Browsing by Subject "nitrate leaching"

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    Investigating Nitrogen and Irrigation Management Strategies to Improve Agronomic and Environmental Outcomes for Potato Production
    (2021-08) Bohman, Brian
    Nitrogen [N] fertilizer and irrigation management practices are both critical factors for determining agronomic and environmental outcomes for potato [Solanum tuberosum (L.)] production. This dissertation was comprised of two overall objectives. First, a small-plot experiment evaluating the effects of six N rate, source, and timing treatments and two irrigation rate treatments on tuber yield, quality, net profitability, nitrate leaching, residual soil nitrate, plant N uptake, N nutrition index [NNI], N uptake efficiency, N utilization efficiency [NUtE], N use efficiency [NUE], biomass, harvest index, biomass, and potential N losses for potato [cv. ‘Russet Burbank’] were investigated in 2016 and 2017 at Becker, MN, on a Hubbard loamy sand. Conventional N fertilizer best management practices [BMPs] (270 kg N ha-1) were compared to reduced N rate (180 kg N ha-1), control N rate (45 kg N ha-1), and a variable rate [VR] N treatment based on the N sufficiency index [NSI] approach using remote sensing. Irrigation treatments included a conventional rate (100%) based on the “checkbook” method and a reduced rate (85%). The VR treatment reduced N applied relative to the recommended rate by 22 and 44 kg N ha−1 in 2016 and 2017, respectively. Irrigation rate was reduced by 29 and 33 mm in 2016 and 2017, respectively. From an agronomic perspective, neither VR N nor reduced irrigation produced significant differences in tuber yield or net return compared to full rate treatments. From an environmental perspective, nitrate leaching losses varied between 2016 and 2017 with flow-weighted mean nitrate N concentrations of 5.6 and 12.8 mg N L−1, respectively, and increased from 7.1 to 10.4 mg N L−1 as N rate increased from 45 to 270 kg N ha−1. Despite reductions in N rate for the VR N treatment, there was no significant difference in nitrate leaching compared with the existing N best management practices (BMPs). However, reducing irrigation rate by 15% decreased nitrate leaching load by 17% through a reduction in percolation. Second, an evaluation of the relationship between NUE, NNI, and their variation across genotype [G] x environment [E] effects was conducted. A novel theoretical relationship between NNI and NUtE was derived: at a constant NNI value, NUtE values increased non-linearly as biomass increased, and at an NNI value of 1.0 this relationship defines the critical N utilization efficiency curve [CNUtEC]. Subsequently, an evaluation of the variation in critical N concentration [%Nc] was conducted using a hierarchical Bayesian framework to infer the critical N dilution curve [CNDC] across G x E effects observed from multiple experimental trials. This statistical method was able to quantify the uncertainty in %Nc, which was used to directly compare CNDCs. Critical N concentration was found to significantly vary across the effect of E, and in some cases for G within E. Therefore, consideration of both NNI and NUE require explicit consideration of the uncertainty in and variation due to G x E effects for %Nc. Overall, the findings of this dissertation improve both the empirical and theoretical understanding of the impact of N fertilizer and irrigation management practices on agronomic and environmental outcomes for potato.
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    SINful Consequences of Cover Cropping: Soil Inorganic Nitrogen (SIN) Provision and Retention from Warm-Season Cover Crops for Northern US Region Vegetable Production
    (2023) Moses, Ezra
    Warm-season cover crops are promising tools to meet vegetable crop nitrogen (N) demands while preventing N losses but more information is needed to achieve these goals in the northern US region. We explored warm-season cover crops in two rotations in Minnesota to evaluate biomass production, N provision and retention benefits, and impacts on vegetable yields. Warm-season cover crop biomass production ranged from 628-13,350 kg ha-1 and did not frequently exceed a weedy control. Soil nitrate decreased beneath cover crops and increased post-termination, demonstrating seasonal patterns potentially synchronous with vegetable demand. Cover crops reduced nitrate leaching to buried resin lysimeters by up to 50% but not significantly. Vegetable yields were often decreased following cover crop treatments, though legumes boosted vegetable yield in limited site-years. Evidence from this study suggests that warm-season cover crops could synchronize seasonal N patterns with vegetable demand but may not boost vegetable yields.
