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排序方式： 共有8694条查询结果，搜索用时 20 毫秒
1.
[目的]本研究旨在对黄河首曲-玛曲湿地的沼生植物进行群系分类。[方法]采用样方法,同时参考植物标本,对玛曲湿地的沼生植物进行调查研究。[结果]玛曲湿地沼生植物的群落类型可分为莎草沼泽和杂类草沼泽2大类共4个群系。建群种主要包括华扁穗草(Blysmussinocompressus)、裸果扁穗苔草(Blysmocarex nudicarpa)、槽秆荸荠(Eleocharis valleculosa)和两栖蓼(Polygonum amphibium);亚建群种主要包括褐鳞苔草(Carex brunnescens)、沿沟草(Catabrosa aquatica)、甘肃嵩草(Kobresia kansuensis)、两栖蓼(Polygonum amphibium)和火绒草(Leontopodiumalpinum)。群落总盖度在5%～90%之间;主要分布在河道洼地、河漫滩、沟谷洼地、阶地陡坎洼地、沟源洼地等常年积水的地方,地下水位埋深大都在20～30cm。[结论]进行沼生植物的群系分类研究,可以为玛曲湿地草原的生态恢复治理提供科学依据。 相似文献
2.
《Agricultural Systems》2008,96(1-3):49-61
This series of two papers describes a mechanistic model that simulates within years the productivity of vegetation and livestock on the communal semi-arid rangeland of the Succulent Karoo of South Africa. The model enables users to evaluate short-term management decisions on the production of milk and meat and to develop sets of equations and rules for long-term models designed to examine the effects of different strategies on the sustainability of the ecosystem.A soil moisture module partitions daily rainfall between runoff, infiltration and drainage and also simulates the loss of soil moisture by evaporation and transpiration. Forage production by different types of plant is modelled in relation to soil moisture and the present potential for growth. Three factors are assumed to influence the animal’s preference for a specific type of plant or part of a plant: relative abundance, ease of harvesting and digestibility. The model combines three mechanisms of food intake regulation: the rate at which the animal is able to eat forage, physical capacity of the digestive system, and, in young animals, their growth potential. Metabolisable energy intake is partitioned between maintenance, accretion/depletion of body protein and fat, conceptus growth and milk production. Reproductive and survival rates are simulated in relation to predicted liveweight and liveweight changes for the different age classes of livestock. 相似文献
3.
《Agricultural Water Management》2006,84(3):259-264
Field experiments were conducted in a tropical region to determine the water-use efficiency (WUE), yield (Y) and evapotranspiration (ET) of a 6-year-old dwarf-green coconut (Cocos nucifera L.) orchard. Three water levels were applied in plots with nine palms. The irrigation treatments denoted as T:50, T:100 and T:150 received 50, 100 and 150 L/plant/day, respectively. The actual evapotranspiration was obtained by the soil water balance (SWB) method. Yield and water-use efficiency were assessed in terms of bunches per plant, fruits per plant and water volume per fruit. The application of the SWB resulted in mean daily ET values of 2.5; 2.9 and 3.2 mm/day for irrigation treatment of T:50, T:100 and T:150, respectively, while the cumulative ET varied from 900 to 1100 mm as irrigation treatment increased from T:50 to T:150. Results also showed that ET values were higher in the beginning and end of the year and lower in the middle of the experimental period. The application of a high irrigation water volume does not necessarily resulted in high coconut fruits yield. Evapotranspiration, fruits yield and water-use efficiency were strongly affected by irrigation water volume in coconut palms. WUE values decreased with increasing irrigation water level for all productivity parameters. 相似文献
4.
土地闲置原因分析及对策研究 总被引：1，自引：0，他引：1
2010年3月8日《国土资源部关于加强房地产用地供应和监管有关问题的通知》中提出,2010年3—7月在全国范围内开展房地产用地专项整治工作,8月19日国土资源部通报了房地产用地专项整治情况,整治过程中,发现违法用地面积近1.26万hm2,其中,闲置土地占90%以上,已成当前最大问题。以城市建设用地为主要研究对象,分析了当前房地产用地中土地闲置产生的原因及其所带来的危害,并对如何预防土地闲置、盘活已闲置土地进行了探讨。 相似文献
5.
《Fitoterapia》2014
Two novel diterpenoids, japodagricanones A (1) and B (2), along with their biogenetically related diterpenoid 15-epi-4E-jatrogrossidentadion (3), were isolated from the leaves and twigs of Jatropha podagrica. Japodagricanones A (1) and B (2) are the first C-5-nor lathyrane-type diterpenoids. Their structures were established using spectroscopic data, including MS, NMR and ECD data. A plausible biosynthetic pathway for their generation was also proposed. 相似文献
6.
A better understanding of the fate of fertilizer nitrogen (N) is critical to design appropriate N management strategies in plastic-mulched croplands. We evaluated the effects of plastic mulch on urea-N recovery by crops and loss from soil in furrow-ridge plots, with and without maize (Zea mays L.) cropping, in a semi-arid rain-fed site in China. We applied the same rate of urea-N (281 kg ha−1) to all treatments during the preparation of the furrow-ridges in 2011 and 2012 but 15N-labeled the urea in 2011 only. We used transparent film to cover all soil surfaces in the mulched treatments and seeded maize in furrows in treatments with crop. In 2011, plastic mulch increased the total N uptake in the aboveground biomass of maize by 53%, whereas it decreased the in-season labeled-N uptake by 19%, compared to non-mulched treatment. At harvest in 2011, in mulched treatments the total labeled-N remaining in the 0−170 cm soil layer was 25% greater whereas unaccounted labeled-N was 69% less, than in non-mulched treatments, regardless of whether maize was cropped. In 2012 the effect of mulch on total maize N uptake was comparable to that in 2011, but the residual soil labeled-N uptake by maize was 63% higher in mulched compared to non-mulched treatment. At harvest in 2012, plastic mulch increased total labeled-N remaining in the 0−170 cm depth in cropped soils and unaccounted labeled-N in non-cropped soils, compared with no mulch. Our results indicate that plastic mulch profoundly changes the fate of urea-N in maize production in cold and dry croplands. 相似文献
7.
