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1.
Summary The effects of frequent and shallow soil wetting by surface drip irrigation on root growth, morphology, and location, and their impact on plant sensitivity to irrigation management were studied in cotton (Gossypium hirsutum L.). Daily drip irrigation, which wetted the 0 to 40-cm soil depth, encouraged root development mainly around the drippers. Water extraction took place mostly from 0 to 20 cm below the drippers, where the roots were concentrated. Shallowness of root growth was not altered by the expansion and deepening of the wetted soil zone which resulted from an increase in amount of irrigation water. The shallow and restricted root system was characterized by a high fraction of thin roots (less than 1 mm dia.) which comprised almost 90% of the root dry matter. Root proximity to the drippers and the limited amount of water in the rooted soil led to a sensitive and quick response of the plants to small amounts of irrigation. A supply of 1.0 mm H2O given at midday to 70 day-old plants resulted in a leaf water potential (L w) increase from –1.64 to –1.32 MPa over a 20-min period. This amount of irrigation comprised 15% of the average daily quantity. A 24 h delay in irrigation to 80 dayold plants was enough to decrease L w from –1.41 to –2.42 MPa. This decrease was caused by a soil water deficit of less than 6 mm H2O. Extending the irrigation delay to 72 h affected yield and earliness, although the deficient amount of water was supplied over the several days after the treatment. A strong response to minor, but continuous, differences in the daily irrigation amount was detected. Differences in irrigation of less than 1 mm H2O per day applied during the whole growth season substantially affected L w, yield and earliness. It was concluded that the establishment of a shallow and restricted root system resulted in strong dependence of the plants on frequent and sufficient supply of water, and temporary minor changes in irrigation affected plant water status and productivity.  相似文献   

2.
Summary Seed-cotton yield, yield components and vegetative growth were determined under different irrigation frequencies and wetting depths with a self-propelled moving-irrigation-system (MSIS) in 1986 and 1987. Irrigation timing was determined in both years by pre-irrigation, mid-day plant water potential (w). The amount of water to be applied was determined by measuring the soil moisture deficit. In 1987, the effect of a change from one irrigation frequency and wetting depth to another at mid-flowering was also examined. Linear responses of relative seed-cotton yield to the amount of evapotranspiration (ET) were found for both years with similar slopes but different intercepts. Significant positive regressions were obtained between pre-irrigation plant w and relative seed-cotton yield, and vegetative growth during the linear growth stage. Seed-cotton yield was affected by both wetting depth and pre-irrigation plant w. The deeper the irrigation the higher was the seed-cotton yield for each pre-irrigation plant w. Irrigation frequencies which maintained plant w above -1.5 MPa during vegetative growth, flowering and boll-filling resulted in maximum production. The boll filling stage appeared to be a very sensitive one, as boll weight was found to be the main yield component responding to irrigation treatments. At a wetting depth of 120 cm, higher seed-cotton yields were obtained than at a more shallow wetting. Different irrigation managements resulted in different turgor potentials (t) mainly during mid-day. Both leaf water vapour conductance and net assimilation rate were sensitive to leaf w.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagon, Israel, No. 2903-E, 1990 series. Research was supported by the U.S.-Israel Binational Agric. Res. and Develop. Fund.  相似文献   

3.
Summary The Lewis-Milne (LM) equation has been widely applied for design of border irrigation systems. This equation is based on the concept of mass conservation while the momentum balance is replaced by the assumption of a constant surface water depth. Although this constant water depth depends on the inflow rate, slope and roughness of the infiltrating surface, no explicit relation has been derived for its estimation. Assuming negligible border slope, the present study theoretically treats the constant depth in the LM equation by utilizing the simple dam-break wave solution along with boundary layer theory. The wave front is analyzed separately from the rest of the advancing water by considering both friction and infiltration effects on the momentum balance. The resulting equations in their general form are too complicated for closed-form solutions. Solutions are therefore given for specialized cases and the mean depth of flow is presented as a function of the initial water depth at the inlet, the surface roughness and the rate of infiltration. The solution is calibrated and tested using experimental data.Abbreviations a (t) advance length - c mean depth in LM equation - c f friction factor - c h Chezy's friction coefficient - g acceleration due to gravity - h(x, t) water depth - h 0 water depth at the upstream end - i() rate of infiltration - f(x, t) discharge - q0 constant inflow discharge - S f energy loss gradient or frictional slope - S0 bed slope - t time - u(x, t) mean velocity along the water depth - x distance - Y() cumulative infiltration - (t) distance separating two flow regions - infiltration opportunity time  相似文献   

