Dissolved Reactive Phosphorus Losses Research Articles

Release of phosphorus and metal(loid)s from manured soils to floodwater during a laboratory simulation of snowmelt flooding.

Phosphorus (P) and metal accumulation in manured agricultural soils and subsequent losses to waterways have been extensively studied; however, the magnitudes and the factors governing their losses during spring snowmelt flooding are less known. We examined the P and metal release from long-term manured soil to floodwater under simulated snowmelt flooding with recent manure additions. Intact soil columns collected from field plots located in Randolph, Southern Manitoba, 2 weeks after liquid swine manure treatments (surface-applied, injected, or control with no recent manure addition) were flooded and incubated for 8 weeks at 4± 1°C to simulate snowmelt conditions. Floodwater (syringe filtered through 0.45µm) and soil porewater (extracted using Rhizon-Mom samplers) samples were periodically extracted and analyzed for dissolved reactive phosphorus (DRP), pH, zinc (Zn), manganese (Mn), iron (Fe), magnesium (Mg), calcium (Ca), and arsenic (As). Mean floodwater DRP concentrations (mg L-1) for manure injected (2.0±0.26), surface-applied (2.6±0.26), and control (2.2±0.26) treatments did not differ significantly. Despite manure application, DRP loss to floodwater did not significantly increase compared to the control, possibly due to the elevated residual soil P at this site from the long-term manure use. At the end of simulated flooding, the DRP concentrations increased by 1.5-fold and 5-fold in porewater and floodwater, respectively. Metal(loid) concentrations were not affected by manure treatments in general, except for Zn and Mg on certain days. Unlike DRP, where porewater and floodwater concentrations increased with time, metalloid concentration in porewater and floodwater did not show consistent trends with flooding time.

Twenty years of catchment monitoring highlights the predominant role of long-term phosphorus balances and soil phosphorus status in affecting phosphorus loss in livestock-intensive regions

Livestock husbandry has raised enormous environmental concerns around the world, including water quality issues. Yet there is a need to document long-term water quality trends in livestock-intensive regions and reveal the drivers for the trends based on detailed catchment monitoring. Here, we assessed the concentration and load trends of dissolved reactive phosphorus (DRP) in streamwater of a livestock-intensive catchment in southwestern Norway, based on continuous flow measurements and flow-proportional composite water sampling. Precipitation and catchment-level soil P balance were monitored to examine the drivers. At the field level, moreover, the relationship between soil P balance and soil test P (measured using the ammonium lactate extraction method, P-AL) was assessed. Results showed that on average of 20 years 95 % of the P was applied to the catchment during March–August, when 40 % of annual precipitation and 25 % of annual discharge occurred. The low runoff helped reduce P loss following P applications. However, flow-weighted annual mean DRP concentration significantly increased with increasingly cumulative soil P surplus (R2 = 0.55, p = 0.0002). With a mean annual P surplus of 8.8 kg ha−1, the annual mean DRP concentration (range: 49–140 μg L−1; mean: 80 μg L−1) and annual DRP load (range: 0.35–1.46 kg ha−1; mean: 0.65 kg ha−1) significantly increased over the 20-year monitoring period (p = 0.001 and 0.0003, respectively). At the field level, P-AL concentrations were positively correlated with soil P balances (R2 = 0.48, p < 0.0001), confirming the long-term impact of P balances on the risks of P loss. The study highlights the predominant role of long-term P balances in affecting DRP loss in livestock-intensive regions through the effect on soil test P.

Resolving new and old phosphorus source contributions to subsurface tile drainage with weighted regressions on discharge and season.

