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1.
The compensation heat-pulse method for measuring sap flow is tested here in olive trees (Olea europaea L.). We describe a rigorous three-way examination of the robustness of the technique for this species, and examine the potential of the technique for an automatic control of the irrigation system. Two tests were carried out using heat-pulse gear inserted into the stem of 12-year-old ‘Manzanilla’ olive trees. One test used forced-flow through a stem section, and the other involved measured water uptake by an excised tree. The measured sap flow in these two tests was in agreement with calculations from heat-pulse velocities when using a standard ‘wound correction’ to account for the presence of the probes and the disruption to the sap flow. Thus, this technique for monitoring transpiration can, we feel, be used with confidence in olives.The third experiment was carried out in the field, where we analysed sap flow data from two 29-year-old olive trees — one tree was under regular drip irrigation and the other was from dry-farming conditions. We use measurements of sap flow in the trunk to examine the hydraulic functioning of the tree, and to explore some diagnostics of water stress. Our heat-pulse measurements in the irrigated olive tree exhibited a profile of sap flow that was weighted towards the outer xylem of the tree trunk while the water-stressed trees in the field showed a profile of sap flow weighted towards the centre of the trunk. The loss of hydraulic functioning in the outermost section of the vascular system, as a result of water stress, we consider to be due both to stomatal control and to embolisms in the xylem vessels.The fourth experiment was also carried out in the field, in which sap flow measurements were made at three locations in the trunk as well as in two roots of another 29-year-old olive tree. The soil explored by each root, on opposite sides of the trunk, was differentially wetted by separate irrigation of each side. Our data showed that the surface roots were able to absorb water immediately after wetting, despite a reasonably prolonged period of moderate drought. Root activity quickly shifted to the regions where the soil had been wetted. A root in dry soil exhibited no flow at night, whereas sap flows of about 0.02 l h−1 were measured around midnight in the root drawing water from the wetter soil. Our observations suggest that the hydraulic behaviour of the trunk and surface roots might be used as a diagnostic of the onset, or severity, of water stress. Here there is not the imperative to replicate, for the prime goal is not transpiration estimation. Rather interpretation of the diurnal dynamics is used to infer the onset, or severity of water stress.The compensation heat-pulse seems a suitable technique for automatically controlling the irrigation system of olives, and probably other trees, based either on the estimation of the short-time dynamics of transpiration, or on changes in the hydraulic behaviour of the trees.  相似文献   

2.
Sprinkler irrigation efficiency declines when applied water intercepted by the crop foliage, or gross interception (Igross), as well as airborne droplets and ponded water at the soil surface evaporate before use by the crop. However, evaporation of applied water can also supply some of the atmospheric demands usually met by plant transpiration. Any suppression of crop transpiration from the irrigated area as compared to a non-irrigated area can be subtracted from Igross irrigation application losses for a reduced, or net, interception (Inet) loss. This study was conducted to determine the extent in which transpiration suppression due to microclimatic modification resulting from evaporation of plant-intercepted water and/or of applied water can reduce total sprinkler irrigation application losses of impact sprinkler and low energy precision application (LEPA) irrigation systems. Fully irrigated corn (Zea Mays L.) was grown on 0.75 m wide east-west rows in 1990 at Bushland, TX in two contiguous 5-ha fields, each containing a weighing lysimeter and micrometeorological instrumentation. Transpiration (Tr) was measured using heat balance sap flow gauges. During and following an impact sprinkler irrigation, within-canopy vapor pressure deficit and canopy temperature declined sharply due to canopyintercepted water and microclimatic modification from evaporation. For an average day time impact irrigation application of 21 mm, estimated average Igross loss was 10.7%, but the resulting suppression of measured Tr by 50% or more during the irrigation reduced Igross loss by 3.9%. On days of high solar radiation, continued transpiration suppression following the irrigation reduced Igross loss an additional 1.2%. Further 4–6% reductions in Igross losses were predicted when aerodynamic and canopy resistances were considered. Irrigation water applied only at the soil surface by LEPA irrigation had little effect on the microclimate within the canopy and consequently on Tr or ET, or irrigation application efficiency.  相似文献   

