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There is a lack of information on denitrifying bioreactors treating subsurface drainage water at the end of their initial design life due to the relative newness of the technology and the relatively long estimated life. A denitrifying bioreactor (15 m L x 7.6 m W x 1.1 m D) installed in August 2008 in Greene County, Iowa, was recharged with new woodchips in November 2017 (age 9.25 years), providing the opportunity to evaluate the properties of the wood media at the end of design life. The objective was to pair a battery of physical, chemical, and nitrate-N removal tests on the wood media harvested from the bioreactor with field observations to assess likely reasons why denitrifying bioreactors treating tile drainage may need to be recharged. The two types of wood media harvested from the bioreactor (termed woodchips and mixed shreds) had median particle sizes (D50) of 12.1 and 7.7 mm, respectively, and saturated hydraulic conductivities of 4.2 ± 3.0 and 3.1 ± 1.0 cm s-1 (mean ± standard deviation), which were within the range of reported values for woodchips, albeit at the low end. The wood media carbon content and quality had degraded (e.g., lignocellulose indices of 0.63 to 0.74, nearing the range of decomposition stabilization), although batch tests suggested the robustness of wood as a carbon source to support nitrate removal (e.g., 65% nitrate concentration reduction in drainage water). Woodchip degradation along with sedimentation from the drainage system likely reduced conductivities over time. Development of preferential flow paths through the bioreactor was indicated by low bioreactor outflow rates (i.e., reduced permeability) and reduced hydraulic efficiency based on conservative tracer testing. These changes in media properties and linked impacts resulted in the need to recharge this bioreactor after nine years. [ABSTRACT FROM AUTHOR]

A denitrification bed is a system that can reduce the nitrate concentration in subsurface drainage water. There is a need to investigate the carbon quality of old woodchips to gain a better understanding of the effect of age on woodchip properties. The objectives of this study were to characterize the carbon quality and carbon to nitrogen (C/N) ratio of aged woodchips and to examine the suitability of a denitrification bed for a replicated experiment. To achieve these goals, we excavated four-year-old woodchips along the length of a 106.4 m long denitrification bed near Willmar, Minnesota, and analyzed them for particle size, C/N ratio, and carbon quality. Particle size analysis showed similarities from 12.5 to 106.4 m along the bed. We found a mean C/N ratio ranging from 58.4 ±3.17 to 153.4 ±9.57 (smallest at the inlet). The mean lignocellulose index (LCI, a measure of carbon quality) of the four-year-old woodchips ranged from 0.47 to 0.57 (highest at the inlet). The woodchip particle sizes, C/N ratios, and LCI from 25.9 to 106.4 m along the bed length were similar. In conclusion, the C/N ratio and LCI of the four-year-old woodchips showed effects of decomposition and increased woodchip carbon recalcitrance over time, respectively. [ABSTRACT FROM AUTHOR]

A survey of the literature and in particular an examination of the terminology use in a previous special collection of modeling calibration and validation articles were conducted to arrive at a list of consistent terminology recommended for writing about hydrologic and water quality model calibration and validation. The terminology list includes rudimentary terms necessary for proper understanding of modeling literature for the novice modeler. This article also provides discussions regarding confusing or conflicting terminology found in the literature, alternative terms to those recommended herein, and alternative definitions for those terms that may be used by some authors. [ABSTRACT FROM AUTHOR]

Applying manure in the fall and winter increases the potential for nutrient loss prior to crop uptake in the spring. In order to minimize the risk of nutrient loss, recommendations are often based on soil temperature, since biological activity has been shown to decrease substantially at temperatures less than 10°C. These recommendations are often targeted toward reducing nitrogen (N) losses; thus, a smaller body of information is available on the fate of phosphorus (P) from fall and winter applied manure. The objective of this research was to determine how soil temperature affects P loss in runoff and leachate, and assess overwinter P losses based on application date and soil temperature. Nitrogen losses are discussed in a separate article. Dairy manure was surface applied to a channery silt loam soil contained in lysimeters at soil temperatures of 15.7°C, 4.8°C, and -1.1°C, which represented early fall, late fall, and winter applications, respectively. Phosphorus losses were determined during a series of rainfall simulations and natural precipitation events from October 2009 through March 2010. Phosphorus losses were significantly influenced by the soil temperature at the time of manure application and first rainfall-runoff event. As the soil temperature decreased, losses of DRP, TDP, and total P increased. Overwinter losses were also significantly impacted by soil temperature. The winter treatment had two times higher total P losses compared to the manure applied during the early fall. Results of this research show that soil temperature is important for determining P losses and that incorporating quantitative tools, such as soil temperature, into manure management plans could enhance P retention and help reduce the risk of overwinter P losses. [ABSTRACT FROM AUTHOR]