4.
Wetting pattern can be obtained by either direct measurement of soil wetting in field, which is site specific, or by simulation using some models. Use of numerical or analytical flow models for design purpose is considered cumbersome and impractical in many situations. Therefore, present study was undertaken to develop a model for wetting pattern under trickle source in sandy soil of Nirjuli, Arunachal Pradesh. In the present study, the drip irrigation system was operated to record observed wetting front advance (vertical and horizontal) of emitters with flow rates of 2, 4 and 10?l?h?1. A fixed quantity of 4?l of water was applied to the bare dry soil kept in a container of perspex sheet (1?m?×?1?m?×?0.9?m). The wetting front advance was observed just after irrigation and its subsequent redistribution after 1, 2, 4, 6, 9, 12, 15, 18, 24 and 48?h respectively after irrigation. Using Buckingham π theorem, a semi-empirical model was developed to simulate the wetting front pattern under trickle point source at the end of irrigation. Performance of the model just after irrigation was evaluated by comparing estimated values against observed values using F test, t test, ME and RMSE values. The redistribution of the wetting front geometry with respect to elapsed time was modelled with regression analysis using four models viz. linear, logarithmic, exponential and power. Power function was found to be the best fit for horizontal wetting front (W) as well as vertical wetting front advance (Z) based on the highest R 2 value.  相似文献   

5.
The capability of mature cotton plants (Gossypium hirsutum L.) to adjust to progressive drying of their root zone by promoting root growth to adjacent wetted zones, and the implications of this process on irrigation design were investigated. Field grown plants that developed shallow root systems in response to a drip irrigation management of daily, surface soil wettings were exposed 85 days after emergence (DAE), while in the flowering stage, to a sudden change in water distribution in the form of deep soil wetting (DSW) followed by termination of irrigation. The shallow rooted plants (SRP) failed to respond to further surface soil wetting and the progressive drying of the profile by rapid root growth to the deeper-wetted zones; consequently, the SRP suffered from water deficiency for at least two weeks, evidenced by a gradual decrease in their leaf water potential (Lw). Potted plants responded similarly. Daily irrigations of the pot surface with water amounts similar to those lost by evapotranspiration led to the development of a system in which most of the roots and available water became concentrated at the pot's upper section. A transition to irrigation from the bottom of the pot led to a reversed soil-water content gradient and failed to promote rapid root spreading to the deeper-wetted layers, in spite of the accelerated drying of the upper zone. The slow deepening of the root system was accompanied by water-stress symptoms as indicated by a considerable reduction in dry matter production. The root shoot ratio in these plants was not much greater than in non-stressed plants in which the surface wetting was continued. This indicated that preferential root growth relative to the shoot did not occur in response to the progressive drying of the shallow root zone. Rewetting of the root zone after a long period of soil water deficiency failed to promote rapid recovery of the root system in the form of root regrowth in this zone. It was concluded that the capability of mature cotton plant roots to adjust their growth to large changes in water distribution in the soil, is slow and that this should be taken into account when determining an irrigation regime in which the depth at which water is applied is changed during the growing season.Contribution from the Agricultural Research Organization, Volcani Center, Bet Dagan, Israel; No. 343-E, 1992 series  相似文献   