Agricultural losses of dissolved reactive phosphorus (DRP) emanate from both historic P applications (i.e., "old P") and recently applied fertilizer (i.e., "new P"). Understanding the relative contributions of these sources is important for mitigating DRP losses from agriculture. This study provides a proof-of-concept for resolving new P vs. old P source contributions to DRP losses in subsurface tile drainage using edge-of-field water quality data and management records from eight fields in Ohio. Weighted regressions on discharge and season (WRDS) were fitted using data from periods without P fertilizer applications and then used to predict DRP losses in tile drainage during new P loss risk periods (default length, 90 d) after fertilizer applications. Differences between observed and predicted DRP concentrations during the new P loss risk period were attributed to the new P source. Remaining losses were attributed to the old soil P source. The WRDS model performance was modest (modified Kling-Gupta efficiency ranged from -0.074 to 0.484). New P sources contributed between 0 and 17% of overall DRP losses (average, 7%), with old soil P contributing 83-100%. Individual P fertilizer applications were associated with new DRP losses up to 192g P ha-1 . Increasing the length of the risk period for new P losses up to 180 d after fertilizer application marginally increased the estimated contribution of the new P source. The WRDS-based analysis provides a novel approach for resolving the contributions of new and old sources to edge-of-field DRP losses.

Phosphorus and iron-oxide transport from a hydrologically isolated grassland hillslope

Dissolved reactive phosphorus (DRP) loss from agricultural soils can negatively affect water quality. Shallow subsurface pathways can dominate P losses in grassland soils, especially in wetter months when waterlogging is common. This study investigated the processes controlling intra- and inter-event and seasonal DRP losses from poorly drained permanent grassland hillslope plots. Temporal flow related water samples were taken from surface runoff and subsurface (in-field pipe) discharge, analysed, and related to the likelihood of anaerobic conditions and redoximorphic species including nitrate (NO3−) over time. Subsurface drainage accounted for 89% of total losses. Simple linear regression and correlation matrices showed positive relationships between DRP and iron and soil moisture deficit; and negative relationships between these three factors and NO3− concentrations in drainage. These data indicate that waterlogging and low NO3− concentrations control the release of P in drainage, potentially via reductive dissolution. The relationship between DRP and metal release was less obvious in surface runoff, as nutrients gathered from P-rich topsoil camoflaged redox reactions. The data suggest a threshold in NO3− concentrations that could exacerbate P losses, even in low P soils. Knowledge of how nutrients interact with soil drainage throughout the year can be used to better time soil N and P inputs via, for example, fertiliser or grazing to avoid to excessive P loss that could harm water quality.

Modeling tillage and manure application on soil phosphorous loss under climate change

Phosphorus (P) losses from non-point sources into receiving water bodies play a significant role in eutrophication. Given their failure to adequately control eutrophication in the Lake Erie, conservation recommendations for agricultural watersheds should be reconsidered, particularly under climate change. Using the Environmental Policy Integrated Climate model, the potential impacts on crop yield, surface runoff, tile drainage, and relevant dissolved reactive phosphorus (DRP) losses from manure-amended corn-soybean rotation plots in the Lake Erie basin were estimated for six tillage methods with different mixing efficiencies and manure broadcast application. These were investigated under twelve different regional and global future climate simulations. Tillage alone proved to have only a minor impact on mean corn yield (± 2%). Climate change led to large uncertainties under the single tillage treatment. As a result of the combined effects of biogeochemical processes (e.g., supply) and hydrological (e.g., transport), strong negative relationships (R2 = 0.98) were found between tillage mixing efficiency and DRP loss in surface runoff, tile drainage, and total DRP loss. The impacts of combined manure application (broadcast) and tillage on crop yield and flow volume were similar as those of tillage alone. With respect to total DRP losses, the effects of labile P content change outweighed those of surface runoff or tile drainage change (hydrologic). This resulted in a change in total DRP losses ranging from − 60% to + 151%, with being closely correlated with decreasing tillage mixing efficiency (R2 = 0.94) from moldboard to no-till. Therefore, rotational tillage should be considered for DRP loss reduction and energy saving.

