Errors in predicting furrow irrigation performance using single measures of infiltration

Commercial performance evaluations of surface irrigation are commonly conducted using infiltration functions obtained at a single inflow rate. However, evaluations of alternative irrigation management (e.g. flow rate, cut-off strategy) and design (e.g. field length) options using simulation models often rely on this single measured infiltration function, raising concerns over the accuracy of the predicted performance improvements. Measured field data obtained from 12 combinations of inflow rate and slope over two irrigations were used to investigate the accuracy of simulated surface irrigation performance due to changes in the infiltration. Substantial errors in performance prediction were identified due to (a) infiltration differences at various inflow rates and slopes and (b) the method of specifying the irrigation cut-off. Where the irrigation cut-off at various inflow rates was specified as a fixed time identified from simulations using the infiltration measured at a single inflow rate, then the predicted application efficiency was generally well correlated with the application efficiency measured under field conditions at the various inflow rates. However, the predictions of distribution uniformity (DU) were poor. Conversely, specifying the irrigation cut-off as a function of water advance distance resulted in adequate predictions of DU but poor predictions of application efficiency. Adjusting the infiltration function for the change in wetted perimeter at different inflow rates improved the accuracy of the performance predictions and substantially reduced the error in performance prediction associated with the cut-off recommendation strategy.     

Rapid degradation of the Cry1F insecticidal crystal protein in soil

The gene for the core Cry1F insecticidal crystal protein (ICP) from Bacillus thuringiensis Berliner (Bt) has been incorporated into the genome of maize plants, Zea mays L. Plants expressing this ICP are protected from attack by various Lepidopteran pests including the European corn borer, Ostrinia nubilalis (Hübner). The stability of the Cry1F ICP in soil was assessed in a laboratory study designed to determine the persistence of the active protein residue in soil over time, using insect bioassay as the analytical quantification method. The GI(50) (concentration estimated to inhibit growth by 50%) rose at each consecutive incubation interval, indicating a consistent decline in Cry1F activity over time. The residue data were poorly described by a first-order model when fit to either the full data or a truncated data set where the last interval (28 days) was excluded. Data were well described by a shift-log model, and this model predicted DT(50) (time until 50% decay) and DT(90) (time until 90% decay) values of 0.6 and 6.9 days, respectively. This rapid degradation rate was consistent with other Bt proteins evaluated in our laboratory.     

Growth trends and nutritional status of sugar maple stands on the appalachian plateau of Pennsylvania,U.S.A.

Growth of sugar maple trees and element concentrations of soil and foliage were investigated at 12 stands in north-central Pennsylvania and southern New York. The goal of this exploratory study was to evaluate growth trends since the 1950s and to determine whether element concentrations were within limits conducive for normal growth. Basal area growth of overstory maple trees increased at six sites, declined at five, and remained nearly constant at one. Overall, the growth of overstory sugar maple trees did not change appreciably since the late 1950s, but growth of subcanopy maples decreased markedly, probably because of intensified shading in these maturing stands. Concentrations of Al, Cu, Fe, K, Mg, N, P, and Zn in soil and maple foliage were within the range of values reported for other sugar maple stands in North America. Calcium concentrations appeared adequate for growth, although at some sites they were near the low end of the typical range. Basal area growth of the overstory maples was correlated to the concentrations of Ca, Al, and the Ca∶Al ratio of soil, whereas growth of the subcanopy maples was not. Growth of the overstory trees was also correlated to the Ca concentration of maple foliage, which in turn was correlated to pH, Ca, Al, and the Ca∶Al ratio of soil. Manganese concentrations in soil and foliage were comparatively high, but were not correlated to trends in growth. The results of this investigation do not indicate abnormal changes in growth of sugar maple since the late 1950s. They suggest, however, that Ca availability limits growth at some sites and indicate that Al concentrations in the soil may be inhibiting Ca uptake.     

Rapid digestion of Cry34Ab1 and Cry35Ab1 in simulated gastric fluid

Two genes were identified in Bacillus thuringiensis Berliner (Bt) that code for the proteins that comprise a Cry34Ab1/Cry35Ab1 binary insecticidal crystal protein. Maize, Zea mays L., plants have been transformed to express the Cry34Ab1/Cry35Ab1 proteins, and as a result, these plants are resistant to attack by western corn rootworm, Diabrotica virgifera virgifera LeConte, a major pest in the Midwestern corn-growing area of the U.S.A. As part of the safety assessment for the proteins, digestibility studies were conducted. Digestion experiments with both proteins demonstrated rapid degradation in simulated gastric fluid, comparable to other registered plant-incorporated protectants. Quantitative and qualitative approaches for determining digestibility are illustrated.     

