Browsing by Subject "nitrogen cycling"

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Evaluating nitrogen losses, soil physical properties, and biological indicators in artificially drained fields in Northwest Minnesota
    (2022-06) Frankl, Aaron
    Subsurface drainage is a common practice to improve agricultural production in fields with poorly drained soils. This practice is becoming increasingly common in the Upper Midwest and NW Minnesota, where changing precipitation patterns are generating an increased need for artificial drainage systems. These systems increase yields, and over time, can reshape the soil ecosystem. By changing soil moisture throughout the profile, drainage can alter microbial activity and soil physical properties. In the first chapter of this study, we examined how drainage installation altered N cycling, which is largely mediated by soil microbes. In the two years following subsurface drainage installation, we observed several differences between the drained and undrained treatments: soil nitrate concentrations (NO3-), nitrous oxide (N2O) emissions, N mineralization, and edge of field losses. In the second chapter, we examined the longer-term changes facilitated by drainage to physical and soil health properties by sampling six sites. Three of these sites had their most recent drainage system installation before 2005; the remaining three had installations since 2015. The fields with older drainage systems had increased saturated hydraulic conductivity (Kfs) rates and increased biological activity (potentially mineralizable carbon, water-extractable organic carbon, and water-extractable organic nitrogen). Together, both studies identify the importance of understanding how drainage systems alter the soil ecosystem and demonstrate the importance of understanding drainage as an on-farm management decision. Additionally, they point to a need for more long-term drainage studies which focus on a wider range of soil properties.
  • Thumbnail Image
    Item
    Fire and vegetation effects on productivity and nitrogen cycling across a forest-grassland continuum
    (Ecological Society of America, 2001) Reich, Peter B; Peterson, David W; Wedin, David A; Wrage, Keith
    Mixed tree–grass vegetation is important globally at ecotones between grasslands and forests. To address uncertainties vis-à-vis productivity and nitrogen (N) cycling in such systems we studied 20 mature oak savanna stands, ranging from 90% woody dominated to 80% herbaceous dominated, growing on comparable soils in a 32-yr-old fire frequency experiment in Minnesota, USA. Fire frequencies ranged from almost annual burning to complete fire protection. Across all stands, aboveground net primary productivity (ANPP) ranged from 2 to 12 Mg·ha−1·yr−1, decreased with fire frequency (r2 = 0.59), increased with woody canopy dominance (r2 = 0.83), and increased with soil net N mineralization rates (r2 = 0.79), which varied from 25 to 150 kg·ha−1·yr−1. ANPP was positively related to total biomass (r2 = 0.95), total canopy leaf N content (r2 = 0.88), leaf area index (LAI; r2 = 0.87), annual litterfall N cycling (r2 = 0.70), foliage N concentration (r2 = 0.62), and fine root N concentration (r2 = 0.35), all of which also increased with increasing tree canopy cover. ANPP, soil N mineralization, and estimated root turnover rates increased with woody canopy cover even for stands with similar fire frequency. ANPP and N mineralization both decreased with fire frequency for stands having a comparable percentage of woody canopy cover. Fine root standing biomass increased with increasing grass dominance. However, fine root turnover rate estimated with a nitrogen budget technique decreased proportionally more with increasing grass dominance, and hence fine root productivity decreased along the same gradient. Via several direct and indirect and mutually reinforcing (feedback) effects, the combination of low fire frequency and high tree dominance leads to high rates of N cycling, LAI, and productivity; while the opposite, high fire frequency and high grass dominance, leads to low rates of N cycling, LAI, and productivity. Carbon and N cycling were tightly coupled across the fire frequency and vegetation type gradients.