3.
The dual crop coefficient approach accounts separately for plant transpiration and soil evaporation by using the basal crop coefficient and the evaporation coefficient, respectively. The SIMDualKc model, which performs the soil water balance simulation with estimation of the actual crop evapotranspiration (ET) with the dual crop coefficient approach, was applied to a drip-irrigated peach orchard under Mediterranean conditions. Orchard ET was obtained with the eddy covariance technique, which was subsequently correlated with tree transpiration estimated from sap flow measurements and soil evaporation determined with microlysimeters, thus providing ET for the whole irrigation season. Two years of field observations were used for model calibration and validation using those ET measurements and taking into account the fraction of ground covered by trees through a density factor which adjusts the basal crop coefficient. Model fitting relative to ET observations during calibration and validation provided indices of agreement averaging 0.90, coefficients of regression close to 1.0, root mean square errors around 0.41 mm and average absolute errors of 0.32 mm. Model fitting relative to transpiration and to soil evaporation produced similar results, so showing the adequateness of modelling.  相似文献   

4.
Sap flow measurements based on the heat balance method offers the opportunity to evaluate directly and quite easily the mass flow rate of water in plants. However, extrapolation of measurements of water use by individual stems to that for a canopy is tricky. In the present study, 14 sugarcane stems, out of a canopy of nearly 200 000, were equipped with Dynamax sap flow gauge. We extrapolated these individual measurements to determine the transpiration of the canopy and compare this transpiration to the crop evapotranspiration calculated on the basis of the Penman–Monteith method. The method used for the extrapolation assumes that the transpiration of a sugarcane plant is proportional to its leaf area. Transpiration of the canopy determined by this method was overestimated by more 35% as compared to the reference evapotranspiration results. Different sources of possible errors were examined and lead to suppose that it is very difficult to determine the transpiration of a heterogeneous canopy in growth by using the sap flow measurement technique.  相似文献   

5.
日光温室负压自动灌溉下番茄蒸腾规律研究   总被引：3，自引：0，他引：3  
李邵  耿伟  薛绪掌  郭文善 《节水灌溉》2008,(1):25-28,32
针对农业生产中蔬菜栽培灌溉费水费时的现状,采用一种自制负压自动灌溉系统,将供水压力设定在负值,利用土壤自动吸水的特性,达到自动灌溉和节水的效果.在此系统灌溉下采用茎热平衡技术测定番茄植株的茎流规律,分析了茎流变化规律与环境因子之间的关系,同时分析了番茄植株不同部位茎流差异以及剪叶对番茄植株茎流的影响.结果表明,在设定灌溉系统负压为60 hPa下,温室土壤含水量基本控制在阴天20.19%、晴天18.75%左右;茎流数据表明番茄植株蒸腾与太阳辐射值呈显著正相关,适当遮阴降温可以减少植株蒸腾.实验也进一步证明了叶片是植株蒸腾的主要器官,植株底层叶片蒸腾速率相对较微弱.  相似文献   

6.
The main goal of this research was to evaluate the potential of the dual approach of FAO-56 for estimating actual crop evapotranspiration (AET) and its components (crop transpiration and soil evaporation) of an olive (Olea europaea L.) orchard in the semi-arid region of Tensift-basin (central of Morocco). Two years (2003 and 2004) of continuous measurements of AET with the eddy-covariance technique were used to test the performance of the model. The results showed that, by using the local values of basal crop coefficients, the approach simulates reasonably well AET over two growing seasons. The Root Mean Square Error (RMSE) between measured and simulated AET values during 2003 and 2004 were respectively about 0.54 and 0.71 mm per day. The basal crop coefficient (Kcb) value obtained for the olive orchard was similar in both seasons with an average of 0.54. This value was lower than that suggested by the FAO-56 (0.62). Similarly, the single approach of FAO-56 has been tested in the previous work (Er-Raki et al., 2008) over the same study site and it has been shown that this approach also simulates correctly AET when using the local crop coefficient and under no stress conditions.Since the dual approach predicts separately soil evaporation and plant transpiration, an attempt was made to compare the simulated components of AET with measurements obtained through a combination of eddy covariance and scaled-up sap flow measurements. The results showed that the model gives an acceptable estimate of plant transpiration and soil evaporation. The associated RMSE of plant transpiration and soil evaporation were 0.59 and 0.73 mm per day, respectively.Additionally, the irrigation efficiency was investigated by comparing the irrigation scheduling design used by the farmer to those recommended by the FAO model. It was found that although the amount of irrigation applied by the farmer (800 mm) during the growing season of olives was twice that recommended one by the FAO model (411 mm), the vegetation suffered from water stress during the summer. Such behaviour can be explained by inadequate distribution of irrigation. Consequently, the FAO model can be considered as a potentially useful tool for planning irrigation schedules on an operational basis.  相似文献   

