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Components of the energy and heat balances were examined in two maize hybrids grown at three different plant densities (40, 70 and 100 thousand plants per hectare). One of the hybrids was drought tolerant, while the other was bred for cultivation under irrigated conditions. An increase in plant density influenced not only the size of the leaf area, but also the distribution of the leaves at various plant heights. The extinction coefficient, which provides a quantification of radiation penetration, was higher in the irrigated treatments. By contrast to the other two treatments, the plant canopy in the thinly sown stands remained open throughout the vegetation period, and thus behaved quite differently to the closed stands, making it impossible to compare them. Smaller albedo values were recorded for the hybrid bred for irrigation and in thinly sown stands. The low plant density allowed more energy to reach the soil, from which it was reflected, making a considerable contribution to the final temperature in the stand. The latent heat, in keeping with the quantity of water transpired, was the greatest in the densely sown stands. There was little difference between the latent heat values of the normal and dense stands in either hybrid, indicating that they both had a similar sensitivity to increased stand density. If sufficient water is available it would appear that the stand density could be increased even for the drought-tolerant hybrid. 相似文献
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J. Hernandez De Anda M.D. Salman J. Mason T.J. Keefe P.A. Webb J.S. Reif R. Akkina 《Preventive veterinary medicine》1992,14(3-4):209-215
A prospective study of vesicular stomatitis was conducted in two bovine herds in southeastern Mexico. In July 1987, an initial serological screening showed that 64% and 87% of the 654 cattle tested negatively to vesicular stomatitis New Jersey and Indiana antibodies, respectively, using the plaque-reduction serum neutralization test. Most seropositive animals were at least 24 months of age. Based on the initial serological screening, cohorts of seronegative and seropositive cattle were monitered (January–December 1988) for the prevalence of vesicular stomatitis virus (VSV) antibodies using an enzyme-linked immunosorbent assay (ELISA). The serological results, using ELISA, indicated that no VSV activity occured in the two study herds. The seronegative cohort of cattle did not yield a positive seroconversion pattern to either VSV Indiana or New Jersey. The seropositive cohort showed a variable antibody response pattern against the VSV. There were no clinical cases of vesicular stomatitis (VS) in the two herds. The data from the national surveillance program for vesicular diseases suggested that 1988 was a year of low VSV infection incidence in southeastern Mexico. 相似文献
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Kelly Lana Araújo Silvaldo Felipe da Silveira Vicente Mussi-Dias Juan Manuel Anda Rocabado Flavio Costa Miguens 《European journal of plant pathology / European Foundation for Plant Pathology》2017,148(2):413-422
Two Camarotella (Phyllachoraceae) species, C. torrendiella and C. acrocomiae are the causative agents of small (SV) and large verrucosis (LV), respectively, which are important diseases affecting Brazilian coconut palms. The small verrucosis produces necrotic lesions in coconut palm leaflets, whereas LV just produces chlorosis. Semi-thin sections of asymptomatic leaflets and of leaves presenting stromata in different development stages were compared through light microscopy in order to characterize the colonization process of these two coconut palm verrucosis agents. Camarotella torrendiella initially colonized the adaxial epidermal cells and the cells underlying the epidermis close to the vascular bundles. In latter colonization stages, the hyphae of C. torrendiella remained limited to the underlying necrotic tissue adjacent to the mature stromata, mostly in the intracellular spaces and in the collapsing cells of necrotized tissues around the vascular bundles. This species does not colonize intracellular intact fiber cells, xylem vessels or phloem sieve tube