Lower Mississippi River Delta Research Articles

Remembering and Forgetting the Past on the Mississippi River: Toward an Environmental History of Catholicism

Abstract: After the flood of 1927, the US government decided to master the Mississippi River. Nowhere was this state-sponsored determination more evident than in the lower Mississippi River delta. An historical examination of a cluster of Catholic churches in Pointe Coupée Parish, Louisiana, permits some understanding of how physical and material alterations to landscapes are not easily traced, especially when we consider the temporal and spatial scales of change to the Mississippi over the last one hundred years. In that time, Catholics of Pointe Coupée Parish managed to retain, erase, and revise aspects of their bonds to a river once central to the lives of their ancestors. This is not at all surprising, as the fallibility of memory is made apparent every time we try to tell stories about our pasts. Pointe Coupée Parish is one site where we can explore how alterations to a landscape have an impact not only on the trajectory of a Catholic community's future, but also on access to its past. Absences of memory in the living, combined with the erasure of material remains in modified landscapes, challenge us to consider how we might account for the relationship between Catholicism and the built environment throughout American history.

Dieback and dredge soils of Phragmites australis in the Mississippi River Delta negatively impact plant biomass

Phragmites australis is exhibiting extensive dieback in the Lower Mississippi River Delta (MRD). We explored the potential for restoration of these marshes by (1) characterizing the chemical profiles of soils collected from healthy and dieback stands of P. australis and from sites recently created from dredge-disposal soils that were expected to be colonized by P. australis and (2) experimentally testing the effects of these soil types on the growth of three common P. australis lineages, Delta, Gulf and European. Soil chemical properties included Al, Ca, Cu, Fe, K, Mg, Mn, Na, P, S, Zn, % organic matter, % carbon, % nitrogen, and pH. Dieback soils were characterized by higher % organic matter, % carbon, % nitrogen, and higher S and Fe concentrations, whereas healthy soils had higher Cu, Al, P and Zn. In comparison, dredge sites were low in nutrients and organic matter compared to healthy soils. Rhizomes of each P. australis lineage were planted in each soil type in a common garden and greenhouse and allowed to grow for five months. Aboveground biomass was 16% lower in dieback and 44% lower in dredge soils than in healthy soils. However, we could detect no significant differences in response to soil types among lineages. Although dredge and dieback sites are not optimal for P. australis growth, plants can thrive on these soils, and we recommend restorative measures be initiated as soon as possible to minimize soil erosion.

Whole Stand Variable Density Yield Equations for Oak-Gum-Cypress Bottomland Hardwood Forests

Abstract Variable density yield equations were constructed using fuzzy linear regression for bottomland oak-gum-cypress forests along the US Gulf Coast and lower Mississippi River Delta region. The USDA Forest Service (Forest Service)’s Forest Inventory and Analysis program provided plot data (n = 526). Predictors included stand age, growing stock basal area per acre, sweetgum site index (base age 50 years), and US Environmental Protection Agency ecoregion dummy variables located in Alabama, Arkansas, Louisiana, Mississippi, Tennessee, and Texas. Dependent variables were per acre growing stock cubic foot yield (GSV) and Doyle board foot sawlog yield (SLV). Plots averaged 58 years, 90 ft2/ac basal area, 79 ft site index, 2,556 ft3/ac GSV, and 11,183 Doyle bf/ac SLV. Adjusted R2 were 0.98 (GSV) and 0.77 (SLV). Basal area possessed fuzziness in the GSV model, whereas the SLV model’s intercept was fuzzy. Six ecoregions possessed fuzziness in each model, but these were not identical across models.

FEASIBILITY OF SHORT STORY CLUBS IN A HEMATOLOGY/ONCOLOGY PROGRAM

Background The death rate from colorectal cancer is high and affects poor and medically underserved populations disproportionately. In the United States, health disparities are particularly acute in the Lower Mississippi River Delta region. Because many in the region have limited access to basic health care resources, they are not screened for cancer, even though screening is one of the most effective strategies to prevent colorectal cancer. Community-based participatory research is a promising approach to prevent colorectal cancer in this population. Community Context The Empowering Communities for Life program was implemented in 2 underserved counties in the Arkansas Lower Mississippi River Delta. The program arose from a 9-year partnership between the University of Arkansas for Medical Sciences and 9 cancer councils across Arkansas. Methods Empowering Communities for Life is a community-based participatory intervention designed to increase colorectal cancer screening in rural, un...

