Simulation of field scale denitrification losses from soils under grass ley and barley

Denitrification losses from soils under barley and grass ley crops were simulated. The model, which includes the major processes determining inputs, transformations and outputs of nitrogen in arable soils, represents a scale compatible with information generally available in agricultural field research. The denitrification part of the model includes a field potential denitrification rate and functions for the effect of soil aeration status, soil temperature and soil nitrate content. Easily metabolizable organic matter is assumed not to limit denitrification. Simulated values were compared with denitrification measurements made during two growing seasons in the barley and grass ley treatments of a field experiment in central Sweden.Calibration revealed that the optimal parameter values describing the effect of soil aeration on denitrification rates were similar for both treatments. The response function derived agreed well with two data sets found in the literature. The potential denitrification rate constant, derived in the simulations, was higher for grass ley than for barley, which was consistent with the differences in overall rates of carbon and nitrogen turnover found between treatments.The simulated mean denitrification rates for the two seasons were within 20% of the mean of the measured values. However, simulated denitrification showed less temporal variability and a less skewed frequency distribution than measured denitrification. Some of the measured denitrification events not explained by the model could have been due to the stimulating effects of soil drying/wetting and freezing/thawing on microbial activity.     

Control of plant growth by nitrogen and phosphorus in mesotrophic fens

A fertilization experiment was carried out in 3 mesotrophic fens to investigate whether plant growth in these systems is controlled by the availability of N, P or K. The fens are located in an area with high N inputs from precipitation. They are annually mown in the summer to prevent succession to woodland. Above-ground plant biomass increased significantly upon N fertilization in the two mid-succession fens studied. In the late-succession fen that had been mown for at least 60 years, however, plant biomass increased significantly upon P fertilization. The mowing regime depletes the P pool in the soil, while it keeps N inputs and outputs in balance. A long-term shift occurs from limitation of plant production by N toward limitation by P. Hence, mowing is a suitable management tool to conserve the mesothrophic character of the fens.     

Hemoglobin Dallas (α97(G4)Asn→Lys):functional characterization of a high oxygen affinity natural mutant

Hemoglobin Dallas, an α-chain variant with a substitution of lysine for asparagine at position 97(G4), was found to have increased oxygen affinity ($\text{p}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 1}\text{mmHg at pH}\text{7.3}\text{and}\text{20°C), diminished cooperativity (0n,}\text{the Hill coefficient}\text{= 1.7}$) and reduced Bohr effect (about 50%). Addition of allosteric effectors (such as 2,3-diphosphoglycerate, inositol hexakisphosphate and bezafibrate) led to a decrease in oxygen affinity and increase in cooperative energy. Kinetic studies at pH 7.0 and 20°C revealed that (i), the overall rate of oxygen dissociation is 1.4-fold slower than that for HbA and (ii), the carbon monoxide dissociation rate is unaffected. The abnormal properties of this hemoglobin variant can be atttributed to a more ‘relaxed’ T-state.     

The choice between desiccation of wetlands or the spread of Rhine water over The Netherlands

The dry summer of 1976 triggered a wholesale installation of sprinkler systems for agriculture. This dry summer also revealed areas in The Netherlands most susceptible to drought, namely sandy regions and the coastal fringe. This resulted in distribution of Rhine water to new areas, and in quantities hitherto unknown. The Second National Water Management Plan (1982) consequently focussed on enlarging the capacity of water distribution works. This distribution has led to a multitude of ecological effects, such as changes in salinity and nutrient concentration, as well as the spreading of contaminants. Consequently, the Third National Water Management Plan (1990) includes fewer distribution works because of the adverse environmental effects and the reduced feasibility due to increasing costs and decreasing agricultural benefits.A climatic change as predicted may result in climatic conditions in The Netherlands resembling those of France or the Mediterranean, implying drier summers and more precipitation in winter. An increased frequency of dry summers will no doubt revive water distribution plans now shelved and may even bring new ones to the drawing board. An increase in Rhine water distribution will have serious consequences for many aquatic and terrestrial ecosystems, as will a lowering of the groundwater table. In this paper we will discuss the dilemma of choosing between allowing increased desiccation of wetlands as the climate becomes drier or increasing the distribution of Rhinewater and the potential ecological effects of these choices. Alternative strategies to water management also are discussed.This article is largely based on Duel et al. 1989.     

