共查询到20条相似文献，搜索用时 15 毫秒
1.
Summary A numerical soil moisture dynamics model was developed for; wheat crop using either observed or generated root length densities with root sink incorporating diminishing rate of water uptake by plant roots due to decreasing soil moisture in drying cycles and loss of absorptive power of roots due to ageing. The simulated soil moisture contents were overestimated by 6.0 and 9.6% on an overall basis by the model when observed and generated root length densities were used, respectively, in comparison to observed moisture contents. The model using generated root length densities simulated less water uptake in comparison with the model which utilized observed root length densities. 相似文献
2.
Modeling water uptake by roots 总被引：12，自引：0，他引：12
W. R. Gardner 《Irrigation Science》1991,12(3):109-114
Summary Most current models of the water uptake by plant roots from the soil profile solve the equation for flow of water in unsaturated soils. The boundary condition at the root-soil interface is represented, whether explicitly or implicitly by some kind of root distribution function. Such models have sufficient number of parameters so that they can be fitted to data reasonably well. Most water uptake patterns, when normalized with respect to root zone depth and plant extractable water reveal, remarkable similarities regardless of soil texture, plant species, or root distribution. This similarity is not predictable with current models. A model based upon non-linear behavior of the root membranes and described by a distributed sink moving downward through the soil profile adequately represents the uptake process. The shape of the sink function is not critical and only two parameters, a root depth parameter, and an extractable water parameter are needed. 相似文献
3.
基于BP神经网络的新安江模型初始土壤蓄水量计算研究 总被引：1，自引：0，他引：1
【目的】克服传统经验折减系数法在计算新安江模型初始土壤蓄水量方面的缺点,并提高新安江模型在湿润半湿润地区的应用效果。【方法】结合流域初始土壤蓄水量的影响因素和神经网络模型特点,提出构建基于BP神经网络的新安江模型初始土壤蓄水量计算方法。【结果】在3种输入因子组合方式下,当BP神经网络隐含层节点大于11时,模拟训练期模型应用效果达到项目精度评价指标的甲等水平,预测检验期的9个样本,均有6个以上样本检验合格;当BP神经网络隐含层节点数从4个变化到21个时,模型评价指标纳什效率系数从0.51变到0.97、均方根误差从11.77降到2.74;与采用传统经验折减系数法计算新安江模型初始土壤蓄水量相比,采用BP神经网络模型应用效果明显占优,且能克服经验折减系数法计算土壤初始蓄水量需要选择流域一场暴雨或久旱未雨才能开始计算和计算过程数据不能中断的缺点。【结论】在湿润半湿润地区采用BP神经网络模型计算新安江模型初始土壤蓄水量具有可行性和适用性;当神经网络输入因子和隐含层节点数选择合理时,模型模拟和预测精度较高。 相似文献
4.
The infiltration and redistribution of soil moisture under surface drip irrigation considering hysteresis were investigated in two soils (loamy sand and silt loam) of different texture. The effect of continuous versus intermittent application of 1, 2 and 4 l/h to the soils was evaluated in terms of wetting front advance patterns and deep percolation under the root zone. For this purpose, a cylindrical flow model incorporating hysteresis in the soil water retention characteristic curve, evaporation from the soil surface, and water extraction by roots was used. The results show that, compared with continuous irrigation, pulse irrigation slightly reduces the water losses under the root zone in both cases (with and without hysteresis). Also, at the total simulation time, in both types of irrigation, hysteresis reduces significantly the water losses under the root zone. Finally, the effect of hysteresis was found to be greater at higher discharge rate (4 l/h) and consequently at higher water content at the soil surface. 相似文献
5.