6.
The science of irrigation scheduling is well advanced, but the field application of this knowledge among irrigators is limited. Case studies are presented to show why irrigators may fail to adopt or persevere with traditional irrigation scheduling methods. This paper describes a funnel-shaped wetting front detector that is buried at an appropriate depth in the root zone. As a wetting front moves into the funnel of the detector, the water content increases due to convergence, so that the water content at the base of the funnel reaches saturation. The free water produced is detected electronically and this provides the signal to stop irrigation. Since the philosophy of drip irrigation in most cases is to supply water little and often, the "when to turn the water on" question becomes redundant and knowing when to turn the water off is more useful. Two further case studies demonstrate the benefits of scheduling micro-irrigation using wetting front detectors. The detectors retain a water sample from each irrigation event and this was used to monitor nitrate movement in and below the root zone.Communicated by P. Thorburn  相似文献   

7.
Tomato rooting patterns, yield and fruit quality were evaluated in a field trial where three irrigation regimes [0.6 (DI), 0.9 (DII) and 1.2 ETc (DIII)] and three drip irrigation depths [surface (R0), subsurface at 20 cm depth (RI) and subsurface at 40 cm depth (RII)] were imposed following a split-plot experimental design, with four replications. The behaviour of the root system in response to the irrigation treatments was evaluated using minirhizotrons installed between two plants, near the plant row. Root-length intensity (L a)—length of the root per unit of minirhizotron surface area (cm cm−2)—was measured at four crop stages. For all sampling dates, none of the factors studied were found to influence L a or rooting depth significantly or the interaction between treatments. For all treatments most of the root system was concentrated in the top 40 cm of the soil profile, where the root-length density ranged from 0.5 cm cm−3 to 1.4 cm cm−3 . The response of tomato fruits to an increase in the water applied was similar in quantitative and qualitative terms for the different drip irrigation depths. Water applied by drip irrigation had the opposite effect on commercial yield (t ha−1) and soluble solids (°Brix) (r=−0.82, P<0.001), however, yield in terms of total soluble solids (t ha−1) was the same for the 0.9 and 1.2 ETc. The increase in commercial yield can be described by the equation   相似文献   

8.
Summary In order to study the drought sensitivity of pea (Pisum sativum L. cv. Bodil) during different growth phases, a field experiment was conducted in 1985 and 1986 on coarse textured sandy soil with low water-holding capacity. Drought occurred naturally or was imposed by shelters during the vegetative, the flowering and the pod filling growth phase, respectively. Drought sensitivities were assessed as the ratio between relative yield decrease (1 – Ya/Ym) and relative evapotranspiration deficit (1 – ETa/ETm) of the individual growth phases, where Ya and ETa are the actual yield and evapotranspiration, respectively, of a drought stressed plot and Ym and ETm are the maximum yield and evapotranspiration of the fully irrigated treatment. Root growth was followed by measuring root density (L v ) in 10 cm soil layers to a depth of 50 cm. The leaf osmotic potential at full hydration ( s 100 ) was measured in the last fully developed leaf during the growing season.The available water capacity was estimated to be 42–50 mm on the basis of a plot of ETa/ETm versus soil water deficit measured by the neutron moderation method or direct measurement of the root depth. The root zone with L v >0.1 cm–2 only reached a depth of 35 cm at the end of the flowering phase and a depth of 45–50 cm at maturity. Root growth continued during the drought periods. The drought sensitivity of pea was high during the flowering phase, especially in 1986 when water stress developed rapidly, and considerably lower during the pod filling phase. The yield reduction caused by drought in the flowering phase was mainly the result of a lower number of pods per stalk. Severe drought did not occur during the vegetative phase. The leaf osmotic potential ( s 100 ) declined from c. -0.75 MPa to c. -1.30 MPa during the growing season. Osmotic adjustment was largest during drought in the early growth phases; in 1985 s 100 decreased 0.5 MPa under relatively slow drought development during the flowering phase while in 1986, when drought stress developed rapidly, s 100 only decreased 0.2 MPa. Osmotic adjustment may have caused the lower drought sensitivity in 1985 than in 1986 and mediated the continued root growth during drought.  相似文献   

