Dissolved Reactive P Losses Research Articles

Modeling phosphorus losses from soils amended with cattle manures and chemical fertilizers

While applied manure/fertilizer is an important source of P loss in surface runoff, few models simulate the direct transfer of phosphorus (P) from soil-surface-applied manure/fertilizer to surface runoff. The SurPhos model was tested with 2008–2010 growing season daily surface runoff data from clay loam experimental plots subject to different manure/fertilizer applications. Model performance was evaluated on the basis of the coefficient of determination (R2), Nash-Sutcliffe efficiency (NSE), percent bias (PBIAS), and the ratio of the root mean square error to the standard deviation of observed values (RSR). The model offered an acceptable performance in simulating soil labile P dynamics (R2 = 0.75, NSE = 0.55, PBIAS = 10.43%, and RSR = 0.67) and dissolved reactive P (DRP) loss in surface runoff (R2 ≥ 0.74 and NSE ≥ 0.69) for both solid and liquid cattle manure, as well as inorganic fertilizer. Simulated direct P loss in surface runoff from solid and liquid cattle manure accounted for 39% and 40% of total growing season DRP losses in surface runoff. To compensate for the unavailability of daily surface runoff observations under snow melt condition, the whole four years' (2008–2011) daily surface runoff predicted by EPIC (Environmental Policy Integrated Climate) was used as SurPhos input. The accuracy of simulated DRP loss in surface runoff under the different manure/fertilizer treatments was acceptable (R2 ≥ 0.55 and NSE ≥ 0.50). For the solid cattle manure treatment, of all annual DRP losses, 19% were derived directly from the manure. Beyond offering a reliable prediction of manure/fertilizer P loss in surface runoff, SurPhos quantified different sources of DRP loss and dynamic labile P in soil, allowing a better critical assessment of different P management measures' effectiveness in mitigating DRP losses.

Simulating crop yield, surface runoff, tile drainage and phosphorus loss in a clay loam soil of the Lake Erie region using EPIC

Useful in evaluating best management practices and nutrient management planning, the prediction of phosphorus (P) transfer from agricultural lands to water bodies via surface runoff and tile drainage remains as a challenge, as few models can provide reasonably accurate P loss simulations. The EPIC (Environmental Policy Integrated Climate) model was firstly applied to simulate crop yields, surface runoff, tile drainage, and dissolved reactive P (DRP) losses under a corn-soybean rotation grown on a “cracking” Brookston clay loam soil (Vertisol) in the Lake Erie basin, Ontario, Canada. Different potential evapotranspiration and curve number equations were compared to determine the most suitable equations (Penman-Monteith equation and variable Daily Curve Number with soil moisture index) for this region. A crack flow coefficient was used to deal with inflow partitioned to cracks. A soil layer below tile drain with low saturated hydraulic conductivity was employed in simulating the experimental site, where most water was leaving the field through tile drain. Lateral subsurface flow was used to substitute for drainage. Annual simulations of crop grain yield, cumulative surface runoff, and cumulative drainage closely matched observed data. Over shorter periods (months), surface runoff (NSE = 0.78), tile drainage (NSE = 0.57), and relevant DRP loss (NSE > 0.5) simulations were satisfactory, except for two periods of DRP loss in surface runoff, where most DRP moved downward through lateral flow and deep percolation due to limitations in the crack flow coefficient. For this vertic soil, EPIC generally simulated crop yields and flow volumes well, while DRP losses were only adequately simulated.

