Microbial indicators for soil quality

The living soil is instrumental to key life support functions (LSF) that safeguard life on Earth. The soil microbiome has a main role as a driver of these LSF. Current global developments, like anthropogenic threats to soil (e.g., via intensive agriculture) and climate change, pose a burden on soil functioning. Therefore, it is important to dispose of robust indicators that report on the nature of deleterious changes and thus soil quality. There has been a long debate on the best selection of biological indicators (bioindicators) that report on soil quality. Such indicators should ideally describe organisms with key functions in the system, or with key regulatory/connecting roles (so-called keystone species). However, in the light of the huge functional redundancy in most soil microbiomes, finding specific keystone markers is not a trivial task. The current rapid development of molecular (DNA-based) methods that facilitate deciphering microbiomes with respect to key functions will enable the development of improved criteria by which molecular information can be tuned to yield molecular markers of soil LSF. This review critically examines the current state-of-the-art in molecular marker development and recommends avenues to come to improved future marker systems.     

Analysis of fiber content in flax stems by near-infrared spectroscopy

The conventional means of measuring the fiber content of flax is time-consuming and laborious, and the results obtained vary with the analysis technique used. The plant tissues must first be "retted", a process by which the fibers are separated from the rest of the stem, either by indigenous organisms in the soil when the stems are left in the field or by water (anerobic bacteria) or enzymatic retting. The fiber content is then determined by mechanical or manual separation. In this study, fiber content of flax stems was measured rapidly and objectively by near-infrared spectroscopy (NIRS) using whole pieces of stem in a large cell, in reflectance mode. Compared to the conventional method, the standard error of performance of the NIRS method was between 0.96 and 1.45% (dry matter basis), depending on the model and data processing used. NIRS calibrations were generated by hand separation of fiber from water-retted specimens. The water retting procedure takes several days to complete and requires considerable trained labor to complete the hand separation step. The NIRS procedure was conducted on pieces of stem to simulate measurement in the field.     

Nitrate leaching losses and their control in a mixed farm system in the Cotswold Hills, England

Abstract. Nitrate leaching was measured for four years at the Royal Agricultural College 's Coates Farm in the Cotswolds, England. Coates is a typical Cotswold mixed farm with thin, well-drained calcareous soils especially prone to leaching. Over the duration of this study there were dairy, sheep and arable enterprises on the farm. A 'Farm Gate' nitrogen (N) budget was constructed. Small 120 m × 20 m 'farmlets' were sited in ten fields across the farm, covering all parts of the rotation, as the sites for detailed measurements. Each farmlet received the same management as the rest of the field in which they were situated. Using ceramic probes inserted to 60 cm, soil water was sampled every two weeks throughout the winter drainage season. The annual drainage varied from 135 mm under grassland in 1996/7 to 600 mm under cereals in 1998/9. Average N losses by leaching were determined mostly by rainfall and were 65 kg N ha^–1 yr^–1, accounting for 25% of the N inputs. Especially leaky parts of the rotation were the ploughing out of a lucerne ley and the grazing of stubble turnips with sheep, both typical Cotswold farm practices. The research highlights some of the difficulties in developing practicable, profitable management practices to decrease nitrate losses.     

Effects of different soil management practices on total P and Olsen-P sediment loss: A field rainfall simulation study

Field rainfall simulations were conducted in 2002 and 2005 to study the effects of different soil management practices on the total phosphorous (TP) and Olsen-P losses by soil erosion and redistribution along a 15 m long slope in Luoyang, Henan province, China. Field plots were set up in 2001 and included the following soil management practices: subsoiling with mulch (SSM), no-till with mulch (NTM), reduced tillage (RT), and a conventional tillage control (CT). The results showed that there were no significant differences in TP and Olsen-P content in the sediment load between different plots after 6 years uniform tillage practices. The enrichment of TP and Olsen-P at the lower slope showed a clear redistribution along the slope. Effects of tillage practices on the temporal pattern of the enrichment ratio (ER) of TP and Olsen-P was not uniform. ER_TP values were initially high and diminished after a short period of time and leveled to the end of the rainfall test in CT and RT plots, but remained ≥ 1. The ER of Olsen-P at the end of rainfall simulation showed a significant difference when compared to the initial stage, 0.78 to 1.60, respectively. However, the temporal loss rate of TP and Olsen-P showed a similar pattern because it was more depending on the sediment loss rate than on the concentration in the sediment. SSM resulted in 96% less TP and Olsen-P erosion loss compared to CT in 2002. Also, SSM showed the highest reduction in TP and Olsen-P loss after 4 years consistent practice. RT reduced TP and Olsen-P loss by 30%, although the runoff reduction was not significant. NTM was the best alternative with respect to TP and Olsen-P conservation, when considering its lower operational costs.     

