A histological evaluation of pansteatitis-affected Mozambique tilapia,Oreochromis mossambicus (Peters 1852), from different geographical locations in South Africa

Pansteatitis is the leading cause for the decline in Nile crocodile populations and the sporadic mortality of fish in the Olifants River System, South Africa. To determine the prevalence of this disease in lentic systems, Mozambique tilapia, Oreochromis mossambicus, were collected from Lake Loskop, Lake Flag Boshielo, Phalaborwa Barrage and Lake Luphephe-Nwanedi. The former three impoundments are located within the main stem of the Olifants River, while the latter, which is geographically isolated and situated in the Limpopo River System, served as a reference site. Mesenteric adipose, liver, serosa of the swim bladder, gill and the skeletal muscle of fish sampled were examined for gross and microscopic evidence of pansteatitis. Microscopically observed changes were used to statistically compare pansteatitis prevalence between samples and sites. Based on histopathological evaluation, the adipose tissue in the liver, swim bladder serosa and coelom from severely debilitated individuals showed the most significant pathological changes. Lesions indicative of steatitis were observed in fish collected from Lake Loskop (75%), Lake Flag Boshielo (22%) and Lake Luphephe-Nwanedi (15%). Further investigation is warranted to understand the pervasiveness and mechanisms driving pathological changes of pansteatitis at Lake Flag Boshielo, Phalaborwa Barrage and Lake Luphephe-Nwanedi.     

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     

Soil heterogeneity at the field scale: a challenge for precision crop protection

Crop protection seldom takes into account soil heterogeneity at the field scale. Yet, variable site characteristics affect the incidence of pests as well as the efficacy and fate of pesticides in soil. This article reviews crucial starting points for incorporating soil information into precision crop protection (PCP). At present, the lack of adequate field maps is a major drawback. Conventional soil analyses are too expensive to capture soil heterogeneity at the field scale with the required spatial resolution. Therefore, we discuss alternative procedures exemplified by our own results concerning (i) minimally and non-invasive sensor techniques for the estimation of soil properties, (ii) the evidence of soil heterogeneity with respect to PCP, and (iii) current possibilities for incorporation of high resolution soil information into crop protection decisions. Soil organic carbon (SOC) and soil texture are extremely interesting for PCP. Their determination with minimally invasive techniques requires the sampling of soils, because the sensors must be used in the laboratory. However, this technique delivers precise information at low cost. We accurately determined SOC in the near-infrared. In the mid-infrared, texture and lime content were also exactly quantified. Non-invasive sensors require less effort. The airborne HyMap sensor was suitable for the detection of variability in SOC at high resolution, thus promising further progress regarding SOC data acquisition from bare soil. The apparent electrical conductivity as measured by an EM38 sensor was shown to be a suitable proxy for soil texture and layering. A survey of arable fields near Bonn (Germany) revealed widespread within-field heterogeneity of texture-related ECa, SOC and other characteristics. Maps of herbicide sorption and application rate were derived from sensor data, showing that optimal herbicide dosage is strongly governed by soil variability. A phytoassay with isoproturon confirmed the reliability of spatially varied herbicide application rates. Mapping areas with an enhanced leaching risk within fields allows them to be kept free of pesticides with related regulatory restrictions. We conclude that the use of information on soil heterogeneity within the concept of PCP is beneficial, both economically and ecologically.     

Prof. Dipl. Ing. Dr. Dr. h. c. Leo Tschermak zum Gedenken

Ohne Zusammenfassung     

Effect of stocking density on vegetation and animal performance within the semi-arid shrublands of the Karoo,South Africa

As the primary land use in the Karoo, extensive small-stock farming contributes significantly towards the agricultural economy of the region. However, the sustainability of this practice has been questioned for many years. This led to the establishment of a long-term stocking-density trial in 1988 at the Carnarvon Research Station. The trial was designed on a three-camp rotational grazing system under four stocking densities (8, 7, 5.5 and 4 ha SSU^–1). Following continuous treatment over 28 years, the results from a once-off assessment in February 2016 portrayed no significant differences between treatments with regard to plant height, cover, species diversity, ecological and grazing index scores. Animal production varied among treatments where the mean production per hectare was found to be the highest under the high stocking-density treatment. Due to the absence of historical data, the results from this study are not conclusive with regards to changes in the vegetation dynamics over time and therefore does not lend itself to making conclusions concerning stocking densities. It can, however, be concluded that the vegetation of the Western Upper Karoo is remarkably resilient to the perceived higher stocking densities set at the time, on condition that an appropriate grazing management strategy is applied.     

Vom Wesen waldbaulicher Arbeit heute und morgen

Summary The crisis of classical silviculture in the middle-european sustained yield forestry becomes evident—above all—in the large discrepancy between scientific findings and practical management. Numerous inhibiting factors are to be held responsible for this: lack of a silivcultural basis for combined objectives in the management of productive and social forests, forest-technical development aid from the boreal wood-exploitation areas, the modernization of forest management being too onesided oriented to industry, a lack of professional improvement, sociological problems as a denaturation of man by technology and economy etc. An integral silviculture, based on ecological fundaments and following a free style, must lead to an optimization of interdisciplinary conflicts of objective under the aspect of long-term objectives. The comprehensive life-work of the man whose jubilee we celebrate has readied the way to a solution.