Chemical and biochemical properties as potential indicators of disturbances

 The response of a series of soil microbial, chemical, and enzymatic chacacteristics to two different tillage systems (conventional and no-tillage) and two crop rotations (continuous corn and soybean–corn) was evaluated in a long-term field experiment in the Rolling Pampas Region, Marcos Juárez, Córdoba, Argentina. The parameters studied included: oxidizable, soluble and respiration C, total and hydrolyzable N, microbial activity, ammonifiers, nitrifiers, cellulolytic and total microflora, protease and urease activities. After 15 years, oxidizable C, total N and hydrolyzable N showed no differences regarding no-tillage systems. However, differences were found regarding control soil. While soluble C did not exhibit any significant differences, respiration C and microbial activity were indicators sensitive to different treatments. Enzymatic activities, protease in particular, did reflect changes due to management. Fluctuation in microbial population counts were more related to plant residues than to tillage systems. Received: 29 May 1999     

Farm-SAFE: the process of developing a plot- and farm-scale model of arable,forestry, and silvoarable economics

Financial feasibility and financial return are two key issues that farmers and land owners consider when deciding between alternative land uses such as arable farming, forestry and agroforestry. Moreover regional variations in yields, prices and government grants mean that the relative revenue and cost of such systems can vary substantially within Europe. To aid our understanding of these variations, the European Commission sponsored a research project called “Silvoarable Agroforestry For Europe” (SAFE). This paper describes the process of developing a new economic model within that project. The initial stages included establishing criteria for the model with end-users and reviewing the literature and existing models. This indicated that the economic model needed to allow comparison of arable farming, forestry and agroforestry systems at a plot- and a farm-scale. The form of comparisons included net margins, net present values, infinite net present values, equivalent annual values, and labour requirements. It was decided that the model would operate in a spreadsheet format, and the effect of phased planting patterns would be included at a farm-scale. Following initial development, additional user feedback led to a final choice on a model name, a final method of collating input data, and the inclusion of field-based operations such as varying the cropped area, replacing dead trees, and pruning. In addition options in terms of improved graphical outputs and the ability to undertake sensitivity analysis were developed. Some of the key lessons learnt include the need to establish clear model criteria and the benefits of developing a working prototype at an early stage to gain user-feedback.     

Periodic emission from the gamma-ray binary 1FGL J1018.6-5856

Gamma-ray binaries are stellar systems containing a neutron star or black hole, with gamma-ray emission produced by an interaction between the components. These systems are rare, even though binary evolution models predict dozens in our Galaxy. A search for gamma-ray binaries with the Fermi Large Area Telescope (LAT) shows that 1FGL J1018.6-5856 exhibits intensity and spectral modulation with a 16.6-day period. We identified a variable x-ray counterpart, which shows a sharp maximum coinciding with maximum gamma-ray emission, as well as an O6V((f)) star optical counterpart and a radio counterpart that is also apparently modulated on the orbital period. 1FGL J1018.6-5856 is thus a gamma-ray binary, and its detection suggests the presence of other fainter binaries in the Galaxy.     

Development of a web tool for action threshold evaluation in table grape pest management

Pest control is a major issue in agricultural management due to crop yield losses caused by pests. In this context, integrated pest management aims to suppress pest populations below an action threshold to minimize their impact. This paper presents the development of a web tool based on the Spanish regulations for the integrated pest management of table grapes; this provides decision support for evaluating when a particular pest action threshold has been crossed thus affecting table grape crops. The tool was built using a model-driven software development approach that enables software system generation from the problem’s knowledge model. The design of the knowledge bases which contain the system’s decision rules is also described. It is divided into knowledge bases that contain general knowledge related to the table grape crop as well as several specific knowledge bases (one per pest) containing the reasoning model that deduces the risk associated with a particular pest. The software has been designed by applying the model-driven development method thus making the system flexible, easy to evolve and adaptable whenever a new pest has to be incorporated into the software.     

Comparing two methods of sequential fractionation in the study of copper compounds in Haplic chernozem under model experimental conditions

Purpose

It is very important to obtain the information on the soils capacity to immobilize HMs and distribute them among soil components. The aim of this work was to study the fractional composition of Cu compounds in Haplic chernozem under model contamination conditions using different fractionation methods.

Materials and methods

The fractional composition of copper compounds in Haplic Chernozem artificially contaminated with copper acetate has been studied under model experimental conditions. General regularities and differences in the distribution of Cu forms in soils at the use of sequential fractionation by the Miller method modified by Berti and Jacobs (1996) and the Tessier method (Tessier et al. 1979) are revealed.

