Distribution of the equilibrium moisture content in four hardwoods below fiber saturation point with magnetic resonance microimaging

Wood Science and Technology - The distribution of liquid and bound water in wood samples under equilibrium moisture contents (EMC) below fiber saturation point (FSP) was assessed by magnetic...     

Residues of chlorpyrifos in various crops II. Residues after field treatments

Five agricultural crops were treated with OO-diethyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate (chlorpyrifos) granular or emulsifiable concentrate formulations at dosages from 0.5 to 6.0 kg (a.i.)/ha and at different periods before harvest. Chlorpyrifos residues were determined by gas chromatography after extraction and sweep co-distillation clean-up. Low residue levels were found. The average values in lettuce were 0.046 and 0.070 part/million, in sugar beet leaves 0.037 to 0.128 part/million and roots <0.005 to 0.038 part/million; no chlorpyrifos was detected in carrots, potatoes and cured tobacco leaves at the limit of the method (0.005 part/million).     

Comparison of 15N natural abundance and difference methods for estimating N2 fixation of soybeans grown in a tropical soil

Abstract

A study was carried out to compare the difference or N-yield method with the ¹⁵N natural abundance method for the estimation of the fractional contribution of biological N₂ fixation in the different plant parts of nodulating and non-nodulating isolines of soybeans. The results indicated that the δ¹⁵N values of most plant parts of soybeans were significantly lower (p<0.05) in the nodulating than in the non-nodulating isoline. However, in the case of the root+nodule component, the δ¹⁵N value was higher in the nodulating than in the non-nodulating isoline possibly due to isotopic discrimination of ¹⁵N over ¹⁴N which may have occurred in the nodules. Inoculation of soybeans with the Bradyrhizobium japonicum strain CB 1809 increased significantly (p<0.05) the δ¹⁵N value of the root+nodule component implying that the effectiveness of the soybean-rhizobium symbiosis had increased by inoculation.

Percentage of plant N derived from atmospheric N₂ fixation (%Ndfa) estimated by the ¹⁵N natural abundance method was highly correlated (r=0.762, p<0.01) with that by the difference or N-yield method and the differences between the two methods were not statistically significant. The agreement between the two methods was closer at maturity than at the early reproductive stage.

The %Ndfa obtained by the difference method ranged from 48.4 to 92.6% whereas the %Ndfa obtained by the ¹⁵N natural abundance method ranged from 43.2 to 92.4% in the different plant parts. Based on the ¹⁵N natural abundance method, approximately 15% of the N in pod, shoot, grain, and shell was derived from the soil but in the case of stover, this fraction was about 55%.     

Comparative data on the insecticide resistance of <Emphasis Type="Italic">Anopheles</Emphasis> <Emphasis Type="Italic">albimanus</Emphasis> in relation to agricultural practices in northern Belize,CA

Anopheles albimanus Wiedemann is one of the primary vectors of malaria in northern Belize. The primary breeding sites for this species in Central America are fresh water wetlands that are found in close proximity to agriculture and, in particular, sugarcane fields. The use of insecticides and herbicides on these crops leads to the introduction of chemicals into the surrounding wetlands. The potential for the development of insecticide resistance is, therefore, quite high. A study was undertaken to obtain comparative data on the resistance status of An. albimanus in northern Belize in relation to agriculture practices. Larval surveys were conducted at four collection points in marshes juxtaposed to different crop types: Dubloon (DB)—control site located 300 m from any agriculture; Little Belize (LB)—mixed crop agricultural with some human settlements; and Chan Chen (CC) and Buena Vista (BV)—year round sugarcane production. Time mortality curves were obtained by exposing F1 larvae to DDT 1 μg/ml, malathion 1 μg/ml, and permethrin 0.05 μg/ml. Significant differences in mortality rates from the four sites were observed only to malathion. The DB sites contained larvae that were the most susceptible overall, in congruence with its distance from crops. Larvae from LB exhibited a medium level of tolerance. Finally, the two populations collected at the edge of sugarcane fields (CC and BV) exhibited the highest tolerance to malathion. These results represent first data on the impact of agriculture on the resistance status of malaria vectors in northern Belize. The effect of malathion on An. albimanus insecticide resistance reinforces the concerns of the potential impact of agriculture usage on the efficacy of vector control program.     

