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To improve understanding of phosphorus (P) retention processes in small constructed wetlands (CWs), we analysed variations in sediment deposition and accumulation in four CWs on clay soils in east-central Sweden. Sediment deposition (in traps) generally exceeded the total suspended solids (TSS) load suggesting that resuspension and wetland base erosion were important. This was confirmed by quantification of particle accumulation (on plates) (1-23 kg m -2  year -1 ), which amounted to only 13-23% of trap deposition. Spatial mean P concentrations in accumulated sediment on plates (0.09-0.15%) were generally similar to temporal mean P concentrations of particles in water (0.11-0.15%). Deposition/accumulation was minor in one wetland with high hydraulic load (400 m year -1 ), suggesting that such small wetlands are not efficient as particle sinks. Economic support for CWs are given, but design and landscape position are here demonstrated to be important for effective P retention.

Assessing mitigation of phosphorus (P) leaching from subsurface drainage systems is challenging due to high spatial and temporal variation in leaching. Mean measured total P leaching from a clayey soil in an eight-year study period (four replicates per treatment) was (kg ha -1  year -1 ): 1.21 from shallow autumn tillage (ShT), 0.84 from unfertilised fallow (UF), 0.81 from conventional autumn ploughing (CT) and 0.57 from structure liming (SL-CT). Treatment was not significant using Richards-Baker flow index or a distance factor as covariate (p = 0.084 and 0.057). A tendency for lower leaching was obtained comparing SL-CT with ShT (p adjusted  = 0.060 and 0.009 respectively). A combination of measures adapted to drainage conditions and clay content in different parts of the field is proposed since P leaching was approximately halved from an adjacent field (4.3 ha) in a three-year post-period compared with a three-year pre-period for structure liming the entire field and drainage system renovation plus structure lime drain backfilling.

Horse paddocks have been identified as a significant contributor of animal waste nutrients to natural waters; thus, modified paddock management is needed. Because chemical amendments pose a health risk to horses, an alternative for reducing nutrient translocation from manure is to add available organic residues to the soil. To examine the feasibility of outdoor use of organic materials to reduce nutrient losses from paddock soils, three commonly available organic materials (peat, wheat straw, and wood chips) were tested for their nutrient retention capacities in batch experiments followed by leaching experiments in an in-house lysimeter station using artificial rainfall. Results showed that the grounded peat and wood chips retained some phosphorus (P), whereas grounded wheat straw released P to the solution. In leaching experiments, peat reduced nitrogen (N) losses by 40% but increased P and carbon (C) losses severalfold. Wheat straw was ineffective in reducing P, N, or C losses and in some cases increased the losses. Wood chips effectively reduced P and C losses, by 70 and 40%, respectively, but not N losses. It was concluded that, among the three organic materials, only the wood chips can be used outdoors to reduce nutrient losses from paddock soils., (Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.)

The series of papers in this issue of AMBIO represent technical presentations made at the 7th International Phosphorus Workshop (IPW7), held in September, 2013 in Uppsala, Sweden. At that meeting, the 150 delegates were involved in round table discussions on major, predetermined themes facing the management of agricultural phosphorus (P) for optimum production goals with minimal water quality impairment. The six themes were (1) P management in a changing world; (2) transport pathways of P from soil to water; (3) monitoring, modeling, and communication; (4) importance of manure and agricultural production systems for P management; (5) identification of appropriate mitigation measures for reduction of P loss; and (6) implementation of mitigation strategies to reduce P loss. This paper details the major challenges and research needs that were identified for each theme and identifies a future roadmap for catchment management that cost-effectively minimizes P loss from agricultural activities.

