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Nutrient leaching from clay soils can show extreme temporal and spatial variation. Using an optical sensor (hourly data storage), a Swedish field with vermiculite clay was monitored for water flow (Q expressed in mm), turbidity values (TURB), and nitrate-nitrogen concentrations (CNO3N, mg L-1) in four hydrological years representing different cropping/soil management regimes. Mean TURB-Q slope (1300) decreased in the order: ploughed soil > winter wheat > unfertilized fallow > winter wheat after drainage system renovation + structure-liming of topsoil and backfill, estimated in the initial phase from 16 selected autumn events. A similar ranking was found for variability in turbidity relative to that in discharge (CVT/CVQ) in the entire autumn. Mean CNO3N-Q slope (=2) was significantly lower under fallow than in the three cropping systems (7-32), confirming results from adjacent experimental plots. A spring-period had no snow cover or intensive rain, but in situ monitoring revealed that nutrient leaching was still substantial. Particulate- and dissolved reactive phosphorus, and nitrate-nitrogen leaching was estimated reasonably well (less than 8% difference) based on in situ high-frequency resolution measurements, compared with laboratory analysis of weekly composite samples. Accurate assessment of C-Q relationships in agricultural drainage water across temporal and spatial scales is therefore important. [ABSTRACT FROM AUTHOR]

Domestication of biennial Lepidium campestre L. offers possibilities for more varied crop rotations in cold regions, with increased crop cover during winter. In the first winter after sowing, L. campestre can reduce nitrogen (N) leaching before harvesting in the second year. In this system no soil tillage is needed during the first year, unlike in systems with annual crops. A three-year leaching study on loam soil in southern Sweden revealed significantly (p < 0.05) lower flow-weighted mean total nitrogen (TN) concentration in drainage water under L. campestre (5.8 mg TN L−1) compared with a control treatment (no catch crop and autumn mouldboard ploughing) (9.6 mg TN L−1). In two years of observations, Lepidium campestre had lower flow-weighted mean TN concentration (6.2 mg L−1) than a mixed Vicia villosa L. (hairy vetch)/Secale cereale (winter rye) catch crop (10.2 mg L−1) and rather similar concentration to a Raphanus sativus (oilseed radish) catch crop (5.7 mg TN L−1), both sown after harvest of the main crop. However, L. campestre appeared to have a negative effect on total phosphorus (TP) leaching, with TP concentration in drainage of 0.05 mg L−1 compared with 0.01-0.02 mg L−1 for the other catch crops and the control. [ABSTRACT FROM AUTHOR]

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 year): 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 = 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. [ABSTRACT FROM AUTHOR]

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]

Risk assessment for elevated leaching losses of phosphorus (P) from agricultural land is commonly based on indices, since such losses are highly episodic and difficult to predict. Here a flashiness index (FI) representing changes in daily water flow from drainage systems was estimated from measured discharge (agrohydrological years 2004–2013) after reconstruction of subsurface drainage systems in 16 fields on a former swine farm. The fields were analysed for ammonium lactate-extractable soil P (P-AL), clay, carbon and other soil parameters in 2004. Transport of total P (TP), dissolved reactive P (DRP) and unreactive P (UP) was estimated from concentrations in composite water samples taken flow-proportionally up to 20 times per year. On average, 2.20 kg TP ha − 1 yr − 1 was leached, with 27% in DRP form, from the entire farm. FI was significantly negatively correlated (Pearson correlation coefficient p < 0.05) to mean yearly discharge from each field. Stepwise regression demonstrated that FI index was the most important single explanatory parameter for flow-proportional yearly mean concentration of unreactive P losses (UP) from each field, with a coefficient of determination ( r 2 ) of 0.67. The corresponding concentration of dissolved reactive P (DRP) was significantly positively correlated ( p = 0.015) to soil P-AL and FI. A regression model for TP leaching losses based on FI, P-AL and yearly discharge ( Q ) from 11 of the fields over nine years ( r 2 = 0.67, p = 0.002) was validated against TP leaching from the remaining five fields (32% of farm area). Root mean square error (RMSE) was 0.43, which represented 20% of measured leaching (mean 2.14 kg TP ha − 1 yr − 1 ). For individual years, RMSE for different fields was 37–80% of measured TP leaching (0.8–3.7 kg TP ha − 1 yr − 1 ). The FI index could be used together with soil P test to predict P leaching from individual fields of a drained farm. [ABSTRACT FROM AUTHOR]

