The influence of a compacted plow sole on saturation excess runoff

Subsoil compaction due to conventional tillage techniques and its relation to subsurface flow and runoff was investigated on a sloped field. The presence of a plow sole was confirmed by significantly higher penetration resistances between 20 and 40 cm depth, a significantly higher soil bulk density and a 14% decrease in drainage pore space compared to the top layer. Ring infiltrometer measurements also confirmed a significant reduction of the saturated hydraulic conductivity at 30 cm depth, indicating a limited permeability. With the use of an extensive grid of tensiometers, matric heads were monitored and the occurrence of a temporary water table on top of the plow sole was confirmed in a number of cases. Equipotential lines in the top saturated layer indicated the occurrence of subsurface flow parallel to the slope surface in a downward direction. For the whole measuring period, when a perched water table was observed, 91% of the rainfall events caused runoff and this number increased with increasing rainfall intensity. For low and medium rainfall intensities (<10 mm h⁻¹), 66% and 63% of the runoff events were related to saturation of the top soil. Therefore, it was concluded that over a period of 20 months saturation excess runoff as a result of subsoil compaction was an important contributor to surface runoff and soil loss.     

Monitoring critical defects of creep rupture in oriented strandboard using acoustic emission: incorporation of EN300 standard

This creep rupture study in commercial oriented strandboard (OSB) used a 4-point flexural test to evaluate the dynamic property changes of a 300×1,000-mm specimen using an acoustic emission (AE) system. Compared to deflection, AE events were more sensitive to damage accumulation than deflection to final failure. Specimens were artificially notched on either the tension- or compression-side and were subjected to 80% stress level at ambient conditions. Defects on the compression side of the bending specimen were found to be more critical than on the tension side in creep-rupture. The in-plane fractures followed patterns of the valleys of low-density spots as defect trenches, demonstrating adverse effects of high variation in horizontal density. An impetus and rationale to incorporate regulatory quality inspection standards and product certification of structural OSB based on the control limits of ±10% panel density as stipulated in EN300 standard is discussed.Experiment conducted at the former University of California Forest Products Laboratory (Nondestructive Evaluation Center), Richmond, CA 94804, USA.     

Bacterial injectisomes: needle length does matter

Many pathogenic bacteria use a type III secretion nanomachine (an injectisome) to deliver virulence proteins into the cytosol of their eukaryotic host cells. Most injectisomes possess a stiff needlelike structure of a genetically defined length. We found that a minimal needle length was required for efficient functioning of the Yersinia enterocolitica injectisome. This minimal needle length correlated with the length of the major adhesin at the bacterial surface. The needle may be required for triggering type III secretion, and its length may have evolved to match specific structures at the bacterial and host cell surfaces.     

Diet energy source affects lysine utilization for protein deposition in rainbow trout (Oncorhynchus mykiss)

We have previously shown that lysine utilization for body protein deposition (PD) in rainbow trout was affected by digestible energy (DE) content of the diet. When lysine intake limits PD, additional DE intake from fish oil improves efficiency of lysine utilization for PD. It is unclear whether other energy-yielding nutrients have the same effect on lysine utilization. Different energy sources that may be converted to different tricarboxylic acid (TCA) cycle metabolic intermediates can have different abilities to spare lysine for PD. An experiment was therefore carried out to examine the effects of different energy-yielding nutrients, on growth, nitrogen gain and lysine utilization by rainbow trout. Fish weighing 5.0 g ± 0.1, were fed diets with either limiting (1.5%) or marginally adequate (2.0%) lysine levels. Acetyl-CoA precursors (fish oil), pyruvate precursors (mixture of alanine, serine, glycine, and cystine) and α-ketoglutarate + oxaloacetate precursors (mixture of aspartate, glutamine and glutamate) were then added to the control diets (at the expense of raw corn starch) to produce a series of experimental diets with 20 MJ DE. Fish were pair-fed for 16 weeks and then to satiation for an additional 6 weeks. Results suggest that different energy sources affect lysine utilization differently. When feed intake was similar, additional DE from pyruvate and α-ketoglutarate/oxaloacetate precursors did not improve PD. When lysine was limiting, pyruvate precursors reduced feed intake and PD. Fatty acids, which similarly to lysine may be converted to acetyl-CoA, appear to be more effective in sparing lysine for PD than other metabolic substrates that have different entry points into the TCA cycle. Rainbow trout appears to have a higher tolerance for an excess of amino acids that are α-ketoglutarate/oxaloacetate precursors (glu, gln, asp) than pyruvate precursors.     

