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81.
[目的]揭示膜下滴灌(MG)、露地滴灌(DG)、沟灌(GA)、交替隔沟灌(JG)、漫灌(CK)5种灌溉方式对春玉米生长和产量的影响,筛选出适合榆林沙区的最有效的节水灌溉方式,为农业高效节水灌溉技术发展提供理论支持。[方法]基于2014年田间试验数据,运用统计分析和水分生产率计算方法。[结果](1)MG处理的春玉米植株生长发育状况优于其他灌溉方式。在各生育期,MG处理的春玉米株高、茎粗和叶片SPAD值(叶绿素相对含量)均高于DG,GA和JG,且显著高于CK(p0.05);(2)在整个生育期,MG处理的春玉米叶片光合速率、气孔导度和水分利用效率均高于其他灌溉方式,且显著高于CK(p0.05);(3)MG处理的春玉米增产节水效果显著,其产量和水分生产率均显著高于其他处理(p0.05)。[结论]同其他4种灌溉方式相比,膜下滴灌是榆林沙区玉米生产中最有效的一种节水灌溉方式。 相似文献
82.
Yongguang Zhang Yongqiu Wu Baoyuan Liu Qiuhong Zheng Jiayi Yin 《Soil & Tillage Research》2007,96(1-2):28-41
Ephemeral gully erosion is an important process in the black soil region, Northeast China and can be responsible for severe damage to agricultural lands. However, little research on gully formation in this area has been published. The study described in this paper attempted to quantify soil losses, the spatial distribution and morphology of the gullies, and the factors that control their development. Ephemeral gullies were measured in spring and summer of 2005 in two small catchments. The critical periods for ephemeral gully formation were late spring and summer in the study area. Mean soil losses due to ephemeral gully erosion were 0.40 and 0.43 kg m−2 year−1 for only croplands despite low slope gradients, and this loss is above the tolerable erosion rates of 0.20 kg m−2 year−1. The erosion rates were greater in spring because the topsoil thawed before deeper layers, reducing infiltration into the soil, and the bare vegetation cover provided no barriers to surface flow. In contrast, summer erosion occurred primarily in response to intense rain events. Development of the gullies was promoted by freeze-thaw cycles in spring and was affected by the type of agricultural operations and crops in summer. A linear regression model for the prediction of ephemeral gully length at the catchment level was established using field data, and although it did not successfully predict the length of individual gullies, it explained 55% of the variation in ephemeral gully length. 相似文献
83.
Microbial activity is known to continue during the winter months in cold alpine and Arctic soils often resulting in high microbial biomass. Complex soil nutrient dynamics characterize the transition when soil temperatures approach and exceed 0 °C in spring. At the time of this transition in alphine soils microbial biomass declines dramatically together with soil pools of available nutrients. This pattern of change characterizes alpine soils at the winter-spring transition but whether a similar pattern occurs in Arctic soils, which are colder, is unclear. In this study amounts of microbial biomass and the availability of carbon (C), nitrogen (N) and phosphorus (P) for microbial and plant growth in wet peaty soils of an Arctic sedge meadow have been determined across the winter-spring boundary. The objective was to determine the likely causes of the decline in microbial biomass in relation to temperature change and nutrient availability. The pattern of soil temperature at depths of 5-15 cm can be divided into three phases: below −10 °C in late winter, from −7 to 0 °C for 7 weeks during a period of freeze-thaw cycles and above 0 °C in early spring. Peak microbial biomass and nutrient availability occurred early in the freeze-thaw phase. Subsequently, a steady decrease in inorganic N occurred, so that when soil temperatures rose above 0 °C, pools of inorganic nutrients in soils were very low. In contrast, amounts of microbial C and soluble organic C and N remained high until the end of the period of freeze-thaw cycles, when a sudden collapse occurred in soluble organic C and N and in phosphatase activity, followed by a crash in microbial biomass just prior to soil temperatures rising consistently above 0 °C. Following this, there was no large pulse of available nutrients, implying that competition for nutrients from roots results in the collapse of the microbial pool. 相似文献
84.
济南泉域岩溶水质演变及其对人类活动的响应 总被引:5,自引:0,他引:5
地下水是岩溶地区水资源的重要赋存形式,也是岩溶地区经济发展的重要支撑点。由于岩溶含水层的本质脆弱性,岩溶水资源在人类活动胁迫下极易蜕变。以20世纪50年代末的地下水化学状况为背景值,结合近20年的水质监测资料,分析了济南泉域岩溶水质演化与人类活动的关系。结果显示:近20年来,地下水质总体呈恶化趋势,水质的区域性、阶段性变化与人类活动强度密切相关,东郊岩溶水质最差,且无污染物增长幅度明显高于市区和西郊。伴随土地利用方式的改变和人类活动强度的空间变化,地下水质从间接补给区、直接补给区到泉水排泄区,单项污染指数和综合污染指数依次升高;具有典型代表性的泉域东部大辛河流域,从上游、中游到下游,地下水污染物的浓度也渐次升高,且愈往下游污染物浓度增幅愈大,显示出与土地利用方式和人类活动的密切相关性。因此优化调整土地利用结构,减少人类活动对下水的污染,对岩溶水资源的可持续利用和济南“泉城”景观的保护有重要意义。 相似文献
85.
86.
