Joosse, P. J. and Baker, D. B. 2011. Context for re-evaluating agricultural source phosphorus loadings to the Great Lakes. Can. J. Soil Sci. 91: 317-327. Over the past decade, scientists have been discussing the re-emergence of harmful algal blooms and excessive growth of Cladophora in some areas of the Great Lakes. An observation that has emerged from these discussions is that management of non-point or diffuse sources of phosphorus will be more important in the future in order to address symptoms of eutrophication in the nearshore. This paper provides context for this renewed focus on managing non-point source tributary loads and is based primarily on materials and discussions from the Great Lakes P Forum. There are changes that have occurred in the lakes and tributaries in the past 15 yr that indicate a greater need to focus on non-point sources, whether urban or rural. Changes have also occurred in land management to reduce non-point P losses from agriculture. While these changes have reduced sediment and particulate P loading in some Ohio tributaries, the more bioavailable, dissolved P forms have increased. As there is incomplete knowledge about the mechanisms that are influencing algal growth, it could be a challenge to demonstrate, in the near term, improvements in water quality with further P reductions from agriculture alone. Regardless, there appears to be a desire for improved accountability and transparency for agricultural non-point source P management.

Kleinman, P. J. A., Sharpley, A. N., Budda, A. R., McDowell, R. W. and Allen, A. L. 2011. Soil controls of phosphorus in runoff: Management barriers and opportunities. Can. J. Soil Sci. 91: 329-338. The persistent problem of eutrophication, the biological enrichment of surface waters, has produced a vast literature on soil phosphorus (P) effects on runoff water quality. This paper considers the mechanisms controlling soil P transfers from agricultural soils to runoff waters, and the management of these transfers. Historical emphases on soil conservation and control of sediment delivery to surface waters have demonstrated that comprehensive strategies to mitigate sediment-bound P transfer can produce long-term water quality improvements at a watershed scale. Less responsive are dissolved P releases from soils that have historically received P applications in excess of crop requirements. While halting further P applications to such soils may prevent dissolved P losses from growing, the desorption of P from soils that is derived from historical inputs, termed here as “legacy P”, can persist for long periods of time. Articulating the role of legacy P in delaying the response of watersheds to remedial programs requires more work, delivering the difficult message that yesterday's sinks of P may be today's sources. Even legacy sources of P that occur in low concentration relative to agronomic requirement can support significant loads of P in runoff under the right hydrologic conditions. Strategies that take advantage of the capacity of soils to buffer dissolved P losses, such as periodic tillage to diminish severe vertical stratification of P in no-till soils, offer short-term solutions to mitigating P losses. In some cases, more aggressive strategies are required to mitigate both short-term and legacy P losses.

Wang, Y. T., Zhang, T. Q., Hu, Q. C., O'Halloran, I. P., Tan, C. S. and Reid, K. 2011. Temporal patterns of soil phosphorus release to runoff during a rainfall event as influenced by soil properties and its effects on estimating soil P losses. Can. J. Soil Sci. 91: 339-347. The phosphorus (P) released in soil runoff during a rainfall event varies as labile P is depleted, and the dynamic pattern can be a function of soil P content and other soil properties. This study was conducted to determine the temporal pattern of runoff dissolved reactive P (DRP) concentration during a simulated rainfall event and the controlling soil properties. Soil samples were collected from six soil types across the province of Ontario, with 10 sites for each, to provide a wide range of soil test P (STP) levels. The instantaneous DRP concentration in surface runoff created during the rainfall event could be predicted by time t (min, since the onset of surface runoff) through a power function: DRP=at^-ß, where a and ß are constants representing initial potential of soil P release to runoff as DRP at the onset of surface runoff and DRP decrease rate with time, respectively. The values of a and ß for a given soil could be determined by DPS_M3-2 (Mehlich-3 P/Mehlich-3 Al) using the following formulas:

The description of the temporal pattern of runoff DRP concentration during a rainfall event with the constants estimated using DPS_M3-2 can aid in the prediction of soil runoff DRP loss.