R. Subbaiah 《Irrigation Science》2013,31(3):225-258
Designing drip irrigation systems involve selection of an appropriate combination of emitter discharge rate and spacing between emitters for any given set of soil, crop, and climatic conditions, as well as understanding the wetted zone pattern around the emitter. The exact shape of the wetted volume and moisture distribution will depend on many factors, including soil hydraulic characteristics, initial conditions, emitter discharge rate, application frequency, root characteristics, evaporation, and transpiration. Multi-dimensional nature of water flow, plant uptake and high frequency of water application increase the complexity in modelling soil moisture dynamics from trickle irrigation. Researchers used analytical methods, semi-analytical methods and numerical methods to Richards’ equation using certain boundary conditions to model the infiltration from point source irrigation for use in design, install, and manage of drip irrigation systems due to their merits over direct measurements. Others developed models based on Green-Ampt equation, empirical models using regression techniques/dimensional analysis techniques/moment approach techniques/artificial neural networks on this topic to describe infiltration from a point/line sources. A review on these models developed under each category is presented in this study. Other knowledge gaps identified include (a) effect of variations in initial moisture content and packing conditions, (b) precision in observing the wetting front and soil–water content, (c) validity of soil surface boundary conditions, (d) effect of crop root architecture and its withdrawal pattern for different input parameters, (e) effects of gravitational gradients, (f) stratification in the soils, and (g) impact of soil hysteresis. The review promotes better understanding of the soil water dynamics under point source trickle emitters and helps to identify topics for more emphasis in future modelling activity. 相似文献
6.
Patterns of water withdrawal beneath an irrigated peach orchard on a red-brown earth 总被引：1，自引：0，他引：1
Summary Water withdrawal from the soil beneath an irrigated peach orchard is described over depth and time after irrigation for a red-brown earth where the hydraulic properties vary with depth. Relationships between water uptake by roots, root concentration and soil-water suction were explored over protracted drying cycles. In the early stages of drying water uptake by roots was well correlated with root concentration over the profile but, over time, water uptake was redistributed over the root system. Theoretical analysis suggests that poor utilization of water from depth on this soil was associated mainly with low root concentrations and low root (radial) conductance. Practical considerations for improved water management in the root zone of peach orchards on shallow soils are discussed. 相似文献
7.
A kinematic-wave model is developed for simulating the movement of soil moisture in unsaturated soils with plants. The model involves three free boundaries. Analytical solutions are derived when the plant roots are assumed to extract moisture at a constant rate and the upstream boundary condition is independent of time. Numerical solutions are the only resort when the moisture extraction and the upstream boundary condition both depend on time. 相似文献
8.
Debashis Chakraborty R.N. Garg Ravender Singh R.K. Singh R.B. Mittal K.H. Kamble 《Agricultural Water Management》2010,97(5):738-748
Field experiments were conducted in 2002-2003 and 2003-2004 to evaluate the relative performance of synthetic (black polyethylene) and organic (paddy husk and straw) mulches on soil and plant water status vis-a-vis N uptake in wheat in a semi-arid environment of India. Scope of better utilization of soil moisture was documented through all the mulches, especially during initial crop growth stages, when the moisture content was 1-3% higher in mulches. Soil temperature was more moderate under organic mulches. Paddy husk recorded significantly higher plant biomass, while the effect of mulching in enhancing root growth was clearly documented. Organic mulches produced more roots (25 and 40% higher root weight and root length densities compared to no-mulch) in sub-surface (>0.15 m) layers, probably due to greater retention of soil moisture in deeper layers and relatively narrow range of soil temperature changes under these systems. Incremental N dose significantly improved all the plant parameters in both mulch and no-mulch treatments. Grain yield was 13-21% higher under mulch and so with increasing N levels. Nitrogen uptake was higher in organic mulches and also with higher N doses, while polyethylene mulch showed mixed trend. Mulches were effective in reducing 3-11% crop water use and improved its efficiency by 25%. Grain yield and biomass were well-correlated with leaf area index (r = 0.87 and 0.91, respectively) and water use was better correlated with root length than its weight. Results indicated substantial improvement in water and N use efficiency and crop growth in wheat under surface mulching, and the organic mulches, especially rice husk performed better than synthetic mulches. 相似文献
9.
