Abbau-, Sorptions- und Verlagerungsverhalten des Herbizides Diuron in einer obstbaulich genutzten Parabraunerde aus Löß

Fate, sorption, and leaching of the herbicide diuron after annual application in an orchard soil (Orthic Luvisol) A three years field trial was conducted in an apple orchard on a loess site (Orthic Luvisol) with annual applications of the herbicide diuron. An accumulation of biologically effective residues of the herbicide was not observed, although a carry-over of herbicide residues in a range of 46–77 μg/kg dry soil in the 0–5 cm layer occurred between different years. After application in May, the residues were rapidly degraded during the following summer months. Disappearance of diuron residues from the 0–5 cm layer conformed to first-order kinetics during the first six months after application. The DT₅₀-values ranged from 14 to 30 days. As the degradation rate decreased with time, the level of remaining residues on a long-term scale was best represented by two combined exponential functions for the fast and slow degradation rate. The distribution coefficient between adsorbed and dissolved residues increased with time, indicating decreasing mobility of herbicide residues. The distribution coefficients and the extractable residue contents were strongly negatively correlated. A few days after a diuron application in May 1994, about 15% of the applied amounts could be analyzed in subsoil samples from 30–60 cm depth (6%) and 60–90 cm depth (9%), while high concentrations of diuron remained in the 0–5 cm soil layer. This was the result of a heavy rainfall (20 mm) and a rapid movement of seepage water into the subsoil due to preferential transport in soil macropores like earthworm channels and shrinkage cracks, which frequently occurred in this untilled loess soil. Different transport patterns were observed during the winter months in 1992/93 and 1993/94, when only low amounts of the diuron applied in spring were leached down to 30–60 cm depth. In winter time, the remaining low concentrations of extractable residues were strongly adsorbed and therefore remained in the upper soil layers.     

Interactions between soil micro- and mesofauna and plants in an ecofarming system

Interactions between crops and soil micro- and mesofauna within the root zone were investigated under field conditions on sandy loam on a larger spatial scale and in columns in the laboratory on a smaller spatial scale. During the vegetation period of summer wheat from April to July 1999 soil samples were taken monthly directly from the root zone within plant rows and between plant rows hardly penetrated by roots. Abundances of Enchytraeidae, Collembola, soil flagellates, enzyme activities and contents of total carbon and nitrogen were determined. Additionally, a laboratory experiment was carried out with soil columns. Soil from the field was defaunated and inoculated with soil fauna (Enchytraeidae, Collembola, earthworms) in different combinations. Furthermore, summer wheat was sown. Enzyme activities, soil flagellate abundance and contents of total carbon and nitrogen were measured after 2, 6 and 14 weeks. Our field results revealed considerable interactions between plant roots, sampling date and soil layer affecting Enchytraeidae and Collembola. Within plant rows flagellate numbers correlated higher with N_t and C_t than between plant rows. In the laboratory close relationships between soil fauna as well as enzyme activities and nutrients contents were found within the root zone.     

Tropical dry forest succession and the contribution of lianas to wood area index (WAI)

The transmission and interception of light through the canopy is an important indicator of forest productivity in tropical forest ecosystems, and the amount of light that eventually reaches the forest floor is influenced by its interactions with leaves, branches, fruits, and flowers among many different canopy elements. While most studies of forest canopy light interception focus on leaf area index (LAI), very few studies have examined wood area index (WAI), which may account for a substantial component of light interception in tropical forests. The influence of lianas on the interception of light and their overall contribution to WAI is a potentially important factor, but it is generally overlooked because of its difficulty to assess. In this paper we evaluate the relative contribution that lianas have to the overall WAI and canopy openness as function of successional stage via a latitudinal comparison of sites across the Americas (Mexico, Costa Rica and Brazil). Our results suggest that lianas significantly increase WAI and decreases canopy openness. However, lianas were absent at all of our study sites where canopy openness exceeded 60%. Our data are the first to explicitly document the role of lianas in the estimation of WAI and, overall, they will contribute to better estimations of ecosystem level LAI in tropical environments, where there is a lack of data on WAI.     

Authentication of the botanical and geographical origin of honey by front-face fluorescence spectroscopy

Front-face fluorescence spectroscopy, directly applied on honey samples, was used for the authentication of 11 unifloral and polyfloral honey types (n = 371 samples) previously classified using traditional methods such as chemical, pollen, and sensory analysis. Excitation spectra (220-400 nm) were recorded with the emission measured at 420 nm. In addition, emission spectra were recorded between 290 and 500 nm (excitation at 270 nm) as well as between 330 and 550 nm (excitation at 310 nm). A total of four different spectral data sets were considered for data analysis. Chemometric evaluation of the spectra included principal component analysis and linear discriminant analysis; the error rates of the discriminant models were calculated by using Bayes' theorem. They ranged from <0.1% (polyfloral and chestnut honeys) to 9.9% (fir honeydew honey) by using single spectral data sets and from <0.1% (metcalfa honeydew, polyfloral, and chestnut honeys) to 7.5% (lime honey) by combining two data sets. This study indicates that front-face fluorescence spectroscopy is a promising technique for the authentication of the botanical origin of honey and may also be useful for the determination of the geographical origin within the same unifloral honey type.     

