Organic C levels in intensively managed arable soils – long-term regional trends and characterization of fractions

Substantial losses of soil organic carbon (SOC) from the plough layer of intensively managed arable soils in western Europe have recently been reported, but these estimates are associated with very large uncertainties. Following soil surveys in 1952 and 1990 of arable soils in West Flanders (Belgium), we resampled 116 sites in 2003 and thus obtained three paired measurements of the OC stocks in these soils. Ten soils were selected for detailed physical fractionation to obtain possible further explanations for changes in SOC stocks. Between 1990 and 2003, the SOC stocks decreased at an average rate of ?0.19 t OC ha^?1 year^?1. This loss is significant but is still less than half the rate of SOC decrease that was estimated previously for the whole region of Flanders, which includes the study area. Variation in SOC stocks or in the magnitude of SOC stock losses could not be related to soil texture, to changes in ploughing depth, or to recent land‐use changes. A good relationship, however, was found between the SOC losses and organic matter (OM) inputs. The results of the physical fractionation also suggested management to be the predominant factor determining variation in SOC stocks because no correlation was found between soil texture and the absolute amounts of OC present in the largest OM fractions, that is, the OC in free particulate organic matter (POM), and OC associated with the silt + clay size fraction. The proportion of OC in free POM was up to 40% of the total OC, which indicates the important impact of management on SOC and also indicates that a substantial part of the SOC still present, may in the future be lost at a time scale of years to decades assuming that the intensive management continues.     

Comparison of approaches towards ecotoxicity evaluation for the application of dredged sediment on soil

Purpose

The toxicity of 36 dredged sediments from the Czech Republic was investigated using a large battery of bioassays. The aim of this study was to investigate the feasibility of ecotoxicity testing in general and of individual bioassays more specific and to investigate how the results of bioassays are determined by the physicochemical properties of sediment samples and/or sediment contamination.

Material and methods

In 2008 and 2010, 36 sediment samples were collected from rivers and ponds and from sediment heaps in different parts of the Czech Republic. Both their physicochemical properties and their levels of contamination with POPs and heavy metals were analyzed. The ecotoxicities of the sediments were evaluated using the four bioassays from the new Czech directive 257/2009 Coll. concerning the application of dredged sediments on agricultural land (Enchytraeus crypticus reproduction, Folsomia candida reproduction, Lactuca sativa root elongation, and potential ammonium oxidation). The results of the four directive bioassays were compared with the results of other soil bioassays (Caenorhabditis elegans mortality, Eisenia fetida avoidance and reproduction) and eluate bioassays (Daphnia magna immobilization, Pseudokirchneriella subcapitata growth inhibition test, and Vibrio fischeri luminescence).

Results and discussion

We demonstrate that the battery suggested in Czech directive 257/2009 Coll. is highly effective in identifying toxic samples; these bioassays clearly revealing different types of toxicity and different exposure routes. Shorter alternative bioassays may be added especially when fast toxicity identification is needed. Eluate bioassays identified samples potentially hazardous to aquatic ecosystems. Their inclusion into the assessment scheme should be considered if the goal of assessment is also the protection of aquatic ecosystems. The results of our multivariate analysis show that specific physicochemical properties and contamination may affect bioassay responses. C. elegans was the most sensitive bioassay to physicochemical properties and also to organic contamination, while eluate bioassays were sensitive to heavy metal pollution.

Conclusions

Most effects detected by the bioassays could not be explained by the levels of toxicants measured or by the natural characteristics of sediments. Our results show that bioassays are irreplaceable in dredged sediment risk assessment because they complement information provided by chemical analyses.     

Thermal transition properties of hoki (Macruronus novaezelandiae) and ling (Genypterus blacodes) skin collagens: implications for processing

Hoki (Macruronus novaezelandiae) and ling (Genypterus blacodes) are cold-water fish caught in New Zealand waters. Their skins are a major component of the post-processing waste stream. Valuable products could be developed from the skins, as they are primarily composed of collagen, which has many commercial applications. We prepared acid soluble collagens (ASC) from hoki and ling skins, and analyzed their thermal denaturation properties using a Rapid Visco™ Analyzer. At slower heating rates the denaturation temperature (TD) of hoki and ling collagens decreased. This result is consistent with the model of irreversible rate kinetics for the denaturation of collagen. We determined the effects of solvents that disrupt hydrogen bonding on ASC stability. Increasing concentrations of urea from 0.1 M to 1.0 M and acetic acid from 0.1 M to 0.5 M decreased TD. This resulted from the effects of these reagents on the hydrogen bonds that stabilize the collagen triple helix.     

Nitrogen and carbon mineralization of surface-applied and incorporated winter wheat and peanut residues

Laboratory incubation experiments were conducted to study the C and N mineralization dynamics of crop residues (fine roots and straw) of the two main crops (winter wheat and peanut) in the Chinese Loess Plateau under different ways of incorporation. The C mineralization patterns of the soil amended with winter wheat residues differed greatly, and the highest C mineralization was observed in the treatment with winter wheat straw incorporated (39% of the total added C mineralized). The way of straw placement had only a minor effect on the pattern of C mineralization for peanut. Generally, winter wheat residues showed a stronger immobilization than peanut residues during the incubation period, without any net N release. Winter wheat straw incorporated showed the strongest N immobilization with 35 mg kg⁻¹ (equivalent to 27% of added N) immobilized at the eighth week. This study indicated that retaining crop residues at the soil surface in the dry land soils of the Chinese Loess Plateau is beneficial for C sequestration. It also showed that N immobilization occurs only during a limited period of time, sufficient to prevent part of the mineral N pool from leaching, and that net N mineralization can be expected during the subsequent cropping season, thus enhancing synchronization of N supply and demand.     