Dynamics of dissolved reactive phosphorus loss from phosphorus source and sink soils in tile-drained systems

Understanding the processes controlling dissolved reactive phosphorus (DRP) loss in tile-drained systems is essential to better define critical source areas and inform nutrient and conservation practice recommendations. Concentration-discharge (C-Q) relationships have been used to infer solute sources, reactivity, proximity, and transport mechanisms governing solute fluxes. In this study, we compare DRP loads and flow-weighted mean DRP (FDRP) concentrations from P source and sink soils at an annual and event scale, and use power law analysis coupled with index-based approaches in order to identify the predominant DRP C-Q behavior in these soils at a daily and event scale. Results indicate that, in general, P source soils consistently lost higher DRP loads and exhibited greater FDRP concentrations when compared to P sink soils when examined at both annual and event scales. At the daily scale, C-Q patterns were linked to the soil P status whereby a chemostatic (<i>b</i> = 1) and dilution (<i>b</i> &lt; 1) behavior was observed for P source and P sink soils, respectively. At the event scale, C-Q patterns were linked to soil P status with a potential contributing influence of flow path connectivity and mixing of event water with matrix and shallow groundwater. Events in P source soils had variable hysteretic behavior with 21%, 7%, 6%, 9%, and 15% exhibiting anticlockwise with dilution, anticlockwise with flushing, clockwise with dilution, clockwise with flushing, and no hysteresis behavior, respectively. These variable C-Q responses suggest that, in addition to discharge and soil P status, rapid exchanges between P pools, the magnitude of discharge events (Q), and the relative number of days to discharge peak (RL) also regulated solute delivery. On the other hand, the predominant nonhysteretic C-Q behavior of events in P sink soils (67%) suggests that DRP loss from these soils can be discounted. These findings highlight the need for nutrient and conservation practices addressing P draw down, P sequestration, and P supply according to crop need, which will likely be required to convert P sources to sinks and to avoid the conversion of P sinks to P sources.

Modeling impacts of climate change on crop yield and phosphorus loss in a subsurface drained field of Lake Erie region, Canada

CONTEXTClimate change is predicted to impose great pressures on crop yield and water quantity and quality. However, the connections among agriculture, climate condition, and water quality are supported by scant studies because of different scales of focus. OBJECTIVEThe present study aimed on the interactions of crop yield, climate change, and water quality at field scale. METHODSUsing the Environmental Policy Integrated Climate (EPIC) model, and drawing on 12 dynamically downscaled regional climate model (RCM) simulations, the impacts of climate change on crop yield, surface runoff, subsurface drainage, and dissolved reactive phosphorus (DRP) losses were determined for a field in the Lake Erie basin under a corn-soybean rotation receiving solid cattle manure fertilization. The combined and individual impacts of different weather variables were evaluated with each of the 12 simulations. RESULTS AND CONCLUSIONSThe mean cross-model climate change impacts included 16% and 14% increases in corn and soybean yield, respectively, as well as 4% rise and 22% decline in runoff and subsurface drainage DRP, respectively, resulting in an overall 11% decline in total DRP losses. An increase of temperature alone increased crop yields (12% for corn and 8% for soybean, respectively) as it decreased temperature stress resulted from delayed planting, which also decreased total DRP loss by 19%. Regardless of having a negligible impact on yield due to negligible water stress, increased precipitation increased total DRP loss by 15%. SIGNIFICANCEThe research site could benefit from climate change in terms of both economic return and environmental quality, notwithstanding, greater attention should be paid to management practices with respect to soil DRP loss in surface runoff due to projected precipitation uncertainty.

Implications of water quality policy on land use: a case study of the approach in New Zealand

Achieving good water quality through output controls is difficult. The New Zealand Government recently proposed enforceable bottom lines to protect ecosystem health of 1mgL–1 dissolved inorganic nitrogen (DIN) and 0.018mgL–1 dissolved reactive phosphorus (DRP), but has now delayed considering them. In examining whether these bottom lines could be met through mitigating DIN and DRP losses from existing land uses, we found that if all known strategies to mitigate N and P loss were implemented by 2035, the proportion of catchments exceeding these bottom lines would be predicted to be 4% for DIN and 9% for DRP. If bottom lines were enforced, land use would likely change, but to change successfully good advice and effective multilevel governance are required. Advice should expand and standardise elements of farm environment plans that spatially isolate critical source areas of N and P loss and apply cost-effective mitigations. Governance should focus on combining these plans with the national bottom lines and technical support to connect practices and land use at the farm scale to meeting water quality bottom line at the catchment scale.

