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Different methods for estimating the non-fertilizer N supply (NFNS) of mineral grassland soils were compared. NFNS was defined as the N uptake on unfertilized plots. The potential mineralization rate (0-12 weeks), macroorganic mat...
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Different methods for estimating the non-fertilizer N supply (NFNS) of mineral grassland soils were compared. NFNS was defined as the N uptake on unfertilized plots. The potential mineralization rate (0-12 weeks), macroorganic matter and active microbial biomass (determined by the substrate-induced respiration method; SIR) were correlated positively with NFNS. The difference between the actual soil organic N or microbial N content (determined by the fumigation incubation method) and their contents under equilibrium conditions (Delta org. N and Delta MB-N), however, gave the best estimations of NFNS. For field conditions the best estimation for NFNS was: NFNS (kg N ha(-1) yr(-1)) = 132.3 + 42.1 x Delta org. N (g kg(-1) soil; r = 0.80). This method is based on the observation that, under old grassland swards, close relationships exist between soil texture and the amounts of soil organic N and microbial N. These relationships are assumed to represent equilibrium conditions as under old swards under constant management, the gain in soil organic N and microbial N equals the losses. Soils under young grassland and recently reclaimed soils contained less soil organic N and microbial N. In such soils the amounts of organic N and microbial N increase with time, which is reflected in a lower NFNS. The annual accumulation of organic and microbial N gradually becomes smaller until organic N, microbial N and NFNS reach equilibrium. The main advantage of the ''difference method'' in comparison with the other methods is its speed and simplicity.
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Winter wheat was grown at ambient and elevated (ambient plus 350 mu L L-1) CO2 concentrations in open top chambers and in field-tracking sun-lit climatized enclosures (elevated is 718 mu L L-1). There was no significant effect of ...
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Winter wheat was grown at ambient and elevated (ambient plus 350 mu L L-1) CO2 concentrations in open top chambers and in field-tracking sun-lit climatized enclosures (elevated is 718 mu L L-1). There was no significant effect of CO2 concentration on sheath, leaf and root biomass and leaf area in the early spring (January to April). 24-h canopy CO2 exchange rate (CCER) was not significantly affected either. However, elevated CO2 concentration increased CCER at midday, decreased evapotranspiration rate and increased instantaneous water-use-efficiency during early spring. Leaf, sheath and root nitrogen concentration per unit dry weight decreased and nonstructural carbohydrate concentration increased under elevated CO2, and N-uptake per unit ground area decreased significantly (-22%) towards the end of this period. These results contrast with results from the final harvest, when grain yield and biomass were increased by 19% under elevated CO2. N concentration per dry weight was reduced by 5%, but N-uptake per unit ground area was significantly higher (+11%) for the elevated CO2 treatment. 24-h and midday-CCER increased significantly more in late spring (period of 21 April to 30 May) (respectively by + 40% and 53%) than in the early spring (respectively 5% and 19%) in response to elevated CO2. Midday evapotranspiration rate was reduced less by elevated CO2 in the late spring (-13%) than in early spring (-21%). The CO2 response of midday and 24-h CCER decreased again (+ 27% and + 23% resp.) towards the end of the growing season. We conclude that the low response to CO2 concentration during the early spring was associated with a growth-restriction, caused by low temperature and irradiance levels. The reduction of nitrogen concentration, the increase of nonstructural carbohydrate, and the lower evapotranspiration indicated that CO2 did have an effect towards the end of early spring; but not on biomass accumulation. Regression analysis showed that both irradiance and temperature affected the response to CO2. [References: 44]
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The microclimate in facilities for studying effects of elevated CO2 on crops differs from ambient conditions. Open-top chambers (OTCs) increase temperature by 1-3 degrees C. If temperature and CO2 interact in their effect on crops...
