Hall, Steven

Profile Picture
Email Address
stevenjh@iastate.edu
Birth Date
Title
Assistant Professor
Academic or Administrative Unit
Organizational Unit
Ecology, Evolution and Organismal Biology

The Department of Ecology, Evolution, and Organismal Biology seeks to teach the studies of ecology (organisms and their environment), evolutionary theory (the origin and interrelationships of organisms), and organismal biology (the structure, function, and biodiversity of organisms). In doing this, it offers several majors which are codirected with other departments, including biology, genetics, and environmental sciences.

History
The Department of Ecology, Evolution, and Organismal Biology was founded in 2003 as a merger of the Department of Botany, the Department of Microbiology, and the Department of Zoology and Genetics.

Dates of Existence
2003–present

Related Units
Organizational Unit
Ecology, Evolution and Organismal Biology

The Department of Ecology, Evolution, and Organismal Biology seeks to teach the studies of ecology (organisms and their environment), evolutionary theory (the origin and interrelationships of organisms), and organismal biology (the structure, function, and biodiversity of organisms). In doing this, it offers several majors which are codirected with other departments, including biology, genetics, and environmental sciences.

History
The Department of Ecology, Evolution, and Organismal Biology was founded in 2003 as a merger of the Department of Botany, the Department of Microbiology, and the Department of Zoology and Genetics.

Dates of Existence
2003–present

Related Units
About
Profile Link
https://dr.lib.iastate.edu/handle/20.500.12876/100262
ORCID iD

Filters

34 17 1
32 1 1
52
Reset filters

Settings
Item Type: Publication ×

Search Results

Now showing 1 - 10 of 52
No Thumbnail Available
Publication

Mechanisms underlying episodic nitrate and phosphorus leaching from poorly drained agricultural soils

2024-07-12 , Lawrence, Nathaniel C. , Hall, Steven , Ecology, Evolution and Organismal Biology

Poorly drained depressions within tile-drained croplands can have disproportionate environmental and agronomic impacts, but mechanisms controlling nutrient leaching remain poorly understood. We monitored nitrate and soluble reactive phosphorus (SRP) leaching using zero-tension soil lysimeters across a depression to upland gradient over 2 years in a corn–soybean (Zea mays L.–Glycine max [L.] Merr.) field in Iowa. We also measured stable isotopes (δ15N and δ18O) of nitrate to examine its sources and transformations. SRP concentrations peaked during winter and early spring after phosphorus (P) fertilization (mean = 3 mg P L−1), with highest values in the depression, and SRP was relatively stable thereafter (mean = 0.3 mg P L−1) irrespective of periods of high soil moisture that led to widespread iron (Fe) reduction across the field. During a near-average precipitation year, nitrate stable isotopes indicated direct leaching of fertilizer nitrate within days of application, followed by nitrification of fertilizer ammonium and several weeks of denitrification in depressional soils. Nevertheless, nitrate concentrations remained high (mean = 28 mg N L−1) in the depression despite strong isotopic evidence for denitrification (>48% N removal). During a wet year, nitrate concentrations were lower in the depression than upland and nitrate isotopes were highly variable, consistent with nearly complete nitrate removal by denitrification in the depression and significant denitrification in upland soils. We conclude that poorly drained depressional soils can potentially decrease nitrate leaching via denitrification under sustained wet conditions, but they inconsistently denitrify and are vulnerable to high nitrate and SRP losses when soils are not saturated, especially following fertilization.