Impact factors and mechanisms of dissolved reactive phosphorus (DRP) losses from agricultural fields: A review and synthesis study in the Lake Erie basin

Dissolved Reactive Phosphorus (DRP) losses from agricultural fields promote algae growth in water bodies, and may increase the risk of Harmful Algal Blooms (HABs). Using existing data from the Lake Erie Basin, we applied multiple regression analysis to better understand the impacts of both site-specific conditions (e.g., soil types/properties) and management practices (e.g., Agricultural Conservation Practices [ACP]) on annual DRP losses in subsurface and surface runoff. Results showed that soil properties significantly impact DRP losses. Greater DRP losses were associated with increased soil pH and Soil Test Phosphorus (STP). By contrast, soil organic matter (SOM) was inversely correlated with DRP losses. Soil clay content was also inversely correlated with DRP subsurface losses, but had no impact on DRP surface losses. The ACPs evaluated had varied effectiveness on DRP loss reduction. Cropping systems involving soybean could reduce DRP subsurface losses, whereas winter cover crops could cause unintended DRP subsurface losses. Cropping systems involving soybean and cover crops, however, had no impact on DRP surface losses. In addition, no-till and conservation tillage also enhanced DRP losses compared to conventional tillage, particularly for soils with high SOM and/or high clay content.Precipitation amount and fertilizer application rate significantly increased DRP surface losses as expected. Fertilizer application rate, however, had no impact on DRP subsurface losses. The impact of precipitation amount on DRP subsurface losses depends on STP levels. Precipitation amount significantly increases DRP subsurface losses when STP is higher (>41 mg kg−1 in this analysis). The optimal STP level for crop growth is 30 to 50 mg kg−1.Results from this study help us to better understand DRP losses and the effectiveness of ACPs for controlling them. We suggest taking soil surveys and soil tests into consideration when designing and/or implementing ACPs to manage DRP losses. Furthermore, the method we used for this study could be applied to other agricultural regions to investigate impacts of site-specific conditions and management practices on water quality.

A SWAT-based optimization tool for obtaining cost-effective strategies for agricultural conservation practice implementation at watershed scales.

To address the harmful algal blooms problem in Lake Erie, one solution is to determine the most cost-effective strategies for implementing agricultural best management practices (BMPs) in the Maumee River watershed. An optimization tool, which combines multi-objective optimization algorithms, SWAT (Soil and Water Assessment Tool), and a computational efficient framework, was created to optimally identify agricultural BMPs at watershed scales. The optimization tool was demonstrated in the Matson Ditch watershed, an agricultural watershed in the Maumee River basin considering critical areas (25% of the watershed with the greatest pollutant loadings per area) and the entire watershed. The initial implementation of BMPs with low expenditures greatly reduced pollutant loadings; beyond certain levels of pollutant reductions, additional expenditures resulted in less significant reductions in pollutant loadings. Compared to optimization for the entire watershed, optimization in critical areas can greatly reduce computational time and obtain similar optimization results for initial reductions in pollutant loadings, which were 10% for Dissolved Reactive Phosphorus (DRP) and 38% for Total Phosphorus (TP); however, for greater reductions in pollutant loadings, critical area optimization was less cost-effective. With the target of simultaneously reducing March-July DRP/TP losses by 40%, the optimized scenario that reduced DRP losses by 40% was found to reduce 51.1% of TP; however, the optimized scenario that reduced TP losses by 40% can only decrease 11.3% of DRP. The optimization tool can help stakeholders identify optimal types, quantities, and spatial locations of BMPs that can maximize reductions in pollutant loadings with the lowest BMP costs.

Modeling and Mitigating Phosphorus Losses from a Tile-Drained and Manured Field Using RZWQM2-P.