Remote sensing-based structural and functional assessments of Phragmites australis diebacks in the Mississippi River Delta

• Extensive wetland changes can be caused by abiotic and biotic stressors. • Changes in wetland structure and condition can significantly impact vital navigation, flood risk, and ecosystem health services. • Remote sensing and hot spot analyses were used to measure episodic disturbance impacts on wetland condition. • The results show remotely collected data can provide enhanced spatial and temporal measures of wetland plant extent and condition as a function of landscape level dynamics. The Lower Mississippi River Delta (MRD) is dominated by Phragmites australis which provides a stabilizing force, protecting marsh communities from erosion and storm-related impacts. The MRD has experienced recent die-offs of Phragmites stands, which have coincided with a number of abiotic (hurricane and water-level) and biotic ( Phragmites scale) stressors. During this event, previously healthy stands have died or experienced stunted growth, resulting in conversion to replacement species or to open water. This study utilized remote sensing methods to (1) evaluate changes in Phragmites health and distribution in the MRD through time; (2) assess changes in plant cover and floristic quality before, during, and after the dieback event; (3) evaluate changes in landscape patterns (i.e., percentage of landscape, patch density, total edge, and aggregation index); and (4) evaluate changes in channel length and width as a function of the dieback event. Normalized Difference Vegetation Index data showed an active delta landscape with below typical plant biomass/health in periods of hurricane and dieback impacts, with recovery to health values more typical for the MRD after the dieback event. Vegetation species level assessments showed the MRD landscape experienced decreasing coverage and floristic quality during the disturbance periods, and low and nominally increasing vegetation cover and quality through the dieback and recovery periods. Landscape metrics showed similar trends, where wetland areas that experienced event-related stress during the hurricane and dieback periods, showed some level of rebound during the recovery period. And finally, bank-line change analyses showed a significant increase in the rate of shortening and widening of the Mississippi River Passes since the die-back event began. This study serves as a methodological basis for deriving vegetation trend assessments and integrating those results with landscape metrics to prioritize areas of interest; all of which are essential for effective management and mitigation of aquatic nuisance vegetation.

Muddy foil: a history of extraction and resistance in the lower Mississippi River Delta

ABSTRACT This article considers Mississippi River Mud as an analytic for unruly ontologies and fugitive spaces. Historic discourses around mud—and by extension, muddy spaces—were mapped onto lawless, not-fully-humans who occupied them. They reflected efforts to impose rational order and naturalize a political economy of monoculture, river shipping, and fossil fuels. This episteme, which reduces complex ecologies to agents of capital extraction, has transformed the once alluvial forests and marshlands of south Louisiana into subsiding oil and gas fields, abandoned wells, and eroding canals. An explication of mud by communication scholars ruptures this discourse in imagining alternative ways of living.

Soil quality indices as affected by long‐term burning, irrigation, tillage, and fertility management

AbstractUnderstanding the impacts of long‐term agricultural practices on soil quality (SQ) is key for sustaining agroecosystem productivity. This study investigated conventional and no‐tillage (NT), residue burning and no burning, residue level (high and low), and irrigation (irrigated and dryland) effects on soil properties, SQ, and crop yields following 16 yr of a wheat (Triticum aestivum L.)–soybean [Glycine max (L.) Merr.] double‐crop system via the Soil Management Assessment Framework (SMAF). A field experiment was conducted in the Lower Mississippi River Delta region on a silt‐loam soil. Bulk density, soil organic C (SOC), total N (TN), pH, electrical conductivity (EC), and soil P and K from the 0‐ to 10‐cm soil depth were used as SQ indicators investigated individually and as an overall soil quality index (SQI). Following 16 yr, residue burning reduced SOC (1.1%) compared with no burning (1.24%). Irrigation resulted in greater soil TN than dryland management systems (p < 0.05). Reduced soil pH and extractable soil P and K occurred under NT, high residue, and irrigated treatments. Irrigation increased soybean yields, regardless of the tillage system. Burned, NT–high residue management increased wheat yields (3.45 Mg ha−1). Irrigation reduced SQ because of low EC and K scores. High residue reduced SQ compared with the low residue treatment within NT systems, owing to low pH scores. The SMAF indices identified the impacts of irrigation, NT, and optimal N fertilization on SQ. Monitoring of soil pH, P, and K may be needed to maintain SQ in long‐term wheat–soybean systems.