View
No Thumbnail Available
Publication

Potential carbon mineralization assays are confounded by different soil drying temperatures

2023-07-07 , Leeford, Matthew , Mavi, Manpreet Singh , Liptzin, Daniel , Hall, Steven , Ecology, Evolution and Organismal Biology

Measuring carbon dioxide (CO2) produced after re-wetting previously dried soil is an increasingly popular soil health assay, but there is disagreement on the optimal soil drying temperature. We tested whether soil drying temperature impacts water-extractable organic carbon (WEOC) and soil CO2 emissions following rewetting. Soils were collected from corn/soybean croplands and adjacent perennial vegetation at four sites in Iowa, USA. Soil replicates were dried at 22 °C, 35 °C, 55 °C, 85 °C, and rewetted for incubation at 22 °C. Soil WEOC and CO2 emissions after re-wetting increased nonlinearly with drying temperature. Effects on CO2 were largest after four days of incubation, but cumulative differences persisted even after 42 days. Responses of CO2 and its stable isotope ratio (δ13C) to increased drying temperature varied among sites and vegetation types, indicating shifts in C sources. Soil health assays performed with different soil drying temperatures may not be directly comparable, effects of drying temperature may vary idiosyncratically among samples, and drying at 22 °C or 35 °C as opposed to higher temperatures may be preferable to avoid increasing C availability.

View
No Thumbnail Available
Publication

Standardized Data to Improve Understanding and Modeling of Soil Nitrogen at Continental Scale

2023-05 , Weintraub-Leff, Samantha R. , Hall, Steven , Craig, Matthew E. , Sihi, Debjani , Wang, Zhuonan , Hart, Stephen C. , Ecology, Evolution and Organismal Biology

Nitrogen (N) is a key limiting nutrient in terrestrial ecosystems, but there remain critical gaps in our ability to predict and model controls on soil N cycling. This may be in part due to lack of standardized sampling across broad spatial–temporal scales. Here, we introduce a continentally distributed, publicly available data set collected by the National Ecological Observatory Network (NEON) that can help fill these gaps. First, we detail the sampling design and methods used to collect and analyze soil inorganic N pool and net flux rate data from 47 terrestrial sites. We address methodological challenges in generating a standardized data set, even for a network using uniform protocols. Then, we evaluate sources of variation within the sampling design and compare measured net N mineralization to simulated fluxes from the Community Earth System Model 2 (CESM2). We observed wide spatiotemporal variation in inorganic N pool sizes and net transformation rates. Site explained the most variation in NEON’s stratified sampling design, followed by plots within sites. Organic horizons had larger pools and net N transformation rates than mineral horizons on a sample weight basis. The majority of sites showed some degree of seasonality in N dynamics, but overall these temporal patterns were not matched by CESM2, leading to poor correspondence between observed and modeled data. Looking forward, these data can reveal new insights into controls on soil N cycling, especially in the context of other environmental data sets provided by NEON, and should be leveraged to improve predictive modeling of the soil N cycle.

View
No Thumbnail Available
Publication

Dinitrogen Emissions Dominate Nitrogen Gas Emissions From Soils With Low Oxygen Availability in a Moist Tropical Forest

2023-01 , Almaraz, Maya , Groffman, Peter M. , Silver, Whendee L. , Hall, Steven , Lin, Yang , O’Connell, Christine , Porder, Stephen , Ecology, Evolution and Organismal Biology

Lowland tropical forest soils are relatively N rich and are the largest global source of N2O (a powerful greenhouse gas) to the atmosphere. Despite the importance of tropical N cycling, there have been few direct measurements of N2 (an inert gas that can serve as an alternate fate for N2O) in tropical soils, limiting our ability to characterize N budgets, manage soils to reduce N2O production, or predict the future role that N limitation to primary productivity will play in buffering against climate change. We collected soils from across macro- and micro-topographic gradients that have previously been shown to differ in O2 availability and trace gas emissions. We then incubated these soils under oxic and anoxic headspaces to explore the relative effect of soil location versus transient redox conditions. No matter where the soils came from, or what headspace O2 was used in the incubation, N2 emissions dominated the flux of N gas losses. In the macrotopography plots, production of N2 and N2O were higher in low O2 valleys than on more aerated ridges and slopes. In the microtopography plots, N2 emissions from plots with lower mean soil O2 (5%–10%) were greater than in plots with higher mean soil O2 (10%–20%). We estimate an N gas flux of ∼37 kg N/ha/yr from this forest, 99% as N2. These results suggest that N2 fluxes may have been systematically underestimated in these landscapes, and that the measurements we present call for a reevaluation of the N budgets in lowland tropical forest ecosystems.