Results and discussion

The differences are related to the metal affinity for specific carrier phases, as well as to the selectivity and extraction capacity of the reagents used in these methods. A significant increase in the most mobile exchangeable Cu fraction is observed in contaminated soils. Aluminosilicates and soil organic matter make the largest contribution to the adsorption and retention of Cu.

Conclusions

The Tessier method is more suitable for the separation of the total technogenic component from contaminated soils. The Miller method is more informative at the determination of loosely bound HM compounds because of the use of weaker extractants.

     

Helium and neon abundances and compositions in cometary matter

Materials trapped and preserved in comets date from the earliest history of the solar system. Particles captured by the Stardust spacecraft from comet 81P/Wild 2 are indisputable cometary matter available for laboratory study. Here we report measurements of noble gases in Stardust material. Neon isotope ratios are within the range observed in "phase Q," a ubiquitous, primitive organic carrier of noble gases in meteorites. Helium displays 3He/4He ratios twice those in phase Q and in Jupiter's atmosphere. Abundances per gram are surprisingly large, suggesting implantation by ion irradiation. The gases are probably carried in high-temperature igneous grains similar to particles found in other Stardust studies. Collectively, the evidence points to gas acquisition in a hot, high ion-flux nebular environment close to the young Sun.     

Isotopic compositions of cometary matter returned by Stardust

Hydrogen, carbon, nitrogen, and oxygen isotopic compositions are heterogeneous among comet 81P/Wild 2 particle fragments; however, extreme isotopic anomalies are rare, indicating that the comet is not a pristine aggregate of presolar materials. Nonterrestrial nitrogen and neon isotope ratios suggest that indigenous organic matter and highly volatile materials were successfully collected. Except for a single (17)O-enriched circumstellar stardust grain, silicate and oxide minerals have oxygen isotopic compositions consistent with solar system origin. One refractory grain is (16)O-enriched, like refractory inclusions in meteorites, suggesting that Wild 2 contains material formed at high temperature in the inner solar system and transported to the Kuiper belt before comet accretion.     

The effect of diet on ontogenic development of the digestive tract in juvenile reared long snout seahorse Hippocampus guttulatus

Ontogenetic development of the digestive tract and associated organs in long snout seahorse Hippocampus guttulatus juveniles was morphologically and histologically examined from the time of release from the male’s pouch until 72 h after the first meal. When released from the male’s pouch, juvenile seahorses are small adult replicates. This means that unlike other teleost fish larvae, the first developmental phase has already taken place, and juveniles are morphologically prepared and able to feed on live prey immediately following parturition. At this stage, the buccopharynx, oesophagus, and intestine already appear to be fully developed. The intestine is divided into the midgut and hindgut by an intestinal valve, and intestinal villi are visible in the midgut. When fed with DHA-Selco^® enriched Artemia, H. guttulatus juveniles developed a severe condition of overinflation of the gas bladder. The continuous overinflation of the gas bladder forced air into the gut (48 h after the first meal), resulting in overinflation of both the gut and the gas bladder (72 h after the first meal), and death occurred within 120 h after the first meal. When fed natural copepods, H. guttulatus juveniles continued a normal feeding activity with no signs of intestinal disorders, and the gas bladder and intestine maintained their normal shape. This is the first study to positively associate gas bladder overinflation of juvenile seahorses with nutritionally unbalanced diets, and not to gas supersaturation alone. It is therefore necessary to develop more adequate feed and/or enrichment products to improve the survival of juvenile seahorses in captivity.     

Quantitative dietary requirement of juvenile Atlantic ditch shrimp Palaemonetes varians for lysine,methionine and arginine

This study was carried out to estimate lysine, methionine and arginine dietary requirements of juvenile Atlantic ditch shrimp, Palaemonetes varians. Three series of five isoproteic and isoenergetic diets [45% crude protein (CP), 14.7 MJ digestible energy (DE)/kg] were formulated to contain increasing levels of either lysine (1.2–2.8 g/100 g of diet), methionine (0.5–1.3 g/100 g of diet + 0.8% cysteine) or arginine (1.1–2.7 g/100 g of diet) and adequate levels of all other essential nutrients. Each experimental diet was fed to three groups of postlarvae (initial weight = 17 mg each) for 45 days at 19.9 ± 0.1°C. The dietary requirements for maximizing weight gain of juvenile P. varians, estimated using broken‐line analysis vs. exponential model and expressed as per cent of dry diet, were 2.42 vs. 2.63; 0.96 vs. 0.99 and 2.05 vs. 2.39 for lysine, methionine and arginine respectively. These estimates of requirements of lysine, methionine and arginine for juvenile P. varians appear to be similar to those reported for penaeid shrimp species.