Impact of deposition on the enrichment of organic carbon in eroded sediment

A substantial part of eroded material can be deposited along the runoff pathway. This deposition process may alter the composition of the transported material. Topography- and vegetation-induced deposition processes were examined under laboratory conditions and at the hillslope and watershed scale. The laboratory experiments showed that the enrichment ratio of the specific surface area, ER_SSA, of the transported sediment followed an exponential increase with decreasing sediment delivery ratio, SDR, regardless of the type of deposition process. However, the increase in ER_SSA with decreasing SDR values was lower than expected. The upper limit of the ER_SSA was estimated to be 1.66, which is much lower than the calculated theoretical upper limit of 5.22. This difference can be attributed to the transport of the eroded material in micro-aggregated form. It was also found that the specific surface area, SSA, is a good predictor of organic carbon, OC. The observations on field plots confirmed the results of the laboratory experiments. Measurements at the watershed level indicated that the intensity of the erosion process had a more important influence on sediment enrichment, while the impact of deposition tended to be rather limited. However, sediment monitoring over a longer period is required to reveal the importance of the different erosion processes with regard to OC losses at the field and watershed level.     

Effects of electroanesthesia and a phenothiazine tranquilizer on thermoregulation in the sheep.

The effects of giving propiopromazine alone and of electroanesthesia-propiopromazine treatment on thermoregulation (body temperature regulation) were studied in 3 sheep at ambient temperatures of 5, 25, and 35 C. Measures of thermoregulation during a 120-minute treatment and 120-treatment recovery period included rectal temperature, respiratory frequency, respiratory evaporative heat loss, metabolic heat production, multiple skin temperatures, and shivering. During cold exposure (5 C), both the propiopromazine administration and the electroanesthesia-propiopromazine treatment resulted in hypothermia which was attributed to increased peripheral and respiratory heat losses, a transient inhibition of shivering thermogenesis, and a reduction in metabolic heat production. At 35 C ambient temperature, both resulted in hyperthermia caused principally by a reduction in respiratory evaporative heat loss. The effects of electroanesthesia-propiopromazine treatment on thermoregulation appeared to be additive at both the cold (5 C) and the hot (35 C) environments, in that simultaneous administration resulted in a more profound thermoregulatory impairment. Nevertheless, shifts in body temperature during electroanesthesia are partly attributable to phenothiazine premedication.     

Characterization of nitrogen dynamics in a pasture soil by electromagnetic induction

The aim of this study was to investigate how electromagnetic induction can be used to improve the characterization of N dynamics in a 1.2 ha pasture. The soil apparent electrical conductivity (ECa) was measured by electromagnetic induction using an EM38DD. At 116 locations, soil samples were taken according to a clustered sampling design, three times during one winter, and analyzed for the NO₃^––N content in the topsoil (0–60 cm). Management zones were delineated using a fuzzy k-means classification of the interpolated ECa measurements. Two ECa zones were found, reflecting mainly differences in soil texture. Since the mean NO₃^––N content was different for the two ECa zones (24 and 65 kg/ha in November 2002), the residuals were interpolated using stratified simple kriging. This allowed evaluating the NO₃^– dynamics during the winter in both zones; one ECa zone showed a higher risk for NO₃^– losses than the other calling for a site-specific N management. As a validation, NO₃^––N was interpolated using ordinary kriging without stratification. This resulted in similar zones confirming the usefulness of the ECa measurements to assess N-specific management zones, even within small fields.     

Influence of soil compaction on carbon and nitrogen mineralization of soil organic matter and crop residues

 We studied the influence of soil compaction in a loamy sand soil on C and N mineralization and nitrification of soil organic matter and added crop residues. Samples of unamended soil, and soil amended with leek residues, at six bulk densities ranging from 1.2 to 1.6 Mg m^–3 and 75% field capacity, were incubated. In the unamended soil, bulk density within the range studied did not influence any measure of microbial activity significantly. A small (but insignificant) decrease in nitrification rate at the highest bulk density was the only evidence for possible effects of compaction on microbial activity. In the amended soil the amounts of mineralized N at the end of the incubation were equal at all bulk densities, but first-order N mineralization rates tended to increase with increasing compaction, although the increase was not significant. Nitrification in the amended soils was more affected by compaction, and NO₃ ^–-N contents after 3 weeks of incubation at bulk densities of 1.5 and 1.6 Mg m^–3 were significantly lower (by about 8% and 16% of total added N, respectively), than those of the less compacted treatments. The C mineralization rate was strongly depressed at a bulk density of 1.6 Mg m^–3, compared with the other treatments. The depression of C mineralization in compacted soils can lead to higher organic matter accumulation. Since N mineralization was not affected by compaction (within the range used here) the accumulated organic matter would have had higher C : N ratios than in the uncompacted soils, and hence would have been of a lower quality. In general, increasing soil compaction in this soil, starting at a bulk density of 1.5 Mg m^–3, will affect some microbially driven processes. Received: 10 June 1999