Tactical management of pasture fallows in Western Australian cropping systems

Agricultural systems in the Western Australian wheatbelt are increasingly moving towards specialist crop production due to elevated cereal prices, depressed markets for livestock products, and ongoing labour scarcity. However, the profitability of crop-only farms is threatened by increasing levels of herbicide resistance and declining soil fertility. This study determines the value of ungrazed pasture fallows grown tactically between crop phases to address these agronomic constraints. A novel metaheuristic optimisation technique, compressed annealing, is used to determine profitable flexible land-use sequences in a complex simulation model. Tactical use of single-year, ungrazed pasture phases is found to be more valuable than the use of break crops in crop-only systems. In contrast to previous analysis, it is identified that rotation of short periods of crop and pasture is more profitable than extended phases of both. Effective weed control without dependence on selective herbicides is the key agronomic characteristic determining the value of intermittent pasture phases. Accordingly, the number of single-year pasture phases employed in a sequence should increase with the severity of herbicide resistance. Compressed annealing is shown to be a practical method of identifying profitable land-use sequences that respond to information that unfolds dynamically.     

Endogeic earthworms alter carbon translocation by fungi at the soil-litter interface

The effect of endogeic earthworms (Octolasion tyrtaeum (Savigny)) on the translocation of litter-derived carbon into the upper layer of a mineral soil by fungi was investigated in a microcosm experiment. Arable soil with and without O. tyrtaeum was incubated with ¹³C/¹⁵N-labelled rye leaves placed on plastic rings with gaze (64 μm mesh size) to avoid incorporation of leaves by earthworms. The plastic rings were positioned either on or 3 cm above the soil surface, to distinguish between biotic and chemical/physical translocation of nutrients by fungi and leaching.Contact of leaves to the soil increased ¹³C translocation, whereas presence of O. tyrtaeum reduced the incorporation of ¹³C into the mineral soil in all treatments. Although biomass of O. tyrtaeum decreased during the experiment, more ¹³C and ¹⁵N was incorporated into earthworm tissue in treatments with contact of leaves to the soil. Contact of leaves to the soil and the presence of O. tyrtaeum increased cumulative ¹³CO₂-C production by 18.2% and 14.1%, respectively.The concentration of the fungal bio-indicator ergosterol in the soil tended to be increased and that of the fungal-specific phospholipid fatty acid 18:2ω6 was significantly increased in treatments with contact of leaves to the soil. Earthworms reduced the concentration of ergosterol and 18:2ω6 in the soil by 14.0% and 43.2%, respectively. Total bacterial PLFAs in soil were also reduced in presence of O. tyrtaeum, but did not respond to the addition of the rye leaves. In addition, the bacterial community in treatments with O. tyrtaeum differed from that without earthworms and shifted towards an increased dominance of Gram-negative bacteria.The results indicate that litter-decomposing fungi translocate litter-derived carbon via their mycelial network in to the upper mineral soil. Endogeic earthworms decrease fungal biomass by grazing and disruption of fungal hyphae thereby counteracting the fungal-mediated translocation of carbon in soils.     

Response of soil microbial biomass and enzyme activities to the transient elevation of carbon dioxide in a semi-arid grassland

Although elevation of CO₂ has been reported to impact soil microbial functions, little information is available on the spatial and temporal variation of this effect. The objective of this study was to determine the microbial response in a northern Colorado shortgrass steppe to a 5-year elevation of atmospheric CO₂ as well as the reversibility of the microbial response during a period of several months after shutting off the CO₂ amendment. The experiment was comprised of nine experimental plots: three chambered plots maintained at ambient CO₂ levels of 360 μmol mol⁻¹ (ambient treatment), three chambered plots maintained at 720 μmol mol⁻¹ CO₂ (elevated treatment) and three unchambered plots of equal ground area used as controls to monitor the chamber effect.Elevated CO₂ induced mainly an increase of enzyme activities (protease, xylanase, invertase, alkaline phosphatase, arylsulfatase) in the upper 5 cm of the soil and did not change microbial biomass in the soil profile. Since rhizodeposition and newly formed roots enlarged the pool of easily available substrates mainly in the upper soil layers, enzyme regulation (production and activity) rather than shifts in microbial abundance was the driving factor for higher enzyme activities in the upper soil. Repeated soil sampling during the third to fifth year of the experiment revealed an enhancement of enzyme activities which varied in the range of 20-80%. Discriminant analysis including all microbiological properties revealed that the enzyme pattern in 1999 and 2000 was dominated by the CO₂ and chamber effect, while in 2001 the influence of elevated CO₂ increased and the chamber effect decreased.Although microbial biomass did not show any response to elevated CO₂ during the main experiment, a significant increase of soil microbial N was detected as a post-treatment effect probably due to lower nutrient (nitrogen) competition between microorganisms and plants in this N-limited ecosystem. Whereas most enzyme activities showed a significant post-CO₂ effect in spring 2002 (following the conclusion of CO₂ enrichment the previous autumn, 2001), selective depletion of substrates is speculated to be the cause for non-significant treatment effects of most enzyme activities later in summer and autumn, 2002. Therefore, additional belowground carbon input mainly entered the fast cycling carbon pool and contributed little to long-term carbon storage in the semi-arid grassland.     