7.
Large areas of vineyards have been established in recent years in arid region of northwest China, despite limited water resources. Water to support these vineyards is mainly supplied by irrigation. Accurate estimation of vineyard evapotranspiration (ET) can provide a scientific basis for developing irrigation management. Transpiration and soil evaporation, as two main components of ET, were measured separately in a vineyard in this region by heat balance sap flow system and micro-lysimeters during the growing season of 2009. Diurnal and seasonal dynamics of sap flow and its environmental controls were analyzed. Daily sap flow rate (SRl) increased linearly with solar radiation (Rs), but showed an exponential increase to its maximum curve as a function of vapor pressure deficit (VPD). Residuals of the two regressions both depended on volumetric soil water content to a depth of 1.0 m (VWC). VWC also significantly influenced SRl. The relationship of them could be expressed by a piecewise regression with the turnover point of VWC = 0.188 cm3 cm−3, which was ∼60% of the field capacity. Conversely, soil evaporation (Es) increased exponentially with VWC. Thus, we recommended keeping VWC in such vineyards slightly above ∼60% of the field capacity to maintain transpiration while reducing soil evaporation. Vineyard transpiration (Ts) was scaled from sap flow by using leaf area (Al) as it explained 60% of the spatial variability of sap flow. Vine transpiration was 202.0 mm during the period from April 28 to October 5; while that of Es was 181.0 mm. The sum of these two components was very close to ET estimated by the Bowen ratio energy balance method (386.9 mm), demonstrating the applicability of sap flow for measuring grape water use in this region.  相似文献   

8.
植物茎干液流量可表征其蒸腾耗水量,反映植被水分传输状况,可用于计算植被生态需水量。以玛纳斯河流域古尔班通古特沙漠南缘典型荒漠植被梭梭、柽柳为研究对象,通过数据监测,研究植被茎干液流及光合蒸腾特性,分析气象因子及土壤含水率对茎干液流的影响。结果表明：（1）梭梭、柽柳茎干液流速率呈明显的昼夜变化规律,白天液流速率远高于夜间。（2）梭梭的净光合速率日变化模式为双峰型;柽柳为单峰型。（3）梭梭蒸腾速率的日变化有明显上升和下降过程,柽柳趋势不明显,呈小幅震荡。（4）液流速率变化与相对空气湿度呈负相关,空气湿度高时液流速率低;气温、总辐射与液流速率的变化趋势基本一致,液流速率随着气温或总辐射的增强而增大。（5）随着土壤含水率降低,液流速率降低。  相似文献   