Many producers practice fall and winter manure spreading for economic and practical reasons. In order to minimize the risk of nitrogen (N) loss between application and crop uptake in the spring, university extension publications and industry professionals often make recommendations based on soil temperature. The objective of this research, therefore, was to determine how soil temperature affects N losses in runoff and leachate, and assess overwinter N losses based on application date and soil temperature. Phosphorus losses are discussed in a separate article. Dairy manure was surface-applied to a channery silt loam soil contained in lysimeters at soil temperatures of 15.7°C, 4.8°C, and -1.1°C, which corresponded to early fall (Oct. 22), late fall (Nov. 17), and winter (Dec. 15) applications, respectively. Nitrogen losses were determined during a series of rainfall simulations and natural precipitation events from October 2009 through March 2010. The soil temperature between manure application and the first rainfall-runoff event three days after application was held constant and significantly influenced N loss. As the soil temperature decreased, losses of NH4-N, organic N, and total N exponentially increased. The form of N losses was also significantly impacted by application date and overwinter soil temperature. Early fall application of manure resulted in significant overwinter NO3-N losses, while the winter-applied manure had significantly more overwinter NH4-N losses. Results of this research show that there are trade-off risks associated with manure application in the fall and winter and that these trade-offs need to be considered in manure management planning in order to enhance N retention and help reduce the risk of overwinter N losses. [ABSTRACT FROM AUTHOR]

Winter application of manure is commonly practiced in the northeastern and north-central U.S. Potential nutrient losses from winter-applied manure are difficult to predict due to uncertainty in weather forecasting and limited knowledge on soil-nutrient-hydrology interactions during the winter. The objective of this study was to extend the understanding of nutrient cycling and transport processes associated with manure application methods during winter months. Specifically, the influence of manure position within the snowpack on nutrient losses, was examined using a laboratory approach. Dairy manure was applied either before, midway through, or upon completion of an artificial snowfall. Runoff and leachate were subsequently collected throughout a snowmelt event and rainfall simulations. Manure application prior to the snowfall increased the losses of total N and NH4-N in snowmelt runoff and resulted in larger losses of both N and P in runoff during the rainfall simulation. Manure application on top of the snow reduced the amount of NH4-N losses but increased the losses of organic N, DRP, and total P in snowmelt runoff. The results of this research show that the relative position of manure within the snowpack plays a significant role in the fate of N and P from winter-applied manure. [ABSTRACT FROM AUTHOR]

The laboratory study of water movement and nutrient dynamics associated with agricultural soils has been limited within an experimental setup to either surface investigation or leaching analysis. This study was conducted to develop a laboratory system for simultaneous investigation of surface and subsurface hydrologic and nutrient dynamics within a soil block. The system consists of a square steel casing 61 cm wide and long by 61 cm deep that is driven into the ground with a 1.1 Mg drop hammer, excavated, and undergirded with a 12.7 mm thick PVC plate to capture an undisturbed soil block. Unique features of the lysimeter system include the use of petrolatum (petroleum jelly) to suppress side wall bypass flow and potential chemical interaction with the steel lysimeter walls, and the capability to investigate overland and subsurface flows in one assemblage. [ABSTRACT FROM AUTHOR]