9.
A relationship between crop yield and irrigation water salinity is developed. The relationship can be used as a production function to quantify the economic ramifications of practices which increase irrigation water salinity, such as disposal of surface and sub-surface saline drainage waters into the irrigation water supply system. Guidelines for the acceptable level of irrigation water salinity in a region can then be established. The model can also be used to determine crop suitability for an irrigation region, if irrigation water salinity is high. Where experimental work is required to determine crop yield response to irrigation water salinity, the model can be used as a first estimate of the response function. The most appropriate experimental treatments can then be allocated. The model adequately predicted crop response to water salinity, when compared with experimental data.Abbreviations A Crop threshold rootzone salinity in Equation of Maas and Hoffman (dS/m) - B Fractional yield reduction per unit rootzone salinity increase (dS/m)–1 - Ci Average salinity of applied water (dS/m) - Cr Average salinity of rainfall (dS/m) - Cs Linearly averaged soil solution salinity in the rootzone (dS/m) - Cse Linearly averaged soil saturation extract salinity in the rootzone (dS/m) - Cw Average salinity of irrigation supply water (dS/m) - Cz Soil solution salinity at the base of the crop rootzone (dS/m) - C Mean root water uptake weighted soil salinity in equation of Bernstein and François (1973) (dS/m) - Ep Depth of class A pan evaporation during the growing season (m) - ETa Actual crop evapotranspiration during the growing season (m) - ETm Maximum crop evapotranspiration during the growing season (m) - I The total depth of water applied during the growing season (including irrigation water and rainfall) (m) - K Empirical coefficient in leaching equation of Rhoades (1974) - Kc Crop coefficient for equation of Doorenbos and Pruit (1977) to estimate crop water use - Ky Yield response factor in equation of Doorenbos and Kassam (1974) - LF The leaching fraction - Ro Depth of rainfall runoff during the growing season (m) - R Depth of rainfall during the growing season (m) - W Depth of irrigation water applied during the growing season (m) - Y Relative crop yield - Ya Actual crop yield (kg) - Ym Maximum crop yield (kg) - /z Dimensionless depth for equation of Raats (1974), and empirical coefficient for the leaching equation of Hoffman and van Genutchen (1983)  相似文献   

10.
Fino lemon trees (Citrus limon L. Burm. fil.) on sour orange (Citrus aurantium L.), growing on a low water retention capacity soil, were submitted to three different irrigation treatments over four years: 100% ETc all year (T-0), 25% ETc all year except during the rapid fruit growth period when 100% ETc was applied (T-1) and 100% ETc all year, except during the rapid fruit growth period when 70% ETc was applied (T-2). A water saving of 30 and 20% was achieved in the T-1 and T-2 treatments, respectively. The plant responses to irrigation treatments were similar in all the years studied. Leaf water potential decreased during deficit irrigation periods in T-1 and T-2 treatments. Larger differences were found in values taken at predawn ( pd) than at midday ( md), indicating that pd is a more useful indicator of plant water status. There was neither osmotic nor elastic adjustment in response to deficit irrigation treatment. A clear separation between the main periods of shoot and fruit growth was found, which can be considered an advantageous characteristic in applying regulated deficit irrigation strategies. Onset of the critical period of rapid fruit growth could be determined precisely by considering the decrease in relative fruit growth rate values. T-2 treatment did not induce a significant reduction in total yield, but it caused a delay in reaching marketable lemon fruit size. T-1 treatment did not affect total yield, with a reduction in yield on the first pick occurring in only one year. Chemical characteristics of lemon fruit were not significantly modified by irrigation treatment.  相似文献   

