Nitrogen Leaching from Douglas‐fir Forests after Urea Fertilization

Flint, Cynthia M.; Harrison, R. B.; Strahm, Brian D.; Adams, Alison

doi:10.2134/jeq2007.0367

Cited by 10 publications

(8 citation statements)

References 37 publications

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“…Six months after application, the fertilized stand in the model gained 9.5 g N m −2 in aboveground phytomass (foliage, wood, and nonstructural) and 7.4 g N m −2 in soil (mostly as nitrate) above values in the unfertilized stand (Figures 6d and 6e). These gains in the model were slightly larger than ones of 5.8 and 6.0 g N m −2 in trees and soil, respectively, measured by Flint et al [2008] 6 months after a spring application of 22.4 g N m −2 as urea on a similar Douglas fir stand in nearby Washington State. However, the gains measured in their study may have been underestimated because the gain in tree N did not account for gain in tree biomass and the gain in soil N was measured only to 0.4 m depth and excluded the coarse organic fraction.…”

Section: Discussionmentioning

confidence: 61%

“…Most of the leaching loss modeled in 2007 occurred under heavier rainfall after mid‐October 2007 when plant growth and hence uptake had slowed (Figure 3). This loss was larger than one of 0.4 g N m −2 measured by Flint et al [2008], most of which also occurred after mid‐October, following a spring application of 22.4 g N m −2 as urea to a Douglas fir stand in nearby Washington State under climate conditions similar to those at BC‐DF49. Substantial downward water movement occurs through the soil profile with heavier rainfall and cooler weather after mid‐October in the Pacific Northwest.…”

Section: Discussionmentioning

confidence: 67%

“…Substantial downward water movement occurs through the soil profile with heavier rainfall and cooler weather after mid‐October in the Pacific Northwest. These leaching losses would thus represent most of the residual mineral N not taken up during the previous summer growing season, indicating that most fertilizer N was taken up soon after application at both sites, but perhaps more so in the study of Flint et al [2008].…”

Section: Discussionmentioning

confidence: 99%

“…Gains may be smaller with lower C/N ratios in tree foliage or the soil LFH layer when N limitations are less severe [ Edmonds and Hsiang , 1987; Hopmans and Chappell , 1994]. Gains may also be smaller when uptake of fertilizer N is reduced by rapid nitrification of fertilizer products [ Matson et al , 1992] and subsequent leaching of nitrate [ Flint et al , 2008].…”

Section: Introductionmentioning

confidence: 99%

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Changes in net ecosystem productivity and greenhouse gas exchange with fertilization of Douglas fir: Mathematical modeling in ecosys

et al. 2010

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[1] The application of nitrogen fertilizers to Douglas fir forests is known to raise net ecosystem productivity (NEP), but also N 2 O emissions, the CO 2 equivalent of which may offset gains in NEP when accounting for net greenhouse gas (GHG) exchange. However, total changes in NEP and N 2 O emissions caused by fertilizer between times of application and harvest, while needed for national GHG inventories, are difficult to quantify except through modeling. In this study, integrated hypotheses for soil and plant N processes within the ecosystem model ecosys were tested against changes in CO 2 and N 2 O fluxes recorded with eddy covariance (EC) and surface flux chambers for 1 year after applying 20 g N m −2 of urea to a mature Douglas fir stand in British Columbia. Parameters from annual regressions of hourly modeled versus measured CO 2 fluxes conducted before and after fertilization were unchanged (b = 1.0, R 2 = 0.8, RMSD = 3.4 mmol m −2 s −1 ), indicating that model hypotheses for soil and plant N processes did not introduce bias into CO 2 fluxes modeled after fertilization. These model hypotheses were then used to project changes in NEP and GHG exchange attributed to the fertilizer during the following 10 years until likely harvest of the Douglas fir stand. Increased CO 2 uptake caused modeled and EC-derived annual NEP to rise from 443 and 386 g C m −2 in the year before fertilization to 591 and 547 g C m −2 in the year after. These gains contributed to a sustained rise in modeled wood C production with fertilization, which was partly offset by a decline in soil C attributed in the model to reduced root C productivity and litterfall. Gains in net CO 2 uptake were further offset in the model by a rise of 0.74 g N m −2 yr −1 in N 2 O emissions during the first year after fertilization, which was consistent with one of 1.05 g N m −2 yr −1 estimated from surface flux chamber measurements. Further N 2 O emissions were neither modeled nor measured after the first year. At the end of the 11 year model projection, a total C sequestration of 1045 g C m −2 was attributed to the 20 g N m −2 of fertilizer. However, only 119 g C m −2 of this was sequestered in stocks that would remain on site after harvest (foliage, root, litter, soil). The remainder was sequestered as harvested wood, the duration of which would depend on use of the wood product. The direct and indirect CO 2 -equivalent costs of this application, including N 2 O emission, were estimated to offset almost all non-harvested C sequestration attributed to the fertilizer.