9.
Quantifying the soil water deficit (SWD) and its relation to canopy or leaf conductance is essential for application of the Penman–Monteith equation to water-stressed plants. As the water uptake of a single root depends on the water content of the soil in its immediate vicinity, the non-uniform distribution of water and roots in the soil profile does not allow simple quantification of SWD from soil-based measurements. Using measurements of stem sap flux (with a heat pulse technique), soil evaporation (with micro-lysimeters) and meteorological parameters the canopy conductance was obtained through inversion of the Penman–Monteith equation. SWD was evaluated by averaging the soil water content profile of the root zone (monitored by layers with the TDR sensors) weighted by root distribution of the layers. The average canopy conductance at midday (11:00–15:00, Israel Summer Time), denoted as Gnoon, was computed for each day of the experimental period. Stable summer weather, typical of the Mediterranean region, and the fully developed crop canopy, made water stress the only plausible cause of a Gnoon decline. However, the daily decline of Gnoon did not occur at the same weighted average soil water content during the successive drying cycles. For the cycle with less irrigation, the decline in Gnoon occurred at higher soil moisture levels. Alternatively, when SWD was determined from the water balance, i.e., by defining water deficit as irrigation minus accumulated evapotranspiration, the Gnoon decline occurred at the same value of water deficit for all irrigation cycles. We conclude that a climate-based soil water balance model is a better means of quantifying SWD than a solely soil-based measurement.  相似文献   

10.
Prediction of plant water status is necessary for the judicious application of regulated deficit irrigation. CropSyst, a generic crop growth model that is applicable to fruit trees, was used to forecast plant water potential for irrigation management recommendations in a pear orchard. Plant water potential is predicted along with tree transpiration using Ohm’s law analogy. The parameters of the model were adjusted by using field measured data on a lysimeter-grown pear tree. After adjustment, and using the same lysimeter data, a satisfactory agreement was found between simulated and measured tree transpiration, light interception, and stem water potential. Model simulations were also performed for other independent field data. These corresponded to eight different conditions of a deficit-irrigated field experiment in a pear orchard. Each condition differed in soil texture, time of irrigation cut-off, crop load, and tree leaf area. Deficit irrigation was managed first by withholding irrigation until reaching a threshold in midday stem water potential of −1.5 MPa. Subsequently, irrigation was applied at fixed proportions of full irrigation requirements. Simulations with CropSyst were used as decision support system that could work independently of stem water potential measurements. Simulations in all eight sites were satisfactory at providing adequate time without irrigation during the first part of the deficit period. A highly significant relationship (r 2  = 0.71) between predicted and measured stem water potentials was found for a simulation period of 40 days. Simulations for longer periods (i.e. 74 days) decreased the r 2 to 0.61, and for this reason after resuming irrigation, slight deviations were found for the average stem water potential in two out of five sites. In conclusion, CropSyst produced relevant information for managing deficit irrigation in simulation periods shorter than 40 days.  相似文献   

11.
Because of the increasing worldwide shortage of freshwater and costs of irrigation, a new plant-based irrigation scheduling method is proposed. In this method, two real-time plant-based measurements (sap flow and stem diameter variations) are used in combination with a mathematical water flow and storage model in order to predict the stem water potential. The amount of required irrigation water is derived from a time integration of the sap flow profile, while the timing of the irrigation is controlled based on a reference value for the predicted stem water potential. This reference value is derived from the relationship between midday values of maximum photosynthesis rates and stem water potential. Since modelling is an important part of the proposed methodology, a thorough mathematical analysis (identifiability analysis) of the model was performed. This analysis showed that an initial (offline) model calibration was needed based on measurements of sap flow, stem diameter variation and stem water potential. Regarding irrigation scheduling, however, only sap flow and stem diameter variation measurements are needed for online simulation and daily model calibration. Model calibration is performed using a moving window of 4 days of past data of stem diameter variations. The research tool STACI (Software Tool for Automatic Control of Irrigation) was used to optimally combine the continuous measurements, the mathematical modelling and the real-time irrigation scheduling. The new methodology was successfully tested in a pilot-scale setup with young potted apple trees (Malus domestica Borkh) and its performance was critically evaluated.  相似文献   

