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1.
Abstract. Usual residue-management options are to remove the residue, use it as mulch with or without undercutting or to incorporate it into the soil. While the role of surface mulch in evaporation has been widely studied, the information on the effect on evaporation of mulch with undercutting or residue incorporated into soil, particularly in relation to soil type and evaporativity (Eo) is lacking. We studied the effect of wheat straw used in various ways on the course of evaporation loss from soil columns with three soils at Ludhiana, India and one soil at Bushland, Texas, USA, under two Eo's Energy-limited evaporation rates under mulch (Eom) followed the soil-specific relation Eom/Eo= a e(bRes+cEo), where Res is residue rate t/ha and a, b and c are constants; Eo, is expressed in mm/d. In an effort to model the total evaporation (CE) during the energy-limited stage ‘U’ was obtained from appropriate CE versus time curves and (CE-U) was regressed over (t - ti)0.5 to obtain the slope ‘α’ (Ritchie 1972) for the soil-limited evaporation stage. The observed ‘U’ was independent of mulch rate and Eo but was strongly affected by soil type, Values of ‘α’ decreased with increase in mulch rate and decrease in Eo and coarseness of soil. The otherwise short lived benefit of evaporation reduction with mulch per se, which peaked after a few days was maintained when residue was mixed with soil at the stage when evaporation reduction reached a maximum; this benefit continued for several weeks. Cumulative evaporation values computed from ‘U’ and ‘α’ agreed closely with the observed values under straw mulch for loamy sand and clay loam soils and for ‘undercut’ and ‘residue mixed’ treatments on all soils regardless of Eo, and for all situations under small Eo. However, for sandy loam and silt loam soils under Eo of 10 mm/d, the modified square root of the time function of Jalota et al. (1988) gave a better fit. 相似文献
2.
Accomodation of important sources of uncertainty in ecological models is essential to realistically predicting ecological processes. The purpose of this project is to develop a robust methodology for modeling natural processes on a landscape while accounting for the variability in a process by utilizing environmental and spatial random effects. A hierarchical Bayesian framework has allowed the simultaneous integration of these effects. This framework naturally assumes variables to be random and the posterior distribution of the model provides probabilistic information about the process. Two species in the genus Desmodium were used as examples to illustrate the utility of the model in Southeast Missouri, USA. In addition, two validation techniques were applied to evaluate the qualitative and quantitative characteristics of the predictions.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
3.
Recent research shows that land use history is an important determinant of current ecosystem function. In the United States,
characterization of land use change following European settlement requires reconstruction of the original property mosaic.
However, this task is difficult in unsystematically surveyed areas east of the Appalachian Mountains. The Gwynns Falls watershed
(Baltimore, MD) was originally surveyed in the 1600-1700s under a system of warrants and patents (commonly known as ‘metes
and bounds’). A method for the reconstruction and mapping of warrant and patent properties is presented and used to map the
original property mosaic in the Gwynns Falls watershed. Using the mapped mosaic, the persistence of properties and property
lines in the current Gwynns Falls landscape is considered. The results of this research indicate that as in agricultural areas,
the original property lines in the Gwynns Falls watershed are persistent. At the same time, the results suggest that the property
mosaic in heavily urbanized/suburbanized areas is generally ‘reset.’ Further, trends in surveying technique, parcel size,
and settlement patterns cause property line density and property shape complexity to increase in the less urbanized upper
watershed. The persistence of original patterns may be damping expression of heterogeneity gradients in this urban landscape.
This spatial pattern of complexity in the original mosaic is directly opposite of hypothesized patterns of landscape heterogeneity
arising from urbanization. The technique reported here and the resulting observations are important for landscape pattern
studies in areas settled under unsystematic survey systems, especially the heavily urbanized areas of the eastern United States.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
There is debate among ecologists about whether total habitat area or patch arrangement contributes most to population and/or
community responses to fragmented or patchy landscapes. We tested the relative effects of patch area and isolation for predicting
bird occurrence in a naturally patchy landscape in the Bear River Mountains of Northern Utah, USA. We selected focal patches
(mountain meadows) ranging in elevation from 1,920 to 2,860 m and in size from 0.6 to 182 ha. Breeding birds were sampled
in each focal meadow during the summers of 2003 and 2004 using variable-distance point transects. Logistic regression and
likelihood-based model selection were used to determine the relationship between likelihood of occurrence of three bird species
(Brewer’s sparrow, vesper sparrow, and white-crowned sparrow) and area, isolation, and proximity metrics. We used model weights
and model-averaged confidence intervals to assess the importance of each predictor variable. Plots of area versus isolation
were used to evaluate complex relationships between the variables. We found that meadow area was the most important variable
for explaining occurrence for two species, and that isolation was the most important for the other. We also found that the
absolute distance was more appropriate for evaluating isolation responses than was the species-specific proximity metric.