Tan, C. S. and Zhang, T. Q. 2011. Surface runoff and sub-surface drainage phosphorus losses under regular free drainage and controlled drainage with sub-irrigation systems in Southern Ontario. Can. J. Soil Sci. 91: 349-359. Soil phosphorus (P) loss and its partition in various pathways may differ depending on water management practices. A study was conducted using large field plots equipped with automatic flow volume measurement and sampling systems over a 5-yr period to determine the effectiveness of regular free drainage (RFD) and controlled drainage with sub-irrigation (CDS) for mitigating soil P losses of various forms [dissolved reactive P (DRP), dissolved un-reactive P (DURP), and particulate P (PP)] and to identify the relative roles of surface runoff and sub-surface tile drainage in soil P loss. For RFD, flow weighted-means (FWM) of DRP, DURP, PP and the total P (TP) concentrations over the 5-yr period were averaged at 0.057, 0.057, 0.627, and 0.741mg P L^-1 in surface runoff water and at 0.034, 0.053, 0.393, and 0.480 mg P L^-1 in tile drainage water, respectively. CDS increased FWM of DRP, DURP and the TP concentrations in surface runoff water and DRP concentration in tile drainage, but decreased the FWM of DURP, PP and the TP concentrations in tile drainage water. The CDS produced similar annual total dissolved P (TDP) loss, the sum of DRP and DURP, but reduced losses of PP by 15% and of TP by 12%, relative to RFD. The PP loss accounted for over 80% of TP loss for both CDS and RFD. Of the total soil P loss, from 3 to 5% was accounted for in surface runoff water, while from 95 to 97% was accounted for in tile drainage water, for RFD. For CDS, from 29 to 35% of the total soil P loss was in surface runoff water, while 65 to 71% was in tile drainage water. Subsurface tile drainage played a predominant role in soil P loss. CDS can be considered a beneficial management practice to reduce soil P loss under the similar climate and relatively flat field conditions in Southern Ontario.

Allaire, S. E., van Bochove, E., Denault, J.-T., Dadfar, H., Thériault, G., Charles, A. and De Jong, R. 2011. Preferential pathways of phosphorus movement from agricultural land to water bodies in the Canadian Great Lakes basin: A predictive tool. Can. J. Soil Sci. 91: 361-374. Preferential flow processes, such as crack flow (CF), burrow flow (BF), finger flow (FF) and lateral flow (LF) are known as factors enhancing phosphorus (P) transport from agricultural soils to water bodies. The objective of this study was to develop a methodology for predicting the likelihood of preferential flow processes in agricultural soils at the landscape scale and their potential occurrence around the Canadian Great Lakes. The methodology considered climate, soil and crop parameters and a water budget that calculated surface runoff and drainage. Crack flow largely depended upon soil clay content, BF on soil texture and climate, FF on layering in sandy soils and LF on the presence of trees, slope and soil restricting layers. Crack flow had a high likelihood to occur southern Lake Ontario and all around Lake Erie. A high likelihood of FF could be found in the area where CF was low (i.e., in the sandy soils north of Lake Huron and Lake Ontario). Burrow flow had a medium likelihood to occur on Manitoulin Island and close to the shoreline north of Lake Ontario. Medium to high likelihood of lateral flow might occur in the area south of Lake Ontario, west of Toronto in a narrow band towards Lake Huron, and to a lesser extend in a large area northeast of Lake Huron. Lateral flow may transport soluble P in areas where P was previously carried downward by FF from inland (in soils) to surface water bodies. In several areas, tile drainage may transport all forms of P carried downward from the soil surface to the subsurface by CF and BF to lake tributaries. Preferential flow distribution maps could be used as tools for supporting the identification of agricultural lands where management might enhance subsurface processes of P transport toward groundwater or surface water bodies.