Researchers are assessing the beneficial effects of conservation practices on water quality with hydrologic models. The assessments depend heavily on accurate simulation of water yield. This study was conducted to improve Soil and Water Assessment Tool (SWAT) hydrologic model daily water yield estimates in the Little River Experimental Watershed (LREW) in south Georgia. The SWAT code was altered to recognize a difference in curve number between growing and dormant seasons, to use an initial abstraction (Ia), of 0.05S rather than 0.2S, and to adjust curve number based on the level of soil saturation in low-lying riparian zones. Refinements were made to two SWAT input paranteters, SURLAG and ALPHA_BF, from a previous set of calibration parameters. The combined changes improved the daily Nash-Sutcliffe model efficiency (NSE) from 0.42 to 0.66 for water yield at the outlet of the 16.9 km² subwatershed K of the LREW for the ten-year period 1995 to 2004. Further calibration of the SURLAG coefficient yielded the largest improvement of five alterations, and changing Ia effected the next largest improvement. Over the ten-year investigation period, the model predicted annual average water yield within 1% of measured streamflow, and deviation between observed and simulated values for stormflow was <2.2%. Annual daily NSEs for each of the ten years were improved; for two years affected by seasonal tropical storm events, NSEs were changed from negative to positive values. The results of this study support rite adjustment of the la ratio in the runoff curve number and suggest that additional changes to SWAT would improve water yield prediction for southern Coastal Plain locations. [ABSTRACT FROM AUTHOR]

Long-term stream water quality data may provide opportunities to study the effectiveness of conservation practices. The first three decades of data for the Little River in south- western Georgia were analyzed for trends as part of the Conservation Effects Assessment Project. Concentrations and loads for chloride, ammortium-N, nitrate plus nitrite-N, total Kjeldahl N, total P, and dissolved molybdate reactive phosphorus were determined from 1974 through 2003 for eight nested subwatersheds in the Little River Experimental Watershed. There was a statistically significant downward trend for annual mean total phosphorus concentration in five subwatersheds and an upward trend for chloride in three subwatersheds. The decrease in total phosphorus concentration occurred primarily in winter. Trends in phosphorus and chloride concentrations did not appear to be related to land use. There were no statistical differences in annual streamflow or nutrient loads expressed on a per area basis among the nested subwatersheds. Annual and seasonal flow-weighted mean concentrations were different among the subwatersheds for nitrate-N and chloride. The larger subwatersheds had significantly higher nitrate-N in winter and spring. The nutrient loads and concentrations from these subwatersheds were an order of magnitude less compared to other agricultural watersheds. Conservation practices were implemented on 11% of the watershed area from 1980 to 2003; however, the affects of the practices on watershed water quality was not clear. Earlier short-term studies attributed the low levels of nutrient transport to the presence of extensive riparian forests and the general prevalence of forest in these mixed land use watersheds. [ABSTRACT FROM AUTHOR]

The USDA Natural Resource Conservation Service curve number (CN) method for estimating surface runoff is frequently used in natural resource modeling. Water yield and subsequently water quality estimates depend heavily on CN selection. This study was conducted to estimate CNs for a cotton-peanut rotation under conventional and strip tillage (ST) methods for growing and dormant seasons. A comparison between alternative methods for calculating CN and their applicability was also made. Rainfall-runoff data measured from 1999 to 2005 at a field study site in South Georgia were used to calculate CNs by averaging, lognormal, and data-censoring methods. For conventional and STs, CNs by the averaging method using year-round data were 89 and 84, respectively, and by the lognormal method were 89 and 83, respectively. Results from the data-censoring method were 81 and 75, respectively, which matched standard table values developed from a long-term series of annual maximum runoff. Values were also found to vary by season. Curve numbers by the lognormal method for ST were 83 and 88 for growing and dormant seasons, respectively; however, there was no difference between growing and dormant seasons, 89, for conventional tillage. The corresponding CNs by the data-censoring method for ST were 71 and 79 for growing and dormant seasons, respectively, and for conventional tillage were 82 and 79 for growing and dormant seasons, respectively. Based upon errors of the estimates, runoff estimates showed no improvement when separate CNs for the two seasons were used. The data-censoring method CNs yielded lower runoff estimate errors than CNs obtained by the lognormal method. The data-censoring method is recommended for determining CNs from plot rainfall-runoff data pairs. [ABSTRACT FROM AUTHOR]