Spatial and temporal patterns of land loss in the Lower Mississippi River Delta from 1983 to 2016

The Mississippi Delta in coastal Louisiana has some of the highest rates of land loss in the world. This land-loss crisis might become a global problem because most major deltas are expected to be vulnerable to land loss during the remainder of the 21st century and beyond. Despite this predicament, we do not understand how land loss in a deltaic environment proceeds in time and space. Here, we evaluate the spatial and temporal trends of land loss in the Lower Mississippi River Delta (LMRD) region using spatial statistics and landscape metrics. We used nearly 4800 Landsat images to construct a series of three-year cloud-free composites from 1983 to 2016. From these data, we created a stability index (SI), which is a dimensionless measure of the number of land-to-water transitions that a land pixel makes before being considered lost. Our results indicate that on the LMRD, 75% of land loss is a single transition from land to water, while about 25% of land pixels have two or more transitions before being considered lost. Using a local indicator of spatial association, we show that pixels with similar SI tend to cluster together. Single transition clusters (low SI) form elongated shapes, they are densely packed, and they are predominantly, but not always, found on marsh edges. On the other hand, multi-transition clusters (high SI) form square-like shapes, they are more fragmented, and they are usually found in marsh interiors. Our analysis further shows that the land-loss area within the spatial patches with both high and low stability is strongly related to the density of land patches and their shape (R2 of 0.717 and 0.545 respectively). Our analysis suggests that land-loss pixels on the marsh edges undergo different temporal patterns of land loss compared to those in the marsh interior. We hypothesize that this arises because wave edge-erosion drives land loss on marsh edges, whereas subsidence-related flooding drives land loss in marsh interiors. The stability index provides a useful way to characterize the processes causing land loss.

Long-term residue and water management practice effects on particulate organic matter in a loessial soil in eastern Arkansas, USA

Long-term sustainability of soils with a prolonged history of crop production can be better understood by characterizing soil aggregation, particularly the distribution of carbon (C) and nitrogen (N) among particulate organic matter (POM) fractions within various soil aggregate-size fractions. The objective of this field study was to evaluate the effects of residue level, residue burning, tillage, and irrigation on macro-aggregate (>250 μm), micro-aggregate (53–250 μm), coarse (>250 μm) and fine POM (53–250 μm), and silt-clay fractions and their associated C and N in the top 10 cm of a highly erodible loessial soil (Glossaquic Fraglossudalf) after 13 years of consistent management in a wheat-soybean, double-crop (WSDC) system in the Lower Mississippi River Delta region of eastern Arkansas. The total aggregated soil fraction was 11.2% greater (P = 0.02) in the no-tillage (NT)-irrigated compared to the average of the other three tillage-irrigation combinations, which did not differ. Averaged over irrigation, burn, and residue-level treatments, the C concentration in the sand-free macro-aggregate fraction was 8.8% less (P < 0.05) under conventional tillage (15.6 g kg−1) than under NT (17.1 g kg−1). Fine POM C and N concentrations within sand-free-adjusted aggregates were 1.9 times greater (P ≤ 0.04) in the burn-low (2.59 and 0.21 g kg−1, respectively) compared to the burn-high treatment (1.35 and 0.11 g kg−1, respectively), while that in the no-burn under either residue level, which did not differ, were intermediate (2.43 and 0.23 g kg−1, respectively). Results showed that alternative management practices, such as NT and non-burning, can contribute to improved soil health and long-term sustainability and the mitigation of climate-change-related greenhouse gas concentrations in the atmosphere by reducing SOM oxidation, microbial respiration, and carbon dioxide emissions.

