The required increase in agricultural production to meet future food demand will further increase pressure on land resources. Integrative indicators of the current status of the agricultural ...production capacity of land and their change over time are needed for promoting land management practices to maintain or improve land productivity and a sustainable use of natural resources. It is argued that such land quality indicators should be obtained with a holistic systems-oriented approach. Two land quality indicators are elaborated that deal with (1) yield gaps, i.e. the difference of actual yield and yield obtained under optimum management practices, or yields determined by the land-based natural resources, and (2) a soil nutrient balance, i.e. the rate with which soil fertility is changing. The yield gap is based on the calculation of land-based cereal productivity at three different levels in terms of potential, water limited, and nutrient limited production, considering weather, soil and crop characteristics. These modelled production levels do not incorporate socio-economic aspects, which may impede agricultural management in its effort to release stress because of inadequate soil fertility, water availability and/or occurrence of pests and diseases. Therefore, location specific actual yield levels are also considered. Besides an evaluation of the actual status of the land, it is important to consider the rate of change. The quantification of changes in soil nutrient stocks is crucial to identify problematic land use systems. The soil nutrient balance, i.e. the net difference between gross inputs and outputs of nutrients to the system, is used as measure for the changes. The indicator for the soil nutrient balance combines this rate of soil nutrient change and the soil nutrient stock. Indicators for yield gaps and soil nutrient balances are defined, procedures for their quantification are described and their general applicability is discussed.
The inclusive production of D*+/-(2010) mesons in deep-inelastic scattering is studied with the HI detector at HERA. In the kinematic region 1 < Q(2) < 100 GeV2 and 0.05 < y < 0.7 an e(+) p cross ...section for inclusive D*+/- meson production of 8.50 +/- 0.42(stat.)(-100)(+1.21)(syst.) nb is measured in the visible range p(tD*) > 1.5 GeV and eta(D*) < 1.5. Single and double differential inclusive D*+/- meson cross sections are compared to perturbative QCD calculations in two different evolution schemes, The charm contribution to the proton structure, F-c(2)(x, Q(2)), is determined by extrapolating the visible charm cross section to the full phase space. This contribution is found to rise from about 10% at Q(2) = 1.5 GeV2 to more than 25% at Q(2) = 60 GeV2 corresponding to x values ranging from 5 x 10(-5) to 3 x 10(-3). (C) 2002 Elsevier Science B.V. All rights reserved.
The response matching model of Lang, Bradley, and Cuthbert (1992) predicts startle reflex facilitation during negative relative to positive emotional states. Using slide and imagery paradigms, larger ...eyeblink responses to startle probes for unpleasant than for pleasant conditions have consistently been reported. The present study extended the previously observed relationship between valence and startle to more complex stimuli, namely 1-min film fragments. Thirty-three subjects viewed a sequence of 27 film fragments with neutral, negative (fearful), and positive (sexual) contents, presented in one of three mixed orders. Blink magnitude to brief bursts of white noise was larger during fearful fragments than during sexual fragments. Blink magnitudes habituated across successive film fragments, but the positive-negative difference remained stable within film fragments and during the entire length of the videotape (approximately 40 min).
The ratio of cross sections for inelastic muon scattering on xenon and deuterium nuclei was measured at very low Bjorken {ital x} (0.000 02{lt}{ital x}{sub Bj}{lt}0.25). The data were taken at ...Fermilab experiment E-665 with a 490 GeV/{ital c} muon beam incident on liquid deuterium and gaseous xenon targets. Two largely independent analysis techniques gave statistically consistent results. The xenon-to-deterium per-nucleon cross-section ratio is constant at approximately 0.7 for {ital x}{sub Bj} below 0.003.