11.
地下水浅埋下层状土壤波涌畦灌间歇入渗模型研究   总被引：1，自引：0，他引：1  
为进一步揭示地下水浅埋下的层状土波涌畦灌间歇入渗机制,通过试验资料分析与理论研究,建立了波涌灌间歇入渗条件下的层状土Brook-Corey和Green-Ampt（BC-GA）改进入渗模型,推导出层状土间歇入渗湿润锋面水吸力与湿润锋运移深度的函数关系,确定了含砂层内部土壤饱和导水率、进气吸力是层状土间歇入渗运移距离变化的主要影响参数。周期数增大,上层土壤饱和导水率减小,饱和含水率减小,进气吸力增大,夹砂层内部仅进气吸力随周期数增加而增大。根据BC-GA模型计算不同埋深的含砂层土壤间歇入渗特性及湿润锋运移特性,对比分析指出,周期数增加,相同含砂层埋深下的累积入渗量减小,湿润锋运移距离增大;含砂层埋深增加,相同供水周期的累积入渗量增大,湿润锋增大;供水周期达到最大时,含砂层埋深对累积入渗量和湿润锋运移距离影响减小。  相似文献   

12.
涌泉根灌在黄土坡地的水分运移规律试验   总被引：1，自引：0，他引：1  
为了了解涌泉根灌这项微灌技术灌水后的水分运移情况,在野外黄土坡地利用剖面法对涌泉根灌在不同孔径、孔深条件下土壤水分运移规律进行了研究.结果表明,在不同孔径、孔深处理下,湿润体水平扩散半径、向上入渗距离和向下入渗深度有不同的影响,且均与时间有显著的幂函数关系;涌泉根灌停止后24 h内的土壤湿润体水平及竖直方向扩散相对变化超过了47%,湿润体平均含水量相对降低了30%;24 h后的扩散较小,平均含水量下降较小.涌泉根灌停止后24 h时的湿润体特征值可作为涌泉根灌系统设计的依据;推荐涌泉根灌适宜的孔洞深度为30~40 cm,孔径为φ6 cm.研究结果可为涌泉根灌技术的实际应用提供理论参考.  相似文献   

13.
【目的】探究冬小麦适宜的计划湿润层深度和土壤含水率控制下限的组合模式,为冬小麦田间用水管理及自动灌溉控制决策提供理论依据。【方法】以冬小麦为研究对象,采用大田试验,设置3个土壤含水率控制下限(L:40%,M:50%,H:60%)和3个计划湿润层深度(60、80、100 cm),共9个处理(T60L、T60M、T60H、T80L、T80M、T80H、T100L、T100M、T100H),研究了不同计划湿润层深度与土壤含水率控制下限对华北地区冬小麦生长发育和水分利用的影响。【结果】计划湿润层深度及土壤含水率控制下限的不同改变了处理间灌水定额及灌水次数,计划湿润层深度过高或土壤含水率控制下限过低均不利于冬小麦植株的生长发育。随着计划湿润层深度(60~100 cm)和土壤含水率控制下限(40%~60%)的增大,冬小麦花前及花后的干物质累积量呈先增大后减小的趋势。产量随土壤含水率控制下限增高呈增加趋势,当计划湿润层深度为80 cm时,产量相对最高,同时耗水量也越多,而计划湿润层深度为60 cm时耗水量最少。计划湿润层深度越低,土壤含水率控制下限越高,冬小麦水分利用效率则越高。T60H处理的水分利用效率最大,为19.96 kg/(hm2·mm),比最小值T100L大21.0%。【结论】本试验条件下,计划湿润层深度为60 cm,土壤含水率控制下限设置为土壤有效含水率的60%时,冬小麦节水高产效果相对最优。  相似文献   

14.
[目的]探究灌水量和灌水器埋深对单坑渗灌红壤水分入渗特性的影响.[方法]通过室内土箱试验模拟大田单坑渗灌过程,研究了单坑渗灌红壤在不同灌水量(1、2L和3L)和不同灌水器埋深(10、15cm和20cm)条件下湿润锋运移距离、累积入渗量和土壤含水率的分布规律,并采用交替方向隐式差分法对土壤水分空间分布进行了模拟.[结果]...  相似文献   