Supplemental Nitrogen Applications on Corn in Lower Mississippi River Delta Alluvial Soils

Core Ideas Corn optimal N rate on two alluvial soils ranged from 200 to 265 kg N ha−1. Supplemental N applied at early silk increases corn grain yield on two alluvial soils. Relative chlorophyll readings did not consistently diagnose need for supplemental N. Nitrogen deficiency may occur late in the corn (Zea mays L.) growing season due to N fertilizer loss, particularly on poorly drained clay soils, or increased plant demand. Results from field trials conducted from 2006 to 2014 at the Northeast Research Station, St. Joseph, LA, were summarized to evaluate the influence of supplemental N (SN) on corn at early silk (R1). Four non‐irrigated and eight irrigated trials on Sharkey clay (Vertic Haplaquept) and six trials on the Commerce silt loam (Aeric Fluvaquent) were evaluated. Early season N (ESN) rates of a no‐N control plus 200, 235, 265, and 300 kg N ha−1 on Sharkey clay and 135, 170, 200, 235, and 265 kg N ha−1 on Commerce silt loam were applied after emergence. Additionally, a SN application of 65 kg N ha−1 was applied along with one of the ESN rates at R1. Grain yield was maximized at 200 to 265 kg N ha−1 on Sharkey clay and 200 kg N ha−1 on Commerce silt loam soil. Averaged across years, SN significantly increased grain yield of corn on irrigated Sharkey clay and non‐irrigated Commerce silt loam soils by 16 and 10%, respectively. The SN application at R1 may be effective if N is deficient; however, in many cases, there were no grain yield differences between the SN and the equivalent ESN rate. Relative chlorophyll reading was not reflective of the need for SN at R1, perhaps due to the significant changes on environmental factors post R1 until harvest.

Understanding the Mississippi River Delta as a Coupled Natural-Human System: Research Methods, Challenges, and Prospects

A pressing question facing the Mississippi River Delta (MRD), like many deltaic communities around the world, is: Will the system be sustainable in the future given the threats of sea level rise, land loss, natural disasters, and depleting natural resources? An integrated coastal modeling framework that incorporates both the natural and human components of these communities, and their interactions with both pulse and press stressors, is needed to help improve our understanding of coastal resilience. However, studying the coastal communities using a coupled natural-human system (CNH) approach is difficult. This paper presents a CNH modeling framework to analyze coastal resilience. We first describe such a CNH modeling framework through a case study of the Lower Mississippi River Delta in coastal Louisiana, USA. Persistent land loss and associated population decrease in the study region, a result of interplays between human and natural factors, are a serious threat to the sustainability of the region. Then, the paper describes the methods and findings of three studies on how community resilience of the MRD system is measured, how land loss is modeled using an artificial neural network-cellular automata approach, and how a system dynamic modeling approach is used to simulate population change in the region. The paper concludes by highlighting lessons learned from these studies and suggesting the path forward for analysis of coupled natural-human systems.

Suspended-sediment concentrations and loads in the lower Mississippi and Atchafalaya rivers decreased by half between 1980 and 2015

The Weighted Regressions on Time, Discharge, and Season (WRTDS) model was used to derive estimates of suspended-sediment concentration (SSC) and suspended-sediment load (SSL), their dependence on discharge, and their trends with confidence intervals, for one site each on the lowermost Mississippi and Atchafalaya Rivers. The WRTDS model reduces uncertainty in SSCs related to variable streamflow conditions. Flow-normalized SSCs in each river were similar, and decreased from about 260 mg/L to 130 mg/L from 1980 through 2015; combined annual SSL in the two rivers decreased from about 200 Megatons per year (MT/y) to about 100 MT/y. Declines in SSC and SSL were more gradual from 2005 through 2015 and show signs of stabilizing. Our estimates of SSL in 2015 differ markedly from several recently published estimates of current and projected future Mississippi River SSLs, which were generally around 200 MT/y. However, these values came mostly from a different site upstream on the Mississippi River. The relationship between SSC and streamflow differed in an important way between the two rivers. SSC increased as streamflow increased for the entire range of observed streamflow in the Atchafalaya River. In the Mississippi River, SSC followed the same pattern during low and moderate streamflow but decreased at the highest streamflow that tended to occur between January and July. Since much of the water flowing in the Atchafalaya originates from the Mississippi River, the difference suggests a within-basin source of suspended sediment for the Atchafalaya River that is absent in the lower Mississippi River. These findings have important implications for the restoration of deltaic wetlands in coastal Louisiana. Accurate estimates of the SSL available in each river are crucial for understanding how effective diversions of river water into adjacent estuaries will be in sustaining these wetlands. Our study demonstrates that there might be far less sediment available than previously reported. Further, the difference in the relationship between SSC and streamflow in the two rivers is highly relevant to the ongoing discussion of coastal restoration strategies because the delta building that is occurring at the mouth of the Atchafalaya River is frequently used as a model of what could be expected with controlled diversions in the lower Mississippi River delta. The differences in the SSC behavior with changes in streamflow between the two rivers needs to be considered when results from the Atchafalaya River system are projected to those of the Mississippi River.