Simulation of soil water dynamics under subsurface drip irrigation from line sources 总被引：2，自引：0，他引：2
A mathematical model which describes water flow under subsurface drip lines taking into account root water uptake, evaporation of soil water from the soil surface and hysteresis in the soil water characteristic curve θ(H) is presented. The model performance in simulating soil water dynamics was evaluated by comparing the predicted soil water content values with both those of Hydrus 2D model and those of an analytical solution for a buried single strip source. Soil water distribution patterns for three soils (loamy sand, silt, silty clay loam) and two discharge rates (2 and 4 l m−1 h−1) at four different times are presented. The numerical results showed that the soil wetting pattern mainly depends on soil hydraulic properties; that at a time equal to irrigation duration decreasing the discharge rate of the line sources but maintaining the applied irrigation depth, the vertical and horizontal components of the wetting front were increased; that at a time equal to the total simulation time the discharge rate has no effect on the actual transpiration and actual soil evaporation and a small effect on deep percolation. Also the numerical results showed that when the soil evaporation is neglected the soil water is more easily taken up by the plant roots. 相似文献
10.
11.
滴灌紫花苜蓿根层水分稳定同位素特征分析 总被引：1，自引：0，他引：1
为了明确滴灌紫花苜蓿根层水分运移,进一步阐明滴灌节水机理,采用液态水稳定氢氧同位素技术,分析了滴灌紫花苜蓿根层水分稳定氢氧同位素分布特征。结果表明,紫花苜蓿根层水分稳定氢氧同位素在下层富集,且随土壤剖面深度的增加同位素富集量有增加的趋势。滴灌条件下,紫花苜蓿根层发育有较多细根,可迅速而高效地利用灌溉水,灌溉后紫花苜蓿对灌溉水的利用不明确偏向于某一深度土层,根层内各土层土壤水均有利用。灌溉前土壤干旱时,滴灌紫花苜蓿以30 cm上下土层土壤水作为主要水分来源的概率较高。 相似文献
12.
为了研究冬小麦根系吸水深度,应用塑料管土柱法在田间进行冬小麦种植试验,测定了冬小麦越冬期、拔节期、抽穗期、灌浆期和成熟期不同土层深度土壤水稳定同位素值,并应用耦合模型和IsoSource多元线性模型对比分析了水源贡献率。结果表明,冬小麦在越冬期、返青期主要利用0~20 cm土层的土壤水,拔节期主要吸水深度为0~40 cm;抽穗期,基于耦合模型的主要吸水深度为0~40 cm,基于IsoSource多元线性模型的为0~40 cm和80~180 cm;灌浆期,基于耦合模型和IsoSource多元线性模型的主要不同吸水深度为180~200 cm,且基于耦合模型的该层贡献率明显高于IsoSource多元线性模型;成熟期主要利用0~40 cm和80~100 cm土层的土壤水,基于2种模型的分析结果相同。应用耦合模型求解贡献率,当分组较多且组间水稳定同位素差异较小时,应结合其他方法来保证其准确性。 相似文献
13.
《Agricultural Water Management》1999,41(1):57-70
The salinity condition in the root zone hinders moisture extraction from soil by plants, because of osmotic potential development in soil water due to presence of salts, which ultimately, decreases transpiration of plants and thereby affects crop yield. Therefore, an effort was made in this study to quantify the impact of salinity on soil water availability to plants. The movement of salts under irrigation and evapotranspiration regimes in root zone of soil profile was studied throughout the growing season of wheat crop with adopting exponential pattern of root water uptake. A model was developed to analyze soil water balance to find out moisture deficit because of salinity. A non-linear relationship was formulated between moisture content and salt concentration for simultaneous prediction. The Crank–Nicolson method of Finite Differencing was used to solve the differential equations of soil water and solute transport. The effect of various salt concentrations on transpiration was analyzed to develop a relationship between relative evapotranspiration and relative yield. Relationships among salt concentration, matric potential, moisture deficit and actual transpiration were also established to provide better understanding about impact of salinization and to provide guidelines for obtaining better crop yields in saline soils. 相似文献
14.
Root growth, grain yield and water uptake by wheat in relation to soil water regime and depth of nitrogen (N) placement were studied in metallic cylinders filled with loamy sand soil. Root-length and -weight densities were greater under irrigated than under unirrigated conditions and they increased with deep placement as compared to surface mixing of fertilizer N. The differences were relatively larger in the deeper than in the upper soil layers and increased during later stages of plant growth. Under non-irrigated conditions, constant water table at 100 cm depth produced maximum root growth in the top 30 cm soil. Water uptake rate increased with increase in root density depending on root age and soil water status. Dry matter accumulation at different stages of plant growth and grain yield varied significantly with moisture regime and depth of N placement. Deep placement of fertilizer N under shallow water table and non-irrigated conditions caused greater root growth, better water utilization and a higher production. 相似文献
15.
