The immobilization of nitrogen by straw decomposing in soil

Immobilization of nitrogen (N) in decomposing straw varies between soils, and the objective of this study was to identify the mechanisms responsible. Internode segments of wheat straw were incubated in Denmark and in Scotland in arable soils fertilized with NH₄NO₃, labelled with ¹⁵N, for periods up to 1 year. Straw was recovered from the soils periodically and analysed for microbial biomass and different forms of N using chemical methods and CPMAS ¹⁵N NMR spectroscopy. The total N content of the straw increased, as long as the soil was not too wet, such that there was overall immobilization. This was accompanied by a rapid increase in the content of amino acid N and to a lesser extent of glucosamine N and a concomitant decrease in the carbohydrate content of the straw. Using direct and plate counts for bacterial and ergosterol content for fungal estimation, we found that fungal biomass was much greater than that of bacteria. This correlated with the forms of N in the straw as determined by CPMAS ¹⁵N NMR, which showed spectra that were more typical of fungi than of bacteria. It seems that immobilization of N is primarily caused by fungi as they decompose the straw.     

Leaching and plant offtake of N in field pea/cereal cropping sequences with incorporation of 15N-labelled pea harvest residues

Abstract. Field peas (Pisum sativum L.) were grown in sequence with winter wheat (Triticum aestivum L.) or spring barley (Hordeum vulgare L.) in large outdoor lysimeters. The pea crop was harvested either in a green immature state or at physiological maturity and residues returned to the lysimeters after pea harvest. After harvest of the pea crop in 1993, pea crop residues (pods and straw) were replaced with corresponding amounts of ¹⁵N‐labelled pea residues grown in an adjacent field plot. Reference lysimeters grew sequences of cereals (spring barley/spring barley and spring barley/winter wheat) with the straw removed. Leaching and crop offtake of ¹⁵N and total N were measured for the following two years. These treatments were tested on two soils: a coarse sand and a sandy loam. Nitrate concentrations were greatest in percolate from lysimeters with immature peas. Peas harvested at maturity also raised the nitrate concentrations above those recorded for continuous cereal growing. The cumulative nitrate loss was 9–12 g NO₃‐N m^–2 after immature peas and 5–7 g NO₃‐N m^–2 after mature peas. Autumn sown winter wheat did not significantly reduce leaching losses after field peas compared with spring sown barley. ¹⁵N derived from above‐ground pea residues accounted for 18–25% of the total nitrate leaching losses after immature peas and 12–17% after mature peas. When compared with leaching losses from the cereals, the extra leaching loss of N from roots and rhizodeposits of mature peas were estimated to be similar to losses of ¹⁵N from the above‐ground pea residues. Only winter wheat yield on the coarse sand was increased by a previous crop of peas compared to wheat following barley. Differences between barley grown after peas and after barley were not statistically significant. ¹⁵N lost by leaching in the first winter after incorporation accounted for 11–19% of ¹⁵N applied in immature pea residues and 10–15% of ¹⁵N in mature residues. Another 2–5% were lost in the second winter. The ¹⁵N recovery in the two crops succeeding the peas was 3–6% in the first crop and 1–3% in the second crop. The winter wheat did not significantly improve the utilization of ¹⁵N from the pea residues compared with spring barley.     

Experimentally induced infection of reindeer (Rangifer tarandus) with Mycobacterium bovis.

In the USA, all species of Cervidae are included in the USDA's uniform methods and rules for the eradication of bovine tuberculosis and, therefore, are subject to regulations regarding intradermal tuberculin testing. In reindeer (Rangifer tarandus), infection with Mycobacterium bovis is exceedingly rare and the response of reindeer to infection with M. bovis in pathologic and immunologic terms is unknown. The objectives of the study reported here were to describe the pathologic changes associated with M. bovis infection in reindeer and evaluate the effectiveness of intradermal tuberculin testing as a means of diagnosis of tuberculosis in reindeer. Thirteen reindeer were inoculated intratonsilarly with 10(5) colony-forming units (CFU) of M. bovis, and 4 noninoculated reindeer served as negative controls. The comparative cervical test (CCT) was done on all reindeer 90 and 240 days after inoculation. Thirteen months after inoculation, all reindeer were euthanized and examined. All experimentally inoculated reindeer developed lesions in the medial retropharyngeal lymph nodes. The CCT accurately identified all M. bovis-inoculated reindeer, but false-positive results were common among negative-control reindeer. Modifications of the method for interpretation of the CCT decreased false-positive results without increasing false-negative results. Reindeer are susceptible to infection with M. bovis; however, lesions are fewer in number, less severe in nature, and less widely disseminated than are those seen in white-tailed deer (Odocoileus virginianus). Comparative cervical skin testing of reindeer can be highly sensitive, but has low specificity. Specificity can be improved by modification of criteria for interpretation of the CCT.     