Leaching losses of nitrogen (N), phosphorus (P) and potassium (K) from arable land can be high, with N and P contributing significantly to the eutrophication of lakes and coastal waters. This study examined whether agriculture management and drain repair changed the chemical properties of shallow groundwater and affected nutrient leaching in the field. The hydrology of a subsurface-drained agricultural observation field included in the Swedish water quality monitoring programme was simulated for the period 1976–2006 using the process-based, field-scale model DRAINMOD. On the assumption that the drainage system operated similarly before and after repair, 54% more water was assigned to low-moderate flow events. Measured concentrations of sulphate-sulphur (SO4-S), sodium (Na), chloride (Cl) and potassium (K) were significantly lower in shallow groundwater in the period before drainage system repair (1980–1998) than afterwards (1998–2010). The concentrations were also significantly correlated with the corresponding concentrations in near-simultaneously sampled drain water. A similar connection was not observed for Na and Cl in the period before drain repair. Elevated concentrations of nitrate-nitrogen (NO3-N) were recorded both in shallow groundwater and in drainage water from 1998 to 2010, especially after incorporation of chicken manure into the soil in 1998. Based on simulated discharge (assuming a functioning measuring station throughout), estimated flow-weighted mean NO3-N concentration in drainage water increased from 5.6 mg L−1(1977–1998) to 15.7 mg L−1in the period 1998–2000. Simultaneously, mean NO3-N concentration in shallow groundwater increased from 0.2 to 4.0 mg L−1, and then to 4.8 mg L−1in the period 2000–2012. It was estimated that after drain repair, a greater proportion of infiltrated NO3-N entered the receiving stream directly via the outlet of the tile drainage system close to the field's monitoring station than was the case before repair. [ABSTRACT FROM PUBLISHER]

Of the EU countries, Sweden utilizes the highest proportion (10%) of its total agricultural land for horses. Horse paddocks commonly hold horses on a limited space, in the present study at a rate of 5–14 livestock units ha −1 . Thus these paddocks receive significant amounts of phosphorus (P) and nitrogen (N) through feed residues and deposition of feces and urine, which can lead to nutrient build-up in the soil. This study examined soil P and N status in different parts of horse paddocks (feeding, grazing and excretion areas) and compared it with that in adjacent, unmanaged reference soils. The paddock areas were then categorized with respect to environmental risk using the threshold concentrations of plant-available P extracted with ammonium acetate lactate solution at pH 3.75 (P-AL) and total N set by the Swedish Environmental Protection Agency. In total, seven horse farms, covering different grazing densities and soil textures representative of Swedish horse paddocks, were examined. The results showed that concentrations of water-soluble P (WSP), P-AL, and total N were highest in feeding and excretion areas within the paddocks. Weighted concentrations of soil P for the whole paddocks amounted to 2.9–10.5 mg WSP kg −1 and 35–224 mg P-AL kg −1 , and were higher than in the corresponding reference fields (0.8–4.9 mg WSP kg −1 and 17–102 mg P-AL kg −1 ). The WSP concentration in the paddocks was strongly correlated with horse density ( R 2 = 0.80*** 1 , n = 13) and P-AL with years of paddock management ( R 2 = 0.78***, n = 13). Total organic C was significantly correlated with P-AL, total P and total N in the feeding and excretion areas. The degree of soil P saturation percentage (DPS%) were important soil parameters determining WSP concentration in the paddocks ( R 2 = 0.63***, n = 110), whereas total P concentration in soils were determining P-AL concentrations ( R 2 = 0.82***, n = 112). According to Swedish environmental guidelines, two of the seven farms studied posed a high risk and three a moderate risk of extensive P leaching losses, but the risk of extensive N losses was moderate for all farms studied. As regards the specific sections of the paddock, the feeding and excretion areas had the highest risk of P leaching losses. Thus paddock soils can be high-risk areas for P leaching comprising about 3.85% of the total high-risk land area in Sweden. [ABSTRACT FROM AUTHOR]

The Baltic Sea is one of the most eutrophied water bodies in northern Europe and more than 50% of its total anthropogenic waterborne phosphorus (P) and nitrogen (N) loads derive from agricultural sources. Sweden is the second largest contributor of waterborne N and the third largest contributor of waterborne P to the Baltic Sea. Horse farms now occupy almost 10% of Swedish agricultural land, but are not well investigated with regard to their environmental impact. In this study, potential P, N and carbon (C) leaching losses were measured from two representative horse paddock topsoils (0–20 cm; a clay and a loamy sand) following simulated rainfall events in the laboratory. Results showed that the leachate concentrations and net release of P, N and dissolved organic C (DOC) from paddock topsoils were highest in feeding and excretion areas and considerably higher from the loamy sand than the clay paddock topsoil. Leaching losses of dissolved reactive P (DRP) were significantly ( p < 0.05) correlated with concentrations of water-soluble P and ammonium acetate lactate-extractable P (P-AL) in the soil, while leaching losses of dissolved organic P and total organic N were significantly correlated with DOC concentration in leachate. Leaching loads of P and N from paddock topsoils greatly exceeded average figures for Swedish agricultural topsoils. It was concluded that: i) horse paddocks pose a potential threat to water quality via leaching of excess P and N, ii) feeding and excretion areas are potential hotspots for highly enhanced leaching losses, and iii) paddocks established on sandy soils are particularly susceptible to high N leaching losses. [ABSTRACT FROM AUTHOR]

