Gypsum Amendment Reduces Redox-Induced Phosphorous Release from Freshly Manured, Flooded Soils to Floodwater

The effectiveness of gypsum in reducing runoff P losses from soils and the mechanisms responsible are well documented; however, gypsum amendment effects in reducing redox-induced P losses from flooded soils are less researched and documented. We examined the effect of gypsum amendment on P release from freshly manured soils to pore water and floodwater with continuous flooding for 56 d in the laboratory. Three soils (Pembina, Denham, and Dencross series) collected from Manitoba, Canada, were preincubated with liquid swine manure. Each preincubated manured soil was packed into vessels with or without recycled wallboard gypsum in triplicates and flooded for 56 d, during which pore water and floodwater were sampled weekly and analyzed for pH and dissolved reactive P (DRP), Ca, Mg, Fe, and Mn concentrations. Change in soil redox potential (Eh) with flooding was also monitored. Wallboard gypsum amendment significantly decreased the pore water and surface floodwater DRP concentrations in all three soils for most days after flooding (DAF). The Dencross soil, which had Olsen P about fivefold greater than the other soils, showed the greatest magnitude decrease in DRP concentration with gypsum amendment, by 1.27 mg L−1 on 49 DAF and 0.99 mg L−1 on 21 DAF for pore water and floodwater, respectively. Gypsum amendment (i) delayed the Eh reduction with flooding beyond +200 mV, (ii) decreased pore water pH, and (iii) increased concentrations of Ca, Mg, and Mn in pore water favoring precipitation of P, all of which may have directly or indirectly reduced the P release from flooded soils to overlying floodwater.Funding for this research was provided by the University of Winnipeg Major Grant and a Natural Sciences and Engineering Research Council Discovery Grant to Darshani Kumaragamage, and a fellowship awarded by the Queen Elizabeth Advanced Scholar Program to R.S. Dharmakeerthi.https://acsess.onlinelibrary.wiley.com/doi/10.2134/jeq2018.08.030

Temperature and freezing effects on phosphorus release from soils to overlying floodwater under flooded-anaerobic conditions

Increased phosphorus (P) availability under flooded, anaerobic conditions may accelerate P loss from soils to water bodies. Existing knowledge on P release to floodwater from flooded soils is limited to summer conditions and/or room temperatures. Spring snowmelt runoff, which occurs under cold temperatures with frequent freeze–thaw events, is the dominant mode of P loss from agricultural lands to water bodies in the Canadian Prairies. This research examined the effects of temperature on P dynamics under flooded conditions in a laboratory study using five agricultural soils from Manitoba, Canada. The treatments were (a) freezing for 1 wk at −20 ◦C, thawing and flooding at 4 ± 1 ◦C (frozen, cold); (b) flooding unfrozen soil at 4 ± 1 ◦C (unfrozen, cold); and (c) flooding unfrozen soil at 20 ± 2 ◦C (warm). Pore water and surface waterwere collectedweekly over 8 wk and analyzed for dissolved reactive phosphorus (DRP), pH, calcium, magnesium, iron (Fe), and manganese (Mn). Soils under warm flooding showed enhanced P release with significantly higher DRP concentrations in pore and surface floodwater compared with cold flooding of frozen and unfrozen soils. The development of anaerobic conditions was slow under cold flooding with only a slight decrease in Eh, whereas under warm flooding Eh declined sharply, favoring reductive dissolution reactions releasing P, Fe, and Mn. Pore water and floodwater DRP concentrations were similar between frozen and unfrozen soil under cold flooding, suggesting that one freeze–thaw event prior to flooding had minimal effect on P release under simulated snowmelt conditions."Funding for this research was provided by a National Sciences and Engineering Research Council (NSERC) Discovery Grant to Darshani Kumaragamage and by a NSERC Undergraduate Student Research Assistantship (USRA) to Angela Concepcion."https://acsess.onlinelibrary.wiley.com/doi/10.1002/jeq2.2006

Mobility of arsenic and vanadium in waterlogged calcareous soils due to addition of zeolite and manganese oxide amendments