One measure used in Sweden to mitigate eutrophication of waters is the construction of small wetlands (free water surface wetland for phosphorus retention [P wetlands]) to trap particulate phosphorus (PP) transported in ditches and streams. This study evaluated P retention dynamics in a newly constructed P wetland serving a 26-ha agricultural catchment with clay soil. Flow-proportional composite water samples were collected at the wetland inlet and outlet over 2 yr (2010-2011) and analyzed for total P (TP), dissolved P (DP), particulate P (PP), and total suspended solids (TSS). Both winters had unusually long periods of snow accumulation, and additional time-proportional water samples were frequently collected during snowmelt. Inflow TP and DP concentrations varied greatly (0.02-1.09 mg L) during the sampling period. During snowmelt in 2010, there was a daily oscillation in P concentration and water flow in line with air temperature variations. Outflow P concentrations were generally lower than inflow concentrations, with net P losses observed only in August and December 2010. On an annual basis, the wetland acted as a net P sink, with mean specific retention of 69 kg TP, 17 kg DP, and 30 t TSS ha yr, corresponding to a reduction in losses of 0.22 kg TP ha yr from the agricultural catchment. Relative retention was high (36% TP, 9% DP, and 36% TSS), indicating that small constructed wetlands (0.3% of catchment area) can substantially reduce P loads from agricultural clay soils with moderately undulating topography., (Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.)

Eutrophication, a major problem in many fresh and brackish waters, is largely caused by nonpoint-source pollution by P from agricultural soils. This lysimeter study examined the influence of P content, physical properties, and sorption characteristics in topsoil and subsoil on P leaching measured during 21 mo in 1-m-long, undisturbed soil columns of two clay and two sandy soils. Total P losses during the period varied between 0.65 and 7.40 kg ha. Dissolved reactive P was the dominant form in leachate from the sandy soils and one clay soil, varying from 48 to 76%. Particulate P dominated in leachate from the other clay soil, where low pH (5.2) in the subsoil decreased aggregate stability and thereby probably increased the dispersion of clay particles. Phosphorus leaching was small from soils with high P sorption index (PSI) and low P saturation (<10% of PSI) in the subsoil, even though extractable P (Olsen P) in the topsoil was high, and large from a soil with low sorption capacity and high P saturation (>35% of PSI) in the profile. High sorption capacity in the subsoil was more important for P leaching in sandy soils than in clay soils with macropore flow, where the effect of high sorption capacity was reduced due to less interaction between percolating water and the soil matrix. The results suggest that P leaching is greatly affected by subsoil properties and that topsoil studies, which dominate current research, are insufficient for assessing P leaching in many soils., (Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.)

In order to explore the influence of site-specific soil properties on nitrogen (N) and phosphorus (P) losses between individual fields and crop sequences, 16 drained fields with clay soils were investigated in a four-year study. Mean total N (TN) loss was 6.6-11.1 from a conventional, 14.3-21.5 from an organic and 13.1-23.9 kg ha(-1) year(-1) from an integrated cropping system across a 4 year period, with 75% in nitrate form (NO(3)-N). Mean total P (TP) loss was 0.96-3.03, 0.99-4.63 and 0.76-2.67 kg ha(-1) year(-1), from the three systems respectively during the same period, with 25% in dissolved reactive form (DRP). Median N efficiency was calculated to be 70% including gains from estimated N fixation. According to principal component factor (PCA) analysis, field characteristics and cropping system were generally more important for losses of N and P than year. Accumulation of soil mineral N in the autumn and (estimated) N fixation was important for N leaching. No P fertilisers were used at the site in either cropping system. Total P concentration in drainage water from each of the fields was marginally significantly (p<0.05) correlated to TP concentration in the topsoil (r=0.52), measured in hydrochloric acid extract (P-HCl). Mean DRP concentrations were significantly (p<0.01) correlated to degree of P saturation (DPS-AL) and soil carbon (C) content in the topsoil (r=0.63). Good establishment of a crop with efficient nutrient uptake and good soil structure was general preconditions for low nutrient leaching. Incorporation of ley by tillage operations in the summer before autumn crop establishment and repeated operations in autumn as well, increased N leaching. Crop management in sequences with leguminous crops needs to be considered carefully when designing cropping systems high efficiency in N utilisation and low environmental impact., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Phosphorus (P) leaching from agricultural soils is a serious environmental concern. Application of aluminium water treatment residuals (Al-WTRs) at a rate of 20 Mg ha(-1) to clay soils from central Sweden significantly increased mean topsoil P sorption index (PSI) from 4.6 to 5.5 μmol kg(-1) soil. Mean degree of P saturation in ammonium lactate extract (DPS-AL) significantly decreased from 17 to 13%, as did plant-available P (P-AL). Concentrations of dissolved reactive P (DRP) decreased by 10-85% in leaching water with Al-WTR treatments after exposure of topsoil lysimeters to simulated rain. Soil aggregate stability (AgS) for 15 test soils rarely improved. Three soils (clay loam, silty loam and loam sand) were tested in greenhouse pot experiments. Aluminium-WTR application of 15 or 30 ton ha(-1) to loam sand and a clay loam with P-AL values of 80-100 mg kg(-1) soil significantly increased growth of Italian ryegrass when fertilised with P but did not significantly affect growth of spring barley on any soil. Al-WTR should only be applied to soils with high P fertility where improved crop production is not required.