Lateral Transfer of Organic Carbon and Phosphorus by Water Erosion at Hillslope Scale in Southern Spain Olive Orchards

Core Ideas A 3‐yr hillslope study presents DOC, DOC, TP, and DRP losses from several olive orchards. Losses of DOC and TOC were higher than those measured in other agricultural systems. Losses of TP were at the high‐end range of losses measured in agricultural systems. Temporary cover crops in lanes can reduce TOC and TP losses through reduced sediment losses. Cover crops did not significantly reduce DOC and DRP in runoff compared with conventional tillage. Dissolved organic C (DOC) and dissolved reactive P (DRP) in runoff and total organic C (TOC) and total P (TP) in sediment were measured in three olive (Olea europaea L.) orchards, during a 3‐yr runoff plot experiment under two soil management systems (temporary cover crop in lanes [CC]; conventional tillage [CT]). Losses of DOC (7.8–13.6 kg ha−1 yr−1) were equivalent and losses of TOC (101–432 kg ha−1 yr−1) were higher than those measured in other agricultural systems, so both sources of organic C, dissolved and in sediment, should not be neglected when accounting fluxes to water bodies in the region and soil organic C (SOC) balances at the hillslope scale in olive orchards. Losses of DRP (0.03–0.21 kg ha−1 yr−1) were in the lower to medium range, while losses of TP (2–39 kg ha−1 yr−1) were in the higher range than those reported from agricultural areas. The average annual concentration of DOC in runoff was similar for both systems (20.9–9.1 vs. 21.4–8.7 mL L−1 for CC and CT, respectively) and also for DRP (0.45–0.02 vs. 0.20–0.02 mg L−1 for CC and CT, respectively). Concentrations of TOC and TP were higher under CC, but under CC the TOC and TP fluxes were lower because of reduced sediment losses. To achieve a large reduction in TP and TOC, CC management should provide early ground cover beginning in early fall, the start of the rainy season. A conceptual model of TOC and TP losses was developed to estimate the impact of different cover crop soil conservation strategies.

Poultry Litter Ash Reduces Phosphorus Losses during Greenhouse Production of Lantana camara L. ‘New Gold’

Phosphorus (P) fertilizers with high water-solubility are often applied in excessive amounts to porous horticultural substrates to produce high-quality plants. As a result, high P losses during containerized plant production have presented an environmental challenge to responsible growers. Poultry litter ash (PLA), a byproduct of bioenergy production, contains P concentrations comparable to conventional P fertilizers but is characterized as having lower water-solubility. Therefore, a series of experiments were conducted to characterize effects of PLA on container-plant growth and P leaching. PLA was compared with superphosphate (SP), a highly water-soluble P source, in ratios of 0:100, 25:75, 50:50, 75:25, and 100:0 (SP:PLA) in the production of Lantana camara L. ‘New Gold’. In 2011, lantana fertilized with higher ratios of PLA exhibited slower growth with lower shoot and root biomasses compared with 100% SP-fertilized lantana. However, in 2012, differences in fertilizer treatments lessened, with 100% PLA-fertilized lantana exhibiting 14% less shoot biomass and no differences in root biomass compared with 100% SP-fertilized lantana. Measurement of shoot:root biomass, a common indicator of P deficiency, was not different between any P treatments in 2011 or 2012. This indicates root growth was most likely the driving factor in P-treatment effects on shoot biomass in each year of the experiment. During a postproduction field trial, no differences in growth or biomass were observed between lantana previously fertilized with P, regardless of source. However, application of PLA as the single P source reduced dissolved reactive P (DRP) concentrations in leachate >90% and total P (TP) mass losses 69% compared with 100% SP-fertilized lantana during container production, with P treatments reducing DRP and TP losses as PLA ratios increased. Therefore, the benefit of P-loss reduction during container production achieved through PLA application may warrant the acceptance of slightly smaller plants or extending production cycles.

Linking Soil Phosphorus to Dissolved Phosphorus Losses in the Midwest

Core Ideas Soil test phosphorus remains an important factor in studying dissolved reactive P loss. Identifying higher risk fields with STP could inform future management practices to reduce DRP loss. STP was linearly related to DRP concentration loads in tile‐drained fields. Monitoring STP in addition to implementing other BMPs should be considered to decrease DRP loss. Harmful and nuisance algal blooms resulting from excess phosphorus (P) have placed agriculture in the spotlight of the water quality debate. Sixty‐eight site years of P loading data (combined surface runoff and tile flow) from 36 fields in Ohio were used to see if a soil test P (STP) concentration could be identified that allowed P application while still meeting recommended loss thresholds. Regression analysis revealed that P application to soils with STP concentration in the “critical level” range would result in P losses above the recommended Annex 4 thresholds. In addition, fertilizer application increased the risk of dissolved reactive P (DRP) loss as compared to years in which fertilizer was not applied. We determined that STP was a good screening method to identify fields that are at risk for greater P loss, but STP alone was not a good predictor of DRP loss, suggesting that a more holistic approach that includes upland management, edge‐of‐field practices, and in‐stream approaches will be required to decrease DRP loading.