12.
Summary A field experiment was conducted on the west side of the San Joaquin Valley in California to determine water use, crop growth, yield and water use efficiency of Acala (SJ-2) cotton (Gossypium hirsutum L.) grown in 0.5 m spaced rows on a Panoche clay loam soil (Typic Torriorthents). Evapotranspiration was determined by water balance techniques utilizing neutron soil moisture measurements. All neutron measurements were made within a 3 m soil profile in 0.20 m increments. The measured evapotranspiration was compared to climatic estimates of potential evapotranspiration, and to calculations using a one-dimensional soil water balance model that separately computed soil water evaporation and plant transpiration. Crop growth was determined by weekly destructive plant sampling. Leaf area was determined along with dry matter components of leaves, stems, fruiting parts (flowers and squares) and bolls. Final yield was determined by machine harvesting (brush stripper) 720 m2 from each plot. Lint yields and fiber quality were determined by sample ginning and fiber analysis at the U.S. Cotton Research Station at Shafter, California. Three irrigation regimes were established that resulted in an evapotranspiration range from a high deficit condition to full irrigation at the calculated atmospheric demand.The measured evapotranspiration of narrow row cotton under a full irrigation regime was 778 mm, 594 mm under a limited irrigation regime and 441 mm under a regime with no post-plant irrigation. The evapotranspiration from these irrigation treatments was accurately simulated by a water balance model. that used inputs of potential evapotranspiration, leaf area index, soil water holding capacity and root development.The average lint yield from narrow row cotton with a full irrigation regime was 1583 kg/ha, the average lint yield from a limited irrigation regime was 1423 kg/ha and the average lint yield from a treatment with no postplant irrigation (fully recharged soil profile at planting) was 601 kg/ha. The full irrigation regime resulted in a dry matter production of approximately 16 t/ha while the limited irrigated regime produce 11 t/ha and the no-postplant irrigation regime produced 7 t/ha of dry matter. The fiber quality results indicated significant (0.05 level) differences only in 50% span length and micronaire, with the 2.5% span length, uniformity index, elongation and strength indicating no difference.Cotton lint yield was found to be directly related to total evapotranspiration although the relationship was slightly non-linear while dry matter yield was found to be linearly related to evapotranspiration. Both lint and dry matter yield were found to have a linear relationship to estimated transpiration from the water balance model calculations.Contribution from the Unived States Department of Agriculture, Agricultural Research Service, Western Region and the University of California  相似文献   

13.
Plant water status is a key factor impacting crop growth and agricultural water management. Crop water stress may alter canopy temperature, the energy balance, transpiration, photosynthesis, canopy water use efficiency, and crop yield. The objective of this study was to calculate the Crop Water Stress Index (CWSI) from canopy temperature and energy balance measurements and evaluate the utility of CWSI to quantify water stress by comparing CWSI to latent heat and carbon dioxide (CO2) flux measurements over canopies of winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.). The experiment was conducted at the Yucheng Integrated Agricultural Experimental Station of the Chinese Academy of Sciences from 2003 to 2005. Latent heat and CO2 fluxes (by eddy covariance), canopy and air temperature, relative humidity, net radiation, wind speed, and soil heat flux were averaged at half-hour intervals. Leaf area index and crop height were measured every 7 days. CWSI was calculated from measured canopy-air temperature differences using the Jackson method. Under high net radiation conditions (greater than 500 W m−2), calculated values of minimum canopy-air temperature differences were similar to previously published empirically determined non-water-stressed baselines. Valid measures of CWSI were only obtained when canopy closure minimized the influence of viewed soil on infrared canopy temperature measurements (leaf area index was greater than 2.5 m2 m−2). Wheat and maize latent heat flux and canopy CO2 flux generally decreased linearly with increases in CWSI when net radiation levels were greater than 300 W m−2. The responses of latent heat flux and CO2 flux to CWSI did not demonstrate a consistent relationship in wheat that would recommend it as a reliable water stress quantification tool. The responses of latent heat flux and CO2 flux to CWSI were more consistent in maize, suggesting that CWSI could be useful in identifying and quantifying water stress conditions when net radiation was greater than 300 W m−2. The results suggest that CWSI calculated by the Jackson method under varying solar radiation and wind speed conditions may be used for irrigation scheduling and agricultural water management of maize in irrigated agricultural regions, such as the North China Plain.  相似文献   