elements. In contrast, C. acrocomiae presented a typical biotrophic parasitism model such as that of some gramineous Phyllachora spp. High densities of C. acrocomiae hyphae were found inside intact sieve tube elements; however, with no evidence of cellular death. The extensive hyphal colonization by C. acrocomiae within sieve tube elements was also observed in tertiary and quaternary bundles, as well as in anastomosing vascular bundles. The dependence of both species on the colonization sites associated with vascular bundles indicates the need for additional studies about these intricate host-pathogen relationships. These studies could be important to define new strategies to control coconut palm verrucosis diseases. 相似文献
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为探索农业功能与景观形态的演变历程及其关系,推动生产、生活、生态“三生”功能融合,理清改革开放以来珠三角农业功能及景观形态的演变历程,本研究引入生态系统单位面积生态服务价值表和景观格局指数进行测算。结果表明,1980—2018年,农业食品与原材料生产功能价值从20.81亿元下降到17.45亿元,休闲与文化功能价值从11.83亿元增长至13.92亿元,生态调节与保护功能价值从215.88亿元增长至217.96亿元。农业景观面积从2 094 233.94 hm2缩减到1 753 198.20 hm2,总斑块数从5 536增长至8 282,聚合度从96.732 6减小至95.878 2,景观形状指数由158.578 8增长至182.868 4。研究表明,农业功能转变及景观形态演变历程可以归纳为三个阶段：改革开放至20世纪90年代以生产功能为主导,农业景观表现为以耕地为主、桑基鱼塘为典型的传统农业景观;20世纪90年代至2010年前后以生活功能为主导,农业景观呈现以观光体验为特征的观光农业景观;2010年前后至今转变为“三生”功能融合主导,农业景观呈现以生态休闲为目的的休闲农业景观。 相似文献
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Risk factors for brucellosis seropositivity of goat herds in the Mexicali Valley of Baja California, Mexico 总被引：1，自引：0，他引：1
Andrea B. Mikolon Ian A. Gardner Jorge Hernandez De Anda Sharon K. Hietala 《Preventive veterinary medicine》1998,37(1-4):185-195
A case-control study was conducted in the Mexicali Valley to identify risk factors for goat-herd seropositivity for Brucella melitensis. Nineteen case herds (≥2 positive results with the 8% rose bengal plate test (RBT)) and 55 control herds (zero positive results in RBT), matched for herdsize and geographic location, were enrolled. Conditional logistic regression was used to construct a multivariable model of the odds of seropositivity using variables assessed in a questionnaire administered to goat ranchers. The final model for herd seropositivity included increased risk from importation of goats from other Mexican states, the presence of La Mancha breed does, and the presence of does born outside the herd. Increasing herdsize was also highly significant (p<0.01). In addition, a significant (p<0.05) positive association was found between the presence of seropositive dogs (as assessed by RBT) and seropositive goats on the same ranch. 相似文献
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Van Anda CV 《Science (New York, N.Y.)》1931,74(1912):187-195
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以不同生长年份的广西铁皮石斛为试材,采用统计法对一二三年生盆铁皮石斛的枝条数、高度、节数、直径、鲜质量、折干率等生长特征进行比较研究,以期为广西铁皮石斛栽培提供参考依据.结果表明:不同生长年限的广西铁皮石斛株高、节数、直径、鲜质量的分析差异性显著(P＜0.05),株高、节数、鲜质量、折干率等都以三年生盆二年生枝条为最高,枝条数以三年生盆一年生枝条数为最多,直径以一年生盆枝条为最粗;相关性分析结果表明枝条数、高度、节数、鲜质量都与直径呈负相关性.枝条数、鲜质量、株高、节数等随着直径的变细而增加,可以控制其直径的粗细以达到提高广西铁皮石斛产量. 相似文献
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胚胎移植受体黄牛的试验研究 总被引：2，自引：0，他引：2
试验期内共选择受体黄牛５９头，冻胚移植３３头，选择移植率达５５．５％，妊娠１１头，移植受胎率达３３．３％，分娩９头，妊娠产犊率达８１．８％，经过选牛实足和资料整理，从中得出几项有价值的数据。 相似文献
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Elin Dahlin Peter Torssander Carl-Magnus Mörth Heléne Strandh Göran Åberg Jan F. Henriksen Odd Anda Runo Löfvendahl 《Water, air, and soil pollution》2001,130(1-4):1475-1480
In the Scandinavian countries, Norway and Sweden, increased weathering rate of cultural property such as rock carvings, mostly dated between 4200 ? 500 BC, has become a serious problem. Observations during the last decades have shown severe deterioration due to a combination of natural and anthropogenic influences. In order to study the rate of weathering of the rock carvings an interdisciplinary group from Norway and Sweden was formed to carry out environmental monitoring on one site in each country, one of them belonging to the UNESCO World Heritage List. The results from this investigation have elucidated the problems concerning weathering of silicate rock surfaces and the different parameters causing the deterioration. Based on the obtained results some counter measures in order to preserve the rock carvings have been tested. 相似文献