In November 2002, biomass phosphorus (P) of submerged aquatic plants with associated epiphyton was measured using P-32 tracer addition in a treatment wetland receiving tertiary treated municipal sewage. The wetland is situated 120 km west of Stockholm, Sweden receiving tertiary treated municipal sewage. During the experiment, inflow water had a total P concentration of 0.3 and an iron concentration of 0.7 mg 1(-1) with a residence time of 3-3.5 days. Samples of submerged plants mainly slender waterweed (Elodea nuttallii, L.) and sago pondweed (Potamogeton pectinatus, L.) were taken in two shallow areas (0.21 and 0.51 ha respectively) adjacent to the inlet of one of the wetland subbasins. The sampled area represented 27% of the total 2.6 ha area of the basin. The young phytomass contained 0.02 kg P and the older vegetation parts and epiphyton 0.04 kg P. The sampling took place 90-96 hours after exposure of a pulse of P-32 (18 GBq), i.e. when 75% had passed. Total phytomass was low, only 2 g m(-2) as dry weight. The young phytomass close to the site of injection had higher average beta activity in disintegrations per minute and milligram dry weight (140 DPM mg dw(-1)) than the older parts of the submerged plants (70 DPM mg dw(-1)) indicating an active plant uptake in the former. The latter was interpreted as epiphyton uptake, but since the biomass of old shoots was higher than of young, more P-32 was removed by processes associated with epiphyton as was removed by the young phytomass. In two shallow central zones, the former was equal to 0.006 per thousand of exposed radioactivity in water, while 0.003 per thousand was found in the young phytomass in the same zones of the basin. Close to the inlet a fast P assimilation by the plant biomass was demonstrated. The role of submerged aquatic plants in phosphorus turnover in sewage treatment basins under winter conditions is discussed.

Long-term median total phosphorus (TotP) and total nitrogen (TotN) concentrations were 0.08 and 5.5 P/N (mg L(-1)), respectively, in 10 agricultural streams monitored since 1988 in Sweden. The areas of the respective catchments are 2-20 km2. The period 1992/2002 was characterised by stable hydrological conditions without any flow trends in nearly all of the streams. The highest average TotP concentration, 0.17 mg P L(-1), was found in a small agricultural stream in the largest Swedish agricultural plain. The soil texture is here characterised by a large specific surface area of the soil particles, and the agriculture by cereal production. The second highest average TotP concentration, 0.14 mg P L(-1), was measured in the surface water from a catchment characterised partly by clay soils and by production of potato, spring cereals and grass. This catchment had twice as many fields with a calculated high risk for P losses compared with another monitored catchment in the same watershed (River Rönneå). There was a significant downward TotP trend during 1992/2002 of 0.0012 mg P L(-1) yr(-1) (Sen's slope estimator) in the catchment where many fields risk P losses and which had a reduced P manure application rate of -20% during 1995/2000. In recent years practically no manure has been spread during autumn. Bypass flow of nitrate through one soil has been suggested to influence the LOWESS (LOcally WEighted Scatterplot Smoothing) fitting curve of TotN. Total nitrogen concentration decreased in most of the catchment. The average downward slope was similar to a general TotN reduction of 0.069 mg N L(-1) yr(-1). During the period 1992/2002 this was equal to slightly more than 10 per cent. Cultivation of catch crops was relatively uncommon until 2002, but this practice is expected to expand to larger areas during 2003 and in the future.

