Mette Lægdsmand

Leaching of colloids and dissolved organic matter from columns packed with natural soil aggregates

Transport of pollutants by colloids and dissolved organic matter (DOM) may increase the leaching of strongly sorbing pollutants (e.g., PAHs, heavy metals, radionuclides, and certain pesticides). A prerequisite for colloid-and DOM-facilitated transport is the release of colloids and DOM from soil. In the present study, the leaching of colloids and DOM from columns packed with natural soil aggregates (2-4 mm) was investigated. Aggregates with different organic matter content were used: Aggregates from Soil 1, with 3.6% organic matter content, and aggregates from Soil 2, with 2.5%. The leaching experiments showed that colloid leaching increased with higher organic matter content. Colloid leaching was strongly affected by the ionic strength of the infiltrating water but less so by the specific type of cation. However, prolonged leaching (20 h) with KCl increased the leaching of colloids, probably because of the ion exchange of naturally occurring polyvalent ions with K+. The accumulated amount of colloids leached during 20-h period was orders of magnitude lower than the amount of dispersible colloids (determined by rotation of soil water mixtures), and the organic carbon fraction (foc) of the leached colloids was 3 to 4 times higher than the foc of the dispersible colloids. The leaching of DOM from Soil 1 was greater, but, relative to the soil organic matter content, it was similar for the two soils. The leaching of DOM was not significantly affected by the chemistry of the irrigation water. Irrigation with solutions of KCl and deionized water increased the hydrodynamic dispersion coefficient on Soil 2, due to swelling of the clay minerals and closure of the soil pores. Irrigation with CaCl2 led to lower hydrodynamic dispersion, because of shrinking clay minerals. Soil 1 was less sensitive to shrinking and swelling of clay minerals because of its higher organic matter content.

Simulating soil N2O emissions and heterotrophic CO2 respiration in arable systems using FASSET and MoBiLE-DNDC

Modelling of soil emissions of nitrous oxide (N2O) and carbon dioxide (CO2) is complicated by complex interactions between processes and factors influencing their production, consumption and transport. In this study N2O emissions and heterotrophic CO2 respiration were simulated from soils under winter wheat grown in three different organic and one inorganic fertilizer-based cropping system using two different models, i.e., MoBiLE-DNDC and FASSET. The two models were generally capable of simulating most seasonal trends of measured soil heterotrophic CO2 respiration and N2O emissions. Annual soil heterotrophic CO2 respiration was underestimated by both models in all systems (about 10–30% by FASSET and 10–40% by MoBiLE-DNDC). Both models overestimated annual N2O emissions in all systems (about 10–580% by FASSET and 20–50% by MoBiLE-DNDC). In addition, both models had some problems in simulating soil mineral nitrogen, which seemed to originate from deficiencies in simulating degradation of soil organic matter, incorporated residues of catch crops and organic fertilizers. To improve the performance of the models, organic matter decomposition parameters need to be revised.