Effect of water quality on soil structure and infiltration under furrow irrigation

The quality of irrigation water has the potential to significantly affect soil structural properties, infiltration and irrigation application efficiency. While the effect of electrolyte concentration (as indicated by the electrical conductivity EC) and sodium adsorption ratio (SAR) have been studied under laboratory conditions, the effect on soil profile structural properties and irrigation performance have not been widely investigated under field conditions. In this paper, water with three different levels of sodium (SAR = 0.9, 10 and 30) was applied as alternative treatments to a clay loam soil. The application of 238–261 mm of medium- to high-SAR water was found to reduce aggregate stability, increase the bulk density of both the surface crust and underlying soil, and reduce the total depth of infiltration and final infiltration rate. Where low-SAR water was used, there was no significant (P<0.05) difference in final infiltration rate after the first four irrigations. However, where moderate- and high-SAR water was applied after the first four irrigations with the low EC-SAR water, the final infiltration rate was found to decrease on each of the successive irrigation events. For the moderate- and high-SAR treatments, this suggests that a steady-state equilibrium had not been reached within that part of the soil profile impeding infiltration. It is proposed that the initial reduction in infiltration is related to the physical processes of slaking leading to the development of an apedal, hardsetting surface soil layer. Similarly, it is proposed that the subsequent increase in bulk density and decline in infiltration where moderate and high EC-SAR water is applied is due to an increase in clay tactoid swelling reducing the size of the conducting micropores, dispersion blocking pores, and/or an increase in the thickness of the apedal surface layer. The reduction in infiltration associated with the use of high-SAR irrigation water was found to reduce the performance of the irrigations, with the application efficiency of the final irrigation decreasing from 40% where the low-SAR water was used, to 21% where the high-SAR water was applied. The implications for surface irrigating with water containing high sodium levels are discussed.Communicated by A. Kassam     

Idiopathic Polyneuropathy in Alaskan Malamutes

Clinical and morphologic features of a progressive polyneuropathy in young mature Alaskan Malamutes are described. Clinical signs included progressive paraparesis, synchronous pelvic limb gait, exercise intolerance, hyperesthesia, hypore-flexia, muscle atrophy, and tetraplegia. Electromyographic testing revealed diffuse fibrillation potentials and positive sharp waves in limb muscles, especially in muscles below the elbow and stifle. Pathologic findings in skeletal muscles and peripheral nerves included neurogenic muscle atrophy, focal or diffuse loss of myelinated nerve fibers, myelinoaxonal necrosis, and variable demyelination or remyelination.
Ultrastructural changes included axonal degeneration, presence of numerous Büngner bands, and denervated Schwann cell subunits. The nature and distribution of abnormal electrophysiologic and pathologic findings were suggestive of a distal sensorimotor polyneuropathy, which we have termed idiopathic polyneuropathy of Alaskan Malamutes to distinguish this condition from hereditary polyneuropathy of Norwegian Alaskan Malamutes, last described in 1982.     

Experimental transmission and electron microscopic demonstration of the virus of haemorrhagic disease of rabbits in Czechoslovakia

Intramuscular administration of the filtrate of organ suspensions, prepared from a dead rabbit, killed 62.9% of inoculated rabbits within 1 to 5 days, while 93.3% died after intranasal administration of the same inoculum. The virus survived freeze-drying and was resistant to treatment with 0.4% formaldehyde when incubated at 37 degrees C for 1 hour and 4 degrees C for the subsequent 12 hours, but lost its infectivity when the treatment was prolonged to 3 hours at 37 degrees C and 3 days at room temperature. Its infectivity was also inhibited by reconvalescent serum. The virus could not be detected after 3 passages in primary rabbit kidney cell cultures. Electron microscopy of negatively stained preparations demonstrated icosahedral virus particles with a diameter of 29 to 33 nm without an envelope. Accurate morphological classification has not yet been completed. Incubation with a reconvalescent serum, diluted 1:20 or 1:40, resulted in the formation of immune complexes, detectable by electron microscopy.     

Survival of Aujeszky's disease virus in infected pig slurry

It has been demonstrated that after experimental infection of pig slurry from the space under the slatted floor (infection dose of 10(6)PFU per ml), the Aujeszky's disease virus (ADV) survived for 72 hours at the temperature of 15 degrees C and at pH 6.5, but was inactivated after 96 hours. When technologically treated pig slurry from the storage tanks was saturated with water and infected with ADV at the dose of 10(5)PFU per ml, the virus survived for 23 days when kept at 15 degrees C and 4 degrees C and at pH 6.8, but was inactivated under the same conditions after 30 days. When the infective ADV dose in the technologically treated pig slurry in the storage tanks was reduced to 10(4)PFU per ml, the virus survived 16 days at +4 degrees C and pH 7.0 and 8.0 but was inactivated within 23 days after infection.