Kumaragamage, D., Flaten, D., Akinremi, O. O., Sawka, C. and Zvomuya, F. 2011. Soil test phosphorus changes and phosphorus runoff losses in incubated soils treated with livestock manures and synthetic fertilizer. Can. J. Soil Sci. 91: 375-384. Source of phosphorus (P) and soil properties influence changes in soil test P (STP) concentrations and P runoff losses in manured and fertilized soils. We compared STP changes and P runoff losses in two soils, a clay loam and a sand, that were either unamended (control), or amended with liquid swine manure (LSM), solid cattle manure (SCM), or monoammonium phosphate (MAP) and incubated for 6 wk. Soil subsamples after incubation were analyzed for STP using Olsen (OP), Modified Kelowna (KP), Mehlich 3 (M3P) and water extraction (WEP) methods. We collected runoff from incubated soils for 60 min under a rainfall simulator, and analyzed for dissolved reactive P (DRP). Magnitude of STP increase in amended soils was greater in sand (19-48%) than in clay loam (7-37%). Increases in STP and DRP runoff concentrations in amended soils generally followed the order; MAP>LSM>SCM. Olsen P, KP and M3P were more accurate than WEP for predicting runoff DRP concentrations and loads, accounting for 43-49% of the variation in P concentrations for the first 30 min of runoff. Olsen P, the currently used STP method for environmental P regulation in Manitoba is sufficiently robust to predict runoff P losses from manure and fertilizer amended soils.

Nellesen, S. L., Kovar, J. L., Haan, M. M. and Russell, J. R. 2011. Grazing management effects on stream bank erosion and phosphorus delivery to a pasture stream. Can. J. Soil Sci. 91: 385-395. Pasture lands may deliver significant sediment and phosphorus (P) to surface waters. To determine the effects of beef cattle (Bostaurus) grazing practices on stream bank erosion and P losses, three treatments [rotational stocking (RS), continuous stocking with restricted stream access (CSR), and continuous stocking with unrestricted stream access (CSU)] were established in six adjacent pastures along Willow Creek in central Iowa, USA. Erosion pins were used to record bank erosion and deposition monthly from May to November of 2005-2007. Soil samples were collected by horizon to estimate P losses. Net bank erosion/deposition and pin activity, calculated as an indicator of bank stability, differed among years and measurement periods within a given year more than among grazing management treatments. Trend analysis of the 3 yr of monthly erosion/deposition data revealed two RS pastures with decreasing bank erosion, suggesting some response to this grazing practice. Mean 3-yr P losses were lower in CSR pastures (5.0 g m^-1 stream) than in RS (9.1 g m^-1 stream) and CSU (12.2 g m^-1 stream) pastures. Both sediment and P losses tended to occur during the winter and early part of the grazing season. In general, our results suggested that at this site bank erosion and P losses to the stream were controlled primarily by natural processes, rather than grazing management.

Giles, C. D., Cade-Menun, B. J. and Hill, J. E. 2011. The inositol phosphates in soils and manures: Abundance, cycling, and measurement. Can. J. Soil Sci. 91: 397-416. This review focuses on recent advances in understanding the origins, abiotic and biotic cycling, and measurement of inositol phosphates (IP_x) in manures and soils. With up to eight orthophosphates bound to inositol via ester linkages, this class of compounds has the potential to be unavailable to enzymatic hydrolysis when sorbed or in complex with soil metals, limiting the release of phosphorus (P) for uptake by plants. However, hydrolysis of IP_x by microbial phytases in aquatic environments could result in a potent source of the eutrophication agent orthophosphate. This review discusses the forms and stereoisomers of IP_x that have been identified in environmental samples. Next, it discusses the various techniques used to identify IP_x, including extraction and concentration, separation techniques such as electrophoresis, spectroscopic methods such as phosphorus-31 nuclear magnetic resonance spectroscopy (³¹P-NMR), mass spectrometry and X-ray absorption near-edge structure (XANES), and enzymatic techniques, such as enzyme hydrolysis (EH). Recent advances in knowledge about abiotic and biotic factors controlling the cycling of IP_x in soil, manure and water are summarised, including soil characteristics affecting IP_x sorption, transportation processes, and the microbial production and degradation of IP_x. Finally, areas for future research focus are discussed.

