云和雪梨产业"二次分配"机制初探     

曾秋敏  章莲芳  严伟东  刘建灵 《浙江林业科技》2005,25(2):75-78

在"公司 基地 农户"的雪梨生产联结关系的基础上,实行了"二次分配"机制,有效地协调了生产者和销售者之间的利益分配关系,最大限度地降低生产者与销售者的经营风险,促进了专业化分工,提高了生产效率和水平,推进了规模化经营,提高了农产品的组织化程度.  相似文献   

Experimental Study on Moment Modulation of Prestressed Frames     

JIAN Bin  SUN Xin-min  WANG Zheng-lin 《保鲜与加工》2004,(4):107-110

Based on the experimental study of two prestressed frames in redistribution of Internal force, it can be concluded that the dominating influence factors on moment modulation are the relative height of equivalent compression zone, the secondary moment, the ratio of beam rigidity to column and development of cracks in the top of columns.The secondary moment is very important in modulation of frames. Especially, the secondary moment will governing the modulation when the relative height of equivalent compression zone is large enough.  相似文献   

Estimation of the role of obstacles in the downslope soil flow with a simple erosion model: the analytical solution and its approximation with the lattice Boltzmann model     

F. J. Jimnez-Hornero  J. V. Girldez  A. Laguna 《CATENA》2004,57(3):272

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绿洲灌区固定道耕作对土壤盐分动态的影响     

吕晓东  马忠明 《中国生态农业学报》2015,23(9):1122-1130

解决节水灌溉与控制土壤次生盐渍化的矛盾,对干旱内陆绿洲灌区农田节水、防止土壤次生盐渍化和保证绿洲农业稳定持续发展具有重要意义。本研究以传统翻耕(CT)、垄作沟灌(FRB)、固定道保护性耕作(PRB)和固定道平作(ZT)4种耕作方式为研究对象,研究了固定道耕作模式下的土壤盐分特征。结果表明:与播前相比,收获后FRB处理0~20 cm、20~40 cm、40~60 cm和60~100 cm土层土壤含盐量分别提高83.3%、77.2%、47.6%和84.0%,PRB处理分别提高62.6%、46.3%、28.2%和103.6%。ZT和CT处理0~200 cm土壤含盐量呈"脱盐"和"聚盐"交替变化趋势,0~60 cm各土层土壤含盐量随灌水显著降低,而60~200 cm各土层土壤含盐量随灌水显著增加。0~20 cm、20~40 cm和40~60 cm土层是PRB和FRB处理土壤盐分的主要累积区,ZT和CT处理土壤含盐量随灌水最终积累在100~160 cm土层。从头水后至收获各个时期,PRB处理0~200 cm各土层土壤含盐量均高于FRB处理,且差异显著。ZT处理0~20 cm、20~40 cm、40~60 cm和60~100 cm土层土壤含盐量均显著高于CT处理。垄床不同位置土壤盐分运动水平方向上均呈"垄边向垄中"迁移特点,但PRB处理迁移能力强于FRB处理。垂直方向上,FRB处理在土壤60~80 cm处形成积盐峰,而PRB处理在土壤40~60 cm处形成积盐峰。随灌溉水分入渗再分布后FRB处理土壤盐分向垄沟中部和垄床表层迁移,PRB处理土壤盐分在垄床40~60 cm土层处形成一个积盐层。结果说明,垄作方式能显著增加土壤剖面盐分累积。随着垄作年限增加,盐分向垄床中部积累的能力和含量均增强,由此垄作种植应考虑适时漫灌以达到淋洗土壤盐分的目的。  相似文献   

The effect of tillage direction on soil redistribution by mouldboard ploughing on complex slopes   总被引：1，自引：0，他引：1  

G. Heckrath  U. Halekoh  J. Djurhuus  G. Govers 《Soil & Tillage Research》2006,88(1-2):225-241

Seven mouldboard ploughing experiments were conducted to systematically investigate the effect of different tillage directions on soil redistribution on hillslopes. The present study included tillage directions other than parallel to the gradient or along the contour, that is, in our experiments the slope gradient changed simultaneously in tillage and in turning direction. Using physical tracers we developed a model of the two-dimensional tracer displacement as a function of topography and tillage variables. The displacements in tillage and in turning direction were separately described as 2nd degree polynomials in both tillage and in turning directions. This model fully accounted for the directionality of tillage. Displacement in turning direction additionally depended on tillage depth, while that in tillage direction was affected by tillage speed and soil bulk density. We found a large effect of tillage directionality on soil redistribution, and tillage at 45° to the gradient turning soil upslope was the least erosive tillage direction. We obtained non-linear relationships between soil redistribution and profile curvature, instead of the linear relationships reported previously. Consequently tillage erosivity varied in tillage direction and a unique tillage transport coefficient could not be obtained for all tillage directions.  相似文献   

红壤积水入渗及土壤水分再分布规律室内模拟试验研究   总被引：10，自引：2，他引：10  

邹焱陈洪松  苏以荣邵明安 《水土保持学报》2005,19(3):174-177

利用室内模拟土柱试验研究了红壤积水入渗及土壤水分再分布规律。结果表明:入渗过程中湿润锋距离、累积入渗量与时间的平方根呈线性关系,湿润锋运移速率与时间呈乘幂关系,而入渗率与时间平方根的倒数呈线性关系;再分布过程中,在隔绝蒸发条件下,土壤含水量随土层深度的增加而下降,同一深度土层含水量则随时间推移而下降。无论在隔绝蒸发还是在自然蒸发条件下,短期内土壤水吸力有随土层深度的增加呈先下降后升高的趋势,而同一深度土层水吸力则随时间的推移而升高;土壤初始含水量对水分的入渗及再分布有较大影响,初始含水量较低时,水分入渗较快,而水分再分布则较慢。  相似文献   

