Comparison and improvement of methods for determining soil dehydrogenase activity by using triphenyltetrazolium chloride and iodonitrotetrazolium chloride

The triphenyltetrazolium chloride (TTC) method described by Thalmann (1968) and the iodonitrotetrazolium chloride (INT) method described by Spothelfer-Magaña and Thalmann (1992), used for measuring soil dehydrogenase activity, have been modified to overcome some methodical short-comings. Absorption maxima of 485 nm for triphenylformazan dissolved in acetone, 491 nm for iodonitrotetrazolium formazan (INTF) dissolved in tetrahydrofuran and 455 nm for INTF dissolved in N,N-dimethylformamide are recommended for measuring wavelengths. Extracting triphenylformazan twice with acetone is less toxic and proved to be at least as efficient as extraction with a mixture of 90% acetone and 10% carbon tetrachloride (Thalmann 1968 method). Tetrahydrofuran and dimethylformamide were equally good in extracting INTF from soils, but the former was less toxic. Anaerobic incubation resulted in the formation of higher amounts of triphenylformazan and INTF as well as reduced standard error. Both TTC and INT reduction showed high reproducibility and good differentiation of the microbial activity of six soils. For several reasons (more easily determined substrate dose depending on different soil types, better reduction, shorter incubation time), INT reduction seems to be a more suitable method of measuring soil microbial activity than TTC reduction.     

Tradeoffs in the Rehabilitation of a Succulent Karoo Rangeland

Rangeland rehabilitation has multiple, sometimes conflicting goals, such as the reestablishment of the predisturbance vegetation, soil protection, and forage production. The rehabilitation techniques should be also cost‐effective and practicable. Given the difficulties and high costs of restoring Succulent Karoo rangelands and the continuously high grazing pressure in the communal lands, tradeoffs should be accepted in the achievement of these goals. We tested the capability of paddock manure redistribution to reverse degradation trends in a heavily grazed Succulent Karoo rangeland in South Africa. Over 3 years, the effects of the manure application were compared with areas planted with mature shrubs as a benchmark for a predisturbance vegetation structure and with four popular rehabilitation techniques: (1) livestock exclusion; (2) brushpacking (coverage of dead shrubs); (3) mineral fertilizing; and (4) microcatchment construction. Manure was, besides planting, the only treatment that resulted in a significant increase in drought‐resistant vegetation cover, but it compromised the dominance of native vegetation. In the manure plots, a pasture‐like vegetation of non‐native forage plants (which germinated mainly from seeds in the dung), developed (foremost Atriplex semibaccata). Manure application counteracted erosion as effectively as the planted shrubs and brushpacks. Expected negative side effects such as a decrease in plant species richness or salinization of topsoil were not detected. We also checked the potential of topsoil salinization by the halophytic A. semibaccata and found it to be low. For sites where a decrease in grazing pressure is unrealistic under current land tenure, redistribution of manure should be further explored to mitigate acute symptoms of degradation. Copyright © 2013 John Wiley & Sons, Ltd.     

Molekulare Diagnostik in der Lebensmittel��berwachung

Molecular diagnostic is frequently a confirmed part in the food microbiological survey of the official food safety control. So the diagnostic tools are used for a fast screening for presence or absence of pathogens or to differentiate the isolates.     

Einfluss von mechanischen Ber��hrungsreizen auf das Wachstum von K��chenkr?utern im Topf

For a compact growth of many potted plants you often have to use chemical growth inhibitors. Various species of herbs tend to an undesirable extension growth too. In general, the use of chemical inhibitors is prohibited in the production of potted herbs. For several years at the State Horticultural College and Research Institute Heidelberg there is employed an alternative method of mechanical stimulation treatment for a compact growth of potted plants. The greatest reduction of elongation was obtained, when the plants were treated with breaks in the early morning. In 2009 and 2010, the employees of the trial station proofed the effect of mechanical stimulation (Thigmomorfogenesis) to a large assortment of organically produced potted herbs. Green and red varieties of basil, parsley, coriander, chervil, lemon balm (2009) and four different varieties of mint (2010) were stimulated with a machine one week after beginning culture continuously 108 times per day. Compared to the untreated plants all mechanically stimulated herb species and varieties showed a tendency or significantly reduced elongation growth and therefore more stability. Depending on species and varieties the quality of these plants was visibly improved.     