Invasion of Nipponaclerda biwakoensis (Hemiptera: Aclerdidae) and Phragmites australis die-back in southern Louisiana, USA

Common reed, Phragmites australis (Cav.) Trin. Ex Steud., is the dominant emergent vegetation in the lower Mississippi River Delta (MRD), Louisiana, USA and is comprised primarily of introduced lineages of different phylogeographic origins. Dense stands of P. australis are important for protecting marsh soils from wave action and storm surges. In the Fall of 2016, while investigating symptoms of die-back of Phragmites stands in the lower marsh, a non-native scale was found infesting affected stands in high densities. Identified as Nipponaclerda biwakoensis (Kuwana) (Hemiptera: Aclerdidae), the scale was well established across the lower MRD. This report represents the first recorded population of Nipponaclerda biwakoensis in North America. Intriguingly, there are noticeable differences in die-back symptoms and in scale densities among different lineages of Phragmites in the MRD, with stands of the well-known European invasive lineage appearing healthier and having lower scale densities than other Phragmites lineages. Given its apparent relationship with the die-back syndrome, the scale may have serious implications for the health and stability of Phragmites marsh communities across coastal Louisiana. Efforts are currently underway to investigate the role of the scale and other abiotic stressors in the die-backs and potential management solutions.

Defining the Delta: Multidisciplinary Perspectives on the Lower Mississippi River Delta ed. by Janelle Collins

Defining the Delta: Multidisciplinary Perspectives on the Lower Mississippi River Delta ed. by Janelle Collins

Arsenic, vanadium, iron, and manganese biogeochemistry in a deltaic wetland, southern Louisiana, USA

Abstract Geochemical cycling of the redox-sensitive trace elements arsenic (As) and vanadium (V) was examined in shallow pore waters from a marsh in an interdistributary embayment of the lower Mississippi River Delta. In particular, we explore how redox changes with depth and distance from the Mississippi River affect As and V cycling in the marsh pore waters. Previous geophysical surveys and radon mass balance calculations suggested that Myrtle Grove Canal and the bordering marsh receive fresh groundwater, derived in large part from seepage of the Mississippi River, which subsequently mixes with brackish waters of Barataria Bay. Additionally, the redox geochemistry of pore waters in the wetlands is affected by Fe and S cycling in the shallow subsurface (0–20 cm). Sediments with high organic matter content undergo SO 4 2 − reduction, a process ubiquitous in the shallow subsurface but largely absent at greater depths (~ 3 m). Instead, at depth, in the absence of organic-rich sediments, Fe concentrations are elevated, suggesting that reduction of Fe(III) oxides/oxyhydroxides buffers redox conditions. Arsenic and V cycling in the shallow subsurface are decoupled from their behavior at depth, where both V and As appear to be removed from solution by either diffusion or adsorption onto, or co-precipitation with, authigenic minerals within the deeper aquifer sediments. Pore water As concentrations are greatest in the shallow subsurface (e.g., up to 315 nmol kg − 1 in the top ~ 20 cm of the sediment) but decrease with depth, reaching values − 1 at depths between 3 and 4 m. Vanadium concentrations appear to be tightly coupled to Fe cycling in the shallow subsurface, but at depth, V may be adsorbed to clay or sedimentary organic matter (SOM). Diffusive fluxes are calculated to examine the export of trace elements from the shallow marsh pore waters to the overlying canal water that floods the marsh. The computed fluxes suggest that the shallow sediment serves as a source of Fe, Mn, and As to the surface waters, whereas the sediments act as a sink for V. Iron and Mn fluxes are substantial, ranging from 50 to 30,000 and 770 to 4300 nmol cm − 2 yr − 1 , respectively, whereas As fluxes are much less, ranging from 2.1 to 17 nmol cm − 2 yr − 1 . Vanadium fluxes range from 3.0 nmol cm − 2 yr − 1 directed into the sediment to 1.7 nmol cm − 2 yr − 1 directed out of the sediment