Nose-rings and transmission of helminth parasites in outdoor pigs

Five growing pigs experimentally infected with low doses of Oesophagostomum dentatum, Ascaris suum, and Trichuris suis were turned out with 5 helminth-na?ve pigs on each of 3 pastures in June 1996 (Group 1). On one pasture all pigs received nose-rings. After slaughter of Group 1 in October, pasture infectivity was monitored using helminth-na?ve, unringed tracer pigs. In 1997, helminth-na?ve young pigs were turned out on the contaminated pastures in May (Group 2) and again in August (Group 3). Again all pigs on one pasture received nose-rings. All pigs and pastures were followed parasitologically and reduction in grass cover was monitored. Based on the acquisition of infection by the na?ve pigs in Group 1, the estimated minimal embryonation times for eggs deposited on pasture were 23-25 days for O. dentatum, 5-6 weeks for A. suum and 9-10 weeks for T. suis. Results from tracer pigs and grass/soil samples indicated that pasture infectivity was light both years. Free-living stages of O. dentatum did not survive the winter. The nose-rings reduced rooting considerably, resulting in three-fold more grass cover on the nose-ring pasture compared to the control pastures by the end of the experiment. Nevertheless, the nose-rings did not significantly influence parasite transmission.     

Jupiter's Magnetosphere: Plasma Description from the Ulysses Flyby

Plasma observations at Jupiter show that the outer regions of the Jovian magnetosphere are remarkably similar to those of Earth. Bow-shock precursor electrons and ions were detected in the upstream solar wind, as at Earth. Plasma changes across the bow shock and properties of the magnetosheath electrons were much like those at Earth, indicating that similar processes are operating. A boundary layer populated by a varying mixture of solar wind and magnetospheric plasmas was found inside the magnetopause, again as at Earth. In the middle magnetosphere, large electron density excursions were detected with a 10-hour periodicity as planetary rotation carried the tilted plasma sheet past Ulysses. Deep in the magnetosphere, Ulysses crossed a region, tentatively described as magnetically connected to the Jovian polar cap on one end and to the interplanetary magnetic field on the other. In the inner magnetosphere and lo torus, where corotation plays a dominant role, measurements could not be made because of extreme background rates from penetrating radiation belt particles.     

Sr lattice clock at 1 x 10(-16) fractional uncertainty by remote optical evaluation with a Ca clock

Optical atomic clocks promise timekeeping at the highest precision and accuracy, owing to their high operating frequencies. Rigorous evaluations of these clocks require direct comparisons between them. We have realized a high-performance remote comparison of optical clocks over kilometer-scale urban distances, a key step for development, dissemination, and application of these optical standards. Through this remote comparison and a proper design of lattice-confined neutral atoms for clock operation, we evaluate the uncertainty of a strontium (Sr) optical lattice clock at the 1 x 10(-16) fractional level, surpassing the current best evaluations of cesium (Cs) primary standards. We also report on the observation of density-dependent effects in the spin-polarized fermionic sample and discuss the current limiting effect of blackbody radiation-induced frequency shifts.     

SOS response induction by beta-lactams and bacterial defense against antibiotic lethality

The SOS response aids bacterial propagation by inhibiting cell division during repair of DNA damage. We report that inactivation of the ftsI gene product, penicillin binding protein 3, by either beta-lactam antibiotics or genetic mutation induces SOS in Escherichia coli through the DpiBA two-component signal transduction system. This event, which requires the SOS-promoting recA and lexA genes as well as dpiA, transiently halts bacterial cell division, enabling survival to otherwise lethal antibiotic exposure. Our findings reveal defective cell wall synthesis as an unexpected initiator of the bacterial SOS response, indicate that beta-lactam antibiotics are extracellular stimuli of this response, and demonstrate a novel mechanism for mitigation of antimicrobial lethality.     

Computers in aquaculture

Computer application to aquaculture operations is a timely and new transition in the management of the business. Decision making using real time data increases efficiency and production economics and aids in market planning. A general overview of computer approaches is discussed and a data management design approach is described which focuses on priority tasks. This method enhances the accuracy of animal inventory data and growth tracking where production costs are reduced through improved feed administration. The examples are only a small portion of the total program and reflect an approach used for a prawn farm. The modules in the programs are individually designed for the type of operation and species.     

The effect of grazing on cow mortality in Danish dairy herds

The effect of summer grazing in large Danish dairy herds and certain management characteristics of grazing were studied for their impact on dairy cow mortality. Mortality data (from the Danish Cattle Database) from 391 Danish dairy herds (>100 cows) were combined with information from a questionnaire survey of grazing procedures on these herds in 2008. In all, 131 of the herds were identified as summer grazing and 260 as zero-grazing herds. The mortality was affected by an interaction of summer grazing and milking system. The risk of a cow dying was reduced to 46% in a grazing compared to a zero-grazing herd having automatic milking system. In traditional milking system, mortality was reduced to 75% in grazing compared to zero-grazing herds. Within the grazing herds, the risk of mortality decreased with increasing number of hours on pasture during the season. Free access between barn and pasture was associated with increased cow mortality.