Growth and yield response of winter wheat to soil warming and rainfall patterns

It is predicted that climate change will increase not only seasonal air and soil temperatures in northern Europe but also the variability of rainfall patterns. This may influence temporal soil moisture regimes and the growth and yield of winter wheat. A lysimeter experiment was carried out in 2008/09 with three factors: rainfall amount, rainfall frequency and soil warming (two levels in each factor), on sandy loam soil in Denmark. The soil warming treatment included non-heated as the control and an increase in soil temperature by 5 °C at 100 mm depth as heated. The rainfall treatment included the site mean for 1961-90 as the control and the projected monthly mean change for 2071-2100 under the International Panel on Climate Change (IPCC) A2 scenario for the climate change treatment. Projected monthly mean changes in rainfall compared to the reference period 1961-90 show, on average, 31 % increase during winter (November-March) and 24% decrease during summer (July-September) with no changes during spring (April-June). The rainfall frequency treatment included mean monthly rainy days for 1961-90 as the control and a reduced frequency treatment with only half the number of rainy days of the control treatment, without altering the monthly mean rainfall amount. Mobile rain-out shelters, automated irrigation system and insulated heating cables were used to impose the treatments. Soil warming hastened crop development during early stages (until stem elongation) and shortened the total crop growing season by 12 days without reducing the period taken for later development stages. Soil warming increased green leaf area index (GLAI) and above-ground biomass during early growth, which was accompanied by an increased amount of nitrogen (N) in plants. However, the plant N concentration and its dilution pattern during later developmental stages followed the same pattern in both heated and control plots. Increased soil moisture deficit was observed only during the period when crop growth was significantly enhanced by soil warming. However, soil warming reduced N concentration in above-ground biomass during the entire growing period, except at harvest, by advancing crop development. Soil warming had no effect on the number of tillers, but reduced ear number and increased 1000 grain weight. This did not affect grain yield and total above-ground biomass compared with control. This suggests that genotypes with a longer vegetative period would probably be better adapted to future warmer conditions. The rainfall pattern treatments imposed in the present study did not influence either soil moisture regimes or performance of winter wheat, though the crop receiving future rainfall amount tended to retain more green leaf area. There was no significant interaction between the soil warming and rainfall treatments on crop growth.

Transport and Distribution of Salmonella enterica Serovar Typhimurium in Loamy and Sandy Soil Monoliths with Applied Liquid Manure

ABSTRACT A leaching experiment, where liquid manure spiked with Salmonella enterica serovar Typhimurium (Tet+) DSM554 was applied to soil surfaces, was conducted on intact soil monoliths (60 cm in diameter and 100 cm long). A total of 6.5 × 1010 CFU was applied to each column. We found that Salmonella serovar Typhimurium could be transported to a 1-m depth in loamy soil at concentrations reaching 1.3 × 105 CFU/ml of leachate. The test strain was found in concentrations ranging from 300 to 1.35 cells/ml in loamy soil throughout the 27 days of the experiment, while concentrations below 20 cells/ml were sporadically detected in the leachates from sandy monoliths. Real-time PCR targeting invA DNA showed a clear correspondence between the total and culturable numbers of cells in the leachate, indicating that most cells leached were viable. On day 28, distribution of Salmonella serovar Typhimurium at five depths in the four monoliths was determined. The highest recovery rate, ranging from 1.5% to 3.8% of the total applied inoculum, was found in the top 0.2 m.

Persistence and leaching potential of microorganisms and mineral N in animal manure applied to intact soil columns.

ABSTRACT Pathogens may reach agricultural soils through application of animal manure and thereby pose a risk of contaminating crops as well as surface and groundwater. Treatment and handling of manure for improved nutrient and odor management may also influence the amount and fate of manure-borne pathogens in the soil. A study was conducted to investigate the leaching potentials of a phage (Salmonella enterica serovar Typhimurium bacteriophage 28B) and two bacteria, Escherichia coli and Enterococcus species, in a liquid fraction of raw pig slurry obtained by solid-liquid separation of this slurry and in this liquid fraction after ozonation, when applied to intact soil columns by subsurface injection. We also compared leaching potentials of surface-applied and subsurface-injected raw slurry. The columns were exposed to irrigation events (3.5-h period at 10 mm h−1) after 1, 2, 3, and 4 weeks of incubation with collection of leachate. By the end of incubation, the distribution and survival of microorganisms in the soil of each treatment and in nonirrigated columns with injected raw slurry or liquid fraction were determined. E. coli in the leachates was quantified by both plate counts and quantitative PCR (qPCR) to assess the proportions of culturable and nonculturable (viable and nonviable) cells. Solid-liquid separation of slurry increased the redistribution in soil of contaminants in the liquid fraction compared to raw slurry, and the percent recovery of E. coli and Enterococcus species was higher for the liquid fraction than for raw slurry after the four leaching events. The liquid fraction also resulted in more leaching of all contaminants except Enterococcus species than did raw slurry. Ozonation reduced E. coli leaching only. Injection enhanced the leaching potential of the microorganisms investigated compared to surface application, probably because of a better survival with subsurface injection and a shorter leaching path.