High application rates of poultry ( Gallus gallus domesticus ) manure can impair drainage water quality through enhanced leaching of phosphorus (P) and nitrogen (N). In two years with application rates of broiler chicken manure corresponding to 99 and 79 kg P ha −1 year −1 to a tile-drained field with loamy soil in SW Sweden, mean concentrations of dissolved reactive P (DRP) were significantly higher ( p < 0.05) elevated in peak water flows in the two winter periods than in 19 previous years without manure application of any kind. With the water sampling strategy used, this effect was observed 5 and 4 months after application, when 160 and 140 mm of water, respectively, had discharged. Flow recession of distinct peak flows was illustrated as exponential decay to time, with half-life 48 h, while recession of elevated DRP concentrations had approximately 2 h half-life. In the following 12 years, only moderate amounts of mineral P were applied (on three occasions) to this topsoil with 11% degree of P saturation measured in acid soil extract (DPS-AL). Mean DRP concentrations in peak, base and intermediate flow in that period were moderate, i.e. similar to those before manure application. In contrast, high concentrations of nitrate N (NO 3 -N) in peak, base and intermediate flows occurred in the 8-year period following manure application. Mean NO 3 -N concentration in peak flows decreased approximately linearly, by 5.6 μg L −1 , for every mm of total water discharge. Thus poultry manure should not be applied in repeated high loads in order to avoid the risk of enhanced P leaching losses during subsequent peak flows. Furthermore, N leaching losses during peak and base flow conditions can persist for longer than a 5-year crop rotation and were shown here to recede at a slower relative rate than P. [ABSTRACT FROM AUTHOR]

Two field experiments with drained plots on clay soils (60% and 25% clay) demonstrated a significant reduction in leaching of total phosphorus after application of structure lime. Aggregate stability was significantly improved. Phosphorus leaching in particulate form was significantly reduced following structure liming at the site with a very high clay content. Sites representing low (50 mg kg−1) and high (140 mg kg−1) levels of phosphorus extractable with acid ammonium lactate in topsoil displayed differing effects on leaching of dissolved reactive P (DRP). This form of phosphorus was only significantly reduced compared with the control at one site with high topsoil phosphorus status and relatively high (17–18%) degree of phosphorus saturation in the subsoil. Laboratory experiments with simulated rain events applied to topsoil lysimeters from the same site also demonstrated a significant reduction in leaching of DRP. These findings indicate that structure liming is an appropriate leaching mitigation measure on soils with both a high clay content and high soil phosphorus status. [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]

Overall, arable soils in Sweden are currently generally close to phosphorus (P) balance, but excessive P accumulation has occurred on animal fur farms, i.e., those rearing mink ( Mustela vison) and foxes ( Alopex lagopus and Vulpes vulpes). Manure P from these farms has sometimes regarded as sparingly soluble. Laboratory lysimeter topsoil trials with simulated rain demonstrated that potential leaching of P in dissolved reactive form (DRP) can be very high, even for heavy clay (50%-65%) soils. The Swedish/Norwegian soil test P-AL (soil P extracted with acid NH4 lactate, AL) proved useful as a potential indicator of DRP leaching risk (regression coefficient [ R2] = 0.89) from fur farms. The upper 5-cm soil layer, with 190% higher (median) soil P status than the 5-20 cm layer, was the major source of potential DRP leaching through soil columns at the site, despite having been under grass or green fallow for the past 8 y. In percolate from topsoil lysimeters, DRP concentration increased by 0.29 mg L-1 after the long-term manure application but only by 0.14 mg L-1 after the single slurry application when compared to no addition of slurry. Therefore, the build-up to a high soil P status due to the long-term application of mink manure was more important than a single application of pig slurry at a rate corresponding to 22 kg P ha-1 with respect to soil leachate DRP losses in this lysimeter study. The study stresses the importance of precision farming, in which the amount of slurry-P applied is based on testing the already existing soil P content. [ABSTRACT FROM AUTHOR]

Highlights: [•] Horse feeding and excretion areas inside the paddocks are enriched with P and N. [•] Horse density and paddock age determines nutrient build-up in paddock soils. [•] Around 34,000ha of Swedish paddock soils are at risk for P and N leaching. [ABSTRACT FROM AUTHOR]

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]

