Effects of Vegetation Stems on Hydraulics of Overland Flow Under Varying Water Discharges     

Chunhong Zhao  Jian'en Gao  Yuefei Huang  Guangqian Wang  Mengjie Zhang 《Land Degradation \u0026amp; Development》2016,27(3):748-757

Vegetation plays an important role in soil erosion control, but few studies have been performed to quantify the effects of vegetation stems on hydraulics of overland flow. Laboratory flume experiments were conducted to investigate the potential effects of vegetation stems on Reynolds number, Froude number, flow velocity and hydraulic resistance of silt‐laden overland flow. Cylinders with diameter D of 2·0, 3·2 and 4·0 × 10⁻² m were glued onto the flume bed to simulate the vegetation stems, and a bare slope was used as control. The flow discharge varied from 0·5 to 1·5 × 10⁻³ m³ s⁻¹ and slope gradient was 9°. Results showed that Reynolds number on vegetated slope was significantly higher than that on bare slope because of the effect of vegetation stems on effective flow width. All the flows were supercritical flow, but Froude number decreased as D increased, implying a decrease in runoff ability to carry sediment. The mean flow velocity also decreased with D, while the velocity profile became steeper, and no significant differences were found in surface flow velocities among longitudinal sections on all slopes. Darcy–Weisbach friction coefficient increased with D, implying that the energy consumption of overland flow on hydraulic resistance increased. Reynolds number was not a unique predictor of hydraulic roughness on vegetated slopes. The total resistance on vegetated slopes was partitioned into grain resistance and vegetation resistance, and vegetation resistance accounted for almost 80% of the total resistance and was the dominant roughness element. Further studies are needed to extend and apply the insights obtained under controlled conditions to actual overland flow conditions. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Nursery‐Box Total Fertilization Technology (NBTF) Application for Increasing Nitrogen Use Efficiency in Chinese Irrigated Riceland: N–Soil Interactions     

Aiping Zhang  Ji Gao  Ruliang Liu  Zhe Chen  Shiqi Yang  Zhengli Yang  Hongbo Shao  Qingwen Zhang  Nagai Yoshikazu 《Land Degradation \u0026amp; Development》2016,27(4):1255-1265

High N fertilizer and flooding irrigation applied to rice in anthropogenic‐alluvial soil often result in N leaching and low use efficiency of applied fertilizer N from the rice field in Ningxia irrigation region in the upper reaches of the Yellow River. Sound N management practices need to be established to improve N use efficiency while sustaining high grain yield levels and minimize fertilizer N loss to the environment. We investigated the effects of Nursery Box Total Fertilization technology (NBTF) on N leaching at different rice growing stages, N use efficiency and rice yield in 2010 and 2011. The four fertilizer N treatments were 300 kg N ha⁻¹ (CU, Conventional treatment of urea at 300 kg N ha⁻¹), 120 kg N ha⁻¹ (NBTF120, NBTF treatment of controlled‐release N fertilizer at 120 kg N ha⁻¹), 80 kgN ha⁻¹ (NBTF80, NBTF treatment of controlled‐release N fertilizer at 80 kg N ha⁻¹) and no N fertilizer application treatment (CK). The results showed that the NBTF120 treatment increased N use efficiency, maintained crop yields and substantially reduced N losses to the environment. Under the CU treatment, the rice yield was 9634 and 7098 kg ha⁻¹, the N use efficiency was 31·6% and 34·8% and the leaching losses of TN were 44·51 and 39·89 kg ha⁻¹; NH₄⁺‐N was 5·26 and 5·49 kg ha⁻¹, and NO₃⁻‐N was 27·94 and 26·22 kg ha⁻¹ during the rice whole growing period in 2010 and 2011, respectively. Compared with CU, NBTF120 significantly increased the N use efficiency and decreased the N losses from the paddy field. Under NBTF120, the N use efficiency was 56·3% and 51·4%, which was 24·7% and 16·6% higher than that of CU, and the conventional fertilizer application rate could be reduced by 60% without lowering the rice yield while decreasing the leaching losses of TN by 16·27 and 14·36 kg ha⁻¹, NH₄⁺‐N by 0·90 and 1·84 kg ha⁻¹, NO₃⁻‐N by 110·6 and 10·14 kg ha⁻¹ in 2010 and 2011, respectively. Our results indicate that the CU treatment resulted in relatively high N leaching losses, and that alternative practice of NBTF which synchronized fertilizer application with crop demand substantially reduced these losses. We therefore suggest the NBTF120 be a fertilizer application alternative which leads to high food production but low environmental impact. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Simulation Study of the Impact of Permanent Groundcover on Soil and Water Changes in Jujube Orchards on Sloping Ground     

Jun Huang  Juan Wang  Xining Zhao  Hongbin Li  Zilong Jing  Xiaodong Gao  Xiaoli Chen  Pute Wu 《Land Degradation \u0026amp; Development》2016,27(4):946-954

Land degradation is recognized as a major environmental problem in rainfed fruit orchards on the Chinese Loess Plateau. Six treatments were used to investigate surface runoff and soil moisture by means of simulated rainfall experiments: (i) a control (clean cultivation) (CC); (ii) strip cock's foot (Dactylis glomerata L.) cover (SCF); (iii) strip crown vetch (Coronilla varia L.) cover (SCV); (iv) strip bird's foot trefoil (Lotus corniculatus L.) cover (SBF); (v) strip white clover (Trifolium repens L.) cover (SWC); and (vi) complete white clover cover (WCC). The time to runoff was significantly longer under WCC than under other treatments (p < 0·05). The total runoff volume and sediment yield were significantly greater under CC than under the vegetation cover treatments (p < 0·05). The mean infiltration rate under WCC and CC was the largest and lowest and differed significantly from that under other treatments (p < 0·05). The change of soil water storage was the largest under WCC and the least under CC. The soil moisture was significantly greater under SCF than under other treatments (p < 0·05). Treatment SCF seemed to be the best groundcover for rainfed sloping jujube orchards on the Chinese Loess Plateau. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