Stochastic modeling provides a useful tool in managing biological variation in the postharvest chain. In the current study, the fruit-to-fruit variability in the postharvest firmness of apples was modeled. Apples from three cultivars (‘Jonagold’, ‘Braeburn’, and ‘Kanzi’) were harvested at different levels of maturity, and stored at different temperatures and controlled atmosphere (CA) conditions. By using a kinetic model describing firmness breakdown as a function of time, temperature, controlled atmosphere conditions and endogenous ethylene concentration, the main stochastic variables were identified as the initial firmness and the rate constants for firmness breakdown and ethylene production. Treating these variables as random model parameters, the Monte Carlo method was used to simulate the propagation of the fruit-to-fruit variability in flesh firmness within a batch of apples during storage under different CA conditions and subsequent shelf-life exposure. The model was validated using independent data sets from apples picked in a different season. The model developed in this study can be used to predict the probability of having apples of certain firmness after long term storage for different scenarios of temperatures and CA conditions. 相似文献
8.
《European Journal of Agronomy》2006,24(1):52-61
The carbon dioxide (CO2) concentration of the global atmosphere has increased during the last decades. This increase is expected to impact the diurnal variation in temperature as well as the occurrence of extreme temperatures. This potentially could affect crop production through changes in growth and development that will ultimately impact yield. The objective of this study was to evaluate the effect of CO2 and its interaction with temperature on growth and development of soybean (Glycine max (L.) Merr., cv. Stonewall). The experiment was conducted in controlled environment chambers at the Georgia Envirotron under three different temperatures and two CO2 regimes. The day/night air temperatures were maintained at 20/15, 25/20 and 30/25 °C, while the CO2 levels were maintained at 400 and 700 ppm, resulting in six different treatments. Plants were grown under a constant irradiance of 850 μmoles m−2 s−1 and a day length of 12 h; a non-limiting supply of water and mineral nutrients were provided. Five growth analyses were conducted at the critical development stages V4, R3, R5, R6 and R8. No differences in start of flowering were observed as a function of the CO2 level, except for the temperature regime 25/20 °C, where flowering for the elevated CO2 level occurred 2 days earlier than for the ambient CO2 level. For aboveground biomass, an increase in the CO2 level caused a more vigorous growth at lower temperatures. An increase in temperature also decreased seed weight, mainly due to a reduction in seed size. For all temperature combinations, final seed weight was higher for the elevated CO2 level. This study showed that controlled environment chambers can be excellent facilities for conducting a detailed growth analysis to study the impact on the interactive effect of changes in temperature and CO2 on soybean growth and final yield. 相似文献
9.
郭杰光 《农业图书情报学刊》2007,19(3):168-171
通过对该馆自动化开架借阅藏书发展工作中投入产出效益的研究,以进一步深化藏书发展工作,提高经费使用效益。 相似文献
10.
《Field Crops Research》2006,95(2-3):256-267
Intercropping advantages may be influenced by both plant density and relative frequency of the intercrop components. In a field study barley (Hordeum vulgare L.) and pea (Pisum sativum L.) were sole cropped and intercropped at three densities and with two relative frequencies when intercropped.Earlier seedling emergence gave barley an initial growth advantage, assessed using the relative efficiency index (REIc), whereas pea was in general more growth efficient once the initial growth phase had been passed. This reversal in relative growth efficiency along with the observation that early barley dominance did not appear to suppress pea growth indicates that differences in phenology played a role in shaping the prevailing dynamics. Whereas increases in plant density had a positive effect on the growth of pea, the growth of intercropped barley was severely limited by increases in density at the end of the growing period and more so in the pea dominated intercrop. At the final harvest land equivalent ratios (LER) of 0.9–1.2 express resource complementarity in almost all studied intercrops, complementarity that was not directly affected by changes in plant density or relative frequency.Intercropped pea did not increase its reliance on atmospheric nitrogen fixation compared to the pea sole crop. With respect to soil nitrogen uptake there were no effect of plant density but a strong effect of the relative frequency of pea in the intercrop, the greater the proportion the lower the uptake.Changes in the competitive strength of the pea and barley crop over the growing season had a marked effect on the proportion of pea in the final grain yields of the intercrops. At low and recommended density the proportions of pea and barley in the final grain yield was not markedly different from the expected proportions sown; however, at high density the suppression of barley strongly increased the proportion of pea in the final grain yield.Weed infestation levels decreased as density was raised and the suppressing effect of density was clearly stronger the greater the frequency of pea in the crop. Earlier germination and tillering ability of barley are seen as likely explanations of lower weed load in the barley dominated crop treatments.This study points at the potential of employing density and relative crop frequency as “regulators” when specific intercrop objectives such as increased competitiveness towards weeds or specific grain yield composition are wanted. 相似文献