Prediction of P losses from manured agricultural fields through surface runoff and tile drainage is necessary to mitigate widespread eutrophication in water bodies. However, present water quality models are weak in predicting P losses, particularly in tile-drained and manure-applied cropland. We developed a field-scale P management model, the Root Zone Water Quality Model version 2-Phosphorus (RZWQM2-P), whose accuracy in simulating P losses from manure applied agricultural field is yet to be tested. The objectives of this study were (i) to assess the accuracy of this new model in simulating dissolved reactive phosphorus (DRP) and particulate phosphorus (PP) losses in surface runoff and tile drainage from a manure amended field, and (ii) to identify best management practices to mitigate manure P losses including water table control, manure application timing, and spreading methods by the use of model simulation. The model was evaluated against data collected from a liquid cattle manure applied field with maize ( L.)-soybean [ (L.) Merr.] rotation in Ontario, Canada. The results revealed that the RZWQM2-P model satisfactorily simulated DRP and PP losses through both surface runoff and tile drainage (Nash-Sutcliffe efficiency > 0.50, percentage bias within ±25%, and index of agreement > 0.75). Compared with conventional management practices, manure injection reduced the P losses by 18%, whereas controlled drainage and winter manure application increased P losses by 13 and 23%, respectively. The RZWQM2-P is a promising tool for P management in manured and subsurface drained agricultural field. The injection of manure rather than controlled drainage is an effective management practice to mitigate P losses from a subsurface-drained field.

Modeling phosphorus reduction strategies from the international St. Clair-Detroit River system watershed

Nutrient loading from nonpoint sources has degraded water quality in large water bodies globally. The water quality of Lake Erie, the most productive of the Laurentian Great Lakes bordering the United States and Canada, is influenced by phosphorus loads from the Detroit River that drains an almost 19,000 km2 international watershed. We used the Soil and Water Assessment Tool (SWAT) to evaluate a range of management practices to potentially reduce total phosphorus (TP) and dissolved reactive phosphorus (DRP) loads. Scenarios included both single practices and bundles of multiple practices. Single practice scenarios included fertilizer rate reduction (Rate) and sub-surface placement (PL), filter strips (FL), grassed waterways, cover crops (CC), wetlands (WT), controlled drainage, and changes in tillage practices. Bundle scenarios included combinations of Rate, PL, FL, CC, and WT with three adoption strategies: application on all applicable areas, on 55% of randomly selected applicable areas, and on 55% of high phosphorus yielding applicable areas. Results showed that among the single practice scenarios, FL, WT, PL, CC, and Rate performed well in reducing both TP and DRP loss from agricultural dominated sub-watersheds. Over all, the CC, FL, WT bundle performed best, followed by the CC, PL, WT bundle, reducing the load up to 80% and 70%, respectively, with 100% implementation. However, targeting high phosphorus yielding areas performed nearly as well as 100% implementation. Results from this work suggest that there are potential pathways for phosphorus load reduction, but extensive implementation of multiple practices is required.

Split phosphorus fertiliser applications as a strategy to reduce incidental phosphorus losses in surface runoff

Organic soils have low sorption capacities for phosphorus (P), and may pose a risk of P loss to water if P applications to these soils coincide with runoff events. Little is known about the magnitude of exports of P in overland flow following application of P fertiliser onto these soils, or on the influence of the frequency on P losses and persistence. The number of P fertiliser applications was surveyed across 39 commercial farms to assess current practice and inform the design of a rainfall runoff experiment to evaluate the effect of frequency of P applications on losses and persistence across time. Superphosphate (16% P) was applied in single (equivalent to 30 and 55 kg P ha−1 applied at day 0) and split (equivalent to 15 and 27.5 kg P ha−1 applied in two doses at days 0 and 55) applications to an organic soil inclined at a slope of 6% in a rainfall simulator experiment. The surface runoff of dissolved reactive phosphorus (DRP) was measured in controlled 30-min rainfall simulations conducted intermittently over an 85-day period. The DRP losses in surface runoff after the first rainfall event were 44.6 and 97.8 mg L−1 for single applications of 30 and 55 kg ha−1, respectively, and 13.3 and 21.8 mg L−1 for the same rates split in two doses, indicating that single P applications had disproportionately bigger impacts on losses than split applications. This supports the idea that frequent, but smaller, P applications can minimise the impact of fertilisation on waters. Dissolved reactive P concentrations remained significantly higher than those from the control samples until the end the experiment for almost all the P treatments, highlighting the long-lasting effects of added P and the elevated risk of P losses on organic soils. For climates with frequent rainfall events, which are likely to coincide with fertiliser applications, smaller but more frequent P applications can reduce the risk of P transfer as opposed to one single application.