Changes in soil nitrogen availability due to stand development and management practices on semi‐arid sandy lands,in northern China

Soil nitrogen (N) availability is one of the limiting factors for plant growth on sandy lands. Little is known about impacts of afforestation on soil N availability and its components in southeastern Keerqin sandy lands, China. In this study, we measured N transformation under sandy Mongolian pine (Pinus sylvestris var. mongolica Litv.) plantations of different ages (grassland, young, middle‐aged, close‐to‐mature) and management practices (non‐grazing and free‐grazing) during the growing seasons using the ion exchange resin bag method. Results showed that, for all plots and growing season, soil NH‐N, NO‐N, mineral N, and relative nitrification index, varied from 0·18 to 1·54, 0·96 to 22·05, 1·23 to 23·58 µg d⁻¹ g⁻¹ dry resin, and 0·76 to 0·97, respectively, and NO‐N dominated the available N amount due to intense nitrification in these ecosystems. In general, the four indices significantly increased in the oldest plantation, with corresponding values in non‐grazing sites lower than those in free‐grazing sites (p < 0·05). Our studies indicated that it is a slow, extended process to achieve improvement in soil quality after afforestation of Mongolian pine in the study area. Copyright © 2009 John Wiley & Sons, Ltd.     

Determination of residues of alachlor and its metabolite in corn, soybeans, and potatoes as heptafluorobutyryl-2,6-diethylaniline

Alachlor [2-chloro-2',6'-diethyl-N-(methoxymethyl)acetanilide] was determined by hydrolysis to 2,6-diethylaniline with 6N HCl and quantitation of the heptafluorobutyryl derivative by gas chromatography with electron capture detection. 2,6-Diethylaniline was isolated from the hydrolysate by steam distillation, derivatized with heptafluorobutyric anhydride, and the derivative was purified by chromatography on silicic acid with 60% toluene in hexane as eluant. Recoveries from potatoes, soybeans, and corn spiked at levels from 3 to 26 ppb averaged 81, 90, and 96% respectively.     

A recording penetrometer to measure the strength of soil in relation to the stresses exerted by a walking cow

A penetrometer has been designed for field use to simulate the stresses exerted on the ground by the hoof of a walking cow, and to measure the resulting deformation of the soil. The extent of deformation produced by the penetrometer in two intact topsoils under pasture was found to be small and independent of water content, whilst significant correlations between soil strength and water content were obtained using a cone penetrometer and a hand-held shear vane. The results imply that the deep hoofprints associated with poached pasture are not produced immediately upon treading wet soil, but only after a progressive loss of soil strength due to repeated treading. Thus the rate of loss, which is deduced to be a measure of the susceptibility of pasture to poaching, cannot be estimated directly from a single measure of soil strength.     

Increase in the abundance of cladocera at pH 5.1 in experimentally-acidified lake 223, Experimental Lakes Area,Ontario

Lake 223 in the Experimental Lakes Area, northwestern Ontario was experimentally-acidified with H₂SO₄ from 1976 to the present. Cladocerans increased in absolute and relative abundance and in total biomass when the pH of Lake 223 was lowered from 6.7 to 5.1. Comparing the cladoceran community at pH 6.7 (1974) with that at pH 5.1 (1981 to 1983), Daphnia galeata mendotae disappeared, Diaphanosoma birgei became rare, Holopedium gibberum increased in abundance and Daphnia catawba, recorded for the first time in 1980, became abundant. Bosmina longirostris became more abundant. Except for the decline in D. birgei, the changes in cladoceran species composition with acidification are consistent with known responses of these species to low pH. The increase in importance of cladocerans in 1981 to 1983 was at the expense of copepods. It was hypothesized to be caused by the decline in predation by small fish during 1981 to 1983 as acidification reduced minnow populations and inhibited reproduction in trout and sucker. The loss of the population of the invertebrate predator, the opposum shrimp, Mysis relicta, in 1979 had little effect on cladoceran biomass.     

Adsorption of cadmium to kaolinite in the presence of organic material

Kaolinite was equilibrated with Cd and with varying amounts of the individual compounds: EDTA, NTA, alginic acid, and humic acid. In experiments in which the Cd and kaolinite concentrations were held constant, and the ligand concentration allowed to vary, conditions under which ligand enhanced and inhibited Cd association with the solid phase were noted. Further experiments at constant Cd: ligand confirmed that, for alginic acid and humic acid, enhancement of uptake occurred, while EDTA diminished uptake. These results were compared with the adsorption of ligand by clay in the absence of organic, and it is suggested that the enhancement of uptake is due to the formation of an adsorbed organic layer on the clay serving as a solid phase ligand.     

Temporal variability of lake waters in the North Cascades mountains (Washington,U.S.A.)

Five lakes in the North Cascades were sampled at regular time and depth intervals during the open water period in 1984. Surface water ANC was depressed during snowmelt and then increased as summer and fall progressed. Shallow lakes circulated completely in the fall, whereas deep lakes ( > 75 m) did not. Sulfate and N03 concentrations in the lakes increased during the snowmelt period and then decreased until iceover. No significant differences were found between surface ANC measurements during fall circulation in successive years.