Phosphorus (P) is one of the main nutrients controlling algal production in aquatic systems. Proper management of P in agricultural production systems can greatly enhance our ability to combat pollution of aquatic environments. To address this issue, a decision support system (DSS) consisting of the Maryland Phosphorus Index (PI), diagnosis expert system (ES), prescription ES, and a nonpoint-source pollution model, Ground Water Loading Effects of Agricultural Management Systems (GLEAMS), was developed and applied to an agricultural watershed in southern Sweden. This system can identify critical source areas (CSAs) regarding phosphorus losses within the watershed, make a diagnosis of probable causes, prescribe the most appropriate best management practices (BMPs), and test the environmental effects of the applied BMPs. The PI calculations identified small parts of the watershed as CSAs. Only 10.4% of the total watershed area in 1995 and 5.2% of the total watershed area in 1996 were classed as "high potential P movement." Four probable causes (high P level in soil, excessive P fertilization, stream proximity, and subsurface drainage) and three BMPs (riparian buffer strips, reduced P fertilizer application, and P fertilizer incorporation) were identified by a diagnosis and prescription expert system. The GLEAMS simulations conducted for one selected CSA field for a 24-yr period showed that the recommended BMP reduced runoff P losses by 55% and sediment P losses by 71%, if applied from the first year. Results showed that using DSS may enable us to select a proper BMP implementation strategy and to realize the beneficial effect of BMPs on a long-term basis.

Poland has the largest agricultural area within the Baltic Sea drainage basin and reducing the risk of phosphorus (P) and nitrogen (N) leaching from Polish soils to water is therefore essential. Increased acidity is known to reduce soil fertility and may trigger P leaching from non-calcareous soils. As part of advisor training, 25 farms each in Pomerania and north-western Mazovia were visited and 1500 ha arable soil, including 180 ha grassland soil, were monitored in 2013–2014. The soil was mainly coarse textured, but 25% of the Pomeranian farms were dominated by silty or clayey soils. More or less regular drainage systems were found on 20% of the farms, while 50% had simpler, older (>30 years) systems with a few single pipes. The farmers often used only ammonium sulphate or other acidifying N mineral fertiliser. Median pH on the Pomeranian farms, analysed in potassium chloride solution [pH(KCl)], was 5.2 and liming was advised for fields on most (72%) of these farms. Soil P content, measured by double-lactate extraction (PDL), was positively and significantly correlated (Pearson coefficient 0.57;p < .001) with soil pH and was generally higher for pig farms. Mean PDL(P given in elemental form) tended to be lower on dairy farms and arable farms and was significantly lower (mean 51 mg PDL kg−1soil) on mixed farms (with just a few cows and poultry) than on pig farms (mean 122 mg PDL kg−1soil). Farm-gate balances indicated deficits of P and potassium (K) on many of the small mixed farms in Pomerania and the soil can be expected to be nutrient depleted. In contrast, the pig farms demonstrated surplus farm-gate P balances (mean 27 kg ha−1). The P leaching risk is discussed relative to soil threshold values and to results from Swedish long-term field experiments. [ABSTRACT FROM PUBLISHER]

