Nutrient leaching driven by rainfall on a vermiculite clay soil under altered management and monitored with high-frequency time resolution

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 waterflow (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-Qslope (1300) decreased in the order: ploughed soil > winter wheat > unfertilized fallow > winterwheat 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 inturbidity 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, butinsitumonitoring 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 ofC-Q relationships in agricultural drainage water across temporal and spatial scales is therefore important

Phosphorus leaching from clay soils can be counteracted by structure liming

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 phosphorus. 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 dissolved reactive phosphorus. 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

Biomass production and phosphorus retention by catch crops on clayey soils in southern and central Sweden

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

Spatial variation in herbicide leaching from a marine clay soil via subsurface drains

BACKGROUND: Subsurface transport via tile drains can significantly contribute to pesticide contamination of surface waters. The spatial variation in subsurface leaching of normally applied herbicides was examined together with phosphorus losses in 24 experimental plots with water sampled flow-proportionally. The study site was a flat, tile-drained area with 60% marine clay in the topsoil in southeast Sweden. The objectives were to quantify the leaching of frequently used herbicides from a tile drained cracking clay soil and to evaluate the variation in leaching within the experimental area and relate this to topsoil management practices (tillagemethod and structure liming). RESULTS: In summer 2009, 0.14, 0.22 and 1.62%, respectively, of simultaneously applied amounts of MCPA, fluroxypyr and clopyralid were leached by heavy rain five days after spraying. In summer 2011, on average 0.70% of applied bentazone was leached by short bursts of intensive rain 12 days after application. Peak flow concentrations for 50% of the treated area for MCPA and 33% for bentazone exceeded the Swedish no-effect guideline values for aquatic ecosystems. Approximately 0.08% of the glyphosate applied was leached in dissolved form in the winters of 2008/2009 and 2010/2011. Based on measurements of glyphosate in particulate form, total glyphosate losseswere twice as high (0.16%) in the second winter. The spatial inter-plot variation was large (72–115%) for all five herbicides studied, despite small variations (25%) in water discharge. CONCLUSIONS: The study shows the importance of local scale soil transport properties for herbicide leaching in cracking clay soils

Seasonal variation in nutrient retention in a free water surface constructed wetland monitored with flow-proportional sampling and optical sensors

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 degrees C), nitrate-nitrogen (NO3N) retention was 32% (C-fp and C-s, 2Q). In the second year, with a mild winter (mean topsoil temp 1.8 degrees 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 NO3N 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%, NO3N 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

Potential phosphorus release from catch crop shoots and roots after freezing-thawing

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

Mitigation of phosphorus leaching losses via subsurface drains from a cracking marine clay soil

In Scandinavia, subsurface transport via tile drains contributes significantly to phosphorus (P) and nitrogen (N) leaching from arable land, which adds to the eutrophication of surface waters. Using flow-proportional water sampling, various options for mitigating subsurface P leaching losses (and N leaching) were examined in 28 experimental plots on a flat, tile-drained site with 60% marine clay. Two crop rotations and unfertilised fallow were monitored for a total of six years. In addition to topsoil management practices (different forms of tillage, structural liming and mineral P fertilisation), local spatial variations in subsurface transport were determined within the experimental area. Mean total P (TotP) leaching losses after conventional autumn ploughing and inverting the soil to a depth of 23 cm were 0.79 kg ha-1 year-1, with 87% occurring as particulate P (PP), and the corresponding mean total N leaching losses were 27 kg ha-1 year-1, with 91% occurring as nitrate. The coefficient of variation in TotP leaching both in spring before the experiment started (64%) and during the six-year experiment (60%) was higher than the coefficient of variation in P-soil status (20%), or drainage (25%), illustrating the importance of local-scale subsurface transport in this cracking clay. However, TotP and PP leaching losses were significantly (pr>FF <0.001) lower from unfertilised fallow than from other treatments and was not significantly lower after shallow autumn tillage than after conventionally ploughing, whereas PP losses tended to be higher. Infiltration measurements with tension infiltrometers revealed a high variation in saturated hydraulic conductivity within plots. In view of the generally high PP losses, efforts to combat eutrophication of the nearby Baltic Sea should concentrate on soil structure improvements, while extensive tillage and totally omitting P fertilisation of cracking soils with low soil P status appears to be inefficient mitigation options

Changes in pore networks and readily dispersible soil following structure liming of clay soils

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 (phi >= 0.3 mm) in soil columns and mesopores (phi > 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 (epsilon( >100 mm) ) and medium sized macropores (epsilon( 0.3-1.0) (mm)) towards smaller macropores (epsilon( 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

Innebär tillförsel av biogödsel runt Bornsjön ökad risk för fosforläckage?

Att använda biogödsel såsom rötat matavfall som ersättning till mineralgödsel diskuteras för att recirkulera fosfor inom jordbruket. I denna pilotstudie undersöktes om fosforläckaget efter tillförsel av avvattnat rötat matavfall skiljde sig jämfört med tillförsel av mineralgödsel (monoammoniumfosfat) och utan gödsling (kontroll). Biogödseln bestod av rötat matavfall med en fosforhalt av 12% beräknad per torrvikt. De tre försöksleden utsattes för fem bevattningscykler som genererade avrinning. Gödselgivan motsvarade den högsta tillåtna och regnintensitet valdes så att det motsvarar ett värsta tänkbara scenario. Denna pilotstudie visar inte på någon förhöjd risk att sprida avvattnad biogödsel på en lerjord av den typ som användes. Effekter på näringsläckage från rötat matavfall behöver dock undersökas vidare i fältförsök