The watershed-scale effects of agricultural conservation practices are not well understood. A baseline calibration and an input parameter sensitivity analysis were conducted for simulation of watershed-scale hydrology in the Little River Experimental Watershed (LREW) in the Coastal Plain near Tifton, Georgia. The Soil and Water Assessment Tool (SWAT) was manually calibrated to simulate the hydrologic budget components measured for the 16.9 km² subwatershed K of the LREW from 1995 to 2004. A local sensitivity analysis was performed on 16 input variables. The sum of squares of the differences between observed and simulated annual averages for baseflow, stormflow, evapotranspiration, and deep percolation was 19 mm²; average annual precipitation was 1136 mm. The monthly Nash-Sutcliffe model efficiency (NSE) for total water yield (TWYLD) was 0.79 for the ten-year period. Daily NSE for TWYLD was 0.42. The monthly NSE for three years with above-average rainfall was 0.89, while monthly NSE was 0.59 for seven years with below annual average rainfall, indicating that SWAT's predictive capabilities are less well-suited for drier conditions. Monthly average TWYLD for the high-flow winter to early spring season was underpredicted, while the low-flow late summer to autumn TWYLD was overpredicted. Results were negatively influenced when seasonal tropical storms occurred during a dry year The most sensitive parameters for TWYLD were curve number for crop land (CN2(crop)), soil available water content (SOL_AWC), and soil evaporation compensation factor (ESCO). The most sensitive parameters for storm flow were CN2(crop), curve number for forested land (CN2(forest)), soil bulk density (SOL_BD), and SOL_AWC. The most sensitive parameters for baseflow were CN2(crop), CN2(forest), ESCO, and SOL_AWC. Identification of the sensitive SWAT parameters in the LREW provides modelers in the Coastal Plain physiographic region with focus for SWAT calibration. [ABSTRACT FROM AUTHOR]

Cover cropping practices are being researched to reduce artificial subsurface drainage nitrate-nitrogen (nitrate-N) losses from agricultural lands in the upper Mississippi watershed. A soil-plant-atmosphere simulation model RyeGro, was developed to quantify the probabilities that a winter rye cover crop will reduce artificial subsurface drainage nitrate-N losses given climatic variability in the region. This article describes the plant growth submodel of RyeGro, Grosub, which estimates biomass production with a radiation use efficiency-based approach for converting intercepted photosynthetically active radiation to biomass. Estimates of nitrogen (N) uptake are based on an empirical plant N concentration curve. The model was calibrated with data from a three-year field study conducted on a Normania clay loam (fine-loamy, mixed, mesic Aquic Haplustoll) soil at Lamberton, Minnesota. The model was validated with data measured from a field trial in St. Paul, Minnesota. The cumulative rye aboveground biomass predictions for the calibration years differed by -0.45, 0.09, and 0.16 Mg ha-1 (-17%, 9%, and 32%), and the plant N uptake predictions differed by - 10.5, 8.0, and 4.0 kg N ha-1 (-16%, 30%, and 21%) from the observed values. The predictions of biomass production and N uptake for the validation year varied by -1.4 Mg ha-1 and 16 kg N ha-1 (-27% and 24%) from the values observed in the field study, respectively. A local sensitivity analysis of eight input parameters indicated that model output is most sensitive to the maximum leaf area index and radiation use efficiency parameters. Grosub demonstrated the capability to predict seasonal aboveground biomass production of fall-planted rye in southwestern Minnesota within an accuracy of ±30% in years when production exceeds 1 Mg ha-1 by mid-May, and to predict seasonal rye N uptake within ±25% of observed values. [ABSTRACT FROM AUTHOR]