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Section: Discussionmentioning

confidence: 61%

Section: Discussionmentioning

confidence: 67%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Changes in net ecosystem productivity and greenhouse gas exchange with fertilization of Douglas fir: Mathematical modeling in ecosys

et al. 2010

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“…Thus, the overall N budget of our low-N sites displays only a small imbalance between known N inputs (3 kg NÁha À1 Áyr À1 ) and losses (1.3 kg NÁha À1 Áyr À1 ), so that even small quantities of unmeasured N 2 gas losses could balance the N budget (e.g., Houlton et al 2006). Alternatively, these low-N sites could slowly be accumulating N, based on their relatively low soil N capital (8608-13 647 kg N/ha) compared to our high-N sites (up to 22 379 kg N/ha), and by the high capacity for N retention in low-N Douglas-fir forests (Flint et al 2008). The N budget of our high-N sites, by contrast, displays large annual net N loss, with inputs (;3 kg NÁha À1 Áyr À1 ) less than outputs (10-28 kg NÁha À1 Áyr À1 ), where any unmeasured N 2 losses would only intensify this imbalance.…”

Section: Discussionmentioning

confidence: 91%

Biogeochemistry of a temperate forest nitrogen gradient

Perakis

Sinkhorn

2011

Ecology

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Wide natural gradients of soil nitrogen (N) can be used to examine fundamental relationships between plant-soil-microbial N cycling and hydrologic N loss, and to test N-saturation theory as a general framework for understanding ecosystem N dynamics. We characterized plant production, N uptake and return in litterfall, soil gross and net N mineralization rates, and hydrologic N losses of nine Douglas-fir (Pseudotsuga menziesii) forests across a wide soil N gradient in the Oregon Coast Range (U.S.A.). Surface mineral soil N (0-10 cm) ranged nearly three-fold from 0.29% to 0.78% N, and in contrast to predictions of N-saturation theory, was linearly related to 10-fold variation in net N mineralization, from 8 to 82 kg N.ha(-1) x yr(-1). Net N mineralization was unrelated to soil C:N, soil texture, precipitation, and temperature differences among sites. Net nitrification was negatively related to soil pH, and accounted for <20% of net N mineralization at low-N sites, increasing to 85-100% of net N mineralization at intermediate- and high-N sites. The ratio of net: gross N mineralization and nitrification increased along the gradient, indicating progressive saturation of microbial N demands at high soil N. Aboveground N uptake by plants increased asymptotically with net N mineralization to a peak of approximately 35 kg N.ha(-1) x yr(-1). Aboveground net primary production per unit net N mineralization varied inversely with soil N, suggesting progressive saturation of plant N demands at high soil N. Hydrologic N losses were dominated by dissolved organic N at low-N sites, with increased nitrate loss causing a shift to dominance by nitrate at high-N sites, particularly where net nitrification exceeded plant N demands. With the exception of N mineralization patterns, our results broadly support the application of the N-saturation model developed from studies of anthropogenic N deposition to understand N cycling and saturation of plant and microbial sinks along natural soil N gradients. This convergence of behavior in unpolluted and polluted forest N cycles suggests that where future reductions in deposition to polluted sites do occur, symptoms of N saturation are most likely to persist where soil N content remains elevated.

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