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991.
Thomas R. Vale 《Biological conservation》1975,8(4):257-260
The Bureau of Land Management, a federal agency administering more than 72 million ha in the western United States, has often been criticised for allowing excessive livestock grazing and neglecting wildlife, watershed and recreation values on its lands. The first draft of a report by Bureau personnel evaluating the agency's policies in the State of Nevada supports the allegations. Congressional action is necessary to provide the Bureau with broader responsibilities, increased funding and greater authority, all of which are necessary to bring better balance to the Bureau's programme. 相似文献
992.
Frederick R. Gehlbach 《Biological conservation》1975,8(2):79-88
Texas experience suggests that amateur naturalists will be heavily involved in preliminary ecological surveys of natural areas, hence a simple key for identification of community-types is presented. Line intercept transects are suggested for amateur use in providing standardised quantitative data on the physiognomy of natural areas. A scheme for the evaluation of each area utilises the weighted values of climax condition, educational suitability, species significance, community representation, and human impact through multiplicative scoring to give a natural area score. With the weighted values-multiplicative scoring scheme, natural areas are clearly distinguished in priority for acquisition. 相似文献
993.
J B Zagar P P Ascione G P Chrekian 《Journal of the Association of Official Analytical Chemists》1975,58(4):822-827
High-pressure liquid chromatography has been applied to the separation and analysis of robenidine hydrochloride in the presence of its chemical precursors. It provides a rapid and specific method for the analysis of robenidine in technical material as well as feed premixes and is capable of distinguishing the intact drug from its degradation products. The chromatographic system employs a mixture of methanol, acetic acid, and methylene chloride as the mobile phase and a controlled pore glass as the stationary phase. Sample manipulation has been automated in 2 ways. In the first, manually prepared samples are automatically injected onto the column for separation and quantitation. In the second, a totally automated sample handling system, weighed samples are extracted, diluted, filtered, and then injected onto the column, all in a sequential manner. These procedures are capable of giving quantitative results at a rate of 10 samples/hr with a relative standard deviation of 1.13%. 相似文献
994.
Red and yellow earths are kaolinitic and generally sesquioxidic soils having massive B horizons with porous, earthy fabrics and weak profile differentiation but usually displaying a gradual increase in clay content with depth. They are widespread in tropical Queensland and northeast Brazil where comparable climates prevail although the vegetation is markedly different. Their parent materials are mostly quartzitic sedimentary rocks or unconsolidated sediments and the soils occur in a wide variety of topographic and geomorphic situations. In both regions it is probable that many of the soils have not formed under the present climatic conditions.Profile morphology, drainage, silt and clay contents, clay mineralogy, and soil chemistry have been compared and contrasted between the red and yellow earths within and between the two regions. Canonical variate analysis has shown that, on the basis of surface soil chemical attributes, the red earths can be separated from the yellow earths within each region and that the Queensland soils can be separated from the Brazilian soils. 相似文献
995.
The effects of five ameliorants for saline-sodic soil reclamation on certain chemical and physical soil properties over a four-year period of observation are reported. Of these ameliorants, three are conventionally used (gypsum, sulphur, manure); the other two are for this purpose either unusual (potassium sulphate) or relatively unknown (molasses meal). Results published in a previous paper demonstrated that molasses meal had a very rapid-acting favourable effect on most soil physical properties whilst soil chemical conditions remained essentially unchanged. The effect on physical properties was presumably due to soil aggregation by the polysaccharide component of molasses meal. As a follow-up this paper shows, however, that this aggregation does not last long; the rigidly arid climatic conditions under which this experiment was carried out apparently do not favour the preservation of structural bonds consisting of polysaccharide gums. Consequently, a gradual decline of structural conditions took place after the second year. Although initially not as effective as molasses meal, gypsum and sulphur retained their favourable influence on physical properties over a longer period. Potassium sulphate and farmyard manure provided virtually no benefits. 相似文献
996.
The Shad fisheries of the Chesapeake Bay in Maryland have been declining since an 1897 peak of 7860 × 103kg. No periods of stability have been recorded. Data are presented to trace the decline not only as a function of specific areas within the Northern Chesapeake Bay but also in terms of environmental problems and recruitment overfishing.The problem is related to improving the commercial fishing yield. An estimation of a maximum effort of 200,000 man-hours is suggested if a stable yield is to be approached. Methods for obtaining this goal include alternating of closed fishing areas, adoption of rest days, enforcement of fisheries regulations and reduction of the number of metres of gill net used per fisherman. 相似文献
997.