Nitrogen Source Effects on Methane Emissions From Drill-Seeded, Delayed-Flood Rice Production

Rice (Oryza sativa L.) cultivation is unique compared with the production of most other upland row crops in that rice is typically produced under flooded-soil conditions, which can result in net emissions of methane (CH4). Nutrient applications for optimum production, specifically nitrogen (N), which can be organic or inorganic sources, are carefully managed in rice production. However, how nutrient-source effects on CH4 emissions from rice production may interact with other known factors affecting CH4 emissions, such as previous crop/crop rotation and soil texture, are poorly understood, particularly in the midsouthern United States where rice production is concentrated. The objective of this study was to evaluate CH4 fluxes and season-long emissions as affected by fertilizer-N source (i.e., ammonium sulfate [AS], pelletized poultry litter [PPL] + urea, and urea only) and previous crop in rotation (i.e., soybean [Glycine max L.] or rice) from rice production on a clayey Epiaquert and a silt-loam Albaqualf in the Lower Mississippi River Delta region of eastern Arkansas. Methane fluxes, measured using 30-cm-diameter, enclosed-headspace chambers, peaked near heading for all treatments, with PPL + urea resulting in greater (P 0.05) by previous crop on the silt-loam soil. Results clearly indicate that the choice of fertilizer-N source for certain soil textures, specifically AS application to a silt-loam soil, has the potential to mitigate CH4 emissions and reduce the large, negatively perceived, C footprint associated with rice production.

Diurnal Methane Fluxes as Affected by Cultivar from Direct-Seeded, Delayed-Flood Rice Production

Methane (CH4) emissions are known to differ between rice (Oryza sativa L.) cultivars, where CH4 emissions from pure-line cultivars are often greater than from hybrids. Numerous field studies have shown that CH4 emissions follow a diurnal pattern, typically reaching their maximum during afternoon hours. However, it is unknown whether cultivar affects CH4 fluxes/emissions at various measurement times of day or how those cultivar effects may differ spatially across soil textures and temporally throughout the rice growing season. The objective of this field study was to evaluate the effects of time of day (300, 800, 1200, 1800, and 2300 hours) and cultivar (one hybrid and one pure-line) on CH4 fluxes before and after heading from a silt-loam and clay soil in a direct-seeded, delayed-flood rice production system. Enclosed headspace chambers, 30 cm in diameter, were used for CH4 gas sampling on 22 July and 19 August at a silt-loam site and on 29 July and 26 August, 2014 at a clay-soil site in the Lower Mississippi River delta region of eastern Arkansas. Methane fluxes measured pre- and post-heading ranged from 0.7 to 2.2 mg CH4-C m-2· hr-1 from the clay soil and from 2 to 7 mg CH4-C m-2·hr-1 from the silt-loam soil. Hourly CH4 fluxes and estimated daily emissions differed among measurement times of day (P 4 flux or daily emissions for a given day differs by soil texture and rice growth stage, but conducting CH4 flux measurements around late morning to mid-day appear to be optimum to best capture the mean CH4 emissions for the day.

The Tradeoffs between Market Returns from Agricultural Crops and Non-Market Ecosystem Service Benefits on an Irrigated Agricultural Landscape in the Presence of Groundwater Overdraft

Groundwater overdraft has consequences in the long-run for the economic and ecological sustainability of an agricultural landscape. In response to aquifer depletion, we examine the tradeoff of non-market ecosystem service benefits (e.g., groundwater supply, greenhouse gases, and surface water quality) and market returns from crops in the Lower Mississippi River Delta. Farmers may turn to conjunctive water management using on-farm reservoirs and tail water recovery when groundwater pumping becomes expensive. We use separate objectives for market returns from crops and the non-market benefits of ecosystem services to study whether on-farm reservoirs are built with optimal cropping and irrigation choices. The use of reservoirs enables the landscape to attain up to 10% higher market returns for a given level of all non-market ecosystem service benefits by lowering the costs of irrigation, increasing groundwater levels, and reducing fuel combustion and associated greenhouse gas (GHG) emissions from groundwater pumping. A landscape that internalizes both non-market ecosystem service benefits and market value from crops has 30% greater social value than a landscape where only market returns or only non-market value is optimized.