16.
《Agricultural Water Management》2003,62(2):79-91
UPFLOW is a simple software tool developed to estimate with limited data availability and appropriate assumptions the expected upward water movement from a shallow water table to the root zone during a specific period (typically 10-day) in a specific environment. The program contains various sets of soil water retention curves that are considered as representative for various soil classes and indicative values for root water extraction for a number of crops. The environmental conditions are specified in fields of a spreadsheet type Main Menu by specifying: (i) the average evapotranspiration (ET) demand of the atmosphere during the period under consideration, (ii) the expected soil wetness in the topsoil as a result of rain during that period, (iii) the depth of groundwater below the soil surface, (iv) the water extraction pattern of the plant roots, (v) the thickness and characteristics of successive layers of the soil profile and (vi) the salt content of the water table. A steady state upward flow is assumed during the period. The simulations are in line with indicative values presented in literature. Additionally, the software displays the deficient aeration conditions in the root zone and its effect on crop evapotranspiration when the groundwater is close to the soil surface.The model was used to estimate the capillary rise from shallow groundwater (1–1.5 m) to the root zone (0.4–0.6 m) of horticultural crops in loamy sand and sandy loam soils in Belgium. The field measurements confirm that UPFLOW simulates the correct order of magnitude of the capillary rise to the root zone.UPFLOW is public domain software and hence freely available. An installation disk and manual can be downloaded from the web. 相似文献
17.
Root system parameters determining water uptake of field crops 总被引：2，自引：0，他引：2
Summary The distribution of a crop rooting system can be defined by root length density (RD), root length (RL) per soil layer of depth z, sum of root length (SRL) in the soil profile (total root length) or rooting depth (z
r
. The combined influence of these root system parameters on water uptake is not well understood. In the present study, field data are evaluated and an attempt is made to relate a daily maximum water uptake rate (WUmax) per unit soil volume as measured in different soil layers of the profile to relevant parameters of the root system. We hypothesize that local uptake rate is at its maximum when neither soil nor root characteristics limit water flow to, and uptake by, roots. Leaf area index and the potential evapotranspiration rate (ET
p
) are also important in determining WUmax, since these quantities influence transpiration and hence total crop water uptake rate. Field studies in Germany and in Western Australia showed that WUmax depends on RD. In general, there was a strong correlation between the maximum water uptake rate of a soil layer (LWUmax) normalized by ET
p
and RL normalized by SRL. The quantity LWUmax · ET
p
-1
was linearly related to (RL/SRL)1/2. The data show that the single root model will not predict the influence of RD on WUmax correctly under field conditions when water-extracting neighboring roots may cause non-steady-state conditions within the time span of sequential observations. Since the rooting depth z
r
was linearly related to (SRL)1/2, the relation: LWUmax · ET
p
-1
= f (RL1/2/z
r
) holds. Furthermore it was found that the maximum specific uptake rate per cm root length URmax was inversely related to RD1/2 and to SRL1/2 or z
r
of the profile. Observed high specific uptake rates of shallow rooted crops might be explained not only by their lower RD-values but also by the additional effect of a low z
r