  • Thumbnail Image
    Item
    Improving soil health and nitrogen cycling through zone tilled cover cropping practices for organic production
    (2017-07) Ginakes, Peyton
    Zone tillage is a reduced-tillage compromise between no-till and full-width tillage that attempts to capture both the environmental advantages of year-round ground cover and the agronomic benefits of in-row tillage. This management tool is especially well-suited to the practice of cover cropping, where plants are grown between cash crops in space, time, or both. Localizing the use of tillage in cover cropped systems may preserve soil quality between crop rows where soil is not tilled, as measured by soil microbial activity and varying indicators of soil organic matter, while also making N available only in crop rows. In this dissertation, two cover cropping systems were assessed for their contributions to soil quality and crop production: 1) a perennial kura clover (KC; Trifolium ambiguum) living mulch in corn (Zea mays), where KC persists between crops rows during the growing season to maintain ground cover of between-row areas, and 2) winter annual cover crops in an organic yellow crookneck squash (Cucurbita pepo) system, where cover crops were maintained between crop rows until they were fully mature, allowing for extended ground coverage and N provisioning. In the KC system, three tillage treatments and one no-till control were tested for their ability to incorporate KC residues between rows and to minimize KC competition with the corn crop. A novel PTO-driven rotary zone till implement was found to increase in-row soil N relative to both no-till and a less disruptive zone till implement consisting of a shank with ground-driven coulters. Corn yields were higher in treatments using this novel implement. In the winter annual system, three cover crop systems were examined at early and late terminations for cover crop N content and soil quality indicators: oat (Avena sativa) + field pea (Pisum sativum), winter rye (Cereale secale) + hairy vetch (Vicia villosa), and medium red clover (Trifolium pretense). Cover crops did gain biomass between samplings, showing that additional growing time between rows was beneficial. While no differences in squash yield were detected, the clover treatment did provide N in rows while conserving it between rows, effectively preventing possible leaching.
  • Thumbnail Image
    Item
    Influence of logging, fire, and forest type on biodiversity and productivity in southern boreal forests
    (Ecological Society of America, 2001) Reich, Peter B; Bakken, Peter; Carlson, Daren; Frelich, Lee E; Friedman, Steve K; Grigal, David F
    The effects of logging on ecosystem sustainability are controversial. Surprisingly, existing data are inadequate to allow a comprehensive evaluation of logging effects on biodiversity, composition, and productivity since appropriate comparisons of stands of similar ages and differing disturbance histories are rare. We addressed this issue using a study of 2000 plots in 80 southern boreal forest stands in northern Minnesota, USA, wherein we contrasted naturally regenerated aspen (Populus tremuloides), jack pine (Pinus banksiana), and black spruce (Picea mariana) stands established following logging or the dominant natural disturbance, wildfire, for stands of two age classes (25-40 and 70-100 yr old). For young stands, those established postlogging had higher vascular plant diversity than those postwildfire. Otherwise, we found no evidence of differing species diversity (including canopy tree, shrub, herbaceous, and bryophyte species), composition, productivity, or nitrogen cycling, in forest stands of comparable age and forest type that originated after logging compared to after wildfire. These variables, however, differed significantly among forest types, with aboveground net primary productivity and plant species diversity generally higher in aspen than jack pine stands, even when growing on comparable soils, and lowest in black spruce. Although there is evidence that logging has increased the proportional landscape dominance by aspen, a forest type with higher diversity, nutrient cycling, and productivity than other types, our evidence refutes the idea that disturbance by logging has diminished stand-scale productivity or plant diversity in comparison to the common natural disturbance, wildfire.
  • Thumbnail Image
    Item
    Invasive species’ leaf traits and dissimilarity from natives shape their impact on nitrogen cycling: A meta‐analysis
    (Wiley, 2017) Lee, Marissa R; Bernhardt, Emily S; Bodegom, Peter M; Cornelissen, J. Hans C; Kattge, Jens; Laughlin, Daniel C; Niinemets, Ülo; Peñuelas, Josep; Reich, Peter B; Yguel, Benjamin; Wright, Justin P
    Many exotic species have little apparent impact on ecosystem processes, whereas others have dramatic consequences for human and ecosystem health. There is growing evidence that invasions foster eutrophication. We need to identify species that are harmful and systems that are vulnerable to anticipate these consequences. Species’ traits may provide the necessary insights. We conducted a global meta-analysis to determine whether plant leaf and litter functional traits, and particularly leaf and litter nitrogen (N) content and carbon: nitrogen (C : N) ratio, explain variation in invasive species’ impacts on soil N cycling. Dissimilarity in leaf and litter traits among invaded and noninvaded plant communities control the magnitude and direction of invasion impacts on N cycling. Invasions that caused the greatest increases in soil inorganic N and mineralization rates had a much greater litter N content and lower litter C : N in the invaded than the reference community. Trait dissimilarities were better predictors than the trait values of invasive species alone. Quantifying baseline community tissue traits, in addition to those of the invasive species, is critical to understanding the impacts of invasion on soil N cycling.