Two experiments were conducted to investigate the effect of dietary crude protein concentration on ammonia (NH3) and greenhouse gas (GHG; nitrous oxide, methane, and carbon dioxide) emissions from fresh dairy cow manure incubated in a controlled environment (experiment 1) and from manure-amended soil (experiment 2). Manure was prepared from feces and urine collected from lactating Holstein cows fed diets with 16.7% (DM basis; HCP) or 14.8% CP (LCP). High-CP manure had higher N content and proportion of NH3- and urea-N in total manure N than LCP manure (DM basis: 4.4 vs. 2.8% and 51.4 vs. 30.5%, respectively). In experiment 1, NH3 emitting potential (EP) was greater for HCP compared with LCP manure (9.20 vs. 4.88 mg/m2 per min, respectively). The 122-h cumulative NH3 emission tended to be decreased 47% (P = 0.09) using LCP compared with HCP manure. The EP and cumulative emissions of GHG were not different between HCP and LCP manure. In experiment 2, urine and feces from cows fed LCP or HCP diets were mixed and immediately applied to lysimeters (61 x 61 x 61cm; Hagerstown silt loam; fine, mixed, mesic Typic Hapludalf) at 277 kg of N/ha application rate. The average NH3 EP (1.53 vs. 1.03 mg/m² per min, respectively) and the area under the EP curve were greater for lysimeters amended with HCP than with LCP manure. The largest difference in the NH3 EP occurred approximately 24 h after manure application (approximately 3.5 times greater for HCP than LCP manure). The 100-h cumulative NH3 emission was 98% greater for HCP compared with LCP manure (7,415 vs. 3,745 mg/m², respectively). The EP of methane was increased and that of carbon dioxide tended to be increased by LCP compared with HCP manure. The cumulative methane emission was not different between treatments, whereas the cumulative carbon dioxide emission was increased with manure from the LCP diet. Nitrous oxide emissions were low in this experiment and did not differ between treatments. In the conditions of these experiments, fresh manure from dairy cows fed a LCP diet had substantially lower NH3 EP, compared with manure from cows fed a HCP diet. The LCP manure increased soil methane EP due to a larger mass of manure added to meet plant N requirements compared with HCP manure. These results represent effects of dietary protein on NH3 and GHG EP of manure in controlled laboratory conditions and do not account for environmental factors affecting gaseous emissions from manure on the farm. [ABSTRACT FROM AUTHOR]

The buffering of phosphorus (P) in the landscape delays management outcomes for water quality. If stored in labile form (readily exchangeable and bioavailable), P may readily pollute waters. We studied labile P and its intensity for >600 soils and sediments across seven study locations in the United States. Stocks of labile P were large enough to sustain high P losses for decades, indicating the transport-limited regime typical of legacy P. Sediments were commonly more P-sorptive than nearby soils. Soils in the top 5 cm had 1.3-3.0 times more labile P than soils at 5-15 cm. Stratification in soil test P and total P was, however, less consistent. As P exchange via sorption processes follows the difference in intensities between soil/sediment surface and solution, we built a model for the equilibrium phosphate concentration at net zero sorption (EPC 0 ) as a function of labile P (quantity) and buffer capacity. Despite widely varying properties across sites, the model generalized well for all soils and sediments: EPC 0 increased sharply with more labile P and to greater degree when buffer capacity was low or sorption sites were likely more saturated. This quantity-intensity-capacity relationship is central to the P transport models we rely on today. Our data inform the improvement of such P models, which will be necessary to predict the impacts of legacy P. Further, this work reaffirms the position of labile P as a key focus for environmental P management-a view Dr. Sharpley developed in the 1980s with fewer data and resources., (© 2024 The Author(s). Journal of Environmental Quality published by Wiley Periodicals LLC on behalf of American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.)