14.
Many models for water flow in cropped soil contain parameters such as rooting density, root permeability, and root water potential. Usually these parameters are chosen by trial-and-error method and direct measurements are difficult and impractical in some cases. This study presents a simulation model capable of analyzing water transport dynamics in a soil–plant–atmosphere continuum (SPAC). This model is developed by combining an existing mathematical model for soil water flow, a modified transpiration model taking into account of the air pressure and diurnal changes of the extinction coefficient of crop canopies, and a new simple model for root water uptake. Using data from lysimeters in a field experiment carried out on a wheat crop, we also developed two new empirical equations for the estimation of total canopy resistance and soil evaporation.We then applied the model for 2 years (1990–1991, 1991–1992) on winter wheat in a semiarid area of northwest China. Required parameters, particularly soil hydraulic and crop parameters, were determined by field and laboratory tests. Outputs from the simulation were in good agreement with the independent field measurements of seasonal changes in soil water content, canopy transpiration, surface evaporation, and root water uptake along the soil profile. In addition, this simulation agreed well with the actual measurements of seasonal crop water consumption and soil water balance among the treatments for different irrigation amounts.  相似文献   

15.
The oft-touted reason for the efficiency of drip irrigation is that roots can preferentially take up water from localised zones of water availability. Here we provide definitive evidence of this phenomenon. The heat-pulse technique was used to monitor rates of sap flow in the stem and in two large surface roots of a 14 year old apple tree (Malus domestica Borkh. cv. Braeburn). The aim was to determine the ability of an apple tree to modify its pattern of root water uptake in response to local changes in soil water content. We monitored the water status of the soil close to the instrumented roots by using time domain reflectometry (TDR) to measure the soil's volumetric water content, θ, and by using ceramic-tipped tensiometers to measure the soil's matric pressure head, h. A variation in soil water content surrounding the two roots was achieved by supplying a single localised irrigation to just one root, while the other root remained unwatered. Sap flow in the wetted root increased straight away by 50% following this drip irrigation which wetted the soil over a zone of approximately 0.6 m in diameter and 0.25 m in depth. Sap flow in the wetted root remained elevated for a period of about 10 days, that is until most of the irrigation water had been consumed. A comparative study of localised and uniform irrigation was then made. Following irrigation over the full root zone no further change in sap flow in the previously wetted root was observed when referenced to the corresponding sap flow measured in the stem of the apple tree. However sap flow in the previously dry root responded to subsequent irrigations by increasing its flow rate by almost 50%. These results show that apple roots have the capacity to transfer water from local wet areas at much higher rates than normally occurs when the entire root zone is supplied with water. They are also able to shift rapidly their pattern of uptake and begin to extract water preferentially from those regions where it is more freely available. Such an ability supports the use of drip irrigation for the efficient use of scarce water resources. We conclude that the soil-to-root pathway represents a major resistance to water uptake by apple, even at the relatively high soil water pressure heads developed during parts of this experiment, during which the tree was not even under any stress.  相似文献   

16.
为探明滴灌条件下温室番茄植株茎流速率变化规律及其影响因素,本文采用Dynamax公司开发的包裹式茎流计观测日光温室番茄植株的茎流变化,研究茎流速率的变化规律及茎流速率监测结果的标准化处理技术,探索植株茎流与气象因子的相互关系,分析水分胁迫对番茄植株茎流速率的影响。研究表明,采用单位叶面积上的茎流速率表征茎流变化规律可在一定程度上降低因探头安装位置不同对监测结果的影响;在充分供水条件下,影响番茄植株茎流速率的主要因子是太阳辐射和饱和水气压差,番茄植株的日茎流速率与太阳辐射呈线性关系,与饱和差呈对数关系（R2＞0.90,P＜0.01）;土壤水分状况会明显影响番茄植株茎流状况,茎流速率随水分胁迫加剧而骤减。研究结果证明番茄植株茎流速率经标准化处理后可以真实的反映植株蒸腾规律。  相似文献   