Manipulation of the soil pore and microbial community structure in soil mesocosm incubation studies

Soil pore structure exerts a profound influence on distribution of moisture, O₂ and micro-organisms, thereby potentially controlling organic matter (OM) decomposition in soils. Although pore space is the habitat for soil micro-organisms and the actual location of soil biochemical processes, to date, very few studies looked into this relation mainly because of practical constraints. New experimental designs need to be developed which allow specific investigations of the relation between soil pore network structure, the microbial community and OM decomposition. We therefore subjected a sandy loam soil to a number of artificial manipulations namely i) compaction, ii) artificial change in particle size distribution, iii) addition of different substrates and iv) change in soil pH to manipulate soil pore structure and the decomposer community for use in lab incubation set-ups. Moisture retention data showed that compaction and artificial change in particle size distribution decreased volumes of large (9–300 μm) and small (<0.2 and 3–9 μm) pore size classes, respectively. PLFA signature analysis showed that acidification promoted fungi, while an effect of application of either sawdust or grass on the decomposer community was smaller. Acidification significantly reduced C mineralization and microbial biomass C. Surprisingly, the largest shift in microbial community (with promotion of fungi and protozoa relative to bacteria) over all treatments was observed in the treatments with artificially changed particle size distribution. We conclude that it is possible to ‘tailor’ soil pore structure and the decomposer community in soil mesocosm incubation experiments by such manipulations. However, non-targeted effects on microbial community structure, microbial biomass and gross C mineralization seem unavoidable.     

Sand detachment under rains with varying angle of incidence

In the case of wind-driven rain, as the angle of rain incidence increases, greater force components act parallel to the surface and lower force components act perpendicular to the surface. Therefore, raindrop impact angle could influence the detachment process in the existence of substantial lateral jet development. This could be particularly significant for a cohesionless sand surface that has a weaker resistance to the dislodgement by a raindrop impact than a soil surface. Experiments of simulated wind-driven rain were conducted to evaluate sand detachment rates under increased lateral jetting induced by wind velocities of 6.4, 10.0, and 12.0 m s^− 1 at nozzle operating pressures of 75, 100, and 150 kPa and incident on windward and leeward slopes of 4 and 9°. With these set-ups, it was possible to have varying angles of incidence and to determine the effect of the compressive stress and shear stress, evaluated by the horizontal and vertical kinetic energy fluxes (E_tx and E_tz, respectively), on the detachment rates from the sand surface. At the same vectorwise sum of E_tz and E_tx, the results showed that there was, for similar values of E_tz and E_tx in windward slopes, more sand detachment rate; however, for dissimilar values of E_tz and E_tx in leeward slopes where E_tx was significantly higher than E_tz, there was less sand detachment rate. Consequently, with certain values of the compressive stress and shear stress, the sand detachment rates under wind-driven rains peaked; and E_tz was the limiting component since the rates significantly decreased as E_tz particularly decreased in spite of very large values of E_tx.     

Effects on pesticide spray drift of the physicochemical properties of the spray liquid

This research was on the effect of the physicochemical properties of the spray liquid on pesticide spray drift. Ten pesticide spray liquids with various physicochemical properties were selected for study. Some of these spray liquids were also examined with the addition of a polymer drift-retardant. In the first part, laboratory tests were performed to measure surface tension, viscosity, evaporation rate and density of the spray liquids. Subsequently, drift experiments were performed in a wind tunnel. From the results it was found that the dynamic surface tension is a major drift-determining factor, and also that the addition of a polymer drift-retardant can reduce drift significantly by increasing the viscosity. Drift reduction was found to be less effective with spray liquids of emulsifiable and suspendable formulation types than with spray liquids of water-dispersible granules and powders.