View
No Thumbnail Available
Publication

Insights on agricultural nitrate leaching from soil block mesocosms

2024-06-09 , Loper, Holly , Tenesaca, Carlos , Pederson, Carl , Helmers, Matthew , Crumpton, William G. , Lemke, Dean , Hall, Steven , Ecology, Evolution and Organismal Biology , Agricultural and Biosystems Engineering

Quantifying nitrate leaching in agricultural fields is often complicated by inability to capture all water draining through a specific area. We designed and tested undisturbed soil monoliths (termed “soil block mesocosms”) to achieve complete collection of drainage. Each mesocosm measures 1.5 m × 1.5 m × 1.2 m and is enclosed by steel on the sides and bottom with a single outlet to collect drainage. We compared measurements from replicate mesocosms planted to corn (Zea mays L.) with a nearby field experiment with tile-drained plots (“drainage plots”), and with drainage from nearby watersheds from 2020 through 2022 under drought conditions. Annual mesocosm drainage volumes were 6.5–24.6 cm greater than from the drainage plots, likely because the mesocosms were isolated from the subsoil and could not store groundwater below the drain depth, whereas the drainage plots accumulated infiltration as groundwater. Thus, we obtained consistent nitrate leaching measurements from the mesocosms even when some drainage plots yielded no water. Despite drainage volume differences, mean flow-weighted nitrate concentrations were similar between mesocosms and drainage plots in 2 of 3 years. Mesocosm annual drainage volume was 8.7 cm lower to 16.7 cm higher than watershed drainage, likely due to lagged influences of groundwater. Corn yields were lower in mesocosms than drainage plots in 2020, but with irrigation, yields were similar in subsequent years. Mean 2020 surface soil moisture and temperature were similar between the mesocosms and nearby fields. Based on these comparisons, the mesocosms provide a robust method to measure nitrate leaching with lower variability than field plots.

View
No Thumbnail Available
Publication

Extreme low-flow conditions in a dual-chamber denitrification bioreactor contribute to pollution swapping with low landscape-scale impact

2023-06-15 , Hartfiel, Lindsey M. , Hoover, Natasha L. , Hall, Steven , Isenhart, Thomas , Gomes, Carmen , Soupir, Michelle , Agricultural and Biosystems Engineering , Ecology, Evolution and Organismal Biology , Natural Resource Ecology and Management , Mechanical Engineering

Denitrification bioreactors are an effective edge-of-field conservation practice for nitrate (NO3) reduction from subsurface drainage. However, these systems may produce other pollutants and greenhouse gases during NO3 removal. Here a dual-chamber woodchip bioreactor system experiencing extreme low-flow conditions was monitored for its spatiotemporal NO3 and total organic carbon dynamics in the drainage water. Near complete removal of NO3 was observed in both bioreactor chambers in the first two years of monitoring (2019–2020) and in the third year of monitoring in chamber A, with significant (p < 0.01) reduction of the NO3-N each year in both chambers with 8.6–11.4 mg NO3-N L−1 removed on average. Based on the NO3 removal observed, spatial monitoring of sulfate (SO4), dissolved methane (CH4), and dissolved nitrous oxide (N2O) gases was added in the third year of monitoring (2021). In 2021, chambers A and B had median hydraulic residence times (HRTs) of 64 h and 39 h, respectively, due to varying elevations of the chambers, with drought conditions making the differences more pronounced. In 2021, significant production of dissolved CH4 was observed at rates of 0.54 g CH4-C m−3 d−1 and 0.07 g CH4-C m−3 d−1 in chambers A and B, respectively. In chamber A, significant removal (p < 0.01) of SO4 (0.23 g SO4 m−3 d−1) and dissolved N2O (0.21 mg N2O-N m−2 d−1) were observed, whereas chamber B produced N2O (0.36 mg N2O-N m−2 d−1). Considering the carbon dioxide equivalents (CO2e) on an annual basis, chamber A had loads (~12,000 kg CO2e ha−1 y−1) greater than comparable poorly drained agricultural soils; however, the landscape-scale impact was small (<1 % change in CO2e) when expressed over the drainage area treated by the bioreactor. Under low-flow conditions, pollution swapping in woodchip bioreactors can be reduced at HRTs <50 h and NO3 concentrations >2 mg N L−1.