17.
Water transfers within mixed crops systems are complicated to understand due to the large number of complex interactions between the various components. Standard techniques fail to provide the proper assessment of the components of the water balance. Experiments and modeling developments are used to understand the dynamics of water transfers within the association of olive trees with annual crops under irrigation in Central Tunisia. The whole system is represented by a unit area made up of three components: a plot with the annual crop, a plot with the olive tree and a plot of bare soil. The modeling approach is based on the concept of reservoir. The model works on a daily time step and accounts for the lateral transfers of water occurring between the components of the system: (i) the water uptake by the roots of olive trees; (ii) the physical flow of water between the irrigated plot and the non-irrigated ones. A field experiment was carried out during 2 years (2002, 2003) and three crop cycles (spring potato, spring pea and autumn potato) in order to calibrate the model and test its validity. Olive tree transpiration was estimated from sap flow measurements and soil moisture in the different compartments was measured by neutron probe technique. The experimental data compare fairly well with the model outputs. The first purpose of the model is to understand the functioning of the olive tree–annual crop association from a water standpoint, but it can be easily extended to other intercropping systems mixing perennial vegetation with annual crops or used as a management tool. The estimates of the water extracted by the olive trees in each reservoir appear to be much more significant than those of the water physically transferred between reservoirs.  相似文献   

18.
温室作物需水信息指标及湿度控制   总被引：2，自引：1，他引：2  
在温室土壤－作物－环境连续体中，作物水分损耗、吸收和水分利用一直是研究的热点。在温室内，作物精量灌溉必须要考虑何时灌和灌多少两个方面的问题。从冠层蒸腾速率、茎流、水势、叶温和作物水分胁迫系数、茎秆果的直径微变化、根源信号、作物生长器官的电特性及图像特征技术方面，回顾和评价了作物水分状况诊断方法中作物需水信息指标的研究进展及存在的问题。同时，为防止过量灌溉带来的高湿矛盾，讨论了温室湿度控制的不同策略，以指导灌溉。最后，初步提出了进一步研究的建议。  相似文献   

19.
Crop water use efficiency of irrigated cotton was hypothesized to be improved by a combination of minimum tillage and sowing a wheat (Triticum aestivum L.) rotation crop. This hypothesis was evaluated in a Vertisol near Narrabri, Australia from 1997 to 2003. The experimental treatments were: continuous cotton sown after conventional or minimum tillage and minimum-tilled cotton–wheat. Soil water content was measured with a neutron moisture meter, and runoff with trapezoidal flumes. Application efficiency of irrigation water was estimated as the amount of infiltrated water/total amount applied. Plant available water was estimated using the maximum and minimum soil water storage during the growing season. Evapotranspiration was estimated with the water balance method using measured and simulated soil water data. Seasonal evapotranspiration was partitioned into that coming from rainfall, irrigation and stored soil water. Crop water use efficiency was calculated as cotton lint yield per hectare/seasonal evapotranspiration. Rotation of cotton with wheat and minimum tillage improved water use efficiency in some years and application efficiency in all years. Average seasonal evapotranspiration was higher with minimum tillage than with conventional tillage. In years when cotton was sown in all plots, average cotton crop water use efficiencies were 0.23, 0.23 and 0.22 kg (lint)/m3 for minimum-tilled cotton–wheat and continuous cotton, and conventionally tilled continuous cotton, respectively. In-season rainfall efficiency, transpiration and soil evaporation were unaffected by cropping system.  相似文献   

20.
Summary Traditional meteorological estimates of evapotranspiration include empirical crop factors which are inadequate for scheduling high frequency irrigation. The performance of a transpiration model was tested and adapted to suit the operational requirements of automated irrigation systems. Hourly measurements of global solar radiation, air temperature, humidity and wind speed, obtained from an automatic weather station are inputs to the model. Additional inputs include daily updated data of plant height and leaf area index. This information is processed to determine the active coupling surface between the crop and the atmosphere. The model takes into account the resistance of the leaf to diffusion of water vapor.Calculated transpiration, based on the model, matched very closely measurements of latent heat flux in an irrigated cotton field. It was also in good agreement with water uptake measured in stems of the cotton plants using a heat pulse technique. The test also showed that implementation of the model in the field under study would have improved the efficiency of water application.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel, No. 1855-E, 1986 series  相似文献   

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