Quantifying moisture and roughness with Support Vector Machines improves spectroscopic soil organic carbon prediction

The challenges of Vis‐NIR spectroscopy are permanent soil surface variations of moisture and roughness. Both disturbance factors reduce the prediction accuracy of soil organic carbon (SOC) significantly. For improved SOC prediction, both disturbance effects have to be determined from Vis‐NIR spectra, which is especially challenging for roughness. Thus, an approach for roughness quantification under varying moisture and its impact on SOC assessment using Support Vector Machines is presented here.     

Determination of Potassium Delivery to the Roots of Cereal Plants

Potassium (K) delivery to the roots of cereal plants in soils is determined by both soil and plant factors, root growth and root length density in particular, being of major importance. In Part A of this paper an evaluative framework is shown for sandy and loamy-silty soils for determination of root length density based on available field capacity, soil depth in 10 cm steps and the climatic water balance. A good correlation (r² = 0.86) was found when the root length densities were determined at ear emergence. With the help of correction functions root length densities can be subsequently estimated for the other phenological stages (stem elongation, flowering and yellow ripeness). The method described is suited for determining root length densities in water and nutrient transport simulation models. In Part B exchange resins were used to simulate the K delivery from the soil to the root. Measurements were made for different soils and water contents. The depletion zone near the exchange resin was 6 mm thick after 4 days. This corresponds to results obtained from root measurements. Comparisons between a sandy and a loamy-silty soil show, that K delivery by diffusion for equal concentrations depends primarily on soil moisture and pore tortuosity. This leads to the conclusion, that soil physical properties must be taken into consideration when evaluating chemical soil analysis and recommendating fertilizer applications.     

Genetic diversity of international bovine viral diarrhoea virus (BVDV) isolates: identification of a new BVDV-1 genetic group

In the last decade, several studies were performed to characterise bovine viral diarrhoea virus (BVDV) isolates and define genetic groups by genotyping. Much data is now available from GenBank, predominantly sequences from the 5' untranslated region (5'-UTR). In order to find out whether genetic grouping of isolates from different countries could be harmonised, 22 new isolates from five countries were analysed in combination with published sequences. Eighteen of these isolates were typed as BVDV genotype 1 (BVDV-1), and one isolate from Argentina and three isolates from Brazil were typed as BVDV-2. BVDV-1 isolates were clustered into five previously defined genetic groups: BVDV-1a, b, d, e and f. Two isolates from Finland and one from Egypt formed a group which was tentatively labelled as BVDV-1j, since statistical support was low. By using a fragment of the Npro gene for typing, we found that these isolates fall into the same group as a deer strain, and are statistically significant. Some Swiss BVDV strains taken from GenBank were found in a new genetic group which was designated as BVDV-1k. The BVDV-2 isolates included in this study seemed to fall into two genetic groups.     

Bestimmung der Boden-Wasser-Verteilung leichtflüchtiger Kohlenwasserstoffe mittels Dampfraum-GC

Rapid Headspace-GC determination of the soil-water partition ratio of volatile hydrocarbons The hydrocarbon load of contaminated soils is usually mainly adsorbed to the soil organic matter. The laboratory determination of the sorption equilibration of volatiles suffers from severe drawbacks due to volatilization losses of the analytes and low recoveries if liquid extraction methods are applied. The presented headspace technique for the determination of partition coefficients produces reliable results, also under adsorptive as well as under desorptive conditions. It was shown that the volatiles tested are subject to rather severe ad-/desorption hysteresis which strengthens the necessity to determine the desorptive K_oc in contaminated sites. Additionally significant data were obtained that demonstrated a very strong effect of the organic matters quality on the partition ratios of volatiles.     

Geochemical and Microbial Processes in Sediments and at the Sediment-Water Interface of Acidic Mining Lakes

Water, Air, &; Soil Pollution -     

Effects of fallow system and cropping frequency upon quantity and composition of earthworm casts

The quantities of earthworm surface casts were monitored in traditional bush fallow regrowth (BFR), Pueraria phaseoloides live mulch (PLM), Leucaena leucocephala alley cropping (LAC) and undisturbed forest. The fallow systems were planted to maize/cassava intercrop either permanently or for one year after three years of fallow i.e. at 100 and 25% cropping frequencies. Earthworm casting activity was lower in fields cropped after clearing three year old fallow than in the respective permanently cropped fallow management system. The reduction in casting was related both to the degree of biomass removed through burning and to re-establishment of cover crops. Higher exchangeable cation concentration in the soil did not cause increased casting activity. Concentrations of organic C, total N and exchangeable Ca and Mg in casts were significantly higher than in the 0–15 cm topsoil. Exchangeable Ca and Mg in casts did not significantly differ between treatments, with the exception of significantly higher Mg in casts after three years of P. phaseoloides fallow. Topsoil (0–15 cm) exchangeable Ca and Mg were not correlated with cast exchangeable Ca and Mg, but concentrations of organic C and total N in casts were significantly correlated with organic C and total N in the topsoil. Coefficients of variability of organic C, total N and exchangeable Ca and Mg were about twice as high in the soil than in casts. Significant negative correlations between the cast to soil ratio (cast enrichment factor) of organic C, total N and exchangeable Ca and Mg and the respective concentrations in the soil show that earthworms are increasingly selective in organic carbon and nutrient uptake as these parameters of soil fertility are declining.