Liu, K., Zhang, T. Q. and Tan, C. S. 2011. Processing tomato phosphorus utilization and post-harvest soil profile phosphorus as affected by phosphorus and potassium additions and drip irrigation. Can. J. Soil Sci. Sci. 91: 417-425. Phosphorus (P) applied in agricultural land not only affects crop P utilization, but can also cause environmental concerns when excessive P applied moves off-site to surrounding water systems. A 2-yr study, 2007-2008, was conducted to determine the effects of fertilizer P (four rates: 0, 30, 60, and 90 kg P ha^-1) and potassium (K) (four rates: 0, 200, 400, and 600 kg K ha^-1) additions and drip irrigation on crop P utilization and post-harvest agronomic (i.e., Olsen P) and environmental [i.e., water extractable P (WEP)] soil test P under processing tomato in loamy sand soils. Plant P uptake increased, but apparent P recovery decreased with increases in fertilizer P rate. Cumulative soil WEP in the 0- to 100-cm soil profile and Olsen P in the 0- to 20-cm depth increased linearly with increases in fertilizer P rate, regardless of water management. No effects of K were found on plant P utilization, soil WEP, or soil Olsen P. Drip irrigation increased plant P uptake by 35% and apparent P recovery by 44%, relative to non-irrigation. Drip irrigation consequently decreased the post-harvest soil profile WEP by 14% and Olsen P by 6.5% averaged across the 2 yr, compared with non-irrigation. Drip irrigation reduced the potential for post-harvest soil P losses by improving P utilization. the addition of fertilizer P needs to be optimized by considering crop P needs in association with actual yield production to ensure processing tomatoes are produced in an environmentally sustainable manner.

Armstrong, S. D., Smith, D. R., Owens, P. R., Joern, B. C., Leytem, A. B., Huang, C.H. and Adeola, L. 2011. Phosphorus and nitrogen loading depth in fluvial sediments following manure spill simulations. Can. J. Soil Sci. 91: 427-436. The depth of nitrogen (N) and phosphorus (P) loading in fluvial sediments following a manure spill has not been documented. Thus, the objectives of this study were: (i) to determine the depth of N and P enrichment as a result of a manure spill under base flow conditions using fluvarium techniques and (ii) to evaluate the impact of sediment particle size distribution on N and P enrichment depth. Manure spills were simulated using stream simulators and ditch sediments collected from agricultural drainage ditches. During the manure spill simulation, the P sorption capacity of all sediments exponentially decreased with time and the NH₄-N sorption capacity remained constant with time. The P and NH₄-N loading in all sediments were observed to the depth of 2 cm, but were most concentrated in the 0- to 1-cm depth ranging in concentrations from 3 to 12 mg P kg^-1 and from 7.2 to 45 mg NH₄-N kg^-1. Data from this study give a basis for the advancement of manure spill remediation that will reduce the impairment of surface waters via the release of nutrients from enriched sediments following a manure spill.

Bruulsema, T. W., Mullen, R. W., O'Halloran, I. P. and Warncke, D. D. 2011. Agricultural phosphorus balance trends in Ontario, Michigan and Ohio. Can. J. Soil Sci. 91: 437-442. Agriculture is one of the sources of phosphorus (P) that feeds into Lake Erie, impacting water quality. A substantial proportion of the agriculture in Ontario, Michigan and Ohio falls in the Lake Erie drainage basin. We examine trends in the balance of the major inputs and outputs of P to the soils of this region. Only a few decades ago, recommended rates of P application for optimum crop nutrition amounted to considerably more P than crops removed. In recent years, actual P applications have come much closer to balancing removals, while crop yields have increased. This trend has positive implications for both crop productivity and water quality. The P balance serves as an appropriate performance indicator for P management reflecting both economic and environmental aspects of sustainability. Depending on assumptions regarding the recoverability of manure and the current implementation of reduced-P feeding strategies in the livestock industry, estimates of the P balance for the region in 2008 range from a surplus equivalent to 1% of crop removal to a deficit amounting to 23% of the amount of P removed by crops.