坐水播种时耕层土壤水分再分布的数值分析   总被引：1，自引：0，他引：1  

李子强  郭维东  杨天恩 《安徽农业科学》2006,34(1):108-109,195

利用朝阳县的旱地土壤取得基本参数后,应用数学模型计算了坐水播种时耕层土壤水分再分布时的土壤湿润状况参数,通过数值分析揭示了坐水播种湿润锋运动和土壤含水率的变化规律。结果显示:湿润锋运动速度和土壤含水率的变化速度都是由快逐渐减慢,所形成的湿润区近似一个球冠体;土壤含水率中的最大值出现在沟底附近;并提出可以用历时7 d的土壤湿润状况参数作为衡量坐水播种灌水质量的指标。  相似文献   

Modeling daily soil water dynamics during vertical drainage using the incoming flow concept   总被引：1，自引：0，他引：1  

Ayman A. Suleiman   《CATENA》2008,73(3):312-320

Crop management models require simulation of daily soil water dynamics. The objective of this study was to develop a model to simulate the daily soil water dynamics during vertical drainage with reasonable accuracy using the incoming flow concept. The execution of this model, which has been developed based on the conservation of mass law, consists of two steps. First, calculating the potential daily change of soil water content (Δθp) for each soil layer in the profile assuming each one receives no water from the above layer. Then, calculating the actual daily change of soil water (Δθa) for each soil layer in the profile by adjusting Δθp using the incoming water flow, which can be defined as the amount of drainage water that reaches a layer in a soil profile from the above layer. The model was compared with the Suleiman and Ritchie [Suleiman, A.A., Ritchie, J.T., 2004. Modifications to the DSSAT vertical drainage model for more accurate soil water dynamics estimation. Soil Sci. 169 (11), 745–757] vertical drainage model (SRVDM) and HYDRUS-1D for diverse soils and was tested using drainage experimental data of a Eutric Regosol in Bekkevoort, Belgium and a sandy soil in Georgia, U.S. The difference in Δθp between the new model and HYDRUS-1D for diverse soils ranged from − 0.01 to 0.016 m³ m^− 3 for the first day and from − 0.005 to − 0.025 m³ m^− 3 for the second day while the difference in Δθp between the SRVDM and HYDRUS-1D for these soils ranged from 0.014 to 0.062 m³ m^− 3 for the first day and from − 0.01 to 0.026 m³ m^− 3 for the second day. The relative maximum absolute errors in Δθa between the new model and HYDRUS-1D was 10% while the relative maximum absolute errors in Δθa between the SRVDM and HYDRUS-1D was 112%. In the experiments, the root mean square difference of the soil water content for the new model was lower than that for the SRVDM at the different soil depths. These results indicated that the new model outperformed the SRVDM in simulating Δθp and Δθa for diverse soil. It can be concluded that the new model was robust and reasonably accurate for diverse soils at different soil depths. The implementation of such model will improve the accuracy and applicability of regional soil water dynamics simulation and will reduce considerably the computational time and the required inputs.  相似文献   

杉木人工林对降水的截留作用   总被引：8，自引：2，他引：6  

樊后保 《福建林学院学报》1998,18(1):92-95

在对杉木人工林对降水的重新分配过程进行定位监测的基础上,本文详细分析了林内降水量、树干茎流量、林冠截留量及截留率与降水量的密切关系,并揭示出林分密度、降水强度、与前次降水的间隔时间对林冠截留的影响  相似文献   

Hydrus-3D模型模拟田间点源入渗与水分再分布准确性评价     

周广林  王全九  李云  苏李君 《干旱地区农业研究》2015,33(2):113-121

滴灌条件下水分入渗与再分布是评价滴灌灌溉效率的重要内容,通过Hydrus3D模型模拟单点源和点源交汇情况下水分入渗及其再分布过程,并利用田间试验实测资料进行验证。结果表明:采用Hydrus3D软件建立的模型可较好地模拟单点源水分入渗、水平湿润锋扩散过程及土壤剖面水分的分布情况,水平湿润锋距离的模拟值和实测值的误差在灌水结束时达到最大,且滴头流量越大,误差亦越明显,其中最大绝对误差为4.6 cm,最大相对误差达0.167,R2在0.95以上,F检验P值大于0.05,且RMSE在2.1以内;模型模拟的土壤体积含水量分布和实测值基本一致,模拟值和实测值的R2在0.90以上,F检验P值大于0.05,RMSE均小于0.07;湿润范围模拟结果和实测结果的吻合度较高。灌水结束后20 h,模拟土壤剖面含水量的分布情况与实测值基本一致,模拟值和实测值R2在0.575~0.652之间,F检验P值大于0.05,RMSE在0.013左右,双点源交汇区整个剖面模拟值和实测值R2为0.526以上,F检验P值大于0.05,RMSE均小于0.01,模拟结果较好,说明Hydrus3D模型可模拟土壤水分再分布情况。  相似文献