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71.
The paper looks, from a perspective of institutional economics, at a process of change of rules and organisational practises in the forestry sector, particularly drawing on a case study of small-scale private forest owners in the Allgäu, Bavaria. It is argued that the process of change may be initiated by the traditional factors mentioned by the various theories of institutional change (technological change, changes in preferences, changes in relative factor prices, etc.). However, the direction of change observed in the short run cannot be understood with the help of efficiency theories of institutional change. Denzau and North (1994) extended those theories by introducing mental models as explanatory variables. Mental models are the interpretations (half-baked theories) people use to understand their environment. As observed, mental models play a crucial role in determining the direction of change. However, the question that arose was: what determines the selection of mental models in an uncertain environment? It is observed that trust plays an important role. Therefore, an extension of the Douglas and North theory is suggested. 相似文献
72.
The objective of this study was the calculation of winter chill for fruit trees in the Meckenheim fruit growing region for all winters since 1958 and the evaluation of long-term trends in response to global warming. A further objective was the comparison of three winter chill models, the Chilling Hours Model (Chilling Hours??CH), the Utah Model (Chill Units??CU) and the Dynamic Model (Chill Portions??CP) with respect to temporal trends and seasonal variation in chilling intensity. To meet these objectives, about 120,000 hourly temperature measurements from Klein-Altendorf were correlated with daily temperature extremes. From this relationship, a long-term record of 466,000 hourly temperature data was constructed and used to calculate winter chill between 1st October of each year and three dates of the following year for all winters since 1958/1959. On average over all years, 955 CH, 1160 CU and 58.0 CP had accumulated in the Meckenheim fruit growing region by 1st January, 1356 CH, 1527 CU and 77.3 CP by 1st February, and 1727 CH, 1883 CU and 96.1 CP by 1st March. Coefficients of variation varied between 14 and 16% for the Chilling Hours Model, between 18 and 19% for the Utah Model and between 9 and 10% for the Dynamic Model. In spite of significant warming of the site, no clear long-term trends were detected. Due to the structure of the winter chill models, which do not consider freezing temperatures as chilling-effective, the highest chilling was not registered in the coldest winters, but rather when average temperatures between early December and late February were between 2 and 6°C. The coldest winter on record (1963/1964; mean winter temperature of ??4°C) had by far the lowest winter chill total, and chilling during the more recent cold winters 2009/2010 and 2010/2011 was also below average. Only very pronounced warming reduced winter chill, with the warmest winter on record (2006/2007; mean winter temperature of 7.1°C) accumulating less winter chill than slightly cooler winters. As long as such extreme temperatures remain exceptional, fulfilment of chilling requirements of local apple and cherry cultivars should not become critical. It is important to note, however, that substantial knowledge gaps exist in the field of fruit tree dormancy, which will have to be closed, before more reliable projections of future fulfilment of chilling requirements can be made. 相似文献
73.
An 11-year-old, neutered male domestic short-hair cat was presented with buphthalmos of the right eye and diagnosed with advanced glaucoma. Sonographic examination revealed an iridial thickening. Neoplasia was suspected and an enucleation was performed. Histopathology of the enucleated eye revealed abundant amyloid deposition predominantly in the anterior uveal tract accompanied by few to moderate numbers of well-differentiated plasma cells. The amyloid deposits were identified by staining with Congo red and showing green birefringence under polarized light. Immunohistochemically, amyloid and plasma cells stained intensely only with anti-ALλ antibody, supporting the amyloid tumor being an immunoglobulin-λ-light chain origin. Additional abnormalities included narrowing of the filtration angle and collapse of the ciliary cleft, and trabecular meshwork. One year post-enucleation, the cat was still healthy without signs of systemic amyloidosis or apparent metastatic disease. This is the first report of a cat with noncutaneous extramedullary plasmacytoma originating in the anterior uveal tract with resulting local amyloid. 相似文献
74.
The objective of the MSc project was to improve fruit quality, i.e. fruit firmness, colour and size, by mechanical blossom thinning. Ten-year-old slender spindle apple cv. ‘Gala, Mondial’ trees at Campus Klein-Altendorf near Bonn, Germany with an intense flowering of 7–8 on the 0–9 scale were blossom-thinned on 21 April 2009; unthinned trees served as control. Rotor speeds were 360 rpm or 420 rpm at 5 or 7.5 km/h tractor speed using the new mechanical thinning device developed at the University of Bonn in 2004–2006. Therein, a vertical mast supports three horizontal rotors, whose vertically rotating tines remove excessive flowers; the device was mounted on the front three point hitch of the tractor with the following results:
- Mechanical thinning reduced the number of apple fruit from 18 per branch section in the un-thinned control, 12–13 in the medium to 8 fruit in the strongest thinning (420 rpm, 5 km/h).
