Organic matter in termite mounds of an Amazonian rain forest.

This study investigates how termites alter the organic matter in rain forests near Manaus, Brazil. Samples were collected from the outer and inner parts of typical termite nests of Nasutitermes, Termes, Embiratermes, Cornitermes, Anoplotermes, and Constrictotermes genera, as well as from the surrounding topsoil (0cm-10cm) and potential wooden food. The termite nests were signficant sinks for organic matter and its associated nutrients. The organic C contents ranged between 100g kg-1 and 500g kg-1 in the nests, compared to 17g kg-1 to 42g kg-1 in the surrounding topsoils. As lignin contents of the mounds were higher than in wood, lignin may be accumulated in preference to other organic compounds. This findings also sugests that the interior part of the nests is a region of higher organic matter turnover and lignin degradation

Soil properties of bare patches in rangelands of South African's grasslands

A loss of grassy cover accompanied by the development of bare soil patches, are the most notable forms of rangeland degradation in grasslands of South Africa. Concerns are growing over the threat of loss of nutritious perennial grass species and the lack of regrowth of the bare patches. Grazing and different rangeland tenure systems -communal and freehold, which is equal to continuous and rotational grazing system - are considered to be of major importance for rangeland degradation. The continuous grazing system is seen to be more affected, but the development of bare patches is not restricted to communal land. We hypothesized that (1) soil properties of bare patches in South Africa´s grasslands are not different in different tenure systems, and (2) soil properties differ with size of bare patches, where big patches are more degraded. To test this, we sampled soils at communal and commercial land in the Thaba Nchu area of South Africa with the following design: we selected three farms per tenure system, 6 randomly chosen plots (100x100m) per farm, and within these plots we sampled 5 bare patches of different sizes (0-10 cm) per plot, where the soil sample (3 replicates) were taken out of the middle of the bare patch. Additionally, soils of adjacent grass were sampled. The results showed that in total, there were more bare patches in continuous grazing systems, evaluated by aerial pictures, but we couldn´t find any differences in bulk density and carbon stocks, between the tenure systems. Additionally, and surprisingly, we found no significant differences in soil organic carbon stocks between bare soil samples and grass samples. There was no clear relationship between bare patch size and nutrient contents. Other nutrients like phosphor were significantly enlarged at the bare patch compared to the grass samples. According to our results, we conclude, that the bare patches seem to develop in different pathways: i) along tracks of grazing animals, (ii) around termite hills, where the termite construction seems to be an initial starting point of bare patches and (iii) on staying and lying places of the grazing animals, which aslo explain the higher nutrient contents at the bare patches

Sequestration of quaternary ammonium compounds in soil and its relevance for the proliferation of antibiotic resistance in the environment

Quaternary ammonium compounds (QACs) are a group of surface-active, biocidal, high production volume chemicals. In the agricultural sector, their applications are especially broad and range from disinfectants and detergents in animal husbandry to their use as adjuvants in pesticide formulations. Inputs of QACs into agroecosystems are potentially high where manures, sewage sludge or wastewater are applied to the farmer’s fields for nutrient recycling. The presence of QACs in the environment has frequently been inflicted in the co-selection for antibiotic resistance genes (ARGs) with unforeseeable risks for environmental and human health [1]–[3]. The selection of ARGs depends on concentrations of QACs in bio-accessible form and the persistence of these compounds. However, a comprehensive overview on i) predicted & measured concentrations of QACs in soils including their analysis, ii) mechanisms of their sequestration in soils based on their physicochemical and structural properties, and iii) the implications of the concentrations and the fate of QACs in soils for the proliferation of ARGs in the environment is missing. Based on a review of these topics, we propose that QACs are sequestered in the interlayer regions of clay minerals in soils, which reduces their acute toxicity, but increases their persistence. The slow release of QACs from the interlayer regions may maintain concentrations levels in soil solution that are large enough to co-select for antibiotic resistant soil bacteria promoting the proliferation of ARGs in the environment

Texture controls on the size distribution and properties of nano- and small microaggreates in soil