Predicting dissolved reactive phosphorus in tile-drained catchments using a modified SWAT model

Phosphorus (P) is mainly leached by subsurface transport pathways in tile-drained landscapes. In this study, we modified the SWAT model (SWAT-P) by incorporating dissolved reactive phosphorus (DRP) losses from drainage water and the deep aquifer. SWAT-P was tested in a tile-drained lowland catchment using a multi-site calibration and validation approach. SWAT reached a good statistical performance regarding discharge for all sub-catchments and a daily time step. As discharge was dominated by subsurface flow, we optimized DRP concentrations for the drainage water (SWAT-P), the shallow aquifer (SWAT, SWAT-P), and the deep aquifer (SWAT-P) and left other P-related parameters at their default settings, since they did not influence the model output. DRP losses were simulated at a monthly time step using SWAT and SWAT-P. The predictive power was weaker compared to discharge for both SWAT and SWAT-P. Nevertheless, SWAT-P performed considerably better than SWAT. Additionally, calibrated DRP concentrations were unrealistically high for SWAT, whereas calibrated DRP concentrations reflected the prevailing conditions in the region using SWAT-P. The results indicated improved prediction accuracy for DRP losses into streams by using SWAT-P, as well as a roughly realistic estimation of DRP losses from tile drainage water. Further research is necessary to account for the temporal DRP concentration dynamics in drainage water. SWAT-P is ready to use after defining DRP concentrations in tile drainage water and the deep aquifer in the SWAT-P input files. In addition, the model output was extended in SWAT-P to visualize DRP losses from drainage water and from the deep aquifer.

Cover Crops for Managing Stream Water Quantity and Improving Stream Water Quality of Non-Tile Drained Paired Watersheds

In the Midwestern United States, cover crops are being promoted as a best management practice for managing nutrient and sediment losses from agricultural fields through surface and subsurface water movement. To date, the water quality benefits of cover crops have been inferred primarily from plot scale studies. This project is one of the first to analyze the impacts of cover crops on stream water quality at the watershed scale. The objective of this research was to evaluate nitrogen, phosphorus, and sediment loss in stream water from a no-till corn-soybean rotation planted with winter cover crops cereal rye (Secale cereale) and hairy vetch (Vicia villosa) in non-tile drained paired watersheds in Illinois, USA. The paired watersheds are under mixed land use (agriculture, forest, and pasture). The control watershed had 27 ha of row-crop agriculture, and the treatment watershed had 42 ha of row crop agriculture with cover crop treatment (CC-treatment). During a 4-year calibration period, 42 storm events were collected and Event Mean Concentrations (EMCs) for each storm event were calculated for total suspended solids (TSS), nitrate-N (NO3-N), ammonia-N (NH4-N), dissolved reactive phosphorus (DRP), and total discharge. Predictive regression equations developed from the calibration period were used for calculating TSS, NO3-N, NH4-N, and DRP losses of surface runoff for the CC-treatment watershed. The treatment period consisted of total 18 storm events, seven of which were collected during the cereal rye, eight in the hairy vetch cover crop season and three during cash crop season. Cover crops reduced TSS and discharge by 33% and 34%, respectively in the CC-treatment watershed during the treatment period. However, surprisingly, EMCs for NO3-N, NH4-N, and DRP did not decrease. Stream discharge from the paired-watersheds will continue to be monitored to determine if the current water quality results hold or new patterns emerge.

Mineral Fertilizer and Manure Effects on Leached Inorganic Nitrogen, Nitrate Isotopic Composition, Phosphorus, and Dissolved Organic Carbon under Furrow Irrigation.

