水肥一体化中水肥混合效果数值模拟研究     

殷鹏飞  邓玉  戴文连  唐科明 《中国农业大学学报》2018,23(5):122-130

为研究水肥一体化技术中的水肥混合特性,以流体力学中的两相流理论为基础,针对水肥混合过程中混合时间、混合区间长度、流速及管径对其混合效果的影响进行相应的数值模拟研究。结果表明,混合时间及混合区间长度越长有利于提高水肥混合效果及最终水肥混合均匀性;水肥流速比较低时管内水肥混合的均匀性较好,且水肥流速越大则其混合效果及均匀性越好;水肥流速较低时输水管及输肥管的管径比对水肥混合均匀性的影响较大,两者管径比越小则混合效果越好,随着流速的提高两者管径比对其混合效果的影响逐渐减弱。  相似文献   

Nutrient cycling and biomass flows in a low-quality forest stand improvement system in the Lesser Khingan Range of China     

Jinzhuo Wu  Linlin Kong  Xibin Dong 《Journal of Sustainable Forestry》2018,37(6):555-573

The material flow and bulk internal flow analyses were used to establish a material accumulation and cycling model for a low-quality forest stand improvement system and a series of processes were considered. The model was applied in a one-hectare low-quality forest plot in the Lesser Khingan Range of China. Results showed that during 1997–2007, the stands absorbed 270.19 kg of N, 74.28 kg of P, and 124.39 kg of K from soils, 51.82 kg of N and 2.38 kg of P were directly absorbed by foliage, and 16.25 kg of K was released to soils by eluviation. Until 2007, the accumulated nutrients in the stands included 236.91 kg of N, 65.28 kg of P, and 108.55 kg of K. When horizontal strip clearcutting was applied in 2007, 50% accumulated nutrients in the stands were shifted due to harvesting operations, and 212.74 kg of N, 26.97 kg of P, and 98.88 kg of K were accumulated in soils, declining by 9.47% for N, 3.68% for P, and 17.60% for K, respectively, compared with year 1997. 94.61 t per hectare of biomass was generated, of which the biomass in stands accounted for 87.36%. The felled tree biomass was 36.89 t per hectare, of which 84.90% and 10.03% of biomass were utilized in terms of logs and other means, and the rest was left on site.  相似文献   

加拿大一枝黄花入侵机理及控制策略     

唐路恒  马利民 《安徽农业科学》2015,(21):138-139

从遗传特征、繁殖特征、生理生态特点、环境的可入侵性、人类活动干扰、化感作用、与土壤微生物的作用7个方面介绍了加拿大一枝黄花的入侵机理,并提出了机械防治、化学防治、生物防治等控制策略.  相似文献   

等壳水电站碾压混凝土重力坝非溢流坝段稳定渗流场有限元分析研究     

王静 《中国农村水利水电》2011,(10)

通过建立等壳水电站的非溢流坝段的准三维有限元模型,模拟了坝体排水管和排水廊道、上下游防渗层、坝基灌浆帷幕、坝基排水管和排水廊道等,对正常蓄水位工况下坝体、坝基的渗流总水头、压力水头、渗透比降、坝基扬压力分布及渗流量进行了计算分析,验证了坝体和坝基的防渗排水措施的合理性。  相似文献   

金融监管信号传递与金融市场有效运行     

王祥兵 《湖南农业大学学报(自然科学版)》2015,(5):2-8

金融市场是金融监管当局与金融市场参与者之间动态博弈、合作共生的信息不对称系统。通过把信号博弈和重复博弈思想引入金融监管理论研究，构建以金融市场有效运行为反馈信号的金融监管当局与金融市场参与者之间的监管信号传递模型，分析金融市场治理中有效监管信号的传递机制。结果表明：金融监管力度与金融市场有效运行水平之间存在分离、混同两种均衡关系；在金融监管声誉效应的驱动下，金融监管当局倾向于选择混同均衡策略，而不是分离均衡。因而只有建立通畅的金融监管信号传递及反馈机制，强化并放大金融监管信号显示，增大监管乘数效应，形成良性的监管声誉效应，才能保障金融市场的有效运行。  相似文献   

Density responses and spatial distribution of cotton yield and yield components in jujube (Zizyphus jujube)/cotton (Gossypium hirsutum) agroforestry     