Lag times in reduced nutrient leaching after improved agricultural practices must be assessed to inform management decisions and evaluate their cost-effectiveness. This study estimated the leaching of phosphorus (P) and nitrogen (N) at two scales, a 33.8-ha nested field (data from 1973 to 2011) and an 820-ha agricultural catchment (data from 1992 to 2010). Field management was evaluated along with long-term nutrient trends. Estimates including and excluding nutrient concentrations in the stream under dry catchment conditions (mean 2.5 months year−1) revealed that wastewater contributed 10% of the total P (TP) catchment leaching, mostly in dissolved reactive (DRP) form. More recent flow-proportional sampling at the two scales demonstrated 45% higher particulate P leaching from the field than with discrete water sampling, whereas a past discrete sampling strategy may have overestimated DRP contributions to the stream. The accumulated field P balance was increasingly negative after 1987, whereas crop yields increased. From 1998, the measured accumulated TP leaching from the field was lower than the mean accumulated leaching, considering the estimated downward trend (−10%) over the 38-year study period ( p < 0.05). The average total N (TN) field leaching of 28 kg ha−1 year−1 (1973-2011) was 10% higher than the catchment leaching (1992-2010). The rates and timing of fields N and P fertilization became better adapted to crop requirements over time, and thereafter, a 14% reduction in TN leaching was estimated. No significant trends were estimated for catchment leaching for either TP or TN over the 18-year period, demonstrating an extended lag period for reduced nutrient leaching and the need for long-term monitoring of the effects of pollution mitigation. Copyright © 2014 John Wiley & Sons, Ltd. Highlights Time lag in P and N leaching responses to reduce nutrient surpluses, Close relationship with N export at nested scale, Scale effects in Q indices and PP transport, Point sources of pollution prolonging the time lag for DRP leaching mitigation [ABSTRACT FROM AUTHOR]

Highlights: [•] Structural liming reduced PP leaching for at least six years. [•] Large spatial variation in P losses but moderate variation in soil P and discharge. [•] Broadcasting or placement of fertiliser P had no clear effect on P leaching. [•] Shallow autumn tillage provided no significant benefits for water quality. [•] Replacing arable land with unfertilised fallow did not reduce P leaching losses. [Copyright &y& Elsevier]

Plant availability and risk for leaching and/or runoff losses of phosphorus (P) from soils depend among others on P concentration in the soil solution. Water-soluble P in soil measures soil solution P concentration. The aim of this study was to understand the effect of wheat residue char (biochar) addition on water-soluble P concentration in a wide range of biochar-amended soils. Eleven agricultural fields representing dominant soil texture classes of Swedish agricultural lands were chosen. Concentrations of water-soluble P in the soils and in biochar were measured prior to biochar incorporation to soils in the laboratory. Experiments with three dominant soil textures-silt loam, clay loam, and an intermediate loam soil with different rates of biochar addition (i.e., 0.5, 1, 2, and 4 %; w/ w) showed that the highest concentration of water-soluble P was achieved at an application rate of 1 %. At higher application rates, P concentrations decreased which coincided with a pH increase of 0.3-0.7 units. When the 11 soils were amended with 1 % ( w/ w) biochar, water-soluble P concentrations increased in most of the soils ranging from 11 to 253 %. However, much of the water-soluble P added through the biochar was retained (33-100 %). We concluded that wheat residue char can act as a source of soluble P, and low and high additions of biochar can have different effects on soil solution P concentration due to possible reactions with Ca and Mg added with biochar. [ABSTRACT FROM AUTHOR]