Losses of commonly used chemical pesticides from agricultural land may cause serious problems in recipient waters in a similar way to phosphorus (P). Due to analytical challenges concerning determination of glyphosate (Gly), transport behaviour of this widely used herbicide is still not well known. The objective of the present study was to quantify and evaluate leaching of Gly in parallel with P. Leaching losses of autumn-applied Gly (1.06 kg ha−1) via drainage water were examined by flow-proportional sampling of discharge from 20 drained plots in a field experiment in eastern Sweden. Samples were analysed for Gly in particulate-bound (PGly) and dissolved (DGly) form. The first 10 mm water discharge contained no detectable Gly, but the following 70 mm had total Gly (TotGly) concentrations of up to 6 µg L−1, with 62% occurring as PGly. On average, 0.7 g TotGly ha−1 was leached from conventionally ploughed plots, compared with 1.7 g TotGly ha−1 from shallow-tilled plots (cultivator to 12 cm working depth). Higher Gly losses occurred in snowmelt periods in spring, but then with the majority (60%) as DGly. All autumn concentrations of PGly in drainage water were significantly correlated (p<0.001) to the concentrations of particulate-bound phosphorus (PP) lost from the different plots (Pearson correlation coefficient 0.84), while PP concentrations were in turn significantly correlated to water turbidity (Pearson correlation coefficient 0.81). Leaching losses of TotGly were significantly lower (by 1.3 g ha−1; p<0.01) from plots that had been structure-limed three years previously and ploughed thereafter than from shallow-tilled plots. Turbidity and PP concentration also tended to be lowest in discharge from structure-limed plots and highest from shallow-tilled plots. This difference in TotGly leaching between soil management regimes could not be explained by differences in measured pH in drainage water or amount of discharge. However, previously structure-limed plots had significantly better aggregate stability, measured as readily dispersed clay (RDC), than unlimited plots. The effects of building up good soil structure, with strong soil aggregates and an appropriate pore system in the topsoil, on mitigating Gly and P losses in particulate and dissolved form should be further investigated. [ABSTRACT FROM PUBLISHER]

One problem in evaluating efforts to reduce phosphorus (P) and nitrogen (N) losses to waters is that variations in weather conditions cause nutrient concentrations and waterflow to vary. Analyses of biweekly stream water samples collected manually from two small, neighbouring Swedish agricultural catchments with clay soil (E23 and E24) demonstrated unpredictability in P and N concentrations. However, particulate P (PP) concentrations in the two separate catchments, usually sampled within 2–3 hours on the same day, were clearly correlated to each other (Spearman correlation coefficient r=0.70). Corresponding nitrate–nitrogen (NO3–N) concentrations were also correlated to each other (r=0.79). Particulate P concentrations could reasonably be predicted from suspended solid (SS) concentrations above base flow (BF) in both catchments (regression coefficient R 2=0.84 and 0.86, respectively). In the period 1993–2009, before eutrophication control programmes were introduced in catchment E23, there was no general trend in PP or SS in either catchment. Mean PP (0.13 mg L−1) predicted (R 2=0.88) from high-resolution (15 minute) turbidity concentrations was significantly higher than flow-weighted mean PP concentration estimated from discrete samples (0.10 mg L−1) collected manually at the catchment E23 outlet. Mean PP concentration estimated directly from flow-proportional sampling was also higher. High synoptic concentrations of PP (up to 0.65 mg L−1) were recorded along the open reach of the stream in the ascending limb of high-flow pulses. Using high-resolution monitoring at the catchment outlet, episodes with a clear clockwise hysteresis effect for PP concentration (seen as turbidity) were frequently observed. By contrast, the NO3–N peak appeared 4–7 hours after the flow peak and anticlockwise hysteresis was observed. Significant erosion along stream banks may take place, and the degree of erosion was estimated based both on farmers’ observations and on results from a distributed erosion model (USPED). Monitoring and erosion mapping are currently being used in practical remedial work. [ABSTRACT FROM PUBLISHER]

Abstract: 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 13.1–23.9kgha−1 year−1 from an integrated cropping system across a 4year period, with 75% in nitrate form (NO3–N). Mean total P (TP) loss was 0.96–3.03, 0.99–4.63 and 0.76–2.67kgha−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 &y& Elsevier]

Phosphorus (P) leaching from agricultural soils is a serious environmental concern. Application of aluminium water treatment residuals (Al-WTR5) 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 imol 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 80-100mg 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-WVR should only be applied to soils with high P fertility where improved crop production is not required. [ABSTRACT FROM AUTHOR]