Soil microaggregates (SMA) with a size of <250 µm are one of the key factors influencing soil properties of ecological and structural relevance. In order to better understand their role in soil ecosystems, a quantitative understanding about the building units (BU) is necessary. The BU (divided into small SMA (<20 µm) and nanoparticles (NP, <220 nm)) where analyzed to quantify their size distribution and chemical composition. This approach will help to evaluate the properties of BU required for SMA formation.Soils with different clay contents of a Luvisol site (Scheyern, Germany) were fractionated into SMA and NP by wet sieving and pressure filtration. The differentiation between free and occluded BU was carried out by mechanical disaggregation using ultrasonic treatment. The size distribution of small SMA was analyzed with a XPT particle analyzer, while the abundance and chemical composition of NP were analyzed by field flow fractionation (AF4) coupled to a UV detector and ICP-MS.According to the mass distribution of the macroaggregate (8 mm-250 µm), large and small SMA fractions, the soils could be grouped into low (15, 18 and 19%) and high (28 and 30%) clay content. The proportion of occluded small and large SMA was increased with clay content. Interestingly the free small SMA proportion was constant and independent from clay content. Also the particle size distribution (PSD) of free small SMA did not correlate with clay content. The similar PSD of free and occluded small SMA was interpreted as a pool of potential BU for the formation of new aggregates. The NP showed three different size fractions. The evaluation of the elements Al, Si and Fe in these size fractions revealed different mass ratios and gave an insight into the composition of free and occluded NP

Topsoil Selling - extreme anthropogenic erosion and its consequences for paddy soil quality (Mekong Delta, Vietnam)

Increasing urbanization and industrialization leads to rising demands for construction material, particularly in low-income countries. Thus, agricultural topsoil is sometimes removed and used as raw material e.g. for brick production. Topsoil selling (TSS) is practiced around the world from America, Europe, and Afrika to Asia. In the Mekong, Delta farmers sell the topsoil from their paddy fields to contractors. The temporal effects of topsoil removal on soil quality are not yet fully understood. We hypothesized that after soil removal, soil quality is significantly lower compared to the original topsoil. To test this hypothesis, we sampled paddy soil chronosequences in two different provinces, ranging between 1 and 8 years after TSS. Soil organic carbon (Corg) stocks at TSS sites were up to 20 t/ha lower than at control sites (control: 50 t/ha) in Sóc Trăng and up to 15 t/ha lower in Trà Vinh (control: 30 t/ha). The C/N ratio was nearly constant around 10. Analysis of inorganic nutrients (e.g. P, K, Na, S, Zn, Cu) showed that changes are variable in space, time and among nutrients. Annual average changes ranged from less than a kg per hectare and year for micronutrients (e.g. Cu, Zn) to several tens and hundreds of kg for macronutrients (e.g. P, S). The so far available data revealed that TSS induces mainly a dramatic loss of soil organic matter. It was ongoing up to the 8th year of the chronosequences but was not necessarily accompanied by losses in inorganic nutrients. As a result, there appears to be a chance for farmers in the Mekong Delta to overcome risks of soil quality decline after topsoil removal. Within the next months, we will receive the results from P- and S fractionation and also results from lignin analysis (lignin-derived phenols) will complement to the available data. Thus, we will gain further insights into soil evolution after topsoil selling shortly

Does sea-dyke construction affect the spatial distribution of pesticides in agricultural soils? – a case study from the Red River Delta, Vietnam

The Red River Delta is a major agricultural production area of Vietnam with year-round use of pesticides for paddy rice cultivation and other production systems. The delta is protected from flooding, storm surges and saline water intrusion by a sophisticated river and sea-dyke system. Little is known about the effects of such a dyke system on pesticide pollution in the enclosed landscape. Our aim was to address this gap by i) determining pesticide prevalence in soils and sediments within a dyked agricultural area, and by ii) assessing whether and to which degree this dyke system might affect the spatial distribution of pesticides. After sampling paddy rice fields (topsoil) and irrigation ditches (sediment) perpendicular to the dyke in Giao Thuy district, we analysed 12 of the most commonly used pesticides in this area. In soils, we detected most frequently isoprothiolane (100% detection frequency), chlorpyrifos (85%) and propiconazole (41%) while in sediments isoprothiolane (71%) and propiconazole (71%) were most frequently found. Maximum concentrations reached 42.6 μg isoprotiolane kg−1 in soil, and 35.1 μg azoxystrobin kg−1 in sediment. Our results supported the assumption that the dyke system influenced residue distribution of selected pesticides. More polar substances increasingly accumulated in fields closer to the sea-dyke (R2 = 0.92 for chlorpyrifos and 0.51 for isoprothiolane). We can thus support initiatives from local authorities to use the distance to dykes as a mean for deliniating zones of different environmental pollution; yet, the degree at which dykes influence pesticide accumulation appear to be compound specific