Leaching of nutrients was studied at a tile drain outlet and in two pairs of groundwater pipes in an arable field in central Sweden in order to identify trends and impacts of the climate. In the study period (1973-2005), crop production was dominated by spring barley, winter wheat, rape and, in later years, potatoes. Winter crops were cultivated 60% of the time. Leaching of total nitrogen (TotN) and total phosphorus (TotP) to drain water was low, on average 10 kg ha-1 year-1 for TotN and 0.07 kg ha-1 year-1 for TotP based on measurements. Nitrogen fertilisation increased slightly from 121 to 142 kg ha-1 year-1 during the period in a balanced way in line with increasing crop yields of cereals, from 5.8 to 6.6 tonnes year-1. For the entire study period, the temperature was estimated to increase significantly by a total of +2 °C for the growing season (April-September). Precipitation (+16 mm) and humidity (+11%) were also estimated to have increased significantly, mainly in June. Simulations with a deterministic and coupled N-leaching database model (SOILN-DB) indicated an increased rate of mineralisation (+2 kg ha-1 year-1) and increased N leaching to the drain pipes (+0.06 kg ha year-1) as a result of climate changes. In this simulation spring tillage instead of autumn tillage was estimated to reduce N leaching by 10%. Mineral P fertilisers were applied to winter crops in autumn until 1999, but thereafter all mineral P fertilisers were applied in spring by drilling in bands. A weak trend for decreasing concentration of dissolved reactive phosphorus was indicated based on the measurements in the tile drain outlet. [ABSTRACT FROM AUTHOR]

Abstract: Large amounts of waterborne nutrients are major problems for society since they can cause harmful algal blooms in surface water bodies. Consequently, there are a variety of national and international guidelines, e.g. Swedish National Environmental Quality Objectives and the EU Water Framework Directive, which include targets to be achieved within a certain time frame. This paper uses the example of a large Swedish lake to show that national and international targets must be adapted to the local situations. Despite decreasing nutrient concentrations, cyanobacterial blooms in the lake have increased over recent years. We found that these blooms coincide with depleted nitrate–nitrogen concentrations and increased water temperatures. We propose a simple model with water temperature, nitrate–nitrogen and total phosphorus concentrations as input variables as a basis for formulation of regional eutrophication targets. Political decisions should be preceded by open discussion between policymakers and scientists to differentiate between real knowledge, assumptions or feelings. For optimal results, recommendations for reducing nutrient load should consider all sources, including urban stormwater and wastewater from rural houses, and should be founded on a balanced reduction in emissions of algae-available nutrients. In addition, climate change calls for more effective environmental policy to protect surface water resources. [Copyright &y& Elsevier]

Abstract: A case study was carried out in central Sweden on local initiatives for a river basin in accordance with the European Water Framework Directive. The catchment has erosion problems and the recipient waters suffer from eutrophication. Collective learning and successively more collaborative measures were introduced. According to stakeholders, the following measures were considered feasible and ranked in order of importance: improved soil fertility (improved organic concentration)>measures at or in the stream>measures in the lake itself>improvements to single household wastewater treatment systems. Personal contacts and dialogue at an early stage between stakeholders in order to motivate actions were found to be necessary for progress in the work. Local demonstration areas and information were found to be important in the collaborative learning process according to interviews with the farmers. They indicated more interest and willingness to change behaviour than was demonstrated from real actions during 2 years when several economic subsides were introduced. Sustained financial backing is crucial and funding must be secured to implement the actions decided upon. Implementation required improved contact between local authority employees, politicians, householders and farmers within the catchment area, and in addition, introduced social values as a factor defining the environmental goal to be reached for the lake. [Copyright &y& Elsevier]

Abstract: A study of erosion and phosphorus problems was carried out in central Sweden in an area with very visible erosion and negative offsite effects on water quality. The Mässingsboån catchment is dominated by agriculture and the recipient Lake Brunnsjön suffers from eutrophication. Local demonstration areas were established and local personal contacts to motivate action and local subsidies were financed for 2 years. Measures identified and/or implemented to reduce phosphorous load on the lake were grouped into: (1) improved soil fertility and minimising of soil erosion; (2) measures at or in the stream; (3) measures in the lake itself; (4) improvements of single household wastewater treatment systems. Soil management that improved aggregate stability was demonstrated to significantly reduce soil erosion and loss of particulate-bound phosphorus. In addition, high soil fertility was generally associated with good aggregate stability. Local experiments in the stream and in the lake were less successful and more research is needed. Maximum phosphorus concentration for water loading the lake without causing excessive eutrophication was calculated to be similar to the background phosphorus concentration from arable land (0.05mgl−1). [Copyright &y& Elsevier]