绿色壁垒下我国农产品出口面临的问题及对策     

孙青  高荣海 《农产品加工．学刊》2007,(11):59-62

绿色壁垒具有多种表现形式。加入WTO后,我国农产品出口屡遭绿色壁垒。在挑战和压力面前,要找出自身存在的劣势,制定相应对策,面向国际市场,建立健全符合我国实际并与国际接轨的各项标准,发展生态经济,挑战绿色壁垒。  相似文献   

JMPR 农药残留急性膳食摄入量计算方法   总被引：5，自引：0，他引：5  

高仁君  王蔚  陈隆智  张文吉 《中国农学通报》2006,22(4):101-101

农药残留急性膳食风险评估直到最近才引起大家的关注。目前，粮农组织和世界卫生组织农药残留联席会议（JMPR）研究国际范围农药急性膳食风险评估；美国、英国、荷兰、澳大利亚和新西兰也开始进行国家农药急性膳食风险评估。农药急性膳食风险是急性或短期接触毒性与农药急性膳食摄入量的函数。急性膳食接触量评估常用的方法有：定点或确定性方法和概率模型法。在确定性方法中选取食物的大部分人群消耗量和高残留量来计算膳食摄入量，为了解决混合样品中食品个体之间的残留差异，在计算中引入了变异因子。JMPR根据具体情况分为情形1、情形2a、情形2b、情形3来计算农药急性膳食摄入量。中国应该尽快建立健全膳食结构和农产品性状数据库，建立健全市场中农产品的农药残留数据库，并在高毒和中等毒性农药登记前应采用JMPR的确定性方法，进行急性膳食风险评估，提高农药膳食摄入的安全性。  相似文献   

新时期稳定高校管理队伍的几点思考     

高增刚  刘怀  王晓文  秦清军 《中国农学通报》2007,23(7):635-638

2007年被教育部定为“高等学校管理年”,管理出质量,管理出效益。一流的大学必须要有一流的管理,建设一支稳定、精干、高效的管理队伍对高校的改革和长远发展至关重要。重视和解决目前高校管理队伍中存在的种种问题,努力构建和稳定一支高素质的管理队伍,是高校可持续发展的必然要求。  相似文献   

Progress of Study on Oriented Growth of Carbon Nanotubes     

WANG Bi ben  WANG Wan lu  LIU Gao bin  Seungho Choi 《保鲜与加工》2002,(8):134-136

Owing to unique structure and characteristics of carbon nanotubes, much more are attracted attentions since they were discovered. In recent years, carbon nanotubes have been successfully synthesized by various methods. Especially, highly aligned carbon nanotubes were grown by chemical vapor deposition (CVD) and the oriented growth of carbon nanotubes became realized, resulting in many applications of carbon nanotubes and researches on them. In the work, the methods and mechanisms of orientation growth of carbon nanotubes were reviewed, and it was analyzed and discussed that different methods influenced on the process of growing carbon nanotubes. Simultaneously, it was emphatically analyzed that catalyst particles affected on orientation growth of carbon nanotubes during their growth.  相似文献   

散装小麦局部环流熏蒸杀虫实仓试验   总被引：2，自引：1，他引：2  

祝超明  杨大成  杜秀琼  郜贺鹏  吴峡  王治德  张再杰  秦军  阳岭峰 《粮食储藏》2003,32(3):18-20,41

针对小麦仓中下层局部生虫，采用粮堆局部处理机环流熏蒸，分两次投药，共计熏蒸处理时间为两周。实验证明：在处理部位PH3浓度100～300ppm可以保持12天左右，粮堆中的害虫全部杀死；经检查埋入粮堆的赤拟谷盗、谷蠹和玉米象，成虫死亡率100％，对虫粮培养42天后，检查F1代为零。  相似文献   

根癌农杆菌介导玉米遗传转化的研究进展     

高武军  卢龙斗  魏开发  孙富丛 《中国农学通报》2004,20(6):26-26

对根癌农杆菌介导的玉米基因转化中包括外植体、基本培养基及其附加物、共培养温度、信号分子与vir基因的活化的几个关键因素研究进展作了论述。近年来的研究发现，大小为1~2mm的幼胚是较为理想的转化外植体，在外植体培养基本培养基一般多选用MS和N6，在基本培养基上附加有机氮和氨基酸、金属离子均有利于转化效率的提高。转化中的共培养温度一般在200C~250C之间。研究认为根癌农杆菌转化禾本科植物的困难在于禾本科植物缺乏酚类物质，难以诱导Vir基因活化表达，因此在转化中多采用加入外源的酚类物质如乙酰丁香酮来提高玉米转化的成功率。  相似文献   

GA和Mn2+对盐渍土棉花种子发芽影响的研究     

汤菊香  高扬帆  陈军 《种子》2006,25(8):7-9

本试验分析了GA和Mn2 对盐渍土棉花种子发芽的影响。对苗高、发芽率、发芽指数、活力指数等指标的测定结果显示:GA和Mn2 混合液对棉花种子发芽的耐盐性有显著影响,其中以3 mg/L GA与200 mg/kgMn2 混合效果最佳。  相似文献