Pollarding and a possible explanation of the neolithic elmfall

Sections of two pollarded parkelms (Ulmus glabra) from Damsgaard, Bergen, west Norway have been studied. Changes in annual ring-width are attributed partly to management, namely pollarding, and partly to pathogenic attacks, probably by Ceratocystis ulmi. The oldest attack on the trees dates back to 1826: so far the oldest known record of Dutch elm disease in Norway. Pollarding may be an important factor in attacks by the pathogen within parkelms. A possible relationship between pollarding, the pathogen and the Neolithic elmfall is suggested.     

Use of the Golden Section search method to estimate the parameters of the Monod model employing spread-sheets

An alternative procedure to obtain the parameters of Monod's growth model in batch culture is presented. It is based on the integral kinetic analysis methodology, employs a one-dimensional Golden Section search optimization method and is implemented on a spread-sheet programme. The procedure is discussed in detail and is illustrated by analysis of batch substrate consumption data by an aerobic bacterial consortium.     

Application of good laboratory practice (GLP) to culture collections of microbial and cell cultures

Although the principles and the necessity for good laboratory practice (GLP) guidelines to confirm the credibility, integrity, and quality of non-clinical laboratory studies have been known for more than a decade, culture collection activities are not subject to them. Because of recent advances in biotechnology, culture collections face increased demands not only for quality cultures but also current information. When applied in culture collections, GLP guidelines prove to be an excellent management tool as well as a cost-effective system of providing authentic and reliable microbial and cell cultures and associated data.     

Use of disease progress curves to study the effects of the biocontrol agent Sporidesmium sclerotivorum on lettuce drop

At the end of the spring 1987 growing season, the mycoparasite Sporidesmium sclerotivorum was applied at 0, 0.2, 2 or 20 kg ha^‐1 to lettuce plants infected with Sclerotinia minor. Disease incidence was monitored in the same plots for five subsequent crops (three fall and two spring crops) without additional application of either pathogen or mycoparasite. Logistic growth curves were fitted to the data to describe disease progression over time for each inoculum level within each of the five crops. Within each crop, increasing the quantity of mycoparasite inoculum resulted in positive horizontal displacement of the curve with respect to time. As quantities of inoculum of S. sclerotivorum increased, inflection points of the disease progress curves increased at a decreasing rate. Thus, additional mycoparasite inoculum resulted in ever‐smaller increases in inflection point, and after a certain threshold level of mycoparasite inoculum (< 0.2 kg ha^‐1), increases in inflection point did not result in meaningful increases in harvestable lettuce. Maximum rates of disease increase were not different among the treatments within each crop, but were different between crops. Maximum rates of disease increase averaged 3.4, 3.4, 2.1, 3.6 and 1.5% day^‐1 for the fall 1987, spring 1988, fall 1988, spring 1989, and fall 1989, respectively. At all inoculum levels, the fall epidemics began later after planting than the spring epidemics.     

一个改进的下丘脑-垂体-甲状腺轴的数学模型

提出一个改进的下丘脑-垂体-甲状腺轴的数学模型.该模型既考虑了此分泌调节系统各激素之间的激活和反馈作用,也考虑了甲状腺激素与蛋白质结合的动力学过程.由该模型推导的结果与实验结果符合得很好.     

Pastoral dairy marketing and household wealth interactions and their implications for calves and humans in Ethiopia

Surveys of pastoral households in a semi-nomadic Borana community during 1987–1988 were used to test the hypothesis that poorer families living closest to a market town would be most affected by the enhanced opportunity to sell dairy products, which would intensify competition between people and calves for milk and have negative implications for calf management. These poorer families indeed reported the highest rates of milk offtake per cow, and the milk increment was probably sold to purchase more grain for human consumption at the expense of milk intake for the calf. Consequently, this strategy may increase the susceptibility of malnourished calves to disease, especially those from lower-producing dams. Benefits of improved human energy intake from grain and retention of livestock capital must be weighed against risks of calf death and possible malnutrition of people from milk restriction when assessing dairy marketing trade-offs that are most acute for the poor. Opportunity to sell dairy products at favorable terms of trade helps the poorest people survive, and their risks could be mitigated by policies that facilitate grain marketing in the rangelands and interventions that improve calf feeding management, diversify human diets, and create alternative opportunities for women to generate income. The households postulated to be most at risk were identified from a complex, but logical, interaction among factors of distance to market, household wealth, and the quality of milking cows held. This indicates that targeting such needy groups for development assistance may require a more detailed and interdisciplinary analysis of production systems than is commonly practiced.