Reports that during a period with pronounced snowmelt via surface runoff, high water concentrations of dissolved molybdate-reactive phosphorus (MRP) were detected in surface runoff water from a clay soil of illite type. Phosphorus fractions that were defined, including phosphorus in particles, colloidal phosphorus caught on filters, and dissolved phosphorus not reacting with molybdate (DUP); Order of concentrations; Amounts of MRP, CPP, and DUP that were lost from a grass?clover ley and a ploughed soil; Heavier phosphorus-containing material that was lost from the ploughed area; Fraction of CPP in drainpipe water, Amount of MRP in stream water; Loss on ignition of the settling material that slowly decreased during the snowmelt period; Total phosphorus concentrations in the material that followed the runoff pattern, with slightly higher phosphorus concentrations during fast runoff; Amounts of readily dissolved or colloidal-bound phosphorus transported from this clay soil during snowmelt that are discussed with regard to the use of grass buffer strips as a measure against phosphorus losses from arable land.

Catch crops are a potential option to reduce phosphorus (P) losses, but little is known about their establishment success and capacity to retain P on clayey soils in regions with short autumns, e.g. Sweden. This study screened biomass production and P retention by eight catch crop species: the perennials chicory ( Cichorium intybus L.), cocksfoot ( Dactylis glomerata L.), perennial ryegrass ( Lolium perenne L.) and red clover ( Trifolium pratense L.) and the annuals phacelia ( Phacelia tanacetifolia L.), white mustard ( Sinapis alba L.), oilseed radish ( Raphanus sativus L. oleiformis ) and white radish ( R. longipinnatus ). The catch crops were grown at six field sites, where the perennial species were under-sown with barley and the annual species were after-sown following barley harvest. Biomass production, P content in above-ground and below-ground plant parts and content of available P in the soil were determined in autumn and survival rate of the catch crops in the following spring. Biomass production and P retention in autumn both differed significantly between species ( p < 0.0001), and were greatly affected by site-specific conditions and time of sowing, which differed between experiments. Growth of catch crops can also be suppressed by low precipitation. Content of P in roots varied substantially between species, a factor which must be considered in species comparisons. The under-sown species produced more or equivalent amounts of biomass, retained more or equivalent amounts of P in autumn and survived better over winter than the after-sown species. Thus under-sown catch crops generally seem more suitable as catch crops for P. [ABSTRACT FROM AUTHOR]

Diffuse phosphorus losses from arable land contribute significantly to eutrophication in many regions. To enable the most efficient measures for reducing P losses to be identified, it is important to quantify the contributions from different sources and the effects of various scenarios aimed at reducing these losses. To account for transport to tile-drains through macropores, we extended the field-scale simulation model ICECREAM with descriptions based on mixing layer and dual porosity concepts. For losses of particulate phosphorus (PP) to tile-drains, a new description of particle generation and detachment was included. The model was applied on a 6-year field experiment on a structured clay soil in south-west Sweden and simulation results were compared with measured water flow and losses of suspended particles (SP), PP and dissolved reactive phosphorus (DRP) to tile-drains. After calibration of parameters related to macropore flow and transport, and to particle generation and detachment, the model could describe the extremely episodic losses of SP, PP and DRP reasonably accurately. However, some short-term fluctuations were not captured (model efficiency during the validation period −2.1 for PP and 0.43 for DRP). Thus, further development and testing are required before the model can be used with confidence for predictive applications or management purposes. Based on this application, we suggest that direct leaching from non-decomposed plant material and infiltration in partly frozen soil be included in the ICECREAM model. We also suggest that the controls on the sorption distribution coefficient for partitioning between DRP and labile phosphorus (P L) and the effects of using the ‘storage routing’ equation for calculation of soil water content instead of the Richards equation be further investigated. [Copyright &y& Elsevier]