In the Netherlands 65% of the drinking water is extracted from groundwater. A quarter of the groundwater wells, in particular those on the sandy soils in the east and the south of the country, face ...rising levels of nitrate, mainly of agricultural origin. In 1998 the Dutch Government launched a policy (MINAS) which aims at a drastic reduction in nitrate leaching by 2010. However, this program will not achieve a sufficient reduction in leaching on the dry sandy soils in the east and south of the country. As a result, drinking water companies are facing purification costs of US$ 35–70 million/year, by the next century. So far, the Government has failed to introduce additional policies. Therefore drinking water companies have extended their own preventive approach, aimed at reducing the total nitrogen load in a catchment area to a sustainable level. In this approach extra measures are to be taken in those parts of the area where they are most effective and cost-effective. This can compensate for higher nitrate leaching in other parts of the area, as long as the average nitrate concentration is safe below the norm of 50 mg NO
3/l. That opens the door to a wide range of measures: e.g. taking land out of cultivation, supporting farmers to change to organic farming, contracting farmers to grow low-leaching crops, and so on. Different measures can supplement each other. The most cost-effective set of measures for each specific catchment area is generated by means of a linear programming model.
In sandy regions of the Netherlands, current agricultural practices result in high nitrate concentrations in the upper groundwater, endangering water resources. A methodology to estimate costs of ...region specific solutions is applied to a groundwater protection area. It requires that for existing farms in the region variants of management are described that differ in nitrogen surplus. Costs of variants relate to investments and losses in income due to changes in farm management additional to those required by existing legislation. The expected nitrate concentration for each combination of variant and groundwater class is calculated from nitrogen and precipitation surplus and a leaching fraction. A linear programming model indicates the optimal spatial allocation of variants such that desired regional and sub-regional nitrate concentrations are reached at minimum regional costs. In the case study, current land use is grouped into non-dairy farms and various types of dairy farms and non-agricultural land use. Management variants are described for most of these groups. The LP model was used to analyze the effect of the following conditions: (a) the scale at which the tolerated maximum NO
3 concentration is effectuated; (b) the level of this maximum; (c) the hydrological situation; (d) the way farms are grouped; and (e) the biophysical situation of farms. Total regional costs show a negative, but not necessarily linear, relation with the resulting regional nitrate concentration. This relation is strongly influenced by the actual situation regarding management at the farms and the groundwater table depths in the region. For each region a specific cost–benefit relation might apply. Higher groundwater tables result in strongly reduced costs for required changes in farm management. Depending on costs and physical feasibility, measures that result in a higher groundwater table could therefore be used in addition to or replacement of measures at farm level. Calculated costs are influenced by the method of grouping of farms into farm types, the largest effect due to differentiating intensities of production. Differences between farms need therefore be considered when analyzing possibilities for and costs of measures to reduce nitrate leaching. Political decisions, specifically about the scale at which the maximum nitrate level should be effectuated (farm-type or region) also have a strong effect on the cost–benefit relation. Requiring all farm types to comply with a given maximum nitrate concentration, resulting in a specific regional average, is more costly than setting a similar regional maximum and allowing regional averaging. Methodology and preliminary results were discussed with policy-makers and representatives of farmers, environmentalists and groundwater extracting companies. They felt that these discussions helped focussing the interaction between the various groups of stakeholders. This is due to the fact that assumptions about effects of changes in land use and costs involved are made explicit and to the possibility of a more objective weighing of interests since wishes and conditions are translated into goals and constraints of the linear programming model.
Di-jet event rates have been measured for deep-inelastic scattering in the kinematic domain \(5 \lesssim Q^2 \lesssim 100\) GeV\(^2\) and \(10^{-4} \lesssim x_{Bj} \lesssim 10^{-2}\), and for jet ...transverse momenta squared \(p_t^{*2}\gtrsim Q^2\). The analysis is based on data collected with the H1 detector at HERA in 1994 corresponding to an integrated luminosity of about 2 pb\(^{-1}\). Jets are defined using a cone algorithm in the photon-proton centre of mass system requiring jet transverse momenta of at least 5 GeV. The di-jet event rates are shown as a function of \(Q^2\) and \(x_{Bj}\). Leading order models of point-like interacting photons fail to describe the data. Models which add resolved interacting photons or which implement the colour dipole model give a good description of the di-jet event rate. This is also the case for next-to-leading order calculations including contributions from direct and resolved photons.
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