Deep soil nitrogen storage slows nitrate leaching through the vadose zone

Weitzman, Julie N.; Brooks, J. R.; Compton, Jana E.; Faulkner, Barton R.; Mayer, Paul M.; Peachey, Ronald Edward; Rugh, W D; Coulombe, R A; Hatteberg, B; Hutchins, Stephen R.

doi:10.1016/j.agee.2022.107949

Cited by 34 publications

(30 citation statements)

References 84 publications

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“…During unsaturated conditions, atmospheric oxygen can fill pore spaces in the soil resulting in more aerobic environments throughout the vadose zone (Green et al, 2008). Legacy N storage, or the accumulation of N within systems, was confirmed in the high-input agricultural soils and groundwater along the Mississippi River Basin (Van Meter et al, 2016 and more recently within agricultural soils of the Willamette Valley (Weitzman et al, 2022). Thus, storage of surplus N within the soils and groundwater of the Willamette Valley is likely responsible for minimizing surface water N exports, as opposed to denitrification, explaining the incongruity in the mass balance of N inputs (high N fertilizer applications) and outputs (low stream N exports) for the region.…”

Section: Core Ideasmentioning

confidence: 93%

“…In this study, we employed a dual stable isotope approach (δH 2 O and δNO 3 − ) at the study site of Weitzman et al (2022), in order to understand the mechanisms driving the declining rates of nitrate leaching with depth. We intensively monitored the movement and concentration of nitrate in the vadose zone over multiple years and depths beneath a sweet corn field in the Willamette Valley (Weitzman et al, 2022). With this approach, we sought to address the following three main objectives:…”

Section: Vadose Zone Journalmentioning

confidence: 99%

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Vadose zone flushing of fertilizer tracked by isotopes of water and nitrate

Weitzman,

Brooks,

Compton

et al. 2024

Vadose Zone Journal

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A substantial fraction of nitrogen (N) fertilizer applied in agricultural systems is not incorporated into crops and moves below the rooting zone as nitrate (NO3−). Understanding mechanisms for soil N retention below the rooting zone and leaching to groundwater is essential for our ability to track the fate of added N. We used dual stable isotopes of nitrate (δ15N–NO3− and δ18O–NO3−) and water (δ18O–H2O and δ2H–H2O) to understand the mechanisms driving nitrate leaching at three depths (0.8, 1.5, and 3.0 m) of an irrigated corn field sampled every 2 weeks from 2016 to 2020 in the southern Willamette Valley, Oregon, USA. Distinct periods of high nitrate concentrations with lower δ15N–NO3− values indicated that a portion of that nitrate was from recent fertilizer applications. We used a mixing model to quantify nitrate fluxes associated with recently added fertilizer N versus older, legacy soil N during these “fertilizer signal periods.” Nitrate leached below 3.0 m in these periods made up a larger proportion of the total N leached at that depth (∼52%) versus the two shallower depths (∼13%–16%), indicating preferential movement of recently applied fertilizer N through the deep soil into groundwater. Further, N associated with recent fertilizer additions leached more easily when compared to remobilized legacy N. A high volume of fall and winter precipitation may push residual fertilizer N to depth, potentially posing a larger threat to groundwater than legacy N. Optimizing fertilizer N additions could minimize fertilizer losses and reduce nitrate leaching to groundwater.

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Section: Core Ideasmentioning

confidence: 93%

Section: Vadose Zone Journalmentioning

confidence: 99%

Vadose zone flushing of fertilizer tracked by isotopes of water and nitrate

Weitzman,

Brooks,

Compton

et al. 2024

Vadose Zone Journal

Self Cite

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“…to 10 or 20 cm depth) are studied due to high nutrient concentrations there, yet subsoil horizons store more total carbon (Hicks Pries et al, 2017) and can influence topsoil microbial activity, ultimately highlighting their relevance to whole profile soil functions. Pedological studies have long recognized that land use history, in addition to the classic five state factors of soils, affects current soil function (Turley et al, 2020), especially tillage and fertilization via changes in soil structure and soil fertility (Weitzman et al, 2022). Additionally, microbes may decompose stable organic matter reserves when new labile organic matter is added, known as soil priming (Kuzyakov, 2006;Bastida et al, 2019;Liu et al, 2020), to which subsoils may be more sensitive (Li et al, 2022), and thus overall priming may offset any expected new carbon storage in topsoils.…”

Section: Soil Depth and Historymentioning

confidence: 99%

Developing systems theory in soil agroecology: Incorporating heterogeneity and dynamic instability

Medina¹,

Vandermeer²

2023

Preprint

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Ecosystem management is integral to the future of soils, yet anthropogenic drivers represent a key source of uncertainty in ecosystem models. First- and new-generation soil models formulate many soil pools using first-order decomposition, which tends to generate simpler yet numerous parameters. Systems or complexity theory, developed across various scientific and social fields, may help improve robustness of soil models, by offering consistent assumptions about system openness, potential dynamic instability and distance from commonly assumed stable equilibria, as well as new analytical tools for formulating more generalized model structures that reduce parameter space and yield a wider array of possible model outcomes, such as quickly shrinking carbon stocks with pulsing or lagged respiration. This paper builds on recent perspectives of soil modeling to ask how various soil functions can be better understood by applying a complex systems lens. We synthesized previous literature reviews with concepts from non-linear dynamical systems in theoretical ecology and soil sciences more broadly to identify areas for further study that may help improve the robustness of soil models under the uncertainty of human activities and management. Three broad dynamical concepts were highlighted: soil variable memory or state-dependence, oscillations, and tipping points or hysteresis. These themes represent less intuitive yet key dynamics that can emerge after assuming nuanced observations, such as reversibility of organo-mineral associations, dynamic aggregate- and pore hierarchies, persistent wet-dry cycles, higher-order microbial community and predator-prey interactions, cumulative legacy land use history, and social management interactions and/or cooperation. We discuss how these aspects may contribute useful analytical tools, metrics, and frameworks that help integrate the uncertainties in future soil states, ranging from micro- to regional scales, including those indirectly affected by human activities and management decisions. Overall, this study highlights the potential benefits of incorporating spatial heterogeneity and dynamic instabilities into future model representations of whole soil processes. Additionally, it advocates for transdisciplinary collaborations between natural and social scientists, extending research into anthropedology and biogeosociochemistry, to better integrate and understand longer-term anthropogenic drivers of soil processes, potentially from soil structural dynamics to microbial community and food web ecology.

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“…Both hydrological and biogeochemical processes can lead to substantial legacy effects that result in accumulation of N in the soil and subsurface, and time lags in the propagation of N input flux to N responses in water bodies (Ascott et al, 2021; Basu et al, 2022). For hydrological processes, long transport times of water and dissolved mobile species of N (in particular nitrate) are documented in soil, unsaturated zone and groundwater (e.g., Ascott et al, 2017; Kolbe et al, 2019; Weitzman et al, 2022), creating a hydrological legacy . Similarly, N can accumulate in immobile organic N pools in soils over long time scales, creating a biogeochemical legacy (e.g.…”

Section: Introductionmentioning

confidence: 99%