Abstract: In 1988–2009, efforts involving manure regulations, subsidies and advisory work were made to reduce losses of nitrogen (N) and phosphorus (P) from arable land to water in Sweden, especially southern Sweden. To evaluate ensuing long-term trends, nutrients in total and dissolved form were monitored in drainage water from 13 fields under ordinary cultivation. The Mann-Kendall test, adjusted for biweekly sampling, revealed significant decreasing trends (magnitude 3% per year) in nitrate–nitrogen (NO3–N) concentrations in two fields. One of these had received no manure and had been subjected to delayed tillage after fallow since 1993, while the other had been frequently cropped with a catch crop combined with spring tillage since 1999. An additional decreasing trend in dissolved reactive P (DRP) was observed over the years from this and another field, both with unfertilised fallow grown as an interior buffer on an area at the field outlet, one in 1999–2010 and the other since 2001. By contrast, there was an increasing trend in DRP in a field with accelerating P loads that included almost yearly manure additions to crops following potatoes and sugar beet. However, the general DRP level in the drainage water was low (4–13μgL−1), probably as a result of high P sorption capacity of the topsoil and subsoil. No significant trends in total P or particulate P were found for any of the fields. The importance of long-term monitoring of nutrients in water leaving agricultural fields in order to estimate trends in nutrient losses is discussed. [Copyright &y& Elsevier]

Summary: A refined version of a conditional phosphorus risk index (PRI) for P losses to waters was developed based on monitoring and analyses of PRI factors from an agricultural catchment in Sweden. The catchment has a hummocky landscape of heavy glacial till overlying moraine and an overall balanced soil P level. Single P source factors and combinations of factors were tested and discussed together with water movement and water management factors important for catchments dominated by drained clay soils. An empirical relationship was established (Pearson correlation coefficient 0.861, p <0.001) between phosphorus sorption index (PSI-CaCl2), measured in a weak calcium chloride solution, and iron (Fe-AL) aluminium (Al-AL) and phosphorus (P-AL) in soil extract with acid ammonium lactate. Differing relationships were found for a field that had not received any manure in the last 15years and a field that had received chicken litter very recently. In addition, a general relationship (Pearson correlation coefficient 0.839, p <0.001) was found between the ratio of phosphorus extracted from fresh soil in water (Pw) to PSI-CaCl2 and the degree of phosphorus saturation in lactate extract (DPS-AL). One exception was a single field, representing 7% of agricultural land in the catchment, that had been treated with glyphosate shortly before soil sampling. Saturated hydraulic conductivity (SHC) in heavy clay in contact with the moraine base (at 1m depth) was on average 0.06mday−1. In clay not in contact with moraine, SHC was significantly lower (mean 0.007mday−1). A reduction in the present tile drain spacing (from 14–16m to 11m) is theoretically required to maintain satisfactory water discharge and groundwater level. Up to 10% of the arable land was estimated to be a potential source area for P, based on different indices. Parts of a few fields close to farm buildings (1% of total arable land) were identified as essential P source areas, with high DPS-AL values and low PSI-CaCl2 values throughout the soil profile. A further 2% of arable land was identified as potential important transport areas, based on visible surface water rills or frequent water-ponded conditions. Fields comprising 10% of the total arable land in the catchment should be re-drained in the near future to improve water infiltration and avoid unnecessary channelised water flow. The need for an improved PRI for erosion and water transport is discussed. [Copyright &y& Elsevier]

Abstract: Concentrations of dissolved reactive phosphorus (CDRP) and particle-bound phosphorus (CPP) were investigated in soil columns taken from different parts of three selected agricultural fields. The columns (mini-lysimeters 20cm in diameter, 20cm high) were exposed to on average 64±6mm of simulated rainfall. Total phosphorus concentrations (CTP) in water percolating from the lysimeters were similar to the CTP observed in drainage water leaving the fields, but the CDRP/CTP ratio was significantly (p <0.001) higher in the percolate. The high CDRP (up to 0.4mgL−1) measured in the percolate may have partly derived from decomposition of accumulated senescing vegetation and litter material, since CDRP in percolating water was related to total organic carbon concentration (TOC) in the shallow topsoil (0–5cm) and to phosphorus concentration in soil extract of ammonium lactate (P-AL) from the same soil layer. Another easily identified factor clearly related to CDRP in percolate from the lysimeters was the degree of phosphorus saturation (DPS) in the same soil P-AL extract. The factors giving best prediction of CPP and leaching were the amount of percolate passing through the soil columns and total phosphorus concentration in the topsoil determined after oxidation with nitric acid (TP-HNO3). One field under grass ley, including the slope and depression close to the field outlet, comprised 24% of total field area. In the other two fields these areas (11 and 17% of total area respectively) were under long-term permanent green fallow as an internal buffer zone (IBZ). The lysimeter studies indicated that these areas had a higher risk of DRP losses than the rest of the fields. In addition, the P content of the particles in water from the depression was unusually high. Aggregate stability, measured indirectly as readily dispersible clay and expressed as nephelometric turbidity units (NTU), was significantly stronger at the lowest point of one IBZ (27–35NTU) than in stubbled parts of the same field (62NTU), and the turbidity of water percolating through the topsoil was lower (5–27NTU). [Copyright &y& Elsevier]