Climate change impacts on plant canopy architecture: implications for pest and pathogen management

Climate change influences on pests and pathogens are mainly plant-mediated. Rising carbon dioxide and temperature and altered precipitation modifies plant growth and development with concomitant changes in canopy architecture, size, density, microclimate and the quantity of susceptible tissue. The modified host physiology and canopy microclimate at elevated carbon dioxide influences production, dispersal and survival of pathogen inoculum and feeding behaviour of insect pests. Elevated temperature accelerates plant growth and developmental rates to modify canopy architecture and pest and pathogen development. Altered precipitation affects canopy architecture through either drought or flooding stress with corresponding effects on pests and pathogens. But canopy-level interactions are largely ignored in epidemiology models used to project climate change impacts. Nevertheless, models based on rules of plant morphogenesis have been used to explore pest and pathogen dynamics and their trophic interactions under elevated carbon dioxide. The prospect of modifying canopy architecture for pest and disease management has also been raised. We offer a conceptual framework incorporating canopy characteristics in the traditional disease triangle concept to advance understanding of host-pathogen-environment interactions and explore how climate change may influence these interactions. From a review of recent literature we summarize interrelationships between canopy architecture of cultivated crops, pest and pathogen biology and climate change under four areas of research: (a) relationships between canopy architecture, microclimate and host-pathogen interaction; (b) effect of climate change related variables on canopy architecture; (c) development of pests and pathogens in modified canopy under climate change; and (d) pests and pathogen management under climate change.     

Corrosion of metal fasteners embedded in acetylated and untreated wood at different moisture contents

ABSTRACT

Acetylated wood is now commercially available and designed to be used in certain outdoor applications as an alternative to preservative-treated wood. Fastener corrosion can be a concern in preservative treated wood when the wood remains wet for long periods. However, little data on the corrosiveness of acetylated wood exists beyond the product literature. Here we examine the corrosiveness of commercially obtained acetylated wood and compare it against unmodified (untreated) southern pine (Pinus spp.). Corrosion rates of plain carbon steel, hot dip galvanized steel, and stainless steel were calculated gravimetrically after a one year exposed in the wood. Four different moisture conditions were examined: 90% relative humidity (RH), 95% RH, 100% RH, and a fully water saturated condition. When compared to literature data on the corrosion of fasteners in preservative treated wood at 100% RH, the acetylated wood had much lower steel corrosion rates than all preservatives examined; the measured corrosion rates for galvanized steel were lower than all preservatives except chromated copper arsenate. These measured corrosion rates across a range of moisture conditions can be used to inform the selection of appropriate corrosion resistant fasteners when building with acetylated wood.     

Nitrogen transformations of ammonium sulfate and alanine in submerged Maahas clay

The fate of added nitrogen in submerged soils was studied using ¹⁵N-labelled ammonium sulfate and alanine. After 8 weeks of incubation 25 and 22%, respectively, of nitrogen from ammonium sulfate and alanine were recovered in the soil. Under the experimental conditions used nitrogen added to presubmerged soils was lost rapidly outside of the soil-water system, regardless of whether the nitrogen was organic or inorganic. Fractionation studies revealed that the amount of tagged N incorporated into exchangeable ammonium, residual fractions, volatilized as NH₃ and chemically fixed nitrogen was not enough to account for the nitrogen loss. The nitrogen loss was attributed to nitrification and subsequent denitrification during the incubation period.

The effect of N-Serve [2-chloro-6-(trichloromethyl)pyrimidine] on nitrification of ¹⁵N-labelled (NH₄)₂SO₄-in submerged soils was studied. About 15% more nitrogen was recovered from non-presubmerged soils, and less nitrate was accumulated in presubmerged soils where N-Serve coated (NH₄)₂SO₄ was applied, than from soils where (NH₄)₂SO₄ was applied without N-Serve. Presubmerged soils provided a more favorable environment for nitrification than for denitrification under the experimental conditions used.     

Effects of temperature and moisture content on selected wood mechanical properties involved in the chipping process

The effects of temperature and moisture content on selected mechanical properties associated with the chipping process were evaluated. In chipping, mechanical properties such as shear parallel to the grain, cleavage, and bending are involved. Matched samples of heartwood and sapwood were obtained from freshly harvested logs of black spruce and balsam fir to determine the variation of the studied mechanical properties between ?30 and 20 °C, at intervals of 10 °C. Moisture content (MC), basic density (BD), and annual ring width (RW) were measured for each sample. For both wood species, temperature had a significant effect on all mechanical properties under freezing conditions (below 0 °C). This effect was more important for sapwood than for heartwood, which was explained by the difference in MC between these two types of wood. Between 0 and 20 °C, temperature and type of wood did not show any significant effect on the mechanical properties. Multiple regression models were obtained to predict the mechanical properties. These regressions showed that MC was the most important factor to explain the mechanical properties below 0 °C. However, for temperatures of 0 °C and higher, BD was the principal factor to predict the mechanical properties. RW was not a significant factor to predict any mechanical property. Cleavage was the most sensitive one to changes in temperature followed by shear, modulus of rupture, and modulus of elasticity. These results could be of great importance in the chipping process.