Woodchip denitrification bioreactors are an effective agricultural practice to reduce nitrogen (N) export from subsurface drainage via the conversion of nitrate (NO 3 - ) to nitrogen gas (N 2 ), but there are challenges associated with limited woodchip supplies and increasing prices. Previous lab studies indicate that corncobs could be a promising woodchip alternative from the perspectives of N removal rate and cost. This field study aimed to provide early performance and cost assessment of denitrification bioreactors with two woodchip-corncob treatments. The objectives were to i) compare N removal rates of bioreactors with different carbon and hydraulic retention time (HRT) treatments, ii) compare bioreactor N removal costs, and iii) conduct sensitivity analysis on full-scale bioreactors (FBR) N removal costs with varying corncob lifespans and prices. Nine replicated field pilot-scale bioreactors (PBRs) using three carbon treatments and three HRTs were assessed for N removal efficiency. The carbon treatments were woodchip-only (WC100), 25% (by vol.) corncobs + 75% woodchips media (CC25) in series, and 75% corncobs + 25% woodchips (CC75) in series set at HRTs of 2, 8, and 16 h. N concentrations were monitored at each PBR inlet and outlet, and the PBR N removal efficiencies were used to estimate FBR N removal rates and costs. At respective HRTs, the estimated N removal rates of CC75 were 1.6- to 10.1-fold higher than WC100, but CC25 exhibited 0.9-fold lower (at 8-hr HRT) to 2.8-fold higher than WC100. A 15-yr cost assessment indicated CC75 ($10.56 to $13.89 kg -1  N) was the most cost-efficient treatment, followed by WC100 ($13.30 to $88.11 kg -1  N) and CC25 ($22.41 to $60.13 kg -1  N). This assessment showed CC75 as a promising alternative to WC100 in terms of N removal rate and cost, but CC25 did not provide sufficient N removal rate increase for it to be a cost-efficient option. Nonetheless, using corncobs as a bioreactor medium is a relatively new approach, and we encourage more field studies to explore the long-term opportunities and challenges., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Aims: This study was done to obtain denitrifiers that could be used for bioaugmentation in woodchip bioreactors to remove nitrate from agricultural subsurface drainage water., Methods and Results: We isolated denitrifiers from four different bioreactors in Minnesota, and characterized the strains by measuring their denitrification rates and analysing their whole genomes. A total of 206 bacteria were isolated from woodchips and thick biofilms (bioslimes) that formed in the bioreactors, 76 of which were able to reduce nitrate at 15°C. Among those, nine potential denitrifying strains were identified, all of which were isolated from the woodchip samples. Although many nitrate-reducing strains were isolated from the bioslime samples, none were categorized as denitrifiers but instead as carrying out dissimilatory nitrate reduction to ammonium., Conclusions: Among the denitrifiers confirmed by 15 N stable isotope analysis and genome analysis, Cellulomonas cellasea strain WB94 and Microvirgula aerodenitrificans strain BE2.4 appear to be promising for bioreactor bioaugmentation due to their potential for both aerobic and anaerobic denitrification, and the ability of strain WB94 to degrade cellulose., Significance and Impact of the Study: Denitrifiers isolated in this study could be useful for bioaugmentation application to enhance nitrate removal in woodchip bioreactors., (© 2020 The Society for Applied Microbiology.)

Phosphorus (P) loss from intensive dairy farms is a pressure on water quality in agricultural catchments. At farm scale, P sources can enter in-field drains and open ditches, resulting in transfer along ditch networks and delivery into nearby streams. Open ditches could be a potential location for P mitigation if the right location was identified, depending on P sources entering the ditch and the source-sink dynamics at the sediment-water interface. The objective of this study was to identify the right location along a ditch to mitigate P losses on an intensive dairy farm. High spatial resolution grab samples for water quality, along with sediment and bankside samples, were collected along an open ditch network to characterise the P dynamics within the ditch. Phosphorus inputs to the ditch adversely affected water quality, and a step change in P concentrations (increase in mean dissolved reactive phosphorus (DRP) from 0.054 to 0.228 mg L -1 ) midway along the section of the ditch sampled, signalled the influence of a point source entering the ditch. Phosphorus inputs altered sediment P sorption properties as P accumulated along the length of the ditch. Accumulation of bankside and sediment labile extractable P, Mehlich 3 P (M3P) (from 13 to 97 mg kg -1 ) resulted in a decrease in P binding energies (k) to < 1 L mg -1 at downstream points and raised the equilibrium P concentrations (EPC 0 ) from 0.07 to 4.61 mg L -1 along the ditch. The increase in EPC 0 was in line with increasing dissolved and total P in water, demonstrating the role of sediment downstream in this ditch as a secondary source of P to water. Implementation of intervention measures are needed to both mitigate P loss and remediate sediment to restore the sink properties. In-ditch measures need to account for a physicochemical lag time before improvements in water quality will be observed., (Copyright © 2019 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Winter cover crops might reduce nutrient loss to leaching in the Upper Midwest. New oilseed-bearing cash cover crops, such as winter camelina ( L.) and pennycress ( L.), may provide needed incentives. However, the abilities of these crops to sequester labile soil nutrients are unknown. To address this unknown, N in shoot biomass, plant-available N and P in soil, and NO-N and soluble reactive P in soil water collected from lysimeters placed at 30, 60, and 100 cm were measured in cover crop and fallow treatments established in spring wheat ( L.) stubble and followed through a cover crop-soybean [ (L.) Merr.] rotation. Five no-till cover treatments (forage radish [ L.], winter rye [ L.], field pennycress, and winter camelina) were compared with two fallow treatments (chisel till and no-till). Pennycress and winter camelina were harvested at maturity after relay sowing of soybean. Winter rye and radish sequestered more N in autumn shoot biomass, ranging from 26 to 38 kg N ha, but overwintering oilseeds matched or exceeded N uptake in spring, ranging 28 to 49 kg N ha before soybean planting. Nitrogen uptake was reflected by reductions in soil water NO-N during cover crop and intercropping phases for all cover treatments (mean = 4 mg L), compared with fallow treatments (mean = 31 mg L). Cash cover crops like pennycress and winter camelina provide both environmental and potential economic resources to growers. They are cash-generating crops able to sequester labile soil nutrients, which protects and promotes soil health from autumn through early summer., (© 2019 The Authors. Re-use requires permission from the publisher.)