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]

Leaching of nutrients and major ions from a tile-drained arable field was evaluated over a 25-year period (1980-2005). The soil, classified as a Gleyic Cambisol, received moderate applications of fertilizers. During later years the soil was more frequently under ley, and since 2002, an area of ravine (29% of the total field) has been managed as a permanent fallow with annual cutting without removing the grass material. A decrease in the concentration of nitrate nitrogen (NO3-N) in the drainwater was estimated in 1980-2005, based on non-parametric tests on concentrations flow-normalized with a robust fitting curve procedure. The average concentration of soluble reactive phosphorus after pre-filtration (RPf) of 0.030 mg l-l corresponded to a calculated degree of phosphorus saturation (DPS) of 6% in acid extract of ammonium lactate from the topsoil. Between 1995 and 2005, concentrations of suspended solids (SS), RP and total organic carbon (TOC) decreased significantly in the drainage water from the entire field. Throughout the entire period, there was a negative net accumulation of the major ions to the soil. The order of decrease in relative terms was calcium (Ca2+)>magnesium (Mg2+)>sulphate (SO42-)>chloride (Cl-)>potassium (K+). In addition, the soil phosphorus (P) balance was negative. A significant reduction in ion concentrations in the drainwater, including sodium (Na+) and hydrogen carbonate HCO3 -, was estimated. The order of reduction in relative terms was: SO4 2->Mg2+>Ca2+>HCO3->Cl->NO3->Na+>HPO4. Altogether these trends were equal to approximately 0.1 mmolc l-1. yr-1 of positively and negatively charged ions. Based on measured concentrations, decreasing trends in SO4 2- and Ca2+ were also observed in the shallow groundwater (3.6 m below the soil surface), while K+, Na+ and HCO3- tended to increase. Trends of cations in deeper groundwater (5.8 m below the soil surface) were in some cases the opposite of the trends in the drainwater. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the long-term (1977-2004) effects of new agricultural practices and reduced acid rain on drainwater and groundwater chemistry for an intensely cultivated arable field with sandy soil in south-west Sweden. Trends in chemical composition of the drainwater were compared with those of atmospheric deposition and groundwater. A modified crop rotation including catch crops significantly decreased the average concentration of nitrate nitrogen (NO3-N) in drainwater from 13.0 to 7.2 mgL-1. This rotation was also found to be a very effective measure against high NO3-N concentrations in shallow groundwater (1.7 m below the soil surface). The degree of phosphorus saturation (DPS) in the subsoil, calculated to be 10% and 9% by two different laboratory methods, corresponded to an average and constant concentration of dissolved reactive phosphate (DRP) in drainwater of 0.006 mg l-1. Generally lower inputs of acid deposition to the soil were confirmed by a decreasing SO4-S trend (by 3% over 24 years) in drainwater. Changes in cropping had reduced the acid load to the soil, while drainwater alkalinity showed a slow but significant positive trend amounting to 0.4% over 24 years. [ABSTRACT FROM AUTHOR]

Abstract: Phosphorus (P) binding to minerals and ion exchange capacity in different clay fractions were examined for a non-calcareous soil in southwest Sweden. The soil had received pig slurry during three decades, 2 kg lower than the recent maximum load of 22 kg P ha−1 year−1 as regulated by livestock density legislation. The topsoil was found to contain 33% clay by weight. Illite was the predominant clay mineral and constituted 13% of total soil. Vermiculite (10%), K-feldspar (14%) and plagioclase (21%) also constituted significant proportions of the mineralogical matrix. Within the most fine-grained clay fraction, 50% of which was less than 0.1 μm in particle size, illite and vermiculite dominated totally, 50 and 23% respectively. In fine-grained (FG), most fine-grained (MFG) and colloidal fractions, there were strong relationships (Pearson correlation coefficient 0.98–1.00) between calcium (Ca) and P. There was a low molar ratio Ca:P in added manure and the presence of Ca–P complexes in the fine soil fractions was indicated. In contrast, in the coarse soil fraction (>2 μm), there was a clear relationship (Pearson coefficient 0.97) between P and iron oxide (Fe2O3) and between P and aluminium oxide (Al2O3) throughout the soil profile. Thus even for non-calcareous soils, formation of Ca–P complexes should be taken into account with regards to losses of colloidal P to drainage water. [Copyright &y& Elsevier]

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 dw1) 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% of exposed radioactivity in water, while 0.003% 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. [ABSTRACT FROM AUTHOR]

