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Item Fallow replacement and alternative fertilizer practices : effects on nitrate leaching, grain yield and protein, and net revenue in a semiarid region(Montana State University - Bozeman, College of Agriculture, 2015) John, Andrew Augustus; Chairperson, Graduate Committee: Clain JonesHigh nitrate concentrations in groundwater have been observed in agricultural regions worldwide. In the Judith River Watershed of central Montana, groundwater nitrate concentrations have increased from 10 to 23 mg L-1 over the span of 20 years. Nitrate leaching from agricultural fields is a major concern for growers and stakeholders in the region. Little research has been conducted in dryland semiarid regions on the effects of agricultural practices on nitrate leaching. We conducted a 2-yr study comparing three alternative management practices (pea rotation, controlled-release urea, split nitrogen application) to grower standard practices (fallow, conventional urea, spring broadcast urea) on grain yield, grain protein, net revenue, and the amount of nitrate leached. Eight field treatment interfaces were established across three farms and each treatment was in duplicate per year. Ten soil and biomass sampling locations were designated on both sides of the interface. Net revenue was calculated by enterprise budgets constructed from local and state data. Nitrate leaching was calculated using a nitrogen mass balance equation. Replacing pea with fallow decreased winter wheat grain yield and protein yet had no effect on net revenue during the first year of the study (2013). In the second year, pea-winter wheat earned $83 ha -1 more (P<0.1) than fallow-winter wheat. Neither fertilizer alternative management practice had an effect on net revenue. In the 2013 treatment year, wheat after pea leached less nitrate (20 kg N ha -1) than wheat after fallow (56 kg N ha -1), indicating more deep percolation of nitrate with fallow practice. In the 2014 treatment year, a greater amount of nitrate leached (P<0.1) while using controlled-release urea than conventional urea, possibly in part because the controlled release urea was applied earlier than conventional urea. The results of our study revealed that replacing fallow with pea can decrease the amount of nitrate that leaches out of the root zone. Also, this practice either increased or had no effect on net revenue, revealing its ability to be economically feasible for a grower to implement. Based on our findings, future research should likely focus on practices that decrease rates of deep percolation.Item Groundwater nitrate transport and residence time in a vulnerable aquifer under dryland cereal production(Montana State University - Bozeman, College of Agriculture, 2013) Miller, Christine Ross; Chairperson, Graduate Committee: Stephanie A. Ewing; Stephanie A. Ewing, W. Adam Sigler, E. N. J. Brookshire, Clain A. Jones, Douglas Jackson-Smith and Gary S. Weissmann were co-authors of the article, 'Groundwater nitrate transport and residence time in a vulnerable aquifer under dryland cereal production' submitted to the journal 'Journal of geophysical research - biogeosciences' which is contained within this thesis.Selection of agricultural management practices to reduce nitrate leaching from soils can only be successful if both nitrate loading rates from soils to shallow aquifers and groundwater residence times are quantified. Elevated nitrate concentrations in shallow unconfined aquifers are commonly observed in agricultural areas as a result of increased N inputs. In the Judith River Watershed (JRW) in central Montana, USA, notably high nitrate concentrations in groundwater and stream water have exceeded the U.S. EPA drinking water standard of 10 mg L -1 for at least two decades. This large (24,400 ha) watershed drains immediately into the Missouri River, a tributary of the Mississippi River. Over an eleven month period in 2012, we measured groundwater and surface water nitrate concentrations across a hydrologically isolated strath terrace. We use the resulting data to constrain nitrate accumulation dynamics in the shallow aquifer. Nitrate is relatively conservative in this location, as it is high in groundwater (17.57 +/- 4.29 mg L -1; all groundwater samples pooled together), and remains high in streams and springs that drain the landform (15.67 +/- 9.45 mg L -1; all surface water and spring samples pooled together). We use a numerical model to simulate the character of nitrate accumulation in the aquifer as a whole, in order to evaluate how the entire period of cultivation has contributed to current nitrate concentrations, and begin to predict response times for effects of land use change. We consider the effect of groundwater residence time and travel time on nitrate loading using particle tracking in a three dimensional model aquifer. We find no correlation with nitrate concentrations in groundwater and emerging surface waters, and suggest approaches for improving both the geometry of the model and the selection of sites in future work. Overall, our results imply that groundwater residence times are several decades at most, suggesting that similar timeframes will be needed to reduce overall nitrate concentrations in groundwater and emergent streams to below drinking water standards. Preliminary evaluation of several management scenarios suggests that both increased fertilizer use efficiency and rotational strategies may be needed to prevent the loss of soil N to groundwater.Item In situ measurements and LEACHM predictions of the transport and fate of nonreactive tracers and dicamba in a silt loam Montana soil(Montana State University - Bozeman, College of Agriculture, 1994) Pearson, R.Item Soil and terrain attributes for evaluation of leaching in a Montana farm field(Montana State University - Bozeman, College of Agriculture, 1995) Landon, Melissa Ann