- Similarly, the number of singlets (one fruitlet/flower cluster) nearly doubled from ca. 2 per branch in the control to 3–4 after mechanical thinning, as intended.
- The natural June drop after mechanical thinning resembled that in the un-thinned control.
- Mechanical thinning increased fruit mass by 20 g—48 g relative to the un-thinned control.
- Mechanical thinning with 420 rpm increased the portion of premium fruit >?70 mm (class I) by 43?% (7.5 km/h) and 63?% (5 km/h); combined mechanical and hand-thinning yielded the largest portion of fruit >?70 mm (70?%), but with a dramatic loss in yield (55?%).
- Mechanical and manual thinning improved the portion of well coloured fruit (75–100?% coloured) (78–98?%) when compared to the un-thinned control fruits with 55?%, probably due to selective removal of shaded fruits from the inner tree canopy.
- Overall, mechanical thinning alone gave better results than hand thinning alone or its combination with hand-thinning in cv. ‘Gala’; mechanical thinning waived the need for hand thinning in this experiment.
- Mechanical thinning improved fruit firmness from 9.4 kg/cm2 in the un-thinned control to 10.4 kg/cm2.
- Neither vegetative growth nor subsequent fruit drop were stimulated by this type of mechanical thinning.
- The risk of both alternate bearing and over-sized fruit was waived due to the variety employed.
- An economic evaluation showed a net profit of € 220/ha in the weak (420 rpm—7.5 km/h) aνô € 1,844/ha in the intermediate (360 rpm—5 km/h), but a net loss of € 1,120/ha (420 rpm—5 km/h) for the strongest thinning treatment, assuming a cost of € 120/ha for the mechanical treatment and a saving of € 200 for reduced hand thinning.
75.
Artificial pores attract barley roots and can reduce artifacts of pot experiments 总被引：1，自引：0，他引：1 
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下载免费PDF全文 Soil compaction is a severe agricultural problem. It is characterized by an increased resistance to root penetration and by a decreased amount of porosity in the soil. Until today it is not clear whether crop roots are able to actively detect remaining pores in compacted soil. Moreover, little is known about the capability of roots to leave pores again if the mechanical resistance of the bulk soil allows so. The aim of this study was to investigate the root growth response of spring barley (Hordeum vulgare L. cv. Ascona) in different configurations of a compacted loamy soil containing pores. The three‐dimensional configurations of the root systems from three well watered and fertilized treatments were analyzed with X‐ray computed tomography. All soil‐filled cylindrical plastic pots (diameter: 60 mm, height: 210 mm) contained loose topsoil but differed in subsoil structure. In treatment ‘Loose' [L] the pots were entirely filled with loose soil. Treatment ‘Lower part compacted' [C] contained compacted soil in the lower part of the pots. Likewise, treatment ‘Pores' [P] contained compacted soil in the lower part too, but here 16 artificial pores (1 mm diameter) were generated in the central part of the compacted subsoil zone. Comparison of the two treatments with compacted soil [C] and [P] showed that the roots were able to detect pores. However, the roots frequently grew across the pores or left the pores again after having grown into them, leading to a significantly higher fraction of roots exploring the compacted soil in the treatment with pores compared to the treatment without pores. These findings are useful for designing controlled experiments in pots of limited size that can mimic root growth in relatively complex soil structures which are more similar to field situations than usual pot experiments. 相似文献
76.
Freisleben A Schieberle P Rychlik M 《Journal of agricultural and food chemistry》2002,50(17):4760-4768
[2H4]Folic acid was synthesized by deuterating p-aminobenzoic acid, which was then coupled to glutamic acid and 6-formylpterin. Using [2H4]folic acid as starting component enabled the preparation of labeled vitamers tetrahydrofolate, 5-formyltetrahydrofolate, 5-methyltetrahydrofolate, and 10-formylfolate which were characterized by electrospray mass spectrometry and collision-induced dissociation. The mass spectrometric studies confirmed that the compounds could be used as internal standards in stable isotope dilution assays. 相似文献
77.