van Bochove, E., Denault, J.-T., Leclerc, M.-L., Thériault, G., Dechmi, F., Allaire, S. E., Rousseau, A. N. and Drury, C. F. 2011. Temporal trends of risk of water contamination by phosphorus from agricultural land in the Great Lakes Watersheds of Canada. Can. J. Soil Sci. 91: 443-453. The indicator of risk of water contamination by phosphorus (IROWC_P) was designed to estimate the level of risk of P contamination in water and how the level of risk has changed over 25 yr (1981-2006) in agricultural watersheds of Canada. IROWC_P allows for a qualitative assessment of this risk in comparison with other regions of eastern and western Canada, and the identification of high to very high risk watersheds may require on-site assessment and the development of remedial action plans. This study presents an in-depth analysis of IROWC_P results in the major Great Lakes watersheds of Canada. The risk of water contamination by P remains acceptable (very low to moderate) in most Great Lakes watersheds, but better management practices (e.g., reduced fertilization and manure application rates) and improved control of surface runoff may be required in watersheds which are at increased risk. The Canadian watersheds of the Great Lakes basin showed a 39% reduction in their P applications in excess of crop requirements between 1981 and 2006 bringing the Ontario provincial P balance close to equilibrium in 2006. Vulnerable areas were found south of Kitchener in the Lower Grand River watershed and east of Lake Simcoe.

Reid, D. K. 2011. A modified Ontario P index as a tool for on-farm phosphorus management. Can. J. Soil Sci. 91: 455-466. The phosphorus index (P index) concept has gained wide acceptance as a tool to aid users in reducing P losses to surface water, but there is a wide range of potential users with differing goals on what the P index could or should do. To effectively change the behaviour of farmers who are applying fertilizer or manure to their fields requires a change in focus of the P index. This paper proposes a modified P Index that assesses the inherent risk of P loss to surface water from a given area separately from the risk of P loss from applied materials, to make it easier for farmers to use the output from the P index for management decisions. It also incorporates changes in index calculations to incorporate the risk of P losses through tile drains as well as overland flow, to reflect the differences in transport of dissolved versus particulate P, and to match the weightings of the P index factors to the relative risk of P loss from the landscape under Ontario conditions.

Ketterings, Q. M., Czymmek, K. J. and Swink, S. N. 2011. Evaluation methods for a combined research and extension program used to address starter phosphorus fertilizer use for corn in New York. Can. J. Soil Sci. 91: 467-477. Since there is no substitute for phosphorus (P), judicious use of P fertilizer is needed to protect water quality, world P reserves and farm economics. In 2001-2003, 78 on-farm corn (Zea mays L.) P trials were conducted on New York State (NY) dairy farms as part of a statewide, integrated (research and extension), outcome-focused project. The data showed fertilizer P could be eliminated or reduced to less than 28 kg P₂O₅ ha^-1 for fields very high or high in soil test P, respectively. We conducted: (1) case study P fertilizer management evaluations using 30 NY, and (2) a producer survey using a postcard evaluation tool, to determine project outcome potential and farmer intent to change P management. The two impact evaluations showed (1) P use could be reduced to 17 kg of P₂O₅ ha^-1 or less with soil-test based decision making, and (2) 81% of producers were likely to change P use in future years. Statewide P fertilizer sales decreased from 12 603 Mg (8.6 kg ha^-1) in 2000 to 10 092 tons (6.8 kg ha^-1) in 2007, a 20% reduction in P use. These results reflect the effectiveness of the impact evaluation tools and of outcome-based projects where extension and research are integrated and farmers and farm advisors are key participants in the design and implementation of the project.

Jokela, W. E and Casler, M. D. 2011. Transport of phosphorus and nitrogen in surface runoff in a corn silage system: Paired watershed methodology and calibration period results. Can. J. Soil Sci. 91: 479-491. Transport of P, N, and sediment via runoff from crop fields, especially where manure has been applied, can contribute to eutrophication and degradation of surface waters. We established a paired-watershed field site to evaluate surface runoff losses of nutrients and sediment from different manure/crop/tillage management systems for silage corn production. During the 2-yr calibration period the four 1.6-ha watersheds, or fields, were treated identically with fall dairy manure application and chisel plowing, and runoff was monitored, sampled, and analyzed for suspended sediment (SS) and total and dissolved forms of P and N. That management was maintained as a control in one watershed, while alternative management systems were initiated on the three treatment fields. During the calibration period both concentrations and loads of SS and total and dissolved P and N varied by field and over 50% of runoff and dissolved P and N was from snowmelt runoff. Linear regressions of treatment fields against the control field were highly significant for runoff and concentrations and loads of all constituents. The estimated minimum detectable change (difference between means) was 10 to 30% for most parameters, suggesting a reasonable probability of success in detecting change in the treatment period.