A better understanding of nutrient leaching in furrow irrigated agriculture is needed to optimize fertilizer use and avoid contamination of water supplies. In this field study (2003-2006), we measured deep percolation fluxes at 1.2-m depth and associated nutrient concentrations and mass losses from dairy manure nitrogen (N) or mineral N (urea, sodium nitrate [NaNO])-amended soils (372 kg available N ha in 4 yr) and nonamended controls and determined the δN-NO and δO-NO isotope ratios in the leached nitrate. Flow-weighted concentration means for individual irrigations varied widely, from near zero to as much as 250 mg L for NO-N, 480 μg L for dissolved reactive phosphorus (DRP), 43 mg L for dissolved organic C (DOC), and 390 mg L for chloride (Cl). Relative to other treatments, mineral fertilizer increased NO-N concentrations 2.6- to 3-fold and Cl concentrations 2.6- to 3.6-fold in deep leachate, particularly when NaNO was applied in 2004 and 2006, and produced maximum mean season-long NO-N and Cl losses. Manure and control treatments produced similar leachate nutrient mass losses, and for some irrigation periods, mineral fertilizer produced 85 and 97% lesser DRP losses and two times greater Cl losses compared with manure and control treatments. Four-year cumulative losses among treatments differed only for Cl. Isotopic composition of deep-leached nitrate indicates that both transformation and biologic cycling of mineral and manure N are rapid in these soils, which, with percolation volume, influence the amounts of NO-N and DOC leached. In light of the potential negative effects associated with either fertilizer type, and because even nonamended soils produced substantial amounts of leached NO-N (69.5 kg ha yr), management must minimize percolation water losses to limit nutrient losses from these fertilized, furrow-irrigated soils.

Potential phosphorus mobilization from above-soil winter vegetation assessed from laboratory water extractions following freeze–thaw cycles

Maintaining crop residue or cover crops on fields during winter is a recommended beneficial management practice (BMP). However, losses of dissolved reactive phosphorus (DRP) to runoff have been attributed to vegetation following freeze–thaw cycles (FTC). Using a factorial design in the laboratory, this study investigated the potential influence of four FTC types at −4 to +4°C (frozen, frozen and thawed 1×, frozen and thawed 5×, frozen and thawed 5× with extraction after each thaw) and one control (never frozen) on DRP loss from the residue of Triticum aestivum (winter wheat) and from two cover crops, Trifolium pretense (red clover) and Avena sativa (oat). DRP losses were measured using three different water extraction techniques: a traditional laboratory determination of water extractable P (WEP), a modified water extraction intended to simulate a rainfall event, and a modified water extraction intended to simulate surface ponding. Both cover crops released more DRP than winter wheat residue did under all treatments, suggesting that winter wheat residues pose little risk for DRP release during the non-growing season (NGS). Of the two cover crops studied, oat was more sensitive to FTC and may therefore pose a greater risk of late autumn/winter DRP loss in comparison to red clover, which is often terminated in early fall. Water extraction technique was also found to be important, as simulated surface ponding extracted more DRP than simulated rainfall did for all three plant types. These results suggest that both cover crop species and placement in the landscape can be optimized to reduce P release from above-ground vegetation in winter. The use of cover crops in sections of fields that are prone to flooding following large events such as snowmelt should be avoided. Field studies are needed to further examine the rates and timing of potential and actual losses of DRP from above-ground vegetation in winter.

Holistic Evaluation of Field-Scale Denitrifying Bioreactors as a Basis to Improve Environmental Sustainability.

Denitrifying bioreactors convert nitrate-nitrogen (NO-N) to di-nitrogen and protect water quality. Herein, the performance of a pilot-scale bioreactor (10 m long, 5 m wide, 2 m deep) containing seven alternating cells filled with either sandy loam soil or lodgepole pine woodchip and with a novel "zig-zag" flow pattern was investigated. The influent water had an average NO-N concentration of 25 mg L. The performance of the bioreactor was evaluated in two scenarios. In Scenario 1, only NO-N removal was evaluated; in Scenario 2, NO-N removal, ammonium-N (NH-N), and dissolved reactive phosphorus (DRP) generation was considered. These data were used to generate a sustainability index (SI), which evaluated the overall performance taking these parameters into account. In Scenario 1, the bioreactor was a net reducer of contaminants, but it transformed into a net producer of contaminants in Scenario 2. Inquisition of the data using these scenarios meant that an optimum bioreactor design could be identified. This would involve reduction to two cells: a single sandy loam soil cell followed by a woodchip cell, which would remove NO-N and reduce greenhouse gas (GHG) emissions and DRP losses. An additional post-bed chamber containing media to eliminate NH-N and surface capping to reduce GHG emissions further is advised. Scenario modeling, such as that proposed in this paper, should ideally include GHG in the SI, but because different countries have different emission targets, future work should concentrate on the development of geographically appropriate weightings to facilitate the incorporation of GHG into a SI.