Addition of manganese(IV) oxides (MnO2) and zeolite can affect the mobility of As and V in soils due to geochemical changes that have not been studied well in calcareous, flooded soils. This study evaluated the mobility of As and V in flooded soils surface-amended with MnO2 or zeolite. A simulated summer flooding study was conducted for 8 weeks using intact soil columns from four calcareous soils. Redox potential was measured in soils, whereas pH, major cations, and As and V concentrations were measured biweekly in pore water and floodwater. Aqueous As and V species were modeled at 0, 4, and 8 weeks after flooding (WAF) using Visual MINTEQ modeling software with input parameters of redox potential, temperature, pH, total alkalinity, and concentrations of major cations and anions. Aqueous As concentrations were below the critical thresholds (<100 μg L−1), whereas aqueous V concentrations exceeded the threshold for sensitive aquatic species (2–80 μg L−1). MnO2-amended soils were reduced to sub-oxic levels, whereas zeolite-amended and unamended soils were reduced to anoxic levels by 8 WAF. MnO2 decreased As and V mobilities, whereas zeolite had no effect on As but increased V mobility, compared to unamended soils. Arsenic mobility increased under anoxic conditions, and V mobility increased under oxic and alkaline pH conditions. Conversion of As(V) to As(III) and V(V) to V(IV) was regulated by MnO2 in flooded soils. MnO2 can be used as an amendment in immobilizing As and V, whereas the use of zeolite in flooded calcareous soils should be done cautiously."This research was financially supported by Environment and Climate Change Canada through Lake Winnipeg Basin Program, University of Winnipeg Major Grant and Canadian Queen Elizabeth II Diamond Jubilee Scholarships: Advanced Scholars program."https://acsess.onlinelibrary.wiley.com/doi/10.1002/jeq2.2045

Degree of Phosphorus Saturation as a Predictor of Redox-Induced Phosphorus Release from Flooded Soils to Floodwater

Phosphorus (P) loss from soils is often enhanced under flooded, anaerobic conditions, increasing the risk of freshwater eutrophication. We aimed to develop a predictive tool to identify soils with greater P release potential under summer‐flooded conditions, which would help in developing strategies to mitigate P losses. One in situ mesocosm study was conducted in field plots with three treatments: cattle manure amended, monoammonium phosphate amended, and unamended. Two ex situ field mesocosm studies were conducted, each having 12 surface soils from agricultural fields. Prior to flooding, soils were analyzed for various soil test P (STP, intensity) and P sorption measures (capacity), and degree of P saturation (DPS) indices were calculated using different intensity and capacity combinations. Mesocosms were flooded and redox potential, pore water, and floodwater dissolved reactive P (DRP) concentrations were determined periodically up to 42 (in situ) and 56 d (ex situ) after the onset of flooding. Floodwater DRP increased significantly in most soils with flooding time, and the maximum DRP (DRPmax) was considered as the flooding‐induced P release risk. Relationships between floodwater DRPmax and STP or DPS indices were established separately for low‐P (Olsen P ≤ 30 mg kg−1) and high‐P (>30 mg kg−1) soils. Several STP indices effectively predicted the P release risk from high‐P soils, but not from low‐P soils. However, DPS calculated using Olsen P (intensity) and P sorption capacity or P saturation index (capacity) performed better in predicting summer flooding‐induced P release across all soil categories, with a higher predictive power."This work was supported by the Manitoba Conservation and Water Stewardship Fund, Environment Canada through the Lake Winnipeg Basin Stewardship Fund (EC no. 1300328), and a University of Winnipeg major grant. We also acknowledge the Manitoba Graduate Scholarship program and the University of Winnipeg Graduate Assistantship Program."https://acsess.onlinelibrary.wiley.com/doi/10.2134/jeq2019.04.015

Flooding-Induced Mobilization of Potentially Toxic Trace Elements from Uncontaminated, Calcareous, Agricultural Soils