Soil phosphorus loss in tile drainage water from long-term conventional- and non-tillage soils of Ontario with and without compost addition.

Recent ascertainment of tile drainage a predominant pathway of soil phosphorus (P) loss, along with the rise in concentration of soluble P in the Lake Erie, has led to a need to re-examine the impacts of agricultural practices. A three-year on-farm study was conducted to assess P loss in tile drainage water under long-term conventional- (CT) and non-tillage (NT) as influenced by yard waste leaf compost (LC) application in a Brookston clay loam soil. The effects of LC addition on soil P loss in tile drainage water varied depending on P forms and tillage systems. Under CT, dissolved reactive P (DRP) loss with LC addition over the study period was 765g P ha-1, 2.9 times higher than CT without LC application, due to both a 50% increase in tile drainage flow volume and a 165% increase in DRP concentration. Under NT, DRP loss in tile drainage water with LC addition was 1447gPha-1, 5.3 times greater than that for NT without LC application; this was solely caused by a 564% increase in DRP concentration. However, particulate P loads in tile drainage water with LC application remained unchanged, relative to non-LC application, regardless of tillage systems. Consequently, LC addition led to an increase in total P loads in tile drainage water by 57 and 69% under CT and NT, respectively. The results indicate that LC application may become an environmental concern due to increased DRP loss, particularly under NT.

Prediction of dissolved reactive phosphorus losses from small agricultural catchments: calibration and validation of a parsimonious model

Abstract. Eutrophication of surface waters due to diffuse phosphorus (P) losses continues to be a severe water quality problem worldwide, causing the loss of ecosystem functions of the respective water bodies. Phosphorus in runoff often originates from a small fraction of a catchment only. Targeting mitigation measures to these critical source areas (CSAs) is expected to be most efficient and cost-effective, but requires suitable tools. Here we investigated the capability of the parsimonious Rainfall-Runoff-Phosphorus (RRP) model to identify CSAs in grassland-dominated catchments based on readily available soil and topographic data. After simultaneous calibration on runoff data from four small hilly catchments on the Swiss Plateau, the model was validated on a different catchment in the same region without further calibration. The RRP model adequately simulated the discharge and dissolved reactive P (DRP) export from the validation catchment. Sensitivity analysis showed that the model predictions were robust with respect to the classification of soils into "poorly drained" and "well drained", based on the available soil map. Comparing spatial hydrological model predictions with field data from the validation catchment provided further evidence that the assumptions underlying the model are valid and that the model adequately accounts for the dominant P export processes in the target region. Thus, the parsimonious RRP model is a valuable tool that can be used to determine CSAs. Despite the considerable predictive uncertainty regarding the spatial extent of CSAs, the RRP can provide guidance for the implementation of mitigation measures. The model helps to identify those parts of a catchment where high DRP losses are expected or can be excluded with high confidence. Legacy P was predicted to be the dominant source for DRP losses and thus, in combination with hydrologic active areas, a high risk for water quality.