Abstract Efficient phosphorus (P) fertilization strategies are essential for intensive crop production with minimal negative environmental impacts. A key factor in sustainable P use is assessment of the plant available soil P pool using soil P tests. This study determined isotopically exchangeable P after six days of reaction with 33PO 4 (P- E (6 d)) to determine how accurately two commonly used P tests, Olsen and AL (acid ammonium acetate lactate) can quantify the amount of labile P. Soil samples were taken from both highly P-amended and unamended plots at six sites within the Swedish long-term soil fertility experiments. According to P K-edge XANES spectroscopy, the P speciation was dominated by Al-bound P and organic P, with additional contributions from Fe-bound P and Ca phosphates in most soils. The results showed that the AL test overestimated P- E (6 d) by a factor of 1.70 on average. In contrast, the Olsen test underestimated P- E (6 d), with the mean ratios of P-Olsen to P- E (6 d) being 0.52 for high-P and 0.19 for low-P soils. The 33P/31P ratio in the Olsen extract of a 33PO 4 spiked soil was closer to that of a 0.005 mol L−1 CaCl 2 soil extract than the corresponding ratio in the AL extract, suggesting that AL extraction solubilized more non-labile P. In conclusion, the AL and Olsen methods are not suitable for direct quantification of the isotopically exchangeable soil P pool after 6 days of equilibration. However, based on the results, Olsen may be superior to AL for classification of soil P status, due to its even performance for calcareous and non-calcareous soils and lower extraction of non-labile P. Highlights • Extraction with sodium bicarbonate (Olsen) underestimated isotopically exchangeable P. • P fertilization increased the ratio of Olsen-P to isotopically exchangeable P. • AL extraction solubilized a large fraction of non-isotopically exchangeable P. • For classification purposes, the Olsen test is probably superior to AL. [ABSTRACT FROM AUTHOR]

With time, different soil-forming processes such as weathering, plant growth, accumulation of organic matter, and cultivation are likely to affect phosphorus (P) speciation. In this study, the depth distribution of P species was investigated for an agricultural clay soil, Lanna, Sweden. Small amounts of apatite-P was demonstrated in the topsoil whereas the speciation of P at 70–100 cm depth consisted of approximately 86% apatite according to P K-edge XANES (X-ray absorption near-edge structure) spectroscopy. Because there were only minor differences in bulk mineralogy and texture, these variations in P speciation were interpreted as the result of apatite weathering of the topsoil. Speciation modeling on soil extracts supported this idea: hydroxyapatite was not thermodynamically stable in the top 50 cm of the soil. Apatite was enriched in the bulk soil relative to the clay fraction, as expected during apatite dissolution. Combined results from batch experiments, XANES spectroscopy and X-ray diffraction suggested chemical transformations of the topsoil as a result from accumulation of organic matter and airing from tillage followed by enhanced weathering of apatite, amphiboles, clay minerals, and iron oxides. This caused the formation of poorly crystalline secondary iron and aluminum (hydr)oxides in the topsoil, which retained part of the released P from apatite. Other P was incorporated into organic forms. Furthermore, the results also showed that short-term acidification below the current pH value (below 5.5 in the topsoil and 7.2 in the deeper subsoil) caused significant solubilization of P. This is attributed to two different mechanisms: the instability of Al-containing sorbents (e.g. Al hydroxides) at low pH (in the topsoil), and the acid-mediated dissolution of apatite (the subsoil). [ABSTRACT FROM AUTHOR]