• Nitrate retention was estimated by flow-proportional sampling and sensors. • Summer nutrient retention was efficient (%), but was a small part of yearly mass. • Organic nitrogen retention was efficient in the first winter, but not the second. • Sensors are essential for evaluating nutrient dynamics and retention. Constructed free water surface wetlands (CWs) are used to reduce nutrient and sediment loads to receiving waters in highly impacted catchments by e.g., agricultural land use. In this paper, we evaluated the retention effectiveness of a Swedish CW in two consecutive hydrological years, 3–4 years after construction respectively. We compared nutrient loads based on concentrations from flow-proportional sampling (C fp) and turbidity and nitrate concentrations measured with optical sensors (C s). CW's retention was estimated based on differences between inlet and outlet concentrations and flow (Q) at both the inlet and outlet (2Q), or only at the inlet (1Q). In the first year (2012/2013), with a cold winter (mean topsoil temperature −0.2 °C), nitrate-nitrogen (NO 3 N) retention was 32% (C fp and C s , 2Q). In the second year, with a mild winter (mean topsoil temp 1.8 °C) and less water runoff, the corresponding values were 37% (C fp , 2Q) and 39% (C s , 2Q). Nitrate-nitrogen retention was significantly correlated to water residence time and temperature, and was most effective relative to the load (80%) in summer and least effective (40%) in winter. Quantitatively, however, summer NO 3 N retention contributed only 7% (2Q) or 8% (1Q) of yearly NO3N mass retention. Particulate phosphorus (PP) concentrations were significantly correlated with suspended solids (SS) concentrations at both inlet and outlet. Seasonal PP retention (C fp , 2Q) was related to particle residence time estimated from turbidity measurements by sensors, and was less effective in the cold winter (3%) than in the mild winter (32%) (C fp , 2Q). Yearly retention (2Q) as a mean of the two years was: SS 40%, total P 36%, PP 34%, dissolved reactive P 30%, total N 56%, NO 3 N 35%, organic N 75%, and organic C 30%. Overall, the wetland satisfactorily removed nutrients from agricultural drainage water. However, longer-term studies over a range of flow and temperature conditions are needed to evaluate climate conditions and hydrological residence time as key factors in nutrient removal efficiency. [ABSTRACT FROM AUTHOR]

A Field experiment to investigate nutrient leaching was established in 2011 on a clay loam. The field site is located about 15 km south of Uppsala in eastern Sweden (59°43'0" N; 17°41'21" E). The experimental field is about 0.42 ha (72 × 50 m), with a slope in the north-south direction of about 1%. At the lower part of the field, grassed buffer strips were established as follows: A) Control, which is managed in the same way as the main field; B) Grass buffer strips; C) As B, but the grass harvested once a year. Each treatment was 6 m by 6 m, and is replicated in four blocks. Each plot is drained with a central 6-m long drain pipe at 1 m depth. The rest of the field is not drained. Surface runoff and drainage water are led to an automated measuring and sampling station. The samples were analyzed for phosphorus, nitrogen and organic carbon. On average, the leaching of particulate phosphorus via drainage tiles was reduced by 17 % in the grass buffer strips but the effect of harvesting the grass on reducing leaching was very little. Nitrate leaching was reduced by 28 %. Surface runoff was scarce during the experimental years and its data was insufficient to draw conclusions. [ABSTRACT FROM AUTHOR]

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 year), 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), 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. [ABSTRACT FROM AUTHOR]

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]

Background and aims: Catch crops used for mitigating nutrient losses to water can release phosphorus (P) when exposed to repeated freezing-thawing cycles (FTCs). This study sought to evaluate potential P losses from shoots and roots of eight catch crops. Methods: Shoots and roots sampled from perennial ryegrass ( Lolium perenne L.), cocksfoot ( Dactylis glomerata L.), chicory ( Cichorium intybus L.), phacelia ( Phacelia tanacetifolia L.), red clover ( Trifolium pratense L.), white mustard ( Sinapis alba L.), oilseed radish ( Raphanus sativus var. oleiformis L.) and white radish ( R. sativus var. longipinnatus L.) were treated with no freezing, one single FTC, four continuous FTCs and four discontinuous FTCs. All samples were analysed for water-extractable P (WEP), and root samples also for characteristics such as specific root surface area (SSA). Results: Freezing-thawing significantly increased potential P losses from both shoots and roots compared with no freezing. The two radish species and white mustard contained significantly higher concentrations of WEP than the other species, among which chicory and phacelia had the lowest WEP. On average, shoots had 43 % higher WEP than roots. Cumulative P release from shoots and roots was strongly correlated with their total-P content ( p = 0.006 and p = 0.002, respectively). Cumulative release of P from taproots was correlated with SSA ( p = 0.03). Conclusions: Chicory, and possibly phacelia, appear to be promising 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]

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. [ABSTRACT FROM AUTHOR]