Spatial distribution of organic carbon in the Atacama Desert, Chile

The Atacama Desert in northern Chile is known as the driest region on earth; however traces of life, can still be found. Soils are the habitat and reservoir for plants and microorganisms, which leave their fingerprints as organic residues. Here we identify and quantify organic carbon in soil profiles and along potential plant dispersal corridors in the Atacama Desert. We hypothesize that preferential pathways or barriers of the dispersal of life exist, which can be related to soil properties such as bulk density. We further assume that due to dust and salt accumulation at the surface, in particular the subsoils will reveal an unique though little explored archive of organic matter. The analytical assessment of Corg at very low levels is challenging. It was found that SOC in hyperarid soils ranged from 1.8 – 125 µg C per g soil for 0-1 m (1). We here present an improved Corg analysis, which is based on a temperature gradient method (DIN19539; Soli TOC cube, Elementar, Hanau). This allows combustion of samples with up to 5 g sample weight without the need to remove carbonate. This avoids loss and increases precision of Corg quantification at lowest concentrations. We can show that Corg contents decrease from 1.47 % to 0.1 % in the first 14 km of the gradient. However, first results suggest that within the hyper-arid core of the Atacama Corg contents increase. This gives first hints to the vegetation history of the desert and the dispersal of life

Temperaturabhängigkeit der Bodenatmung (Q10): Räumliche Muster und Einflussfaktoren im Rur-Einzugsgebiet

Der Umsatz der organischen Substanz im Boden verläuft bei steigenden Temperaturen schneller. Die Temperaturabhängigkeit der Bodenatmung wird dabei oft über den Q10-Wert beschrieben. Q10 ist der Faktor, mit dem die Bodenatmung bei 10°C Temperaturerhöhung steigt. Obwohl bekannt ist, dass der Q10-Wert variabel ist, haben viele (Klima-)Modelle einen konstanten Wert von 1.5 oder 2 implementiert. Grund hierfür ist, dass die Einflussfaktoren dieser Variabilität bisher wenig untersucht wurden. In dieser Studie haben wir räumliche Muster und Einflussfaktoren der Bodenatmung und Q10-Variabilität im Rur-Einzugsgebiet (2868 km²) untersucht. Ziel war eine Systematisierung der Q10-Variabilität. Unsere zentrale Hypothese war, dass sich die Q10-Variabilität mittels „environmental soil classes“ (ESC), einer Kombination aus Landnutzung, Bodentyp und Bodenart, flächendeckend abschätzen lässt. Dazu haben wir aus 12 ESCs jeweils 9 Bodenproben bei 4 Feuchtestufen (30-75% der Wasserkapazität) und 5 Temperaturen (5-25°C) inkubiert. Unsere Ergebnisse zeigen, dass der Q10-Wert bei niedriger Bodenfeuchte in der Reihenfolge Acker (1.68) < Grünland (1.99) < Wald (2.16) zunimmt und zusätzlich von Bodentyp und Bodenart abhängt. Damit erfassen ESCs 44% der Q10-Variabilität. Auch der Effekt von Bodenfeuchte auf Q10 lässt sich mithilfe von ESCs systematisieren: Q10 steigt mit zunehmender Feuchte in Ackerböden, bleibt im Grünland konstant, und nimmt in Wäldern deutlich ab. Die Berücksichtigung von ESC-spezifischen Q10-Werten bei der Berechnung der Bodenatmung ergibt eine um bis zu 45% niedrigere CO2 Freisetzung aus dem Rur-Einzugsgebiet im Vergleich zu konstanten Q10-Werten. Wir empfehlen daher einen ESC-basierten Ansatz, um die Q10-Variabilität zu erfassen und variable Q10 Werte in Klimamodelle zu integrieren. Damit kann eine genauere Modellierung und Vorhersage der Bodenatmung erreicht werden