Could soil degradation contribute to farmland bird declines? Links between soil penetrability and the abundance of yellow wagtails Motacilla flava in arable fields

Major changes to the extent and quality of farmland habitats, brought by the intensification of agricultural practice, are thought to be the main factors driving declines in a suite of farmland bird species in Europe. Recent changes in agricultural techniques have also contributed to widespread soil degradation, arising from increased soil exposure to erosion forces, declining soil organic content and increasing soil compaction. Although soils have a fundamental influence on ecosystem properties, the implications of soil degradation for farmland biodiversity have received little attention. In this study, we measure the influence of soil conditions on the distribution of a declining insectivorous farmland bird, the yellow wagtail Motacilla flava, relative to other habitat features in arable fields. Soil penetrability was found to have a significant influence on the abundance of territorial yellow wagtails at the field scale, together with crop type. Other measured habitat features had little effect on territory abundance, including soil organic content, crop height (within preferred crop types), field boundary habitats and availability of bare ground. Monitoring of invertebrate abundance across 20 cereal fields revealed a significant influence of both soil penetrability and soil organic content on aerial invertebrate capture rates. This relationship was strongest during the latter part of the breeding season, implying that settling yellow wagtails could use soil penetrability as a predictive indicator of prey abundance during the chick-rearing period. The strong relationship between yellow wagtails and soil penetrability suggests a potential causative link between soil degradation and population decline. The role of soils in determining abundance patterns and population declines of other farmland species may have been overlooked in previous studies.     

Functional resilience of soil microbial communities depends on both soil structure and microbial community composition

The effects of soil structure and microbial community composition on microbial resistance and resilience to stress were found to be interrelated in a series of experiments. The initial ability of Pseudomonas fluorescens to decompose added plant residues immediately after a copper or heat stress (resistance) depended significantly on which of 26 sterile soils it was inoculated into. Subsequent studies showed that both the resistance and subsequent recovery in the ability of P. fluorescens to decompose added plant residues over 28 days after stress (resilience) varied significantly between a sandy and a clay-loam soil. Sterile, sandy and clay-loam soil was then inoculated with a complex microbial community extracted from either of the soils. The resulting microbial community structure depended on soil type rather than the source of inoculum, whilst the resistance and resilience of decomposition was similarly governed by the soil and not the inoculum source. Resilience of the clay-loam soil to heat stress did not depend on the water content of the soil at the time of stress, although the physical condition of the soil when decomposition was measured did affect the outcome. We propose that soil functional resilience is governed by the physico-chemical structure of the soil through its effect on microbial community composition and microbial physiology.     

Efficacy of artificial refuge to enhance survival of young Barrens topminnows exposed to western mosquitofish

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The influence of organic matter in reducing the destabilization of soil by simulated tillage

Different agricultural practices can result in a decline in soil organic carbon (SOC) and a consequent reduction in soil structural stability. Experiments were conducted on soils with a range of SOC values, to quantify the destabilizing effects of increased tillage intensity. Different tillage intensity was simulated with the use of a falling weight, where specific energy levels, similar to those experienced during tillage, were reproduced. The level of destabilization was assessed by the quantity of mechanically dispersed clay (using a turbidimetric technique) and the quantity of water-stable aggregates (WSA) > 0.25 mm remaining after being shaken in water.

The quantity of clay dispersed increased with increasing water content, in the absence of any mechanical pretreatment, the rate of increase rising sharply with declining SOC. Following simulated tillage, and at water contents above the plastic limit, clay dispersion increased in proportion to the energy of disruption, and also increased with decreasing SOC levels. Below the plastic limit all the soils were relatively insensitive to mechanical disruption. A simple empirical model was derived to link clay dispersion to SOC, water content and energy of disruption.

The proportion of WSA declined sharply with decreasing SOC, and to a lesser extent following tillage. The quantity of WSA following simulated intensive tillage (300 J kg⁻¹) of grassland (SOC, 2.8–3.2 g (100 g)⁻¹) was greater than that present, prior to tillage from fallow, arable and arable/ley rotation treatments (SOC 1.1–2.5 g (100 g)⁻¹). Aggregate tensile strength was found to be relatively insensitive to differences in SOC. However, variations of strength within treatments, an indicator of soil friability, increased in proportion with SOC. A turbidity index was derived in which the turbidity of natural and remoulded aggregates was compared. Variation of this index with increasing mechanical energy is used as an indicator of the sensitivity of soils to damage during tillage. A visual representation is constructed to link the sensitivity of soils to damage during tillage with both SOC and water potential. These experiments illustrate that management practices, which lead to a long term reduction in SOC, are responsible for an increase in aggregate strength and reduction in stability plus an increase in sensitivity of soils to structural decline following subsequent tillage.     