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    Winter Camelina Response to Nitrogen for Double Cropping with Maize and Soybean in the Upper Midwest
    (2021-09) Gregg, Stephen
    Winter camelina [Camelina sativa (L.) Crantz] is a potential third crop that could be used to intensify maize [Zea mays L.]-soybean [Glycine max (L.) Merr.] rotations. It is considered a low-input crop, but previous studies have shown that it responds to added N. Yet, no formal fertilization studies have been conducted to determine optimum N levels for conditions in the upper Midwest. A study on camelina response to fertilizer N was conducted from fall 2018 to fall 2020 at three locations in Minnesota. The objectives were to: (i) determine the response of winter camelina to N and (ii) assess the effects of N fertilization strategy (fall-spring split or spring only application) on the productivity and quality of winter camelina. Data collected included grain yield, biomass, grain quality, and yield components. Grain yield and biomass were both affected by N in all locations and years, and both were higher in 2019 compared to 2020; among N rates, grain yield was significantly different, while no differences were found for biomass. Both, oil and protein content in grain were affected by N, with oil content generally declining with N rates increasing beyond 67 or 100 kg N ha-1, depending on location and year. Among yield components, branches and silicles per plant were significantly different among N rates; the former, along with the seed:shell ratio were significantly different in all years and locations. Based on the results of this study, a fertilization rate of 97 kg N ha-1 was found to maximize grain and oil yield of winter camelina in southwest Minnesota. Maize (Zea mays L.) and soybean [Glycine max (L.) Merr.] in the upper Midwest are productive, but decades of these monocultures with winter fallow and late spring planting are in part responsible for loss in agroecological functioning as well as nitrogen (N) pollution in the agricultural communities and downstream. Winter camelina [Camelina sativa (L.) Crantz] is a third crop that could grow during this fallow period, but the environmental impacts of its N requirements are not well known. A study was conducted at three locations in Minnesota to determine the response of winter camelina do N. Five N rates (0, 33, 67, 100, 135 kg N ha-1) and two application timings (spring, and fall-spring split) were used to assess the N use efficiency (NUE) and residual N in winter camelina grown for grain yield from fall 2018 to fall 2020. Results showed higher NUE for fall-spring split application compared to spring only application. The agronomic efficiency (AE), internal efficiency (IE), and nitrogen recovery efficiency (NRE) tended to decrease with increasing N rates; AE generally decreased beyond 67 kg N ha-1 in most instances. Total N uptake ranged from 34 to 176 kg ha-1 across N rates. Residual soil N increased with increasing N rates, especially at the 15 cm depth. Based on declining NUE and increasing residual soil N with increasing N rates, an N rate between 33 to 67 kg N ha-1 could balance an efficient use of fertilizer with less environmental risk of higher N rates. Double cropping with winter camelina is a diversification option for the typical maize-soybean rotation in the upper Midwest, a strategy that promises environmental and economic benefits. Studies on double-cropping maize and soybean with non-fertilized- (Study 1) and nitrogen (N)-fertilized (Study 2) winter camelina were compared to assess the growth and yield, N, water use (WU), and water productivity (WP) of winter camelina in two locations in Minnesota. Study 1 was conducted from 2015–2017 in one location and the Study 2 was conducted from 2018–2020 in two locations, both studies in Minnesota. Yield of winter camelina was as much as six times higher in Study 2 compared to Study 1; averaged across treatments, Study 2 yielded 1157 kg ha-1 compared to 556 kg ha-1 from Study 2. In Study 1, oil and protein content ranged from 26.4 to 27.2% and 19.4 to 27.1% respectively. In Study 2, oil and protein content ranged from 31.7 to 35.9% and 14.9 to 20.8% respectively. Water use tended to follow similar trends between studies. Winter camelina average WU across cropping systems was similar between Study 1 and Study 2 (165 compared to 168 mm). Camelina WP was higher in Study 2 compared to Study 1, and ranged from 0.60 to 0.84 and 0.20 to 0.42 respectively. Fertilizer N was generally found to increase biomass, yield, WU, WP, and residual soil N in winter camelina double cropped with maize and soybean.