Phosphorus losses in runoff from manured grassland of different soil P status at two rainfall intensities

In many areas, excessive manure application on agricultural land has led to a substantial build-up of soil phosphorus (P) stocks, increasing the risks for diffuse pollution of surface waters. Recent studies highlight the need to differentiate between runoff types for better prediction of these risks. In a factorial field-plot experiment we investigated the role of soil-P status, band-applied manure and rainfall intensity on P losses from two Swiss grassland sites. Artificial rainfall was applied on each plot first at medium intensity using a sprinkler and then at high intensity using a watering can, simulating two different runoff conditions. Under both conditions, dissolved reactive P (DRP) in runoff increased linearly with water soluble P in the soil (WSP), but the extraction coefficients differed substantially between the two phases of runoff generation. It was 0.017kgL−1 for runoff generated with the watering can (WCR), and 0.085kgL−1 for runoff generated with the sprinkler (SR). Manure application increased DRP losses, but did not override the effect of soil P status. Phosphorus losses with runoff were more sensitive to soil P status for SR than for WCR. Reducing soil-P is therefore crucial to reduce runoff-P.

Manure Composition and Incorporation Effects on Phosphorus in Runoff Following Corn Biomass Removal

Greater demand for corn ( L.) stover for bioenergy use may lead to increased corn production acreage with minimal surface residue cover, resulting in greater risk for soil erosion and phosphorus (P) losses in runoff. A rainfall simulation study was conducted to determine the effects of spring-applied dairy cow () manure (none, in-barn composted, and exterior walled-enclosure pit) with >200 g kg organic solids content following fall corn biomass removal with and without incorporation (chisel plow [CP] and no-till [NT]) on sediment and P in runoff. Runoff was collected from a 0.83-m area for 60 min following the onset of rainfall simulation (76 mm h), once in spring and once in fall. Runoff dissolved reactive P (DRP) and dissolved organic P (DOP) concentrations were positively correlated with manure P rate and were higher in NT compared with CP. Conversely, sediment and particulate P (PP) concentrations in runoff were inversely correlated with manure P rate (and manure solids) and were higher in CP compared with NT. Runoff volume where no manure was applied was higher in NT than in CP in spring but similar in fall. The addition of manure reduced runoff volumes by an average of 82% in NT and 42% in CP over spring and fall. Results from this study indicate that surface application of dairy manure with relatively high solids content may reduce sediment and PP losses in runoff without increasing the risk of increased DRP and DOP losses in the year of application where corn biomass is harvested.

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

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=αt−β, where α and β 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 α and β for a given soil could be determined by DPSM3-2 (Mehlich-3 P/Mehlich-3 Al) using the following formulas:[Formula: see text] The description of the temporal pattern of runoff DRP concentration during a rainfall event with the constants estimated using DPSM3−2 can aid in the prediction of soil runoff DRP loss.

Swine Manure Injection with Low‐Disturbance Applicator and Cover Crops Reduce Phosphorus Losses

Injection of liquid swine manure disturbs surface soil so that runoff from treated lands can transport sediment and nutrients to surface waters. We determined the effect of two manure application methods on P fate in a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] production system, with and without a winter rye (Secale cereale L.)-oat (Avena sativa L.) cover crop. Treatments included: (i) no manure; (ii) knife injection; and (iii) low-disturbance injection, each with and without the cover crop. Simulated rainfall runoff was analyzed for dissolved reactive P (DRP) and total P (TP). Rainfall was applied 8 d after manure application (early November) and again in May after emergence of the corn crop. Manure application increased soil bioavailable P in the 20- to 30-cm layer following knife injection and in the 5- to 20-cm layer following low-disturbance injection. The low-disturbance system caused less damage to the cover crop, so that P uptake was more than threefold greater. Losses of DRP were greater in both fall and spring following low-disturbance injection; however, application method had no effect on TP loads in runoff in either season. The cover crop reduced fall TP losses from plots with manure applied by either method. In spring, DRP losses were significantly higher from plots with the recently killed cover crop, but TP losses were not affected. Low-disturbance injection of swine manure into a standing cover crop can minimize plant damage and P losses in surface runoff while providing optimum P availability to a subsequent agronomic crop.