Nitrate transport in soils of a river flood plain under organic and conventional farming — analytical results, modeling and balances Over a period of two years the transport of nitrate was investigated in Fluvi-Eutric Cambisols of a river flood plain of the Rhine tributary Sieg (Nordrhein-Westfalen, Germany). The soils were cultivated according to organic and conventional farming systems. Time series of NO3 concentrations in soil solutions sampled by ceramic cups down to a depth of 180 cm are given. The interpretation of the results was possible by model calculations using the model DELPHI, which had been calibrated before by tracer experiments. N-mineralization and N-leaching were quantified. For different crop residues reaction coefficients for the mineralization of the easily decomposed organic material were calculated. They were extremely high for bean residues (19.0 × 1012) × exp (-9800/T) and mustard-vetch residues (12.0 × 1012 × exp (-9800/T). The lowest reaction coefficient of 3.0 × 1012 × exp (-9800/T) was calculated for the decomposition process during winter time. For the two farming systems a detailed N-balance was calculated. It is shown that under conventional farming over a time period of two years 199 kg N/ha were leached. Within the same period 53 kg N/ha were leached under organic farming. These differences depend in part on different crop rotation. Especially intercropping on the organically cultivated plots reduced the leaching of nitrate. 相似文献
78.
Paulina Schuller Achim Ellies Alejandra Castillo Itilier Salazar 《Soil & Tillage Research》2003,69(1-2):69-83
The purpose of this research was to evaluate the applicability of conventional 137Cs sampling and a simplified approach, for estimating medium-term tillage- and water-induced soil erosion and sedimentation rates on agricultural land in Chile. For this purpose, four study sites under contrasting land use and management were selected in central-south Chile. First, a conventional 137Cs approach, based on grid sampling was applied, adapting a mass balance conversion model incorporating soil movement by tillage to the site specific conditions of the study region. Secondly, using the same conversion model, the feasibility of estimating soil redistribution rates from measurements of 137Cs inventories based on composite soil samples taken along contour lines was also tested at all four sites. The redistribution rates associated with tillage and water and the total rates estimated using both methods correlated strongly at all four sites. The conventional method provides more detailed information concerning the redistribution processes operating over the landscape. The simplified method is suitable for assessing soil loss and sediment accumulation in areas exhibiting simple topography and almost similar slopes along the contour lines. Under these conditions, this method permits faster estimation of soil redistribution rates, providing the possibility of estimating soil redistribution rates over larger areas in a shorter time. In order to optimise the costs and benefits of the methods, the sampling and inventory quantification strategy must be selected according to the resolution of the required information, and the scale and complexity of the landscape relief. Higher tillage- and water-induced erosion rates were observed in the annually ploughed cropland sites than in the semi-permanent grassland sites. Subsistence managed crop and grassland sites also show greater erosion effects than the commercially managed sites. The 137Cs methods used permit discrimination between redistribution rates observed on agricultural land under different land use and management. The 137Cs technique must be seen as an efficient method for estimating medium-term soil redistribution rates, and for planning soil conservation and sustainable agricultural production under the climatic conditions and the soil type of the region of Chile investigated. 相似文献
79.
Translocation and dispersion of chloride, bromide, nitrate and sulfate tracers in two typical Fluvi-Eutric Cambisols Chloride, bromide, nitrate and sulfate were applied as tracers on two weakly to moderately acidic Fluvi-Eutric Cambisols. The soil solution was sampled by ceramic suction cups down to a soil depth of 180 cm. At definite time intervals also soils material was taken from different depth to produce the soil saturation extract. The concentrations of the non-adsorbed anions chloride, bromide and nitrate were very similar in the suction cup solutions and in the saturation extracts, whereas the concentrations of the weakly adsorbed sulfate partially showed considerable differences. Obviously both methods extract in acid soils different fractions of the dissolved sulfate. By comparison of marked sulfate peaks with those of chloride, bromide or nitrate, which occur at the same time in different soil depth, a Kd value of 0.16 1/kg can be calculated for the Ap horizon and of 0.02 1/kg for the subsurface horizons of one Fluvi-Eutric Cambisol. Values of the dispersivity of the different horizons were estimated by varying the values of the dispersivity reported in the literature until the best fit of the simulated anion depth distribution to the measured values was found. The estimated dispersivities varied between 1.0 cm in the Ap horizon and 1.8 and 10.0 cm in the subsurface horizons. 相似文献
80.