. The relations found in this paper are helpful for realistically describing the sink term of dynamic water uptake models.Growing plants extract water from the soil to meet transpiration needs. Rates of transpiration and of water uptake are set by evaporative demand and by plant and soil factors which influence capacity to meet that demand. These factors include crop canopy size and leaf characteristics, root system characteristics and hydraulic properties of the soil and the soil-root interface. Soil and root system properties vary with depth and all factors vary in time, so that parameters related to them require constant updating over a crop season.Dynamic simulation models describe water uptake by root systems under field conditions as a function of soil depth and time. Many of these simulation approaches are based on Gardner's (1960) single root model (Feddes 1981). These simulation procedures follow the assumption that water uptake is proportional to a difference in water potential between the bulk soil and the root surface or the plant interior, to the hydraulic conductivity of the soil-plant system and to the effectiveness of competing roots in water uptake. The effectiveness factor accounts more or less empirically for the influence of various root system parameters on water uptake such as percentage of active roots absorbing water, root surface permeability, root length density determining the distance between neighbouring roots, or total root length and depth of the root system. Such models however, will not always reflect correctly the influence of root system characteristics on water uptake since these assumptions have rarely been tested under field conditions. In many instances, there is better agreement between simulated and measured total water use of plants than between predicted and observed water depletion by roots within individual layers of the soil profile (Alaerts et al. 1985).Water uptake by an expanding root system as a function of depth and time has been studied under field conditions for several crops (listed in Herkelrath et al. 1977a; Feddes 1981; Hamblin 1985). They show that the dynamics of water uptake depend on root length density and the availability of soil water. However, the combined influence of root length density, total root length and rooting depth on the water uptake pattern has not been assessed. An evaluation of root system parameters with respect to soil water extraction should aid our understanding of how roots perform under field conditions and may assist our efforts to formulate the water uptake function of roots in dynamic simulation studies more realistically.The aim of the present investigation is to develop an approach that relates measured water uptake rates to relevant parameters of the root systems. This approach will be confined to situations where water uptake in a soil layer is not restricted by unfavorable soil conditions, such as in wet soil, by insufficient aeration and, in dry soil, by reduced water flow towards roots or by increased contact resistance (Herkelrath et al. 1977b). We will define a maximum water uptake rate WUmax that is neither soil-limited nor appreciably limited by the decreasing permeability of aging roots. This WUmax will be related to relevant root system parameters as they exist when WUmax is observed. Hence, water uptake by roots in a very wet, as well as in a dry soil, has been excluded from consideration. 相似文献
18.
质地和根系深度对水分探头埋设的仿真模拟 总被引：1，自引：0，他引：1
利用Hydrus-1D模型模拟不同植物根系深度和不同土壤质地条件下的土壤水分动态与平衡,研究了根系分布深度和质地对控制灌溉土壤水分探头埋设深度的影响,并利用试验进行了验证. 土壤质地和植物根系分布深度对探头埋设深度有显著影响,砂壤土和壤土分别采用高频低灌量和低频率高灌量的方法.浅根系植物（10 cm）在砂壤土条件下探头埋设5 cm深度最佳,但是根系深度增大到30 cm,探头应该埋设到20 cm深度.对壤土而言,利用位于根系1/2至1/3处的探头控制灌溉. 太浅的埋设深度会导致灌溉频率增大,太深的埋设可能造成植物缺水.黏土条件下,结果较为复杂,探头的埋设深度需要田间试验研究. 研究结果表明：针对具体植物,因其需水规律和生理特征的不同,根据植物需水规律来调整探头的控制范围达到高效节水目的. 相似文献
19.
为解决植物根系原位三维观测的技术难题,采用XCT层析成像技术获取原位根系的断层序列图像,然后利用计算机图像图形处理技术实现对植物根系的原位三维可视化.为了提高图像分割的精确性,提出一种利用根系几何形态特征的综合分割方法,有效清除了与根系密度极其近似的杂质体素,完成了对序列图像的三维分割.并利用VTK工具箱采用移动立方体算法(MC)实现了对分割后序列图像的三维重建.编程实验证实,本文提出的技术路线和方法能够有效地实现对生长在介质环境中原位根系的三维可视化观测. 相似文献
20.
根系吸水模型参数的混合遗传算法估算方法 总被引：2，自引：0，他引：2
构建了遗传算法与Levenberg-Marquardt算法相结合的混合遗传算法,用于求解根系吸水模型参数.分别进行数值试验和棉花根系吸水试验对混合遗传算法求解精度进行验证.数值试验表明,采用混合遗传算法优化求解根系吸水模型参数的优化值具有较高的精度,含水率资料的时间步长和空间步长对根系吸水模型参数的优化精度有较大影响,在实际中时间步长可取值5～10 d,空间步长取值5～10 cm.对室内棉花根系吸水进行模拟分析,结果表明混合遗传算法求解的根系吸水模型可以很好地模拟根系吸水.该方法可用于求解根系吸水参数. 相似文献