Influence of Aeration Implements, Phosphorus Fertilizers, and Soil Taxa on Phosphorus Losses from Grasslands

Attenuation of rainfall within the solum may help to move contaminants and nutrients into the soil to be better sequestered or utilized by crops. Surface application of phosphorus (P) amendments to grasslands may lead to elevated concentrations of P in surface runoff and eutrophication of surface waters. Aeration of grasslands has been proposed as a treatment to reduce losses of applied P. Here, results from two small-plot aeration studies and two field-scale, paired-watershed studies are supplemented with previously unpublished soil P data and synthesized. The overall objective of these studies was to determine the impact of aeration on soil P, runoff volume, and runoff P losses from mixed tall fescue [Lolium arundinaceum (Schreb.) Darbysh.]-bermudagrass (Cynodon dactylon L.) grasslands fertilized with P. Small-scale rainfall simulations were conducted on two soil taxa using three types of aeration implements: spikes, disks, and cores. The-field scale study was conducted on four soil taxa with slit and knife aeration. Small-plot studies showed that core aeration reduced loads of total P and dissolved reactive P (DRP) in runoff from plots fertilized with broiler litter and that aeration was effective in reducing P export when it increased soil P in the upper 5 cm. In the field-scale study, slit aeration reduced DRP losses by 35% in fields with well-drained soils but not in poorly drained soils. Flow-weighted concentrations of DRP in aerated fields were related to water-soluble P applied in amendments and soil test P in the upper 5 cm. These studies show that the overall effectiveness of mechanical soil aeration on runoff volume and P losses is controlled by the interaction of soil characteristics such as internal drainage and compaction, soil P, type of surface-applied manure, and type of aeration implement.

Surface and Subsurface Phosphorus Losses from Sugarcane Fields with Different Management Practices

Phosphorus losses in runoff from sugarcane fields can contribute to non-point source pollution of surface and subsurface waters. The objective of this study was to evaluate the effects of three different management practices on P losses in surface runoff and subsurface leaching from sugarcane (Saccharum officinarum L.) fields. Field experiments with treatments including conventional burning (CB), compost application with burning (COMB), and remaining green cane trash blanketing (GCTB) treatments were carried out to assess these management practice effects on P losses from sugarcane fields. In the CB treatment, sugarcane residue was burned after harvest. The COMB treatment consisted of compost applied at “off bar” with sugarcane residue burned immediately after harvest. Compost was applied in the amount of 13.4 Mg ha−1 annually, 8 weeks before planting. In the GCTB treatment, sugarcane residue was raked off from the row tops and remained in the wheel furrow after harvest. Surface runoff was collected with automatic refrigerated samplers, and subsurface leachate was collected with pan lysimeters over a period of 3 years. Measured concentrations of total P (TP), dissolved reactive P (DRP), and particulate P (PP) in surface runoff from the COMB treatment were significantly higher than concentrations from the CB and GCTB treatments. The mean losses of P (TP and DRP) after burning (postharvest, years 2 and 3) were significantly greater than the no-burn treatment (preharvest, year 1) in the CB, COMB, and CB/COMB/GCTB combined options. Additionally, the mean losses of total suspended solid and total combustible solids in residue burning were, on average, 2.7 and 2.2 times higher than the no-burn practices, respectively (preharvest and GCTB treatment). Annual P losses from surface runoff in the third year of study were 12.90%, 6.86%, and 10.23% of applied P in CB, COMB, and GCTB treatments, respectively. However, the percent of annual DRP losses from applied P in COMB and GCTB treatments was similar magnitude, and their values were less than 50% compared to the value from CB treatment. In the leaching study, percent of monthly mean TP and DRP losses in the COMB and GCTB treatments were greatly reduced. Based on these results, the COMB and GCTB procedures were equally recommended as sugarcane management practices that improve water quality in both surface runoff and subsurface leachate.