Transport and fate of estrogenic hormones in slurry-treated soil monoliths.

The naturally occurring hormones, such as 17-beta-estradiol, 17-alpha-estradiol, and estrone, present in livestock manure may have detrimental environmental effects if released into surface waters. In areas where manure application is intensive, estrogens have been found in surface waters in concentrations known to affect the endocrine system of fish and amphibians. How the estrogens reach the surface waters is unclear. To investigate whether leaching through the soil profile plays a significant role, we conducted leaching experiments on intact soil cores. Lysimeter soil monoliths (60 cm in diameter and 100 cm long) were excavated from two sites in Denmark (one loamy and one sandy soil). The soil monoliths were treated with pig slurry containing estrogenic hormones and amended with an estrogen tracer (17-alpha-ethinylestradiol) and a conservative tracer (bromide). 17-alpha-ethinylestradiol is a synthetic analog of 17-beta-estradiol with sorption characteristics and molecular structure similar to those of the naturally occurring estrogens in slurry. The monoliths were exposed to a short-term irrigation event (12 h) followed by a long-term semi-field experiment (16 wk), during which leaching of natural estrogens and tracers was followed. Estrogens from slurry were transported to a depth of 1 m in loamy soil and sandy soil. The estrogen concentrations in the leachate were at a level known to affect the endocrine system of aquatic organisms.

Leaching of cyanogenic glucosides and cyanide from white clover green manure

Use of crops for green manure as a substitute for chemical fertilizers and pesticides is an important approach towards more sustainable agricultural practices. Green manure from white clover is rich in nitrogen but white clover also produces the cyanogenic glucosides (CGs) linamarin and lotaustralin; CGs release toxic hydrogen cyanide (HCN) upon hydrolysis which may be utilized for pest control. We demonstrate that applying CGs in the form of a liquid extract of white clover to large columns of intact agricultural soils can result in leaching of toxic cyanide species to a depth of at least 1m. Although degradation of the CGs during leaching proceeded with half lives in the interval 1.5-35 h depending on soil characteristics, a fraction of the applied CGs (0.9-3.2%) was recovered in the leachate as either CGs or toxic cyanide species. Detoxification of the HCN formed was rapid in soil and leachate from both sandy and loamy soil. However, 30% of the leachate samples exceeded the EU threshold value of 50 micrgl(-1) total cyanide for drinking water and 85% exceeded the US threshold of 5 micrgl(-1) for cyanide chronic ecotoxicity in fresh water. This study demonstrates that even easily degradable natural products present in crop plants as defense compounds pose a threat to the quality of groundwater and surface waters. This aspect needs consideration in assessment of the risk associated with use of crops as green manure to replace chemical fertilizers and pesticides as well as in genetic engineering approaches to design crops with improved pest resistance.

Sensitivity of crop yield and N losses in winter wheat to changes in mean and variability of temperature and precipitation in Denmark using the FASSET model

Abstract Sensitivity of wheat yield and soil nitrogen (N) losses to stepwise changes in means and variances of climatic variables were determined using the FASSET model. The LARS-WG was used to generate climate scenarios using observed climate data (1961–90) from two sites in Denmark, which differed in climate and soil conditions. Scenarios involved changes to (i) mean temperature alone, (ii) mean and variability of temperature, (iii) winter and summer precipitation amounts and (iv) duration of dry and wet series. The model predicted lower grain yield and N uptake in response to increases in mean temperatures, caused by early maturity, with little change in variability. This, however, increased soil mineral N causing increased N losses. On sandy loam, larger temperature variability lowered grain yields and increased N losses coupled with higher variability at all the mean temperature ranges. On coarse sand, grain yields either remained unaltered or were slightly reduced when larger temperature variability was introduced to increase in mean temperatures of up to +2°C above baseline. However, introducing variability to further increase in mean temperatures lowered yields without any change in variability. Larger temperature variability did not affect soil mineral N and N2O emissions, but increased N leaching on coarse sand. Large response in grain yield, N uptake and soil N cycling, and in their variability was predicted when summer precipitation was varied, whereas only N leaching responded to changes in winter precipitation. Doubling the duration of dry series lowered grain yield and N removed by grain, but increased N leaching, whereas doubling the duration of wet series showed opposite effect. Predicted responses to changes in precipitation patterns were larger on coarse sand than on sandy loam. This study illustrates the importance of considering effects of changes to mean climatic factors, climatic variability and soil types on both crop yield and soil N losses.