地下水埋深对春玉米田土壤水分及产量的影响 总被引:17,自引:3,他引:17
通过6种地下水位控制处理和对照春玉米试验,探讨了地下水埋深对春玉米农田土壤水分、产量以及水分利用效率的影响。结果表明,地下水埋深对春玉米0~100cm层次土壤水分的影响较大。地下水位越浅这种影响显得越明显;无论地下水埋深深浅,田间累计地下水补给量变化规律可分为4个阶段,即稳定增长期、缓慢增长期、快速增长期和趋于稳定期。地下水位越高,累计地下水补给量越大,土壤排水量越大。较大降雨后土壤开始排水日期随着地下水埋深加深而滞后;地下水埋深1.0m时春玉米产量和水分利用率最高。地下水位在1.0m以下时,水分利用效率随地下水位加深而减少。 相似文献
87.
Joo Youn Oh † ‡ Mee Kum Kim † ‡ Hyun Ju Lee † ‡ Jung Hwa Ko † ‡ Won Ryang Wee † ‡ Jin Hak Lee † ‡ 《Veterinary ophthalmology》2009,12(S1):50-56
Objective Although variations exist between species with respect to outcomes after cryopreservation, little is known about the differences in the susceptibility of the corneal stroma to cryoinjury. We performed this study to investigate freeze–thaw-induced damage in keratocytes and collagen in rabbit, pig, and human corneas.
Animals studied Rabbit, pig, and human.
Procedures We prepared 250-μm-thick anterior stroma from rabbit, pig, and human corneas after scraping off the epithelium and endothelium. Each 250-μm-thick corneal stroma without epithelium was placed in a 50-mL tube, frozen with liquid N2 for 15 min and taken out to thaw rapidly at 37 °C. This procedure of rapid freezing and thawing was repeated three times. Differences between the species with respect to cells and collagen structures were examined using hematoxylin–eosin (H&E) staining, terminal deoxynucleotidyl transferase-mediated nick end labeling (TUNEL) assay, and transmission electron microscopy (TEM). We orthotopically transplanted the pig and rabbit corneal transplants after the triple freeze–thaw cycle into rabbit eyes and evaluated graft survival.
Results On gross examination, rabbit corneas became opaque after the triple freeze–thaw procedure, while pig and human corneas remained transparent. Histologically, keratocytes were apoptotic on TUNEL assay and TEM in rabbit, pig, and human corneas. Collagen fibrils were fragmented and the arrangement of collagen fibrils was severely disturbed in rabbit corneas on H&E staining and TEM; collagen was well preserved in pig and human corneas. Rabbit corneal stroma underwent autolysis after transplantation, whereas the pig corneal stroma remained clear for 1 month.
Conclusions Our study showed that rabbit corneal stroma was more susceptible to freeze–thaw injury than pig and human corneas. 相似文献
Animals studied Rabbit, pig, and human.
Procedures We prepared 250-μm-thick anterior stroma from rabbit, pig, and human corneas after scraping off the epithelium and endothelium. Each 250-μm-thick corneal stroma without epithelium was placed in a 50-mL tube, frozen with liquid N
Results On gross examination, rabbit corneas became opaque after the triple freeze–thaw procedure, while pig and human corneas remained transparent. Histologically, keratocytes were apoptotic on TUNEL assay and TEM in rabbit, pig, and human corneas. Collagen fibrils were fragmented and the arrangement of collagen fibrils was severely disturbed in rabbit corneas on H&E staining and TEM; collagen was well preserved in pig and human corneas. Rabbit corneal stroma underwent autolysis after transplantation, whereas the pig corneal stroma remained clear for 1 month.
Conclusions Our study showed that rabbit corneal stroma was more susceptible to freeze–thaw injury than pig and human corneas. 相似文献
88.
89.
The amounts of N2O released in periods of alternate freezing and thawing depend on site and freezing conditions, and contribute considerably to the annual N2O emissions. However, quantitative information on the N2O emission level of forest soils in freeze‐thaw cycles is scarce, especially with regard to the direct and indirect effect of tree species and the duration of freezing. Our objectives were (i) to quantify the CO2 and N2O emissions of three soils under beech which differed in their texture, C and N contents, and humus types in freeze‐thaw cycles, and (ii) to study the effects of the tree species (beech (Fagus sylvatica L.) and spruce (Picea abies (L.) Karst.)) for silty soils from two adjacent sites and the duration of freezing (three and eleven days) on the emissions. Soils were adjusted to a matric potential of –0.5 kPa, and emissions were measured in 3‐hr intervals for 33 days. CO2 emissions of all soils were similar in the two freeze‐thaw cycles, and followed the temperature course. In contrast, the N2O emissions during thawing differed considerably. Large N2O emissions were found on the loamy soil under beech (Loam‐beech) with a maximum N2O emission of 1200 μg N m–2 h–1 and a cumulative emission of 0.15 g N m–2 in the two thawing periods. However, the sandy soil under beech (Sand‐beech) emitted only 1 mg N2O‐N m–2 in the two thawing periods probably because of a low water‐filled pore space of 44 %. The N2O emissions of the silty soil under beech (Silt‐beech) were small (9 mg N m–2 in the two thawing periods) with a maximum emission of 150 μg N m–2 h–1 while insignificant N2O emissions were found on the silty soil under spruce (0.2 mg N m–2 in the two thawing periods). The cumulative N2O emissions of the short freeze‐thaw cycles were 17 % (Sand‐beech) or 22 % (Loam‐beech, Silt‐beech) less than those of the long freeze‐thaw cycles, but the differences between the emissions of the two periods were not significant (P ≤ 0.05). The results of the study show that the amounts of N2O emitted in freeze‐thaw cycles vary markedly among different forest soils and that the tree species influence the N2O thawing emissions in forests considerably due to direct and indirect impacts on soil physical and chemical properties, soil structure, and properties of the humus layer. 相似文献
90.