Nutrients in Runoff from a Furrow‐Irrigated Field after Incorporating Inorganic Fertilizer or Manure

Use of dairy manure to supply crop nutrients is gaining broader acceptance as the cost of fertilizer rises. However, there are concerns regarding manure's effect on water quality. In 2003 and 2004, we measured sediment, NO3-N, NH4-N, K, dissolved reactive P (DRP), and total P (TP) concentrations in runoff from furrow irrigated field plots (6-7 irrigations yr(-1)) cropped to corn (Zea mays L.) in the semiarid climate of southern Idaho. Annual treatments included 13 (Year 1) and 34 Mg ha(-1) (Year 2) stockpiled dairy manure (M); 78 (Year 1) and 195 kg N ha(-1) (Year 2) inorganic N fertilizer (F); or control-no amendment (C). Available N in manure applied each year was similar to amounts applied in fertilizer. Constituent concentrations (mg L(-1)) in runoff ranged widely among all treatments: sediment, 10 to 50,000; NO3-N, 0 to 4.07; NH4-N, 0 to 2.28; K, 3.6 to 46.4; DRP, 0.02 to 14.3; and TP, 0.03 to 41.5. Over both years, fertilizer and manure treatments increased irrigation mean values (averaged across irrigations) for NO3-N runoff concentrations (M = 0.30, F = 0.26, C = 0.21 mg L(-1)) and mass losses (M = 0.50, F = 0.42, C = 0.33 kg ha(-1)) relative to the control. Over both years, the manure treatment also increased mean irrigation runoff concentrations of DRP (M = 0.19, F = 0.09, C = 0.08 mg L(-1)) and K (M = 1.13, F = 0.79, C = 0.62 mg L(-1)) compared with fertilizer and control plots. Average DRP and K runoff mass losses were 2.0 to 2.4 times greater in manure treatments than in control plots. Neither F or M affected season-long cumulative infiltration. Runoff DRP and inorganic-N losses appeared to be influenced more by the timing of the amendment application and environmental conditions than by the quantity of nutrients applied. Nutrient additions to furrow irrigated soils, whether from fertilizer or manure, can potentially increase nutrient losses in irrigation runoff, with the degree of impact depending on the nutrient, amount, and timing of application and whether inorganic fertilizer or manure was applied.

Soil tillage methods to control phosphorus loss and potential side-effects: a Scandinavian review

In Scandinavia high losses of soil and particulate-bound phosphorus (PP) have been shown to occur from tine-cultivated and mouldboard-ploughed soils in clay soil areas, especially in relatively warm, wet winters. The omission in the autumn of primary tillage (not ploughing) and the maintenance of a continuous crop cover are generally used to control soil erosion. In Norway, ploughing and shallow cultivation of sloping fields in spring instead of ploughing in autumn have been shown to reduce particle transport by up to 89% on highly erodible soils. Particle erosion from clay soils can be reduced by 79% by direct drilling in spring compared with autumn ploughing. Field experiments in Scandinavia with ploughless tillage of clay loams and clay soils compared to conventional autumn ploughing usually show reductions in total P losses of 10–80% by both surface and subsurface runoff (lateral movements to drains). However, the effects of not ploughing during the autumn on losses of dissolved reactive P (DRP) are frequently negative, since the DRP losses without ploughing compared to conventional ploughing have increased up to fourfold in field experiments. In addition, a comprehensive Norwegian field experiment at a site with high erosion risk has shown that the proportion of DRP compared to total P was twice as high in runoff water after direct drilling compared to ploughing. Therefore, erosion control measures should be further evaluated for fields with an erosion risk since reduction in PP losses may be low and DRP losses still high. Ploughless tillage systems have potential side-effects, including an increased need for pesticides to control weeds [e.g. Elytrigia repens (L.) Desv. ex Nevski] and plant diseases (e.g. Fusarium spp.) harboured by crop residues on the soil surface. Overall, soil tillage systems should be appraised for their positive and negative environmental effects before they are widely used for all types of soil, management practice, climate and landscape.