Prokaryotic chromosomes and disease

Recent insights into bacterial genome organization and function have improved our understanding of the nature of pathogenic bacteria and their ability to cause disease. It is becoming increasingly clear that the bacterial chromosome constantly undergoes structural changes due to gene acquisition and loss, recombination, and mutational events that have an impact on the pathogenic potential of the bacterium. Even though the bacterial genome includes additional genetic elements, the chromosome represents the most important entity in this context. Here, we will show that various processes of genomic instability have an influence on the many manifestations of infectious disease.     

Phosphate aquisition by red clover and black mustard on a humic podzol

Recent investigations have shown that phosphate (P) mobilization by root exudates is an important feature of genotypes to acquire P even in soils of low‐P availability. We, therefore, investigated P mobilization processes in the rhizosphere of red clover (Trifolium pratense L.) and black mustard (Brassica nigra L.) on a humic podzol. As measured by the Kuchenbuch‐Jungk method (Kuchenbuch and Jungk, 1982), both species accumulated similar quantities of citrate (12 μmol/g soil) in the rhizosphere in about 1 mm distance from the soil‐root interface. Despite of similar concentrations of P‐mobilizing citrate in the rhizosphere of both species, red clover took up nearly the two‐fold of P compared to black mustard. Differences in rhizosphere pH were determined between both species. Black mustard did not acidify the rhizosphere, whereas red clover decreased the pH in the rhizosphere from 5.8 to about 4.0 (in 0.01M CaCl₂). The simultaneous acidification and excretion of citrate compared to citrate excretion alone had consequences for P mobilization processes in the rhizosphere. Phosphate mobilization from the soil solid phase was higher at higher pH. Thus, the citrate‐induced P desorption was not the limiting step in P acquisition by red clover and black mustard. Calculations of P distribution in the soil solution between free ortho‐P and humic‐associated P showed that at higher pH most of the P was associated with dissolved humic substances, whereas at pH < 5, most of the P was present as free ortho‐P. These P species can readily be taken up by the roots whereas humic‐associated P must probably be desorbed from the humic surface before uptake. Phosphate species calculations, therefore, explained the higher P uptake of red clover compared to black mustard. Aluminum species distribution calculations in the soil solution further show that even at pH < 5.0 in the soil solution, citrate strongly complex Al and thereby reduce the activity of monomeric Al species. The excretion of citrate can, therefore, counteract the root induced acidification of the rhizosphere with respect to Al toxicity.     

Determining leaf nutrient concentrations in citrus trees using UAV imagery and machine learning

Precision Agriculture - Nutrient assessment of plants, a key aspect of agricultural crop management and varietal development programs, traditionally is time demanding and labor-intensive. This...     

Can agroforestry improve soil fertility and carbon storage in smallholder banana farming systems?

Soil fertility depletion is a major constraint to agricultural production for smallholder farming households in many sub‐Saharan countries, and it is worsened by climate variability. In order to sustain food security for a growing population, measures have to be taken against C and nutrient losses from soils. This study examines whether banana–coffee agroforestry systems can improve soil fertility and C pools in smallholder farms in E Africa amidst observed climate variability. We selected 20 farms in Central Uganda, where soil samples were obtained from the top and subsoil layers. Samples were analyzed for several soil fertility parameters including soil organic matter (SOM), total soil organic C, pH, total N, plant‐available P, exchangeable K, texture, and bulk density. Soil C stocks were calculated based on soil organic C concentrations and bulky density. We measured tree diameter and height and calculated aboveground plant biomass using allometric equations. Belowground biomass was estimated using equations based on the respective aboveground plant biomass. Our results show that banana–coffee agroforestry farming systems had significantly higher total SOM and total N compared to the banana monoculture. Similar trends were observed for soil C stocks and total C pools. The former contained 1.5 times higher soil C stocks than the latter. Likewise, the mean total C pools for the banana–coffee agroforestry farm plots were 26% larger than that under banana monoculture. However, exchangeable K was higher in the soil of banana monocultures. Plant‐available P levels were limiting under both farming systems. The study demonstrates that beyond socio‐economic benefits banana–coffee agroforestry farming systems have beneficial effects on soil fertility and C sequestration compared to banana monocultures in the study area. However, precautions to avoid P depletion have to be taken under current climate conditions.