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71.
72.
McDermott R Trabesinger AH Muck M Hahn EL Pines A Clarke J 《Science (New York, N.Y.)》2002,295(5563):2247-2249
We obtained nuclear magnetic resonance (NMR) spectra of liquids in fields of a few microtesla, using prepolarization in fields of a few millitesla and detection with a dc superconducting quantum interference device (SQUID). Because the sensitivity of the SQUID is frequency independent, we enhanced both signal-to-noise ratio and spectral resolution by detecting the NMR signal in extremely low magnetic fields, where the NMR lines become very narrow even for grossly inhomogeneous measurement fields. In the absence of chemical shifts, proton-phosphorous scalar (J) couplings have been detected, indicating the presence of specific covalent bonds. This observation opens the possibility for "pure J spectroscopy" as a diagnostic tool for the detection of molecules in low magnetic fields. 相似文献
73.
Phosphorus uptake of maize as affected by ammonium and nitrate nitrogen - Measurements and model calculations - 总被引:1,自引:0,他引:1
Phosphorus uptake is often enhanced by ammonium compared to nitrate nitrogen nutrition of plants. A decrease of pH at the soil-root interface is generally assumed as the cause. However, an alteration of root growth and the mobilization of P by processes other than net release of protons induced by the source of nitrogen may also be considered. To study these alternatives a pot experiment was conducted with maize using a fossil Oxisol high in Fe/Al-P with low soil solution P concentration. Three levels of phosphate (0, 50, 200 mg P kg?1) in combination with either ammonium or nitrate nitrogen (100 mg N kg?1) were applied. Plants were harvested 7 and 21 d after sowing, P uptake measured and root and shoot growth determined. To assess the importance of factors involved in the P transfer from soil into plants, calculations were made using a model of Barber and Claassen. In the treatments with no and low P supply NH4-N compared to NO3-N nutrition increased the growth of the plants by 25 % and their shoot P content by 38 % while their root growth increased by 6 % only. The rhizosphere pH decreased in the NH4-N treatments by 0.1 to 0.6 units as compared to the bulk soil while in the NO3-N treatments it increased by 0.1 to 0.5 units. These pH changes had a minor influence on P uptake only, as was demonstrated by artificially altering the soil pH to 4.7 and 6.3 respectively. At the same rhizosphere pH, however, P influx was doubled by the application of NH4-compared to NO3-N. It is concluded that in this soil the enhancement of P uptake of maize plants after ammonium application cannot be attributed to the acidification of the rhizosphere but to effects mobilizing soil phosphate or increasing P uptake efficiency of roots. Model calculation showed that these effects accounted for 53 % of the P influx per unit root length in the NO3-N and 72 % in the NH4-N supplied plants if no P was applied. With high P application the respective figures were only 18 and 19%. 相似文献
74.
Integration of bio-physical and economic models to analyze management intensity and landscape structure effects at farm and landscape level 总被引:1,自引:0,他引:1
Martin Schönhart Thomas Schauppenlehner Erwin Schmid Andreas Muhar 《Agricultural Systems》2011,104(2):122-134
We present an integrated spatially explicit land use modeling framework, which integrates two key components of agricultural systems, the bio-physical production system and the management system, by coupling the bio-economic farm optimization model FAMOS[space], the crop rotation model CropRota, and the bio-physical process model EPIC (Environmental Policy Integrated Climate). The integrated modeling framework has been developed to analyze the cost-effectiveness of selected agri-environmental program (AEP) measures. We also focus on the landscape development and therefore include a detailed representation of landscape elements such as fields or orchard meadows in our analysis. An indicator set represents all main environmental AEP objectives, i.e. preservation of water and soil resources, mitigation of climate change, protection of biodiversity, maintenance of cultural landscapes as well as farm income support. The integrated modeling framework is applied to 20 farms in the Austrian ‘Mostviertel’ region, which are selected from the Integrated Administration and Control System (IACS) of the European Union. The cost-effectiveness of AEP measures is assessed under different premium levels. The implementation of the AEP clearly affects environmental quality in a positive way. Nitrogen rates are reduced, landscape elements can be sustained, and the landscape becomes more diverse. The program also increases farm gross margins on average. However, the cost-effectiveness ratios (CER) are declining with increasing premium levels. The results indicate that the cost-effectiveness of AEP measures can be improved by spatial targeting. 相似文献
75.
Gerard H. Ros Adriaan G. van Leeuwen Erwin J.M. Temminghoff 《Soil biology & biochemistry》2011,43(4):862-865
Amino acids can interfere with NH4+ in spectrophotometric NH4+ determination hampering accurate quantification of the fate of NH4+ and dissolved organic N in soils. Serious interference has been reported for soils rich in organic matter, and for soils that have been fumigated, oven-dried or fertilized where between 5 and 60% of the NH4+ detected could be attributed to amino acid interference. We investigated whether a combination of gas diffusion and the classical Berthelot method can eliminate this interference, increasing the selectivity of the NH4+ analysis. We tested this approach using synthetic amino acid solutions and a large set of terrestrial samples (n = 353), including pore water samples, (fumigated or dried) soil extracts, and extracts of manures, composts and crop residues. The evaluated method produced accurate (recovery > 99.7%) and reproducible (standard error = 2.2%) NH4+ concentrations, eliminating any interference between amino acids and NH4+ (interference < 0.3%). Interference from K2SO4 was also eliminated. The method is robust, broadly applicable and will improve our understanding of nitrogen cycling in various ecosystems, in particular those where high levels of amino acids occur. 相似文献
76.
Erwin Schimitschek 《Journal of pest science》1936,12(11):134-136
Ohne Zusammenfassung 相似文献
77.
Dr. Erwin Lindner 《Journal of pest science》1940,16(2):20-21
Ohne Zusammenfassung 相似文献
78.
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