Abstract: The use of biochar as a soil amendment has recently increased because of its potential for long-term soil carbon sequestration and its potential for improving soil fertility. The objective of this study was to quantify the effects of biochar soil incorporation on pesticide adsorption and leaching for two Swedish topsoils, one clay soil and one loam soil. We used the non-reactive tracer bromide and the pesticides sulfosulfuron, isoproturon, imidacloprid, propyzamid and pyraclostrobin, substances with different mobility in soil. Adsorption was studied in batch experiments and leaching was studied in experiments using soil columns (20cm high, 20cm diameter) where 0.01kgkg−1 dw biochar powder originating from wheat residues had been mixed into the top 10cm. After solute application the columns were exposed to simulated rain three times with a weekly interval and concentrations were measured in the effluent water. The biochar treatment resulted in significantly larger adsorption distribution coefficients (Kd ) for the moderately mobile pesticides isoproturon and imidacloprid for the clay soil and for imidacloprid only for the loam soil. Relative leaching of the pesticides ranged from 0.0035% of the applied mass for pyraclostrobin (average Kd =360cm3 g−1) to 5.9% for sulfosulfuron (average Kd =5.6cm3 g−1). There were no significant effects of the biochar amendment on pesticide concentrations in column effluents for the loam soil. For the clay soil concentrations were significantly reduced for isoproturon, imidacloprid and propyzamid while they were significantly increased for the non-mobile fungicide pyraclostrobin suggesting that the transport was facilitated by material originating from the biochar amendment. [Copyright &y& Elsevier]

• Structure liming modified macropore networks, but not mesopore networks. • Structure lime tended to reduce macroporosity, macropore diameters and connectivity. • Structure liming tended to reduce readily dispersible soil. • Liming effects on pore networks differed substantially between sites. • Although quantitatively different, effects generally pointed in the same direction. Structure liming aims to improve soil structure (i.e., the spatial arrangement of particles and pores) and its stability against external and internal forces. Effects of lime application on soil structure have received considerable interest, but only a few studies have investigated effects on macro- and mesopore networks. We used X-ray computed tomography to image macropore networks (ø ≥ 0.3 mm) in soil columns and mesopores (ø ≥ 0.01 mm) in soil aggregates from three field sites with (silty) clay soils after the application of structure lime (3.1 t ha−1 or 5 t ha−1 of CaO equivalent). Segmented X-ray images were used to quantify soil porosity and pore size distributions as well as to analyse pore architecture and connectivity metrics. In addition, we investigated the amount of readily dispersible soil particles. Our results demonstrate that structure liming affected both, macropore networks and amounts of readily dispersible soil to different degrees, depending on the field site. Significant changes in macropore networks and amounts of readily dispersible soil after lime application were found for one of the three field sites, while only some indications for similar changes were observed at the other two sites. Overall, structure liming tended to decrease soil macroporosity and shift pore size distribution from larger (ε >1.0 mm) and medium sized macropores (ε 0.3–1.0 mm) towards smaller macropores (ε 0.1–0.3 mm). Furthermore, liming tended to decrease the critical and average pore diameters, while increasing the surface fractal dimension and specific surface area of macropore network. Structure liming also reduced the amounts of readily dispersible soil particles. We did not find any changes in mesopore network properties within soil aggregates or biopore networks in columns and aggregates. The effects of lime on macropore networks remain elusive, but may be caused by the formation of hydrate phases and carbonates which occupy pore space. [ABSTRACT FROM AUTHOR]

Soil structure influences water infiltration, aeration and root growth and, thereby, also the conditions for sustainable crop production. Our objective was to quantify the effects of different soil management methods, with a focus on liming, on the topsoil structure of clay soils in Sweden. We sampled 32 intact soil columns (18 cm high, 12.7 cm diameter) from an experimental field with four treatments: conventional tillage (CT), conventional tillage followed by liming (CTL), reduced tillage (RT) and unfertilized fallow (UF). The samples were taken in autumn after harvest, seven years after CaO was applied to the CTL plots. We also sampled in total 72 smaller columns (6 cm high, 6 cm diameter) from the same experiment and from two additional liming experiments where a mixture of Ca(OH)2 and CaCO3 had been applied three years prior to sampling. All columns were analysed using X-ray tomography. One soil aggregate (diameter approximately 5 mm) were isolated from each small column and analysed with the same method. Despite a relatively large number of replicates per treatment for the large columns, there were no significant differences between any of the investigated macropore network properties related to tilled treatments. It is possible that the effects of liming on soil structure was limited to a few years, which means that any effect would have diminished by the time of sampling. The UF treatment, in contrast, exhibited more vertically oriented macropores, which were also better connected compared to the other treatments. This confirms previous findings that tillage may disrupt the vertical continuity of macropore clusters. Liming had generally reduced total imaged porosity for pores >100 μm) for the smaller columns resulting in less connected pore networks. Liming had no significant effects on the pore networks (pores>11 μm) of the aggregates. [ABSTRACT FROM AUTHOR]