Effects of tillage practices on phosphorus transport in tile drain effluent under sandy loam agricultural soils in Ontario, Canada

Abstract Agricultural watersheds have been identified as a source of nutrients to surface water bodies, contributing to the degradation of water quality. Reduced till (RT) management practices have been employed to reduce the potential for particulate P loss in surface runoff, but may increase the transfer of dissolved reactive phosphorus (DRP) into tile drains. It is unclear if RT increases P losses in tile drainage when nutrient management strategies are used and fertilizers are applied in the subsurface. It is also unclear how these management strategies perform year round, including during the snowmelt period. The objectives of this study are to quantify year round losses of runoff, DRP and total phosphorus (TP) losses from drainage tiles beneath annual disk till (AT) and reduced till (RT) plots, and, to investigate the role of seasonality (particularly winter snowmelt) on runoff and P losses. Results indicate that both runoff and P-export were episodic across all plots and most annual losses occurred during a few key events under heavy precipitation or snowmelt events. Runoff and P losses through drainage tiles were primarily observed between October and May, with most losses occurring in March during snowmelt. Tillage practices did not affect DRP or TP concentrations or loads in tile drainage. This study has highlighted the importance of the non-growing season (particularly winter) in annual P loss, and has demonstrated that the cumulative Best Management Practices (BMPs) used at the study sites may be an effective way to reduce P losses in tile drain effluent.

Impact of Variable Rate Fertilization on Nutrients Losses in Surface Runofffor Wild Blueberry Fields

Abstract. Wild blueberry producers apply agrochemicals uniformly without considering substantial variation in soil properties and topographic features that may affect fruit yield within a field and pollute environment. A wild blueberry field was selected in central Nova Scotia, Canada to evaluate the impact of variable rate (VR) fertilization on nutrient losses in surface runoff, from steep slope to low lying areas, and crop productivity. The field was divided into three subfields (Field 1, Field 2, and Field 3) under three management zones (Zone 1, Z1; Zone 2, Z2; and Zone 3, Z3). The runoff plots were installed to collect surface runoff samples from different zones of the field. Three fertilizer (NPK: 16.5 – 34.5 – 4.5, respectively) rates (200,150, and 100 kg ha -1 for Z1, Z2, Z3, respectively) were applied in runoff plots of VR treatment using fertilizer spreader. Uniform fertilizer rate of 200 kg ha -1 for comparison was applied in runoff plots of uniform application (UA) treatment. No fertilizer was applied in runoff plots of control treatment. The surface runoff samples were collected after every heavy rainfall event and analyzed for total phosphorus (TP), dissolved reactive phosphorus (DRP), particulate phosphorus (PP), and inorganic nitrogen concentrations. The VR treatment significantly (p≤0.05) decreased TP, DRP, PP, and inorganic nitrogen losses in surface runoff as compared to UA. Plant growth parameters and fruit yield were also collected from runoff plots. Plants in UA treatment were taller than VR treatment in low lying areas. Numbers of buds per stem were significantly affected by fertilizer treatments. The fruit yield in VR treatment was non-significantly different than UA treatment. The VR fertilizer application used 40% less fertilizer than standard UA of fertilizer. The VR fertilization could reduce nutrients loading in surface runoff from wild blueberry fields. The runoff plots could be used to accurately determine the surface runoff from small-scale runoff plots. However, the construction of runoff plots and data collection at field scale is laborious and time consuming.