Long-term monitoring of buffer zone efficiency under different cultivation techniques in boreal conditions

Vegetative buffer zones (BZs) between fields and watercourses are one way to minimize phosphorus (P) losses from fields to surface runoff and thus decrease eutrophication and blue-green algal blooms in lakes and coastal waters. A 6-plot experimental field was established in clay soil (Vertic Cambisol) in SW Finland in 1991 to study long-term changes in functioning of BZs and their retention capacity for total solids (TS), total P (TP), dissolved reactive P (DRP) and particulate P (PP) in different seasons. The steep slope in lower sections of four plots (18 m wide × 70 m long) was planted with 10-m-wide mowed grass buffer zones (GBZ) or unmowed vegetated buffer zones (VBZ) growing natural herbage and shrubs. Surface runoff water samples from the GBZ and VBZ plots were compared to samples from plots cultivated without a buffer (NBZ). The source field area in all plots and the steep slope (12–18%) on the NBZ were ploughed in autumn, and sown with barley ( Hordeum vulgare) or oats ( Avena sativa) in spring (conventional tillage, 1991–2001), sown with grass and grazed (72–234 cow grazing days ha −1 yr −1; 2003–2005) and direct drilled without tillage (2006–2008). Surface soil samples (0–2 cm) were taken from the BZs in autumn and spring to evaluate the level of plant-available P ( P Ac) extracted with 0.5 M NH 4–acetate–0.5 M acetic acid at pH 4.65. The BZs were most effective at decreasing TS, TP and PP with conventional tillage, less so with direct drilling and least effective with grazing. In a conventionally tilled field, the TS and TP removal efficiencies were over 50% and 27–36%, respectively, for the BZs as compared to the NBZ. In the VBZ plots, the DRP load was, however, 60% greater than in the NBZ or GBZ plots. In direct drilling, the surface runoff losses were smaller than in conventionally tilled NBZ plots. The lowest losses of TS, TP and PP were found during grazing for all plots, but with grazing the DRP load, 0.3–0.4 kg ha −1 yr −1, was higher than during grain growing in all treatments. The GBZ and VBZ were effective in retaining P in summer and autumn, whereas in spring their retention capacity was decreased. The reason for high DRP losses in spring was the high P Ac in surface soil and frozen broken plant tissues in the VBZ and the grazed source field. Mowing and removing of swathe from the GBZ decreased the DRP losses.

Phosphorus losses from a subdrained clayey soil as affected by cultivation practices

Conservation tillage practices are included in the Finnish Agri-Environmental Program as phosphorus (P) loss control measures, but only few experiments have been performed to check their effectiveness in the local conditions. We studied surface and subsurface losses of P from a clayey underdrained field (Jokioinen/ Kotkanoja; Vertic Cambisol/Typic Cryaquept), with 2% mean slope, during two separate experimental periods. Primary tillage treatments of the first experimental period of three years were moldboard ploughing (to 20–23 cm depth) vs. no autumn tillage (wintertime stubble). During the second experimental period of five years, the treatments were moldboard ploughing (20–23 cm) vs. shallow (to 5–8 cm) autumn tillage. The stubble treatment of the first experimental period produced higher dissolved reactive P (DRP) losses (104–259 g ha–1 yr–1) than autumn ploughing (77–96 g ha–1 yr–1), and equally high particulate P (PP) losses (mean 660, 235–1300 g ha–1 yr–1). During the second experimental period, shallow autumn tillage produced 28% higher DRP losses (mean 120, 107–136 g ha–1 yr–1) than ploughing (83–117 g ha–1 yr–1) and 11% higher PP losses (mean 1090, 686–1336 g ha–1 yr–1) than ploughing (783–1253 g ha–1 yr–1). Surface runoff made up 28% and 16% of the total flow from the ploughed soil during the first and the second experimental period, respectively, as compared to 50% for the stubble and 44% for the shallow autumn tillage. Routing of flow between surface and subsurface pathways had a major influence on the P losses. In the relatively flat landscapes of the main agricultural areas of southern Finland, the potential for decreasing agricultural P losses by reduced tillage appears limited.;