Impacts of projected climate change on productivity and nitrogen leaching of crop rotations in arable and pig farming systems in Denmark

The effects of projected changes in climate and atmospheric CO2 concentration on productivity and nitrogen (N) leaching of characteristic arable and pig farming rotations in Denmark were investigated with the FASSET simulation model. The LARS weather generator was used to provide climatic data for the baseline period (1961–90) and in combination with two regional circulation models (RCM) to generate climatic data under the Intergovernmental Panel on Climate Change (IPCC) A1B emission scenario for four different 20-year time slices (denoted by midpoints 2020, 2040, 2060 and 2080) for two locations in Denmark, differing in soil and climate, and representative of the selected production systems. The CO2 effects were modelled using projected CO2 concentrations for the A1B emission scenario. Crop rotations were irrigated (sandy soil) and unirrigated (sandy loam soil), and all included systems with and without catch crops, with field operation dates adapted to baseline and future climate change. Model projections showed an increase in the productivity and N leaching in the future that would be dependent on crop rotation and crop management, highlighting the importance of considering the whole rotation rather than single crops for impact assessments. Potato and sugar beet in arable farming and grain maize in pig farming contributed most to the productivity increase in the future scenarios. The highest productivity was obtained in the arable system on the sandy loam soil, with an increase of 20% on average in 2080with respect to the baseline. Irrigation and fertilization rates would need to be increased in the future to achieve optimum yields. Growing catch crops reduces N leaching, but current catch crop management might not be sufficient to control the potential increase of leaching andmore efficient strategies are required in the future. The uncertainty of climate change scenarios was assessed by using two different climate projections for predicting crop productivity and N leaching in Danish crop rotations, and this showed the consistency of the projected trends when used with the same crop model.

Sorption of 17β-Estradiol to Pig Slurry Separates and Soil in the Soil–Slurry Environment

Contamination of freshwater by estrogens from manure applied to agricultural land is of grave concern because of the potentially harmful effects on aquatic life and human health. Recent developments in liquid manure (slurry) management include partial removal of particulate slurry dry matter (PSDM) by separation technologies, which may also remove parts of the estrogens and enhance infiltration of the slurry on field application and hence the interaction between estrogens and the soil matrix. This study investigated how 17β-estradiol (E2), a natural estrogen commonly found in pig manure, sorbs to agricultural soils, to different size fractions of pig slurry separates, and to soils amended with each size fraction to simulate conditions in the soil-slurry environment. A crude fiber fraction (SS1) was prepared by sieving (<500 μm) the solids removed by an on-farm separation process. Three other size fractions (SS2 > SS3 > SS4) were prepared from the liquid fraction of the separated slurry by sedimentation and centrifugation. Sorption experiments were conducted in 0.01 mol L(-1) CaCl(2) and in natural pig urine matrix. Sorption in 0.01 mol L(-1) CaCl(2) was higher than that in pig urine for all solids used. Sorption of E2 to soil increased with its organic carbon content for both liquid phases. The solid-liquid partition coefficients of slurry separates were 10 to 30 times higher than those of soils, but the organoic carbon normalized partition coefficient values, reflecting sorption per unit organic carbon, were lower for slurry separates. Mixing slurry separates with soil increased the sorption of E2 to the solid phase significantly in the order: SS1 < SS3 < SS2 for both liquid phases. In contrast, SS4 reduced the sorption of E2 to the solid phase by increasing the sorption to suspended or dissolved organic matter. The study suggested that potentially 50 to 75% of E2 in slurry can be removed from the liquid fraction of slurry by physical separation.