Determination of residues of promecarb and its metabolite, 3-methyl-5-isopropylphenol,in cattle

A procedure is described for the colorimetric determination of promecarb as 3-methyl-5-isopropylphenol in tissues using 2,6-dichlorpbenzoquinone-4-chlorimine as the chromogen. Cattle were exposed to either 1, 3, 5 or 8 spray applications of a 0·2% promecarb emulsion at 3-day intervals or were fed promecarb at 2 ppm or 20 ppm daily in the diet for 20 days. All animals were slaughtered 30 h after final exposure. Of the animals in the spraying trial, residues in omental fat ranged from 0·9 ppm to 1·5 ppm promecarb and 0·4 ppm to 1·9 ppm 3-methyl-5-isopropylphenol. Residues in perirenal fat ranged from 0·8 ppm to 1·9 ppm promecarb and 0·9 ppm to 1·6 ppm 3-methyl-5-isopropylphenol. Residues in diaphragm muscle did not exceed 0·06 ppm. In the feeding trial, the maximum residues induced were 2·2 ppm promecarb and 1·4 ppm 3-methyl-5-isopropylphenol in omental fat of an animal fed for 20 days on a diet containing 20 ppm promecarb.     

Transient expression vectors for functional genomics,quantification of promoter activity and RNA silencing in plants

Background  

We describe novel plasmid vectors for transient gene expression using Agrobacterium, infiltrated into Nicotiana benthamiana leaves. We have generated a series of pGreenII cloning vectors that are ideally suited to transient gene expression, by removing elements of conventional binary vectors necessary for stable transformation such as transformation selection genes.     

Treatment of septic common digital extensor tenosynovitis by complete resection in seven horses

OBJECTIVE: To describe and evaluate a technique for radical resection of the entire intrathecal component of the common digital extensor tendon (CDET) in horses. STUDY DESIGN: Prospective clinical study. ANIMALS OR SAMPLE POPULATION: Seven client-owned horses. METHODS: Seven horses with wounds that resulted in septic tenosynovitis of the CDET sheath were treated by complete surgical resection of the affected tendon and ablation of the tendon sheath; 5 had previous surgery that was unsuccessful. Time from initial injury to complete resection was 1-22 weeks. In 6 horses, the wound was closed primarily using a closed suction (4 horses), penrose (1), or passive open drainage system (1). In 1 horse, the surgical wound healed by second intention. All horses had postoperative bandaging, antibiotic administration, and physiotherapy. RESULTS: Surgical wounds healed primarily in 6 horses and by second intention in 1 horse. Follow-up (mean, 26.4 months; range, 18-38 months) was available for 6 horses; all returned to their athletic performance level without lameness or gait abnormality. CONCLUSIONS: Complete resection of the CDET was an effective surgical technique for management of chronic septic tenosynovitis. CLINICAL RELEVANCE: Horses with infection of the CDET and its sheath may be returned to long-term soundness without gait abnormality after radical resection.     

Ectoparasites of livestock in Europe and the Mediterranean region

Arthropod ectoparasites can have a major impact on the productivity and welfare of livestock. In recent years, many parts of Europe have seen important changes in the nature of animal husbandry and parasite control, which have increased the need for a precise understanding of the current distribution and prevalence of livestock ectoparasites. In some cases, these changes have been associated with moves towards increased productivity, such as higher-stocking densities, large-scale rearing units, indoor confinement, reduced genetic diversity and large-scale movement of animals and, in others, with a move towards organic farming. There have also been changes in parasite control, associated with the development of new parasiticides, such as the macrocyclic lactones, and concern over the continued use of some of the older neurotoxic compounds. These changes have been exacerbated by outbreaks of endemic disease, the threats of exotic disease introduction and fears of potential changes in arthropod distribution associated with climate change. This paper therefore, reviews the current status of livestock ectoparasites in Europe and the Mediterranean region.     

Malignant teratoid medulloepithelioma with brain and kidney involvement in a dog

ANIMAL STUDIED: A tumor of the left eye with involvement of the brain and kidney was diagnosed in a 4-year-old Neapolitan mastiff. PROCEDURE: The dog presented with acute glaucoma of the left eye. Peripheral corneal vascularization and severe corneal edema obscured examination of deeper structures. Because of concurrent progressive neurologic signs the dog was euthanized and a postmortem examination was performed. The eyes, brain and samples from the lung, heart, liver and kidneys were fixed in 4% neutral buffered formalin and embedded in paraffin wax. Sections were examined by light microscopy including histochemical and immunohistochemical staining. RESULTS: The ocular tumor originated from the ciliary body and was composed of small islets and cords of poorly differentiated, oval to polyhedral cells surrounded by abundant ground substance. Areas with chondroid differentiation were observed. Rosettes were not found. Metastases with the same morphology were present in the brain and in one kidney. CONCLUSION: An intraocular malignant teratoid medulloepithelioma with metastases to the brain and kidney is presented.     

Degradation of an Atrazine and Metolachlor Herbicide Mixture in Pesticide-Contaminated Soils from Two Agrochemical Dealerships in Iowa

The fate of atrazine and metolachlor,applied as a mixture, in soil taken from twopesticide-contaminated sites in Iowa (denoted as Alphaor Bravo) were determined in laboratory studies. Atrazine and metolachlor degradation, as well asatrazine mineralization, were greater in soilcollected from Kochia scoparia L. (Schrader)rhizosphere than in soils from unvegetated areas. Theradiolabeled ¹⁴C-carbinol and¹⁴C-morpholinone metabolites were identified in¹⁴C-metolachlor-applied soil 60 d aftertreatment. The half-life for atrazine in Alpha soilwas significantly less in the rhizosphere soil (50 d)than in unvegetated soil (193 d). Quantities ofspecific atrazine degraders were one to two orders ofmagnitude greater in Bravo soils than in Alpha soils. In an experiment with plants present, significantlymore ¹⁴C-atrazine was taken up by K.scoparia (9.9% of the applied ¹⁴C) than by Brassica napus L. Significantly less atrazine wasextractable from soils vegetated with K.scoparia than from soils vegetated with B.napus or unvegetated soils.