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The microclimate in facilities for studying effects of elevated CO2 on crops differs from ambient conditions. Open-top chambers (OTCs) increase temperature by 1-3 degrees C. If temperature and CO2 interact in their effect on crops, this would limit the value of OTC experiments. Furthermore, interaction of CO2 and temperature deserves study because increases in atmospheric CO2 concentration are expected to cause global warming. This paper describes two experiments in which a recently developed cooling system for OTCs was used to analyse the effects of temperature on photosynthesis, growth and yield of spring wheat (Triticum nestivum L., cv. Minaret). Two levels of CO2 were used (350 and 700 ppm), and two levels of temperature, with cooled OTCs being 1.6-2.4 degrees C colder than noncooled OTCs. Photosynthetic rates were increased by elevated CO2, but no effect of temperature was found. Cross-switching CO2 concentrations as well as determination of A-Ci curves showed that plant photosynthetic capacity after anthesis acclimated to elevated CO2. The acclimation may be related to the effects of CO2 on tissue composition: elevated CO2 decreased leaf nitrogen concentrations and increased sugar content. Calculations of the seasonal mean crop light-use efficiency (LUE) were consistent with the photosynthesis data in that CO2 increased LUE by 20% on average whereas temperature had no effect. Both elevating CO2 and cooling increased grain yield, by an average of 11% and 23%, respectively. CO2 and temperature stimulated yield via different mechanisms: CO2 increased photosynthetic rate, but decreased crop light interception capacity (LAI), whereas cooling increased grain yield by increasing LAI and extending the growing season with 10 days. The effects of CO2 and temperature were not additive: the CO2 effect was about doubled in the noncooled open-top chambers. In most cases, effects on yield were mediated through increased grain density rather than increased individual grain weights. The higher growth response to elevated CO2 in noncooled vs. cooled OTCs shows that a cooling system may remove a bias towards overestimating crop growth response to CO2 in open-top chambers. [References: 22]
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Fibre hemp (Cannabis sativa L.) may be an alternative to wood as a raw material for pulp and paper production. Research was done to assess the potential productivity of fibre hemp and to identify constraints to that productivity. ...
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Fibre hemp (Cannabis sativa L.) may be an alternative to wood as a raw material for pulp and paper production. Research was done to assess the potential productivity of fibre hemp and to identify constraints to that productivity. Growth analyses were done on hemp crops in three consecutive years, using several cultivars and seeding rates. In 1987 the crops suffered severely from fungal diseases; stem dry matter yields were 9.4 t ha(-1). In 1988 and 1989 fungicides were applied and stem dry matter yields were respectively 11.9 t ha(-1) and 13.6 t ha(-1). The number of living plants m(-2) ranged from 86 to 823 at emergence, depending on treatment, and from 38 to 102 at final harvest. Increased seeding rates led to earlier canopy closure and higher initial biomass production, but more plants died during the growing season and the stem yield at final harvest was not affected by seeding rate. Average radiation-use efficiency (RUE; above-ground accumulated dry matter divided by intercepted photosynthetically active radiation) for the entire growing season under favourable growing conditions was 1.9 g MJ(-1), which is low compared to other C-3 crops. Leaf photosynthesis rates at saturating light intensities, however, were high: 30 kg CO(2)ha(-1) h(-1). The light extinction coefficient of hemp canopies was high (0.96), and may have reduced canopy photosynthesis rate and RUE. The high lignin content of the stems, and the high fat and protein content in the seed, also reduced RUE. Furthermore, dry matter invested in the tap root and in shed dead leaves was ignored. The RUE was also underestimated because an appreciable proportion of the biomass of plants that died during the growing season could not be collected. More research is needed to optimize cultural practices in fibre hemp.
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Blackspot related pigments were partially purified from bruised tubers of two commercial potato cultivars (cv. Bildstar and cv. Lady Rosetta). Chemical characterization showed that these pigments consisted of protein and a relativ...
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Blackspot related pigments were partially purified from bruised tubers of two commercial potato cultivars (cv. Bildstar and cv. Lady Rosetta). Chemical characterization showed that these pigments consisted of protein and a relatively small amount of covalently bound constituents. These polymeric structures absorbed light throughout the visible spectrum without any maximum. They did not contain eumelanin. Quinic acid was detectable in hydrolysates of the pigments from Bildstar, but not in those of Lady Rosetta, which indicated that chlorogenic acid may take part in blackspot formation, but is not essential for the discoloration. The results support the hypothesis that blackspot pigments are products of non-regulated reactions between nucleophilic amino acid residues in proteins, and quinones, which are derived from endogenous substrates of polyphenol oxidase. This means that blackspot formation most probably takes place in disintegrated cells.