Nutrient management on US dairy farms must balance an array of priorities, some of which conflict. To illustrate nutrient management challenges and opportunities across the US dairy industry, the USDA Agricultural Research Service Dairy Agroecosystems Working Group (DAWG) modeled 8 confinement and 2 grazing operations in the 7 largest US dairy-producing states using the Integrated Farm System Model (IFSM). Opportunities existed across all of the dairies studied to increase on-farm feed production and lower purchased feed bills, most notably on large dairies (>1,000 cows) with the highest herd densities. Purchased feed accounted for 18 to 44% of large dairies' total operating costs compared with 7 to 14% on small dairies (<300 milk cows) due to lower stocking rates. For dairies with larger land bases, in addition to a reduction in environmental impact, financial incentives exist to promote prudent nutrient management practices by substituting manure nutrients or legume nutrients for purchased fertilizers. Environmental priorities varied regionally and were principally tied to facility management for dry-lot dairies of the semi-arid western United States (ammonia-N emissions), to manure handling and application for humid midwestern and eastern US dairies (nitrate-N leaching and P runoff), and pasture management for dairies with significant grazing components (nitrous oxide emissions). Many of the nutrient management challenges identified by DAWG are beyond slight modifications in management and require coordinated solutions to ensure an environmentally and economically sustainable US dairy industry., (The Authors. Published by FASS Inc. and Elsevier Inc. on behalf of the American Dairy Science Association®. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).)

Anthropogenic perturbation of the global nitrogen cycle and its effects on the environment such as hypoxia in coastal regions and increased N 2 O emissions is of increasing, multi-disciplinary, worldwide concern, and agricultural production is a major contributor. Only limited studies, however, have simultaneously investigated NO 3 - losses to subsurface drain flow and N 2 O emissions under corn-soybean production. We used the Root Zone Water Quality Model (RZWQM) to evaluate NO 3 - losses to drain flow and N 2 O emissions in a corn-soybean system with a winter rye cover crop (CC) in central Iowa over a nine year period. The observed and simulated average drain flow N concentration reductions from CC were 60% and 54% compared to the no cover crop system (NCC). Average annual April through October cumulative observed and simulated N 2 O emissions (2004-2010) were 6.7 and 6.0kgN 2 O-Nha -1 yr -1 for NCC, and 6.2 and 7.2kgNha -1 for CC. In contrast to previous research, monthly N 2 O emissions were generally greatest when N loss to leaching were greatest, mostly because relatively high rainfall occurred during the months fertilizer was applied. N 2 O emission factors of 0.032 and 0.041 were estimated for NCC and CC using the tested model, which are similar to field results in the region. A local sensitivity analysis suggests that lower soil field capacity affects RZWQM simulations, which includes increased drain flow nitrate concentrations, increased N mineralization, and reduced soil water content. The results suggest that 1) RZWQM is a promising tool to estimate N 2 O emissions from subsurface drained corn-soybean rotations and to estimate the relative effects of a winter rye cover crop over a nine year period on nitrate loss to drain flow and 2) soil field capacity is an important parameter to model N mineralization and N loss to drain flow., (Published by Elsevier B.V.)