Reduction of N2O in moist soil was inhibited completely by 10?2 atm C2H2 and partially by 10?5 atm C2H2. The effect of C2H4 was 104 times less than that of C2H2. Denitrification of NO?3 occurred in anaerobically or aerobically incubated waterlogged soil and in anaerobic but not in aerobic moist soil. In the absence of C2H2 there was transient accumulation of N2O. In the presence of C2H2 there was stoichiometric conversion of NO?3 to N2O. Some kinetics of the reduction of N2O and of NO?3 to N2O are presented. Denitrification of 1 μg added NO?3-N.g? could be measured within 1 h. Stoichiometries of production of N2O from NO?2 and NO?3, respectively, and production of CO2 attributable to denitrification were consistent with reported energy yields. Reduction of C2H2 to C2H4 occurred immediately following complete denitrification of added NO?3. The incubation of soil in the presence and in the absence of C2H2 thus permits assay of both denitrification and N2 fixation and provides information on the mole fraction of N2O in the products of denitrification. 相似文献
998.
A survey was made in 1972, of the status of Rhododendron pronticum L. at Winterton, Norfolk, and aerial photographs were used to assess its spread in recent years. The ecological implications of the continuing presence of this invsive alien shrub on the dunes are discussed. Comparisons with the highly successfull dune shrub Hippophaë rhamnoides L. help put into perspective the present and likely future role of Rhododendron at Winterton. The implications of controls are discussed together with methods by which this may be achieved. 相似文献
999.
B Borsje A Heyting J R Roborgh D B Ross K W Shillam 《Journal of the Association of Official Analytical Chemists》1977,60(5):1003-1009
Two biological assays were conducted in which the antirachitic activity in chicks of 5,6-trans-vitamin D3 added to feed is compared with that of 5,6-cis-vitamin D3. On the basis of the results obtained it is concluded that the relative potency of the trans isomer is, at the most, 5% and that the antirachitic activity of the trans isomer is not markedly enhanced (an increase to a relative potency of 16%, at the most) if the cis isomer is also included in the diet. The results are not conclusive on the inhibition or lack of inhibition of the antirachitic activity of 5,6-cis-vitamin D3 by the presence of 5,6-trans-vitamin D3 in the feed. 相似文献
1000.
Perennial ryegrass cv. S23 was preserved by fermentation (C), or with the addition of 8.7 1 formalin (35% w/w formaldehyde) per t fresh herbage (F) or of 9.0 1 equal mixture (by vol.) of formalin and formic acid (85% w/w solution) per t fresh herbage (FF). These three silages comprised the treatments in a three-period, crossover design in which urea (u) was given at the rate of 20 g per kg dietary DM to half the animals. Twelve calves were allocated to the treatment sequences when they were approximately 12 weeks of age from within groups which had previously received diets with or without urea. Calves ate significantly (P< 0.001) less of silages F or FF than of silage C when each was offered alone, but when urea was given, intakes of silages F and FF were significantly (P < 0.001) increased such that the intakes of all three silages with urea were similar (23.6, 19.6, 19.3, 24.2, 24.2, 24.7 ± 0.51 g DM per kg LW for C, F, FF, Cu, Fu and FFu, respectively). Significantly (P<0.01) more of the DM in silage C was digested than in F or FF and the addition of urea significantly (P<0.05) increased the digestibility of DM from silage FF only (73.8, 71.3, 69.8, 74.6, 70.7, 72.5 ± 0.72% for C, F, FF, Cu, Fu and FFu, respectively). When the silages were given alone, calves spent longer eating and ruminating per kg DM ingested with F or FF than with C. The time spent on F and FF was significantly (P<0.01) reduced by the addition of urea (303, 388, 411, 297, 299, 290 ± 18.9 min per kg DM ingested for C, F, FF, Cu and Fu and FFu, respectively). The results presented suggest that urea partially alleviated the reduction in voluntary intake by calves given herbage preserved using formalin, but the mode of action was not clear. 相似文献