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Application of ethanol as a solvent for cytokinins strongly inhibited growth and development of axillary buds of Rosa hybrida 'Madelon' at concentrations exceeding 0.2% (v/v). This inhibition could be avoided by dissolving cytokin...
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Application of ethanol as a solvent for cytokinins strongly inhibited growth and development of axillary buds of Rosa hybrida 'Madelon' at concentrations exceeding 0.2% (v/v). This inhibition could be avoided by dissolving cytokinins in NaOH (additional Na+ of 1.7% (w/w)).
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To avoid the current water pollution from intensive glasshouse horticulture, closed systems have to be developed with recirculating drainage water. For crops with a high planting density, such as lettuce, shallow beds of coarse sa...
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To avoid the current water pollution from intensive glasshouse horticulture, closed systems have to be developed with recirculating drainage water. For crops with a high planting density, such as lettuce, shallow beds of coarse sand may be used if water and nutrient supply can be regulated adequately. The aim of the present study was to determine the rooting characteristics and root distribution of lettuce in sand beds, as affected by substrate depth, the distance to a drain, drip lines and drip points, and the excess of nutrient solution applied. The hypothesis was tested that a small excess and a large distance between drip points leads to local salt accumulations in the root environment and thus to a less homogeneous root distribution.
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The endoperoxide sesquiterpene lactone artemisinin and its derivatives are a promising new group of drugs against malaria. Artemisinin is a constituent of the annual herb Artemisia annua L. So far only the later steps in artemisin...
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The endoperoxide sesquiterpene lactone artemisinin and its derivatives are a promising new group of drugs against malaria. Artemisinin is a constituent of the annual herb Artemisia annua L. So far only the later steps in artemisinin biosynthesis - from artemisinic acid - have been elucidated and the expected olefinic sesquiterpene intermediate has never been demonstrated. In pentane extracts of A. annua leaves we detected a sesquiterpene with the mass spectrum of amorpha-4,11-diene. Synthesis of amorpha-4,11-diene from artemisinic acid confirmed the identity. In addition we identified several sesquiterpene synthases of which one of the major activities catalysed the formation of amorpha-4,11-diene from farnesyl diphosphate. This enzyme was partially purified and shows the typical characteristics of sesquiterpene synthases, such as a broad pH optimum around 6.5-7.0, a molecular mass of 56 kDa, and a K(m) of 0.6 mu M. The structure and configuration of amorpha-4,11-diene, its low content in A. annua and the high activity of amorpha-4,11-diene synthase all support that amorpha-4,11-diene is the likely olefinic sesquiterpene intermediate in the biosynthesis of artemisinin.
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The aim of our study was to follow the transfer of C-14-labeled ryegrass between size and density fractions of soil organic matter in a sandy and a loam soil. Our hypotheses were a) that the applied C-14 would be transferred from ...
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The aim of our study was to follow the transfer of C-14-labeled ryegrass between size and density fractions of soil organic matter in a sandy and a loam soil. Our hypotheses were a) that the applied C-14 would be transferred from light and soluble fractions to intermediate and heavy macroorganic matter fractions (> 150 mu m) and finally become stabilized in microaggregates (< 150 mu m), and b) that the physical protection of C-14 associated with microaggregates against decomposition would decrease with increasing saturation of the microaggregates with soil organic matter. Generally, the hypotheses were confirmed. Immediately after application most of the label was present in the soluble and light macroorganic matter fractions. Newly synthesized microbial biomass fed on the labeled components of the fractions. The amounts of C-14 in the soluble and light macroorganic matter fractions decreased rapidly, while the amounts of C-14 in the intermediate and heavy macroorganic matter fractions and in microaggregates remained more or less stable. At the end of the incubation most of the residual soil C-14 was found in the microaggregates. In the sandy soil C-14 was concentrated in the 20-150 mu m fraction, whereas in the loam a larger proportion was present in the < 20 mu m fraction.
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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 c...
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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.
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