Quantifizierung der wichtigsten Mechanismen zur Säurepufferung carbonatfreier Böden

Quantifying the most important mechanisms of acid buffering in carbonate-free soils From the release of cations from the soil matrix during pH-stat-titrations, characteristic values for assessing buffer rates were derived separately for single elements. Recorded buffer reactions became almost exclusively apparent in the release of Al and Fe, however the contribution of Fe to the total turnover only amounted to 1–3%. The release of each element and of DOC in the course of time was due to the overlapping of two first-order reactions, respectively. In the fast initial reaction all measured elements were released at nearly the same velocity, whereas in the 2nd, slower reaction the rate of Al-release corresponded to that of DOC but was at least seven times higher than that of Fe. Correlations between the maxima of release and soil chemical properties revealed a dominating contribution of organically bound Al (Al_p) to proton buffering. It is assumed that also the amount of Fe released is originating in organic complexes.     

Apparent electrical conductivity integrated from layered soil profiles

Time domain reflectometry (TDR) trace analysis aims at extracting the water content profile along TDR probes. This can be done by applying a TDR forward solver inversely. Thus, TDR‐trace inversion is basically an optimization problem. As in any optimization procedure, it is worthwhile to include as much a priori information as possible about the problem to be solved. In this study, we discuss the feasibility to use the apparent electrical conductivity as constraint for the TDR inversion. The resistors‐in‐parallel circuit can be used to integrate a multislice soil model to obtain the apparent electrical conductivity. We apply additionally Archie's law to link the water content of a particular slice with its electrical conductivity. We compare the results from this approach with measured TDR traces and show that the problem is solved exactly. Finally, we address the thin‐layer issue because thin layers with a high permittivity contrast result in a delay of the run time of an electromagnetic pulse. We test numerically whether a similar behavior can be observed for a thin layered electrical conductivity profile. Our results show that the thickness of the soil layer with respect to electrical conductivity has no effect on the apparent electrical conductivity. We conclude that the apparent electrical conductivity is appropriate as boundary condition in TDR inversion as long as a procedure is known to convert the water content of a slice to its electrical conductivity     

Paratuberculosis in farmed and free-living wild ruminants in the Czech Republic (1999-2001)

Due to the occurrence of the infection of Mycobacterium avium subspecies paratuberculosis among domestic ruminants and the rapid development of farmed deer industry and the market of cloven-hoofed game we have carried surveys of paratuberculosis, beginning in 1997, in the most common four species of wild ruminants in the Czech Republic [Pavlik et al., Vet. Microbiol. 77 (2000) 231-251]. From 1999 the prevalence of paratuberculosis has been slightly reduced in all three types of husbandry of wild ruminants. Nevertheless paratuberculosis has been diagnosed in wild ruminants in three districts, in four game parks and in five farms. M. a. paratuberculosis was isolated from 128 (5.3%) out of 2,403 wild ruminants of four animal species: 106 red deer, 2 roe deer, 4 fallow deer and 16 mouflons. In red deer farms, the highest number of clinical paratuberculosis cases was in yearling deer. RFLP type B-C1 of M. a. paratuberculosis predominated during the second period (1999-2001) in all types of husbandry with no relationship to wild ruminant species. New "cattle" RFLP types B-C5 and B-C16 of M. a. paratuberculosis were described in infected farmed red deer and one "intermediate" RFLP type R-I4 in fallow deer from one game park. The survival of M. a. paratuberculosis was found to be 4 months during winter in the pasture after destocking of all cattle infected with paratuberculosis. We found that non-vertebrates, wild ruminants or non-ruminant wildlife can be vectors and potentially become a risk factor in the spread of M. a. paratuberculosis infection.     

Equivalence or complementarity of soil‐solution extraction methods

Several methods are used for the extraction of soil solution. The objective of this study was to find out to what extent the different extraction methods yield complementary or equivalent information. Soil solutions were sampled once at 10 different forest sites in Germany, with 4 sampling points per site, using 5 different extraction methods. Concentrations of the major ions in the 1:2 extracts and the equilibrium soil‐pore solutions (obtained from percolation of field‐fresh soil cores) were generally lower than in desorption solutions, suction‐cup solutions, and saturation extracts. Surprisingly, the latter three methods generally yielded equivalent results. However, possible systematic differences between these methods could have been masked by the high small‐scale spatial variability within the sites.     

Herbage utilisation efficiency of continuously stocked pastures during periods of restricted pasture growth

ABSTRACT

The aim of this study was to evaluate the defoliation patterns of individual tillers, efficiency of herbage utilisation, and forage production in continuously stocked Brachiaria humidicola cv. Comum swards during periods of the year of restricted pasture growth. The experiment was conducted at the Embrapa, Campo Grande-MS, Brazil, from April to October 2012. Treatments consisted of two grazing management strategies, defined by two ranges of sward height (10–15 and 20–25 cm) managed under continuous and variable stocking rates. The experiment was conducted as a completely randomised block design with three replications. During periods of resource constraints, grazing management strategies based on ‘steady state’ sward heights did not alter defoliation patterns, herbage utilisation efficiency (HUE), and forage production in Brachiaria humidicola swards under a continuous stocking method. A direct implication of our results is that grazing management strategies during the driest and coldest periods of the year in the tropics should be developed based on the conditions most suitable for better promoting faster pasture recovery and a return to production in the following spring; it is unlikely that any grazing management strategy would be successful in increasing herbage production and/or HUE in periods of restricted pasture growth.     

Effects of basal debris on glacier flow

Glacier movement is resisted partially by debris, either within glaciers or under glaciers in water-saturated layers. In experiments beneath a thick, sliding glacier, ice containing 2 to 11% debris exerted shear traction of 60 to 200 kilopascals on a smooth rock bed, comparable to the total shear traction beneath glaciers and contrary to the usual assumption that debris-bed friction is negligible. Imposed pore-water pressure that was 60 to 100% of the normal stress in a subglacial debris layer reduced shear traction on the debris sufficiently to halt its deformation and cause slip of ice over the debris. Slip resistance was thus less than debris shearing resistance.