Selection for quality in marrow-stem kale

A selection technique is described for marrow-stem kale involving penetration of the stem by a needle shot from a spring loaded gun. Significant correlation was found between readings using this technique and the width of lignification of the vascular tissue measured from transverse sections.     

A simplified method for the gas-liquid chromatographic determination of methyl mercury in fish and shellfish.

A simple acetone wash of the fish sample which removes lipids and other organic materials replaces the cystein cleanup specified in other methods. Methyl mercury is freed by hydrochloric acid, extracted into benzene, and determined with a gas-liquid chromatograph equipped with an electron capture detector. The method is quantitative for methyl mercury levels as low as 0.10 ppm in fish and shellfish. Ethyl mercury chloride may be used as an internal standard to detect unsuspected error or instrumental parameter variation.     

The inheritance of curding periods in early summer and autumn cauliflower

Two series of diallel crosses were made between (a) eight varieties of autumn cauliflowers and (b) six inbred lines from a single variety of early summer cauliflowers in order to study the inheritance of curding periods. F₁'s and parents from each diallel were grown in separate randomised block experiments and the analyses presented as conventional Wr Vr graphs.The array points from the diallel analysis of autumn cauliflowers were spread along a regression line of unit slope thus indicating that the gene system controlling curding periods was additive with no evidence of gene interaction in these crosses. Varieties of early/mid period maturity with the exception of Veitch's Autumn Giant possessed most dominant polygenes while late maturity was controlled by recessive polygenes. The diallel analysis of curding periods for the early summer cauliflower inbreds indicated the presence of some interaction which was due to the influence of two lines. On reanalysis without these lines the regression of Wr Vr agreed with a slope of 1, although there was a higher degree of dominance than was shown by the autumn cauliflowers. Analysis of the early summer cauliflower lines for numbers of leaves produced before curding indicated an association between low leaf numbers and early curding, and between high leaf numbers and late curding.None of the F₁ hybrids in either series of crosses curded earlier than the earlier curding parent.     

Validation of Dual‐energy X‐ray Absorptiometry to Predict Body Composition of Channel Catfish,Ictalurus punctatus

Dual‐energy X‐ray absorptiometry (DXA) provides a noninvasive way to determine lean tissue mass (LTM), fat mass (FM), bone mineral content (BMC), and bone mineral density (BMD) in humans and small mammals. Live channel catfish (n = 74, 78–1200 g) were anesthetized and scanned in both a lateral position and a dorsa‐ventral position. Six individual fish (300–600 g) were scanned five times each to determine precision by the coefficient of variation. Precision was good for LTM (0.75–1.06%) and for BMC and BMD (2–2.6%). Precision for FM was not good (27–34%), which was due to the very low FM (0–1 g) recorded by the DXA. However, using the predicted values, FM precision improved to 5–5.5%. DXA values for LTM, FM, and BMC were significantly different from chemical analysis (P < 0.001). DXA overestimated LTM and underestimated FM and BMC. However, all three compartments were strongly correlated with carcass values (P < 0.0001). Using the prediction equations and the jackknife procedure, predicted values of LTM, FM, and BMC were not significantly different from the carcass values (P > 0.05). DXA may also be a valuable tool for evaluating body condition longitudinally in commercial or in threatened or endangered fish species, where noninvasive procedures would be invaluable.     

A porous-matrix sensor to measure the matric potential of soil water in the field

The matric potential of soil water is probably the most useful assessment of soil water status. However, the water‐filled tensiometer (the benchmark instrument for measuring matric potential) typically only operates in the range 0 to ?85 kPa. In this paper, we report the development of a porous‐matrix sensor to measure matric potential in the approximate range ?50 to ?300 kPa. The sensor uses a dielectric probe to measure the water content of a ceramic material with known water retention characteristics. The calculation of matric potential takes into account hysteresis through the application of an appropriate model to measured wetting and drying loops. It is important that this model uses closed, rather than open, scanning loops. The calibrated sensors were tested in the field and the output compared with data from water‐filled tensiometers and dielectric measurements of soil water content. These comparisons indicated that conventional tensiometers gave stable but false readings of matric potential when soil dried to matric potentials more negative than ?80 kPa. The porous‐matrix sensors appeared to give reliable readings of matric potential in soil down to ?300 kPa and also responded appropriately to repeated wetting and drying. This porous‐matrix sensor has considerable potential to help understand plant responses to drying soil.