Enhanced mobilization of potentially toxic trace elements (PTTE) is well documented for contaminated floodplains, wetlands and rice paddies. Limited information is available on flooding-induced PTTE release from uncontaminated, agricultural soils from temperate regions. We conducted an incubation study with simulated flooding using calcareous, uncontaminated agricultural soils to assess the release dynamics of a few PTTE and identify the controlling factors. Packed soils were flooded, and soil Eh, pH, total dissolved metals and S concentrations in pore water and floodwater were measured for eight weeks. Pore water arsenic (As) and nickel (Ni) concentrations were initially low, but significantly increased with flooding by 12- and 6-fold, respectively. Copper (Cu) concentration declined with flooding, while zinc (Zn) showed no consistent trend. Arsenic and Ni concentrations correlated negatively with Eh, and positively with other redox-sensitive elements, while Cu behaved in a manner opposite to that of As and Ni; however, correlating positively with S. Pore water Zn correlated negatively with pH and Ca, and positively with Al. Principal component analysis confirmed the role of Eh on As, Ni and Cu release from flooded soils and the pH dependency on Zn release. Prolonged flooding released environmentally significant quantities of some PTTE from uncontaminated, agricultural soils.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Ammonia emission from manures treated with different rates of urease and nitrification inhibitors

Urease inhibitors have been successfully used to reduce ammonia (NH3) emission from urea-based fertilizers. However, studies on its effectiveness with manures have produced inconclusive results. Field and greenhouse studies were conducted to investigate the effectiveness of different rates of urease [N-(n-butyl) thiophosphoric triamide; NBPT] with and without nitrification inhibitor (NI) in reducing NH3 emission from surface-applied liquid pig manure (LPM) and solid beef manure (SBM). Ammonia emission was measured with acid-charged discs at seven dates for 28 d. Total NH3 emission (% of applied N) ranged from 4.3% to 8.2% in untreated LPM and 8.2% in untreated SBM. The corresponding NH3 emission was 6.8%–7.4% in LPM treated with NBPT, 5.0%–12.3% in LPM treated with NBPT + NI (double inhibitor; DI), and 6.0%–10.8% in SBM treated with DI. In the field study, NH3 emission was not significantly different between either LPM or SBM treated with and without DI. In the greenhouse, NBPT did not significantly reduce NH3 emission from LPM, whereas DI applied at a lower rate significantly increased NH3 emission from LPM. In conclusion, addition of NBPT to manure did not have any significant environmental benefit, whereas a combination of NBPT and NI increased NH3 emission from manure.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Efficacy of a new N-(n-butyl) thiophosphoric triamide formulation in reducing ammonia volatilization from urea-based fertilizers

N-(n-Butyl)thiophosphoric triamide (NBPT) has been reported to reduce ammonia volatilization from surface-applied urea and urea ammonium nitrate (UAN). A new NBPT formulation (ARM U™, 18% NBPT) that contains a polymer allowing for lower application rate of NBPT was evaluated for its efficacy relative to Agrotain® (30% NBPT) and Arborite® (24% NBPT). Trials consisted of (i) a greenhouse study that compared two rates of ARM U-treated urea (360 and 540 mg NBPT kg−1 urea) with Arborite- or Agrotain-treated urea (480 and 600 mg NBPT kg−1 urea, respectively) and (ii) a field study that compared urea and UAN treated with either ARM U (360 mg NBPT kg−1 urea) or Agrotain (600 mg NBPT kg−1 urea) at two sites. Static chambers fitted with acid-charged discs were used to measure ammonia volatilization at six or seven dates over 28 d. In the greenhouse study, ammonia volatilization was reduced by 96% with either ARM U or Agrotain and 95% with Arborite. In the field study, ARM U and Agrotain reduced ammonia volatilization from urea by 80% and 66%, respectively, across sites. Similarly, ammonia volatilization from UAN was reduced by 46% and 60% with ARM U and Agrotain, respectively. Despite the lower NBPT application rates with ARM U, ammonia reduction by ARM U, Agrotain, and Arborite was not significantly different. The addition of ARM U to urea and UAN enabled lower application rate of NBPT without compromising its efficacy.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Importance of terrain attributes in relation to the spatial distribution of soil properties at the micro scale, a case study.