Residue and Water Management Effects on Aggregate Stability and Aggregate-Associated Carbon and Nitrogen in a Wheat-Soybean, Double-Crop System

Agricultural sustainability rests on the principle that the needs of the present population can be met while protecting the ability of future generations to meet their needs. Consequently, soil sustainability is paramount to assuring continued agricultural production. Soil structure and C storage can be influenced by producers' choices regarding residue and water management techniques. The objective of this study was to evaluate the long-term effects of alternative residue (i.e., tillage, residue burning, and fertility–residue level) and water management (irrigated and dryland) practices and soil depth after 10 yr of consistent management on total water-stable aggregate (TWSA; >0.25 mm) concentrations, size-separated aggregate concentrations, and corresponding C and N concentrations in a wheat (Triticum aestivum L.)–soybean [Glycine max (L.) Merr.] double-crop production system in the lower Mississippi River Delta region of eastern Arkansas. The TWSA concentration was unaffected by residue burning and not always negatively impacted by conventional tillage (CT). The TWSA concentrations were 19% greater (P < 0.05) under CT than no-tillage (NT) within the dryland low-fertility–residue treatment combination. High-fertility–residue resulted in 18% less (P < 0.05) TWSA than under low-fertility–residue within the irrigated-NT treatment combination. Under high-fertility–residue, TWSA concentrations were 13% less (P < 0.05) in the 5- to 10-cm depth under irrigation and were 10% less (P < 0.05) in the top 5 cm under dryland management compared to the low-fertility–residue treatment. The smallest two size classes (0.25–0.5 and 0.5–1.0 mm) comprised over 80% of the TWSA. Water-stable aggregate concentrations in the largest two size classes (1–2 and >2 mm) were unaffected by all treatments imposed. Results of this study indicate that interactions between long-term residue and water management practices can significantly impact soil aggregate stability, and thus are useful for aiding the determination of long-term agricultural management practices that improve soil quality in the Lower Mississippi River Delta region.

Long-term Residue Management Effects on Soil Respiration in a Wheat-Soybean Double-Crop System

One of the most significant contributors to the greenhouse effect is carbon dioxide (CO2) gas in the atmosphere. Soil respiration, the combined production of CO2 from soil, as a result of root and microorganism respiration, is the largest flux of CO2 from the terrestrial ecosystem to the atmosphere. Considering land use can greatly impact soil C storage and cycling, agricultural management practices can also greatly affect soil respiration and CO2 emissions. Therefore, the effects of long-term residue management (i.e., residue burning and nonburning, and conventional [CT] and no-tillage [NT]) and residue level (i.e., high and low) on soil respiration during the soybean [Glycine max (L.) Merr.] growing season were examined over 2 consecutive years (i.e., 2011 and 2012) in a wheat (Triticum aestivum L.)–soybean, double-crop system in a silt-loam soil (Aquic Fraglossudalf) in the Mississippi River Delta region of eastern Arkansas after more than 9 years of consistent management. Soil respiration rates from individual plots ranged from 0.53 to 40.7 and from 0.17 to 13.1 μmol CO2·m−2·s−1 throughout the 2011 and 2012 soybean growing seasons, respectively, and differed (P < 0.05) among treatment combinations on two and five of nine and 11 measurement dates in 2011 and 2012, respectively. Regardless of residue level, soil respiration was generally greater (P < 0.05) from CT than NT. Estimated season-long CO2 emissions were 10.2% less (18.5 Mg CO2·ha−1) from residue burning than from nonburning (20.6 Mg CO2·ha−1; P = 0.032). Averaged over years and all other field treatments, estimated season-long CO2 emissions were 15.5% greater from CT (21.0 Mg CO2·ha−1) than from NT (18.1 Mg CO2·ha−1; P = 0.020). Understanding long-term management effects on soil C losses, such as soil respiration, from common and widespread agricultural systems, such as the wheat-soybean, double-crop system, in eastern Arkansas can help improve policies for soil and environmental sustainability throughout the lower Mississippi River Delta region.