Residual Effects of Compost and Plowing on Phosphorus and Sediment in Runoff

Manure application can lead to excessive soil test P levels in surface soil, which can contribute to increased P concentration in runoff. However, manure application often results in reduced runoff and sediment loss. Research was conducted to determine the residual effects of previously applied compost, plowing of soil with excessive soil test P, and application of additional compost after plowing on volume of runoff and loss of sediment and P in runoff. The research was conducted in 2004 and 2005 under natural rainfall events with plots of 11-m length where low-P and high-P compost had been applied during April 1998 to January 2001. During this initial application period, Bray-P1 in the surface 5-cm of depth was increased from 14 to 553 mg kg(-1) for the high-P compost. Inversion plowing in the spring of 2004 greatly decreased P levels in the surface soil and over the following year reduced runoff by 35% and total P losses by 51% compared with the unplowed compost treatments. Sediment loss was increased with plowing compared with the unplowed compost applied treatments but less than with the no-compost treatment. The application of additional compost after plowing increased surface soil P and dissolved reactive P (DRP) in runoff but did not increase particulate P in runoff. Unplowed compost-amended soil continued to reduce sediment loss but exhibited increased DRP loss even 5 yr after the last application. Plowing to invert excessively high-P surface soil was effective in reducing runoff and DRP loss.

Mineralogy in Relation to Phosphorus Sorption and Dissolved Phosphorus Losses in Runoff

The relationship between soil test P (STP) and dissolved reactive P (DRP) in runoff has been shown to vary with soil type due to differences in soil properties. This study was conducted to determine the effect of mineralogy on P sorption behavior and DRP losses in runoff using simulated rainfall. Nine different soil types were sampled from four different fields to provide a range in STP. Unamended soils were packed into runoff boxes for use in a rainfall simulation study (7.5 cm h−1 for 30 min). A mineralogical analysis and adsorption‐desorption isotherm was conducted on one representative sample from each soil type. Results indicated that P retention for adsorption and desorption in separated clay fractions and whole soils was well correlated to Al bearing minerals such as hydroxy‐interlayered‐vermiculite (HIV), gibbsite, and amorphous Al. However, P retention was negatively related to kaolinite content, which was also confirmed by isotherms conducted on pure clay minerals. Based on the isotherm results, all soils were split into two groups based on the ratio of HIV/kaolinite. Soils with a HIV/kaolinite ratio >0.5 had a significantly lower concentration of DRP in runoff for a given soil water soluble P level compared with soils with a ratio <0.5.

Influence of cultivation methods on suspended solids and phosphorus concentrations in surface runoff on clayey sloped fields in boreal climate

Abstract Methods for decreasing agricultural phosphorus (P) loadings to surface waters are needed to achieve good water quality. To reliably find out the efficiency of different methods in changing hydrological conditions, long-term experiments are of invaluable importance. Here the effects of various cultivation methods on total suspended solids (TSS) and P concentrations in – and the volume of – plough layer runoff (PLR) were studied in a sloping experimental field in southwest Finland during a 9-year period. Yearly means of PLR and flow-weighted mean concentrations from the treatment plots were compared with a control, winter wheat ( Triticum aestivum ) treatment (WW), of which the values assigned were equal to 1. No major differences were found in PLR for cultivation methods up and down slope, except for the cross-ploughing treatment (0.49). Normal ploughing and cultivation treatments produced the highest TSS concentrations (1.38 and 1.18, respectively), whereas values between 0.44 and 0.53 were measured for three treatments with reduced (or no) tillage. Particle-bound P (PP) concentrations closely followed those of TSS. Dissolved reactive P (DRP) showed contrasting behaviour, with the greatest treatment effects from the three reduced tillage treatments (1.58–2.29). This study showed that by changing over from intensive autumn tillage to permanent vegetation cover, erosion and PP loss were markedly decreased. Methods employing no autumn tillage and leaving an undisturbed soil surface during winter showed particularly high reductions in loading. The simultaneous increase in DRP loss is an undeniable drawback that should be resolved separately. This study, as a part of a wider complex of integrated studies, will be utilized in a decision-making tool for the assessments of loading effects and load reduction possibilities in terms of cultivation methods.