Our findings add clarity to the debate between ecologists regarding the relative importance of area and isolation in species
responses to patchy landscapes. 相似文献
5.
加利福尼亚州位于美国西部,受自然和社会因素影响,园林植物种类丰富,以常绿植物种类为主,亦有不少落叶种类。园林绿地类型多样,包括公共绿地、道路绿化带、建筑物周围绿地以及众多壮丽的植物公园和典雅的私家花园。加州全民绿化和环保意识较高,值得国人借鉴。 相似文献
6.
7.
美洲帘蛤Mercenaria mercenaria(Linnaeus,1758)隶属于软体动物门Mollusea、瓣鳃纲Lamellibrachia、帘蛤目Veneroida、帘蛤科Veneridae,又称硬壳蛤、北方帘蛤或小圆蛤。原产于美国佛罗里达州Cawrence湾,墨西哥湾,加利福尼亚Hamboldt湾到英格兰海域,在美国东、西海岸北纬25°~38°海域均有分布。美洲帘蛤与我国的文蛤(Meretrixmeretrix)同属帘蛤科,是一种生长快,适应能力强,适温、适盐范围广,经济价值高的大型双壳贝类[4-10]。美洲帘蛤软体部的蛋白质含量高达60.69%(DS),氨基酸的总含量为524.2mg·g-1,蛋白质的氨基酸含量为893.5mg·g-1… 相似文献
8.
欧、美中华绒螯蟹源于中国长江水系中华绒螯蟹的遗传证据 总被引:8,自引:0,他引:8
用包括Z2和Opp17两个10碱基随机引物在内的10个引物,对来自荷兰斯科克莱(Skodely)、美国加州圣何塞(San Jose)的中华绒螯蟹群体与中国长江水系中华绒螯蟹群体进行RAPD遗传比较分析。结果发现:(1)中华绒螯蟹群体特有的Z2引物扩增的700bp标记带(Z2^700bp),在荷兰与美国2个中华绒螯蟹群体中同时出现,而不出现日本绒螯蟹南流江种群中特有的880bp标记带(Z2^880bp),表明欧洲、美国中华绒螯蟹与中国中华绒螯蟹为同种Eriocheir sinensis,而非日本绒螯蟹Eriocheir japonicus;(2)Opp17引物扩增的947bp片段在中国长江、荷兰及美国3个中华绒螯蟹群体内的出现频率均达100%。结合Z2引物扩增结果,欧洲与美国中华绒螯蟹群体极可能是从中国长江水系中华绒螯蟹引入繁衍的。 相似文献
9.
In a national survey of US dairy producers, only 2.7 ± 0.5% of Holstein dairy operations reported achieving recommended target ranges of age ≤ 24 months and body weight (BW) ≥ 550 kg at first calving. Allowing for wider target ranges, still only 14.6 ± 1.3% of Holstein dairy operations reported achieving age ≤ 25 months and BW ≥ 544.3 kg at first calving. Ages of individual first-calf heifers observed at calving were heavily skewed toward older individuals. Dairy producers reported an average age at first calving that was 1.3 months lower than the mean and 1.0 months lower than median age of first-calf heifers' observed calving on the operations. Stepwise logistic regression was used to identify the herd characteristics associated with producers reporting first calvings within the wider age and BW target ranges for Holsteins. Rolling herd average milk production ≥ 7711 kg/yr, using a computer for recordkeeping, and not tying preweaned heifers in a barn with cows, were associated with achieving the target BW and age at first calving. 相似文献
10.
Animal surveys were conducted in six habitat types within the timber concession of PT International Timber Corporation Indonesia, East Kalimantan. Species diversity was found to be similar in undisturbed forest and in 3- to 5-year-old selectively logged forest, although densities in the latter were considerably less. Both diversity and density declined drastically in forestry plantations, but certain of the species remaining caused significant damage to young trees. Although few animals were observed in areas where there was active road construction and timber felling, their densities in adjacent undisturbed forest areas did not increase, suggesting that the level of local migration actually is low. It is suggested that recolonisation of old logged forest can occur successfully provide that the level of hunting is low and that adjacent areas of undisturbed forest remain to provide a population pool from which colonists can spread. 相似文献