Micro-topography and spatial variability of soil properties influence the environmental consequences of site-specific management. This study investigated the spatial structure of soil properties in relation to the micro-topography of an agricultural field in the Canadian Prairies. The geospatial sampling scheme had 178 soil cores to a depth of 120 cm. Soil texture and soil water content (SWC) at 0-120 cm, total nitrogen (TN), total carbon (TC) and soil organic carbon (SOC) at 0-15 cm were measured and spatially interpolated using semi-variograms calculated with GS+. The correlation of terrain attributes, calculated from digital elevation models, with soil properties was also assessed. Texture was strongly spatially dependent in the surface layers, and the significance of spatial dependency declined with depth. Spatial autocorrelation of sand content declined from 96% at the soil surface (0-15 cm) to 90% at 30-45 cm, 53% at 75-90 cm. SWC, TC, TN and SOC were similarly auto-correlated. Elevation, relative slope position and vertical distance to channel network influenced the distribution of texture and SWC based on analysis with partial least squares, though this relationship decreased with depth. Terrain attributes are correlated with the spatial variability of soil properties and should be considered in environmental analyses at the micro-scale.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

A laboratory assay of in-situ stabilization of toxic metals in contaminated boreal forest soil using organic and inorganic amendments

Metal-contaminated soils present a great threat to natural ecosystems and human health. Remediation studies focusing on metal-polluted soils with high organic matter (OM > 20%) are limited. This study evaluated the effectiveness of biochar, compost, diammonium phosphate (DAP), and iron oxides (Fe-O), in immobilizing metals from an OM-rich boreal forest soil contaminated with arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn). A laboratory incubation study was conducted with soil amended with biochar (5% w w−1), compost (5% w w−1), DAP (0.2% w w−1), or Fe-O (0.2% w w−1), and a control (without amendment) for 6 months at field capacity moisture content. Metal concentrations were determined in pore water collected at 0, 2, 4, and 6 months after incubation. Soil was extracted sequentially for metals after the incubation period. Metal concentrations in pore water were significantly reduced by different amendments as follows: As by biochar and Fe-O, Cd by biochar, compost, and DAP, Cu by biochar, Pb by compost and DAP, and Zn by biochar and compost. Sequential extractions revealed biochar and (or) compost transferred Cd, Cu, Pb, and Zn from the labile pool to the non-labile pool confirming their effectiveness as amendments for remediation of metal-contaminated OM-rich boreal forest soil.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Alum and Gypsum Amendments Decrease Phosphorus Losses from Soil Monoliths to Overlying Floodwater under Simulated Snowmelt Flooding

Phosphorus (P) loss from soils poses a threat of eutrophication to downstream waterbodies. Alum (Al2(SO4)3·18H2O) and gypsum (CaSO4·2H2O) are effective in reducing P loss from soils; however, knowledge on their effectiveness under cold temperatures is limited. This study examined the reduction of P loss from soils with alum and gypsum amendment under simulated snowmelt flooding. Intact soil monoliths (15 cm depth) collected from eight agricultural fields in flood-prone areas of Manitoba, Canada, were surface amended with alum or gypsum, pre-incubated for 2 weeks, then flooded and incubated at 4 °C for 8 weeks. Porewater and floodwater samples collected weekly were analyzed for dissolved reactive P (DRP), dominant cations and anions. An enhanced P release with flooding time was observed in all soils whether amended or unamended; however, alum/gypsum amendment reduced DRP concentrations in porewater and floodwater in general, with alum showing a more consistent effect across soils. The reduction in floodwater DRP concentrations (maximum DRP concentration during flooding) with alum and gypsum ranged from 34–90% and 1–66%, respectively. Based on Visual MINTEQ thermodynamic model predictions, precipitation of P and formation of P-sorbing mineral species with alum and gypsum amendment reduced DRP concentrations at latter stages of flooding