View
No Thumbnail Available
Publication

Poorly drained depressions can be hotspots of nutrient leaching from agricultural soils

2023-02-10 , Hall, Steven , Helmers, Matthew , Lawrence, Nathaniel C. , Heaton, Emily , VanLoocke, Andy , Ecology, Evolution and Organismal Biology , Agricultural and Biosystems Engineering , Agronomy

Much of the US Corn Belt has been drained with subsurface tile to improve crop production, yet poorly drained depressions often still flood intermittently, suppressing crop growth. Impacts of depressions on field-scale nutrient leaching are unclear. Poor drainage might promote denitrification and physicochemical retention of P, but ample availability of water and nutrients might exacerbate nutrient leaching from cropped depressions. We monitored nitrate, ammonium, and reactive P leaching across multiple depression-to-upland transects in north-central Iowa, USA, using resin lysimeters buried and retrieved on an annual basis. Crops included conventional corn/soybean (Zea mays/Glycine max) rotations measured at fields with and without a winter rye (Secale cereale) cover crop, as well as juvenile miscanthus (Miscanthus X giganteus), a perennial grass. Leaching of N and P was greater in depressions than in uplands for most transects and years. The median difference in nutrient leaching between paired depressions and uplands was 56 kg N ha-1 y-1 for nitrate (P = 0.0008), 0.6 kg N ha-1 y-1 for ammonium (P = 0.03), and 2.4 kg P ha-1 y-1 for reactive P (P = 0.006). Transects managed with a cover crop or miscanthus tended to have a smaller median difference in nitrate (but not ammonium or P) leaching between depressions and uplands. Cropped depressions may be disproportionate sources of N and P to downstream waters despite their generally poor drainage characteristics, and targeted management with cover crops or perennials might partially mitigate these impacts for N, but not necessarily for P.

View
No Thumbnail Available
Publication

Resolving the influence of lignin on soil organic matter decomposition with mechanistic models and continental-scale data

2023-07-13 , Yi, Bo , Lu, Chaoqun , Huang, Wenjuan , Yang, Jihoon , Howe, Adina , Weintraub-Leff, Samantha R. , Hall, Steven , Ecology, Evolution and Organismal Biology , Agricultural and Biosystems Engineering

Confidence in model estimates of soil CO2 flux depends on assumptions regarding fundamental mechanisms that control the decomposition of litter and soil organic carbon (SOC). Multiple hypotheses have been proposed to explain the role of lignin, an abundant and complex biopolymer that may limit decomposition. We tested competing mechanisms using data-model fusion with modified versions of the CN-SIM model and a 571-day laboratory incubation dataset where decomposition of litter, lignin, and SOC was measured across 80 soil samples from the National Ecological Observatory Network. We found that lignin decomposition consistently decreased over time in 65 samples, whereas in the other 15 samples, lignin decomposition subsequently increased. These “lagged-peak” samples can be predicted by low soil pH, high extractable Mn, and fungal community composition as measured by ITS PC2 (the second principal component of an ordination of fungal ITS amplicon sequences). The highest-performing model incorporated soil biogeochemical factors and daily dynamics of substrate availability (labile bulk litter:lignin) that jointly represented two hypotheses (C substrate limitation and co-metabolism) previously thought to influence lignin decomposition. In contrast, models representing either hypothesis alone were biased and underestimated cumulative decomposition. Our findings reconcile competing hypotheses of lignin decomposition and suggest the need to precisely represent the role of lignin and consider soil metal and fungal characteristics to accurately estimate decomposition in Earth-system models.