15.
无压地下灌溉新技术试验   总被引：6，自引：0，他引：6  
对局部控水灌溉(无压地下灌溉)技术从理论上进行了分析，并给出了其土壤水分运动方程。在大田试验的基础上，研究分析了无压灌溉不同孔径孔口出水规律和根区局部湿润状况。试验结果表明：无压孔口出水规律与孔口孔径、地温和土壤含水量等因素有关；出水孔口孔径和初时土壤含水量对湿润锋推进速度影响较大，孔径和初时土壤含水量越大，湿润锋推进速越快；适宜的出水孔径沿管道长度方向出水均匀，5～35cm深度的土壤含水量变化无明显差异，能够满足作物需水和生理需水要求。  相似文献   

16.
A priori knowledge of the in situ soil field water capacity (FWC) and the soil-water retention curve for soils is important for the effective irrigation management and scheduling of many crops. The primary objective of this study was to estimate the in situ FWC using the soil-water retention curve developed from volumetric water content (θ), and water potential (ψ) data collected in the field by means of soil moisture sensors in two contrasting-textured soils. The two study soils were Lihen sandy loam and Savage clay loam. Six metal frames 117 cm × 117 cm × 30 cm high were inserted into the soil to a depth of 5–10 cm at approximately 40 m intervals on a 200 m transect. Two Time Domain Reflectrometry (TDR) sensors were installed in the center of the frame and two Watermark (WM) sensors were installed in the SW corner at 15 and 30 cm depths to continuously monitor soil θ and ψ, respectively. A neutron probe (NP) access tube was installed in the NE corner of each frame to measure soil θ used for TDR calibration. The upper 50–60 cm of soil inside each frame was saturated with intermittent application of approximately 18–20 cm of water. Frames were then covered with plastic tarps. The Campbell and Gardner equations best fit the soil–water retention curves for sandy loam and clay loam soils, respectively. Based on the relationship between soil ψ and elapsed time following cessation of infiltration, we calculated that the field capacity time (t FWC) were reached at approximately 50 and 450 h, respectively, for sandy loam and clay loam soils. Soil-water retention curves showed that θ values at FWC (θ FWC) were approximately 0.228 and 0.344 m3 m−3, respectively, for sandy loam and clay loam soils. The estimated θ FWC values were within the range of the measured θ FWC values from the NP and gravimetric methods. The TDR and WM sensors provided accurate in situ soil–water retention data from simultaneous soil θ and ψ measurements that can be used in soil-water processes, irrigation scheduling, modeling and chemical transport.  相似文献   

17.
The Penman-Monteith model with a variable surface canopy resistance (rcv) was evaluated to estimate hourly and daily crop evapotranspiration (ETc) over a soybean canopy for different soil water status and atmospheric conditions. The hourly values of rcv were computed as a function of environmental variables (air temperature, vapor pressure deficit, net radiation) and a normalized soil water factor (F), which varies between 0 (wilting point, WP) and 1 (field capacity, FC). The performance of the Penman-Monteith model (ETPM) was evaluated using hourly and daily values of ETc obtained from the combined aerodynamic method (ETR). On an hourly basis, the overall standard error of estimate (SEE) and the absolute relative error (ARE) were 0.06 mm h–1 (41 W m–2) and 4.2%, respectively. On a daily basis, the SEE was 0.47 mm day–1 and the ARE was 2.5%. The largest disagreements between ETPM and ETR were observed, on the hourly scale, under the combined influence of windy and dry atmospheric conditions. However, this did not affect daily estimates, since nighttime underestimations cancelled out daytime overestimations. Thus, daily performances of the Penman-Monteith model were good under soil water contents ranging from 0.31 to 0.2 (FC and WP being 0.33 and 0.17, respectively) and LAI ranging from 0.3 to 4.0. For this validation period, calculated values of rcv and F ranged between 44 s m–1 and 551 s m–1 and between 0.19 and 0.88, respectively.Communicated by R. Evans  相似文献   