《European Journal of Agronomy》2016

Trees are the dominant species in agroforestry systems, profoundly affecting the performance of understory crops. Proximity to trees is a key factor in crop performance, but rather little information is available on the spatial distribution of yield and yield components of crop species under the influence of trees in agroforestry systems. Also, little information is available on how crop density may be exploited to optimize the yield in such systems. Here we studied the performance of cotton in jujube/cotton agroforestry. Field experiments were conducted in 2012 and 2013 in Hetian, Xinjiang, China. Cotton was grown at a row distance of 60 cm in three densities, 13.5, 18.0 and 22.5 plants m⁻² in six m wide paths between tree lines in a jujube plantation. Plant density affected both cotton aboveground dry matter and yield significantly. The highest yield was attained at the intermediate density of 18.0 plants m⁻² (20.0 plants m⁻² corresponding in sole cotton), lower than the optimal density in sole cotton (25.0 plants m⁻²). Yield at the lower density was constrained by the low number of bolls per m² as a direct consequence of the low density, whereas at the high plant density yield was constrained by a lower allocation of assimilates to cotton seed and lint, as a consequence of intraspecific and interspecific competitions. There were strong gradients in yield and yield components in relation to the distance from the tree rows. Leaf area and total dry matter of cotton in rows close to the tree lines were reduced, especially in the rows next to the trees. Moreover, biomass allocation to cotton fruits was reduced in these rows. Competitive influences from the trees on cotton performance extended two rows deep in a six-year old jujube stand, and even three rows deep in a seven-year old stand. Shading effects on cotton yield were compensated by increasing plant density as a result of greater boll numbers per unit ground area. Data from this study help guide the design of optimal plant density of cotton in jujube plantations and give insight in the spatial distribution and dynamics of competitive effects in agroforestry systems in general.  相似文献   

毛乌素沙地东南缘植被恢复中优势灌木的保育作用分析     

田丽  王孝安  李晓炜 《干旱区研究》2016,(6):1202-1208

以毛乌素沙地东南缘优势灌木作为保育植物,选择油松(Pinus tabulaeformis)和樟子松(Pinus sylvestris)幼苗作为目标物种,将其分别种植在开阔地和优势灌木冠层下,连续3 a统计松树幼苗的存活率和主枝生长长度,从而确定毛乌素沙地优势灌木对松树幼苗的定居是否存在保育作用。同时,测量开阔地和灌木冠层下的环境指标,揭示优势灌木保育作用产生的机理。结果表明:1优势灌木冠层下松树幼苗的总存活率显著高于开阔地(P0.05),说明优势灌木可增加松树幼苗的存活率。2在持续3 a的恢复实验期间,优势灌木对松树幼苗定居的保育作用不随时间的变化而发生改变。3优势灌木冠层下松树幼苗的主枝生长良好,并未受到抑制。4优势灌木通过改善微环境,从而对其冠层下松树幼苗的定居产生保育作用,其中改善最为明显的是光照强度和土壤湿度,其次是土壤的有机质和全氮含量。总的来说,优势灌木对松树幼苗的定居存在保育作用,保育植物技术可作为一种有效的恢复措施,应用在毛乌素沙地东南缘的植被恢复中,从而为该区植被的恢复与生态保护提供基础数据。  相似文献   

Short‐term releases of CO2 from newly mixed biochar and calcareous soil          下载免费PDF全文

R. Cardelli  M. Becagli  F. Marchini  A. Saviozzi 《Soil Use and Management》2016,32(4):543-545

The work aimed to quantify native organic C mobilized in one calcareous soil in the 21 days after addition of biochar at a range of large to very large applications. The experiment was carried out in unplanted microcosms, and CO₂ flux was used as a measure of net mineralization. A rapid methodological approach, which does not require ¹³C as a tracer, was used to assess any priming effects induced by the biochar. The amount of CO₂‐C mobilized was small relative to the amount of biochar C and proportional to the amount of the biochar added. The additional CO₂‐C was similar to the content of the water‐soluble organic carbon in the biochar added with each application. No interaction with native soil C, that is priming effect, was observed.  相似文献   

家畜养殖生产的环境效应研究——基于浙江省67个县市的农业经济截面数据     

姚文捷  王学渊 《湖北农业科学》2016,(20):5403-5407

利用浙江省67个县市的农业经济截面数据,以环境负荷量为因变量,以肉产量和耕地面积为自变量构建模型,对家畜养殖生产的环境效应进行研究。结果表明,2013年绍兴市区、衢州市区、龙游县和江山县的环境负荷量超过警戒值,金华市区、德清县和淳安县的环境负荷量超过适宜值;家畜养殖生产存在着环境负效应,并受到耕地资源的约束,其环境负荷量与肉产量正相关,与耕地面积负相关。  相似文献   

土地规模化经营对农业生态效率影响及城乡市场分割调节作用探析     

潘明明 《北方园艺》2021,(7):154-161

土地规模化经营是农业生态效率改善的重要动力,但土地规模化经营作用农业生态效率受到城乡市场分割的门槛调节。该研究借助2001—2017年全国30个地区(因数据缺失,西藏及港澳台地区未涵盖,下同)面板数据,运用面板门槛模型,就城乡市场分割调节土地规模化经营作用农业生态效率过程展开研究。结果表明:(1)我国农业生态效率总体向好,但地区间差异悬殊;(2)土地规模化经营驱动农业生态效率改善,但存在城乡市场分割门槛调节,弱市场分割地区土地规模化经营促进农业生态效率,强市场分割地区作用相反;(3)城乡市场分割调节土地规模化经营作用农业生态效率主要通过限制农产品、劳动力、资本城乡合理流动,削弱农业新型经营主体绿色农业发展意愿和能力途径展开;(4)我国多数地区城乡市场分割水平偏高,区域发展中城市资源偏向和工业优先发展突出,需进行及时改革。该研究可为政府制定绿色农业发展策略提供参考依据。  相似文献