View
No Thumbnail Available
Publication

Field-applying an inexpensive, 13C-depleted, labile carbon source to study in situ fate and short-term effects on soils

2023-06-11 , Potter, Stephen W. , Kin, Christar , Hall, Steven , Sawyer, John , McDaniel, Marshall , Agronomy , Ecology, Evolution and Organismal Biology

Background: Labile carbon (Clabile) limits soil microbial growth and is critical for soil functions like nitrogen (N) immobilization. Most experiments evaluating Clabile additions use laboratory incubations. We need to field-apply Clabile to fully understand its fate and effects on soils, especially at depth, but high cost and logistical difficulties hinder this approach.
Aims: Here, we evaluated the impact of adding an in situ pulse of an inexpensive and 13C-depleted source of Clabile—crude glycerol carbon (Cglyc), a by-product from biodiesel production—to agricultural soils under typical crop rotations in Iowa, USA.
Methods:We broadcast-applied Cglyc at three rates (0, 216, and 866 kg C ha−1) in autumn after soybean harvest, tracked its fate, and measured its impact on soil C and N dynamics to four depths (0–5, 5–15, 15–30, and 30–45 cm). Nineteen days later, we measured Cglyc in microbial biomass carbon (MBC), salt-extractable organic C, and potentially mineralizable C pools.We paired these measurements with nitrate N (NO3−–N) and potential net Nmineralization to examine short-term effects on N cycling.
Results: Cglyc was found to at least 45-cm depth with the majority in MBC (18%–23% of total Cglyc added). The δ13C values of the other measured C pools were too variable to accurately track the Clabile fate. NO3−–N was decreased by 13%–57% with the 216 and 866 kg C ha−1 rates, respectively, and was strongly related to greater microbial uptake of Cglyc (i.e., immobilization via microbial biomass). Crude glycerol application had minor effects on soil pH—the greatest rate decreased pH 0.18 units compared to the control.
Conclusions:Overall, glycerol is an inexpensive and effectiveway to measure in situ,Clabile dynamics with soil depth—analogous to how mobile, dissolved organic C might behave in soils—and can be applied to rapidly immobilize NO3−–N.

View
No Thumbnail Available
Publication

Controls on organic and inorganic soil carbon in poorly drained agricultural soils with subsurface drainage

2023-02-07 , Huang, Wenjuan , Mirabito, Anthony J. , Tenesaca, Carlos G. , Mejia-Garcia, William F. , Lawrence, Nathaniel C. , Kaleita, Amy , VanLoocke, Andy , Hall, Steven , Ecology, Evolution and Organismal Biology , Agricultural and Biosystems Engineering , Agronomy

Many productive agricultural soils have naturally poor drainage characteristics and may intermittently pond water even where artificial drainage infrastructure is present, especially in topographic depressions. Soil organic carbon (SOC) is often higher in depressions than uplands, but whether temporary ponding increases SOC by suppressing decomposition remains an important knowledge gap. We measured SOC and inorganic C (carbonate) along topographic gradients from tile-drained depressions to adjacent uplands and tested their relationships with hydrological and biogeochemical properties in corn/soybean fields in Iowa, USA, and examined soil respiration and its stable C isotopes (δ13C) by lab incubation. The 0–30 cm SOC concentration was greatest at depression bottoms, as expected, while carbonate C was highest at boundaries between depressions and uplands. However, only carbonate C, not SOC, increased in depressions with increasingly poor drainage (greater ponding duration). Silt+clay content was the strongest positive predictor of SOC, while ponding duration and oxalate-extractable iron were negatively related to SOC in a statistical model (R2 = 0.83). These negative relationships are consistent with suppression of crop biomass production and iron-mediated decomposition in periodically anoxic soil. Soil C/N ratios were similar in depressions and uplands, indicating that plant detritus did not accumulate with ponding. Stable C isotopes of respiration from incubated soils indicated a similar C3/C4 plant mixture in depressions and uplands, consistent with decomposing soybean and corn residues. In contrast, depression soil organic matter had lower δ13C and δ15N values than uplands, more consistent with pre-agricultural prairie plants than crop residues. Accumulation of SOC in these agricultural depressions is more likely explained by erosion than by suppression of decomposition due to temporary ponding. Gaining additional SOC may require fundamental changes in management, or wetland restoration.

View