Influence of soil parameters on the effect of 3,4-dimethylpyrazole-phosphate as a nitrification inhibitor

Nitrification inhibitors specifically retard the oxidation of NH₄⁺ to NO₂^- during the nitrification process in soil. In this study, the influence of soil properties on the nitrification-inhibiting effect of 3,4-dimethylpyrazole-phosphate (DMPP), a newly developed nitrification inhibitor, has been investigated. Based on short-term incubation experiments, where the degradation of DMPP could be largely disregarded, the oxidation of the applied NH₄⁺ was more inhibited in sandy soils compared with loamy soils. The influence of soil parameters on the relative NO₂^- formation could be described by a multiple regression model including the sand fraction, soil H⁺ concentration and soil catalase activity (R²=0.62). Adsorption studies showed that the binding behaviour of DMPP was influenced markedly by soil textural properties, viz. the clay fraction (r²=0.61). The adsorption of DMPP was found to be an important factor for the inhibitory effect on NH₄⁺ oxidation in a short-term incubation (r²=0.57). It is concluded that the evaluated soil properties can be used to predict the short-term inhibitory effect of DMPP in different soils. The significance of these results for long-term experiments under laboratory and field conditions needs further investigation.     

Nitrogen availability of various biogas residues applied to ryegrass

Biogas plants in Germany are producing an increasing amount of biogas residues to be recycled via agricultural crop production. To test whether the wide range of various substrates used in the anaerobic digestion can affect the chemical composition and nutrient availability, seven biogas residues derived from different substrates were investigated with respect to their N supply to ryegrass. Both the short‐term and the long‐term N availability were studied in a 309‐d pot experiment lasting for five successive growth cycles each starting with a fertilizer application. The organic fertilizers were applied based on an equal amount of ammonium‐N (300 mg N per pot) and compared to mineral N from ammonium nitrate of equal dosage. Biogas residues varied greatly in their chemical composition (ammonium‐N 0.20% to 0.51%, N_total 0.36% to 0.75%, and C_org 1.85% to 4.75% in fresh matter). After the first growth cycle, the N availability of the biogas residues applied based on ammonium‐N was at least equal to that from ammonium nitrate. Differences in N offtake after one fertilizer application were negatively correlated to the C_org : N_org ratio of the organic fertilizers. After five successive fertilizer applications, the N utilization of most of the organic fertilizers was increased compared to that of the mineral fertilizer. It is concluded that biogas residues provide plant‐available N at least corresponding to their ammonium content and that the accumulation of organic N in soil through repeated application of biogas residues contributes to N release.     

Cereal aphid control by generalist predators in presence of belowground alternative prey: Complementary predation as affected by prey density

Generalist predators are important antagonists of pest species in agroecosystems. Increasing populations of alternative prey through detrital subsidies is one way to foster these predators. However, alternative prey may also distract generalist predators from their prey thereby diminishing the efficiency of biological control. To develop reliable predictions for biological control, it is essential to evaluate the relative importance of generalist predators, pests, alternative prey and their respective interactions. We investigated the effects of an assemblage of generalist predators on the grain aphid Sitobion avenae in winter wheat. Treatments with 10, 100 and 1000 aphids were established inside 2 m² sized caged plots with control and reduced density of predators. Three weeks after the experiment started, samples were taken to estimate the size of aphid populations and those of alternative prey. Three prey taxa were significantly reduced by generalist predators: the grain aphid S. avenae (Aphidina), the click beetle Adrastus pallens (Elateridae) and the springtail Isotoma viridis (Collembola). Springtails were decreased by generalist predators independent of aphid densities, indicating complementary predation of springtails and aphids. At high aphid densities, grain aphid population peaks were decreased to the threshold level of economic damage, demonstrating efficient aphid suppression by the predator community. Click beetle numbers declined only at low and medium aphid densities. The results suggest that generalist predators preferentially fed on click beetles at low and medium aphid densities and switched to aphids at high aphid densities. Early-season predators likely had the greatest influence on aphid suppression. Our results indicate that alternative prey from the belowground system forms a substantial food resource for generalist predators, suggesting that the belowground subsystem modulates predator–prey interactions above the ground.     