18.
大田滴灌条件下土壤水分运移规律的试验研究   总被引：4，自引：0，他引：4  
研究了大田滴灌条件下,不同灌水量、不同滴头流量以及不同的土壤剖面容重条件下水分在土壤中的迁移规律。结果表明:在大田滴灌条件下,地表沿滴头土壤湿润锋基本呈圆形分布,在一定灌水量和滴灌流量条件下,土壤垂直湿润锋明显地大于水平湿润锋,且随着灌水量的增加呈线性关系;在同一灌水量下,随着滴头流量的增大,湿润体水平扩散半径(r)和竖直入渗深度(h)也相应变大;在不同灌水量下,湿润体水平和竖直湿润速度随着时间的增大都逐渐变小;随着剖面土壤容重的增加,水平湿润锋的迁移加快,水平湿润锋随时间的变化呈显著的幂函数关系;随着灌水量的增加,不同剖面容重下的土壤水平湿润锋速率的增加逐渐变小,而垂直湿润锋则呈变大的趋势。  相似文献   

19.
Effective irrigation uniformity as related to root zone depth   总被引：1，自引：0，他引：1  
Summary In models used for relating the yield to irrigation uniformity it has been assumed that the spatial distribution of irrigation water, as measured at the soil surface, is indeed the water distribution at any depth throughout the root zone. In the present paper the distribution of infiltrated water within the soil bulk, as determined by an analytic solution of the two-dimensional unsaturated flow equation, did not conform to this assumption. A new alternative definition of irrigation uniformity is proposed under the assumption that water uptake by roots does not affect the flux distribution within the soil profile. In this analysis the spatial distribution of irrigation water flux at the soil surface, which is the upper boundary condition of the flow equation, is assumed to be a sine function. The solution to this problem indicates that there is a damping effect, which increases with soil depth, on the surface flux fluctuations. Furthermore, the actual irrigation uniformity at a given depth below the soil surface depends upon the initial uniformity at the surface and the distance between adjacent water sources. The closer the water sources are to each other, the shallower is the depth needed to damp the oscillations down to a certain level. This may explain why the actual uniformity of drip irrigation is high while the detailed distribution is very nonuniform and on the other hand, why the actual uniformity of sprinkler guns is low while the detailed actual distribution is close to uniform. Two uniformity coefficients are derived in this study: 1. A depth dependent coefficient which is made up of the damping factor that multiplies the flux fluctuations at the soil surface; 2. An effective uniformity coefficient, which is an average of the depth dependent coefficient over a part or the entire root zone. Different degrees of uniformity are expected when water is applied by different irrigation systems having similar uniformity coefficients at the soil surface, but dissimilar distances between the emitters. Assuming that crop yield depends to some extent on the uniformity of water depth actually available to the roots, the yields associated with such irrigation systems will probably also vary.  相似文献   

20.
Irrigation of Lucerne under semi-arid conditions in Cyprus   总被引：1，自引：0，他引：1  
Summary Three amounts of water –1.0, 0.8 and 0.6 of the irrigation requirement — were used to irrigate lucerne at two frequencies of application — once or twice during each growth cycle. Screened Class A pan evaporation, adjusted by monthly crop coefficients, proved a dependable guide for irrigation. Irrigating once per growth cycle was sufficient, and the highest yield was obtained when the full irrigation requirement was applied. The average annual dry matter yield for the three amounts of irrigation water — 1390, 1110 and 829 mm per year — was 20 285, 16 353 and 12 952 kg ha–1 respectively, i. e., yield decreased linearly with decreasing amount of water applied. As the water used was saline — with an electrical conductivity of 3 mmhos/cm–1 — the main root zone became gradually salinized with the drier treatments, while with the wettest treatment salts accumulated below 80 cm depth. Yields were drastically reduced during the hot summer months, even when adequate water was available in the soil profile. This combined with the high irrigation requirement resulted in very low efficiency of irrigation during summer.  相似文献   

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