. A scenario with a reduced input of nitrogen was then simulated.</p><p>The resemblance between simulated and measured water content in the different soil layers was quite poor. The simulated inorganic nitrogen content in the soil was significantly lower than the measured during great parts of the simulation period. This could be due to an inappropriate simulation of the mineralization of organic N under these conditions, or an underestimated decomposition rate of manure. It is also possible that the poor water simulations contributed to the underestimated inorganic N content in the soil. There were similar results for the two plots, except for an unexplained 20% increase in leaching and erosion losses of N in Plot B. For simulation of scenarios to find best management practices, the model parameterization should be further refined.</p>

Den snabba utvecklingen och urbaniseringen i stora delar av Kina har ett flertal konsekvenser för miljön. Yangtzedeltats ytvatten är till stor del eutrofierade, delvis p.g.a. diffusa förluster från jordbruket. I denna studie har kväve- och, till viss del, fosforflöden och förluster från två odlingsrutor i ett intensivt odlat grönsaksfält i ett tätortsnära område i Nanjing, med hög tillförsel av organiskt gödsel, undersökts med hjälp av den fältskaliga simuleringsmodellen GLEAMS. GLEAMS parametriserades och kalibrerades mot mätvärden av jordens vatten- och kväveinnehåll. Ett scenario med minskad kvävetillförsel simulerades sedan. Simuleringen av vattenhalten i de olika horisonterna var inte utmärkt. Den simulerade mängden mineralkväve i marken var avsevärt lägre än den uppmätta. Detta kan bero på en felaktig simulering av mineraliseringen av organiskt kväve eller en för långsam nedbrytning av gödsel. Det är också möjligt att felen i vattensimuleringarna bidrog till underskattningen av mängden mineralkväve i marken. Simuleringarna på de båda odlingsrutorna gav liknande resultat, förutom att ruta B hade 20% större förluster av N via simulerad erosion och läckage. För fortsatt simulering av alternativa odlingsmetoder bör modellens parametrisering förbättras, särskilt vad avser parametrar kopplade till gödselns mineralisering. / Many parts of China are going through a rapid development and urbanization resulting in various environmental impairities. The Yangtze Delta Region surface water bodies are affected by eutrophication, partly caused by diffuse losses from agriculture. In this study, nitrogen, and to some extent also phosphorus, flows and losses from two plots in an intensively cultivated vegetable field in a peri-urban area of Nanjing, with a high input of organic fertilizer, were analysed by the use of the field-scale simulation model GLEAMS. The GLEAMS model was parameterized and calibrated against measurements of soil water and nitrogen content in two plots. A scenario with a reduced input of nitrogen was then simulated. The resemblance between simulated and measured water content in the different soil layers was quite poor. The simulated inorganic nitrogen content in the soil was significantly lower than the measured during great parts of the simulation period. This could be due to an inappropriate simulation of the mineralization of organic N under these conditions, or an underestimated decomposition rate of manure. It is also possible that the poor water simulations contributed to the underestimated inorganic N content in the soil. There were similar results for the two plots, except for an unexplained 20% increase in leaching and erosion losses of N in Plot B. For simulation of scenarios to find best management practices, the model parameterization should be further refined.