Microvascular anatomy of ovary and oviduct in the adult African Clawed Toad (Xenopus laevis DAUDIN, 1802)–Histomorphology and scanning electron microscopy of vascular corrosion casts

Ovaries and oviducts of the adult African Clawed Toad (Xenopus laevis DAUDIN, 1802) were studied by light microscopy (LM) of paraplast embedded tissue sections and scanning electron microscopy (SEM) of vascular corrosion casts (VCCs). Histomorphology revealed that ovarian vessels located in the thecal layers. Ovarian and interlobar arteries displayed a horse-shoe shaped longitudinally running bundle of vascular smooth muscle cells. Follicular blood vessels showed flattened profiles, which were confirmed by scanning electron microscopy in vascular corrosion casts. The flattened profiles obviously led to high intravasal pressures, which locally prevented filling of the follicular capillary bed. Oviduct arteries pierced the fibrous stroma surrounding the oviduct mucosa. In the pars convoluta, the mucosa consisted of a ciliated simple columnar epithelium and tubular oviduct glands that opened between ciliated epithelial cells into the oviduct lumen. Oviduct arteries branched at the basolateral surfaces of tubular glands. After a short tangential course, arterioles branched into capillaries which ran radially between oviduct glands towards the subepithelium. Anastomoses at different heights connected capillaries of neighbouring glands. Subepithelially, capillaries ran longitudinally and undulated. Postcapillary venules radiated centrifugally towards the stroma to finally drain into oviduct veins located in the stroma. Oviduct vascular densities clearly reflected non-ovulatory and ovulatory states.     

Voluntary testing procedures of farm animal housing equipment according to the Animal Welfare Act of 1998]

Before its broad application in practice, housing equipment should be tested, in particular with regard to animal welfare. The differing positions of the German Federal Council (Bundesrat) and the German Federal Parliament (Bundestag), whether such testing should be mandatory or voluntary, have been conciliated in the amended animal welfare act by empowering the Federal Ministry of Food, Agriculture and Fisheries (BML) to fix official standards for voluntary testing procedures by regulation. On request of the BML, a report as scientific basis for a draft regulation is currently prepared by the scientific animal welfare committee of the German Agricultural Society (DLG). The scientific animal welfare committee has been appointed by the DLG in order to provide support in the effort to strengthen animal welfare aspects in the DLG-utility testing procedure of housing equipment, which is in place since 1953. The committee elaborates standards concerning testing methods, assessment criteria and the necessary size of investigations. As required, the scientific animal welfare committee may support the DLG-testing bodies in the implementation of the animal welfare part of the testing procedure. It will, moreover, be involved in the welfare assessment based on the testing results. The amendments of the already established testing procedure will help to fulfill the general requirements on an acceptable animal welfare testing procedure. While keeping in mind that there are certain limits in what can be achieved by a voluntary testing procedure, the enhanced consideration of animal welfare aspects within the DLG-utility testing procedure has the advantage to be relatively unbureaucratic and in line with EU legislation, and is, therefore, an appropriate tool for a contibrution to improved animal welfare in livestock housing.     

An improved and accurate method for determining the dehydrogenase activity of soils with iodonitrotetrazolium chloride

Summary Conditions for a rapid, precise [100 g iodonitrotetrazolium chloride (INT)-formazan ml^-1 assay mixture], and easily reproducible assay of potential soil dehydrogenase activity are described, using 2(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyl tetrazolium chloride (iodonitrotetrazolium chloride, INT) as the substrate. Reduced iodonitrotetrazolium formazan (INTF) was measured by spectrophotometry (464 nm) after extraction with N,N-dimethylformamide and ethanol. With this method, the coloured complex formed is highly stable. The effects of pH, buffer concentration, temperature, substrate concentration, amount of soil weight, and reaction time on dehydrogenase activity were investigated. The rate of substrate hydrolysis was proportional to soil weight; the optimal INT reduction was achieved with 1 M TRIS buffer (pH 7.0) at 40 °C. It was possible to determine the biotic and abiotic substrate reduction by comparing assays of autoclaved and unsterile soil samples. Different investigations have confirmed that the intracellular enzyme is highly correlated with the microbial biomass, and indicate that this activity is suitable as an indirect parameter of microbial biomass, measurement.     

Genetic regulation of growth and nutrient content under phosphorus deficiency in the wild barley introgression library S42IL

Phosphorus (P) is an important macronutrient required for plant growth and yield formation. Since decades, breeders aim to optimize P efficiency in crops. We studied a set of 47 wild barley (Hordeum vulgare ssp. spontaneum, Hsp) introgression lines (ILs) in hydroponic culture to identify quantitative trait loci (QTLs) improving growth and nutrient content under P deficiency. Applying a mixed model analysis, a total of 91 independent QTLs were located among 39 ILs, of which 64 QTLs displayed trait‐improving Hsp effects. For example, an unknown Hsp allele on barley chromosome 4H increased shoot dry weight under P deficiency in three overlapping ILs by 25.9%. Likewise, an Hsp allele on barley chromosome 6H increased root dry weight under P deficiency in two overlapping ILs by 27.6%. In total, 31 QTLs confirmed Hsp effects already identified in previous field and glasshouse experiments with the same ILs. We conclude that wild barley contains numerous trait‐improving QTL alleles, which are active under P deficiency. In future, the underlying genes can be subjected to cloning and, simultaneously, used in elite barley breeding.     

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