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1.
《Agricultural Systems》1999,59(1):41-55
Environmental fate models are increasingly used to evaluate potential impacts of agrochemicals on water quality to aid in decision making. However, errors in predicting processes like evapotranspiration (ET), which is rarely measured during model validation studies, can significantly affect predictions of chemical fate and transport. This study compared approaches and predictions for ET by GLEAMS, Opus, PRZM-2, and RZWQM and determined effects of the predicted ET on simulations of other hydrology components. The ET was investigated for 2 years of various fallow–corn growing seasons under sprinkler irrigation. The comparison included annual cumulative daily potential ET (ETp), actual ET, and partitioning of total ET between soil evaporation (Es) and crop transpiration (Et). When measured pan evaporation was used for calculating ETp (the pan evaporation method), Opus, PRZM-2, and RZWQM predicted 74, 65, and 59%, respectively, of the 10-year average ET reported for a nearby site. When the energy-balance equations were used for calculating ETp (the combination methods), GLEAMS, Opus, PRZM-2, and RZWQM predicted 84, 105, 60, and 72% of the reported ET, respectively. The pan evaporation method predicted a similar amount of ET to the combination methods for bare soil, but predicted less ET when both Es and Et occurred. RZWQM reasonably predicted partitioning of ET to Es, while GLEAMS and Opus over-predicted this partitioning. A close correlation between soil water storage in the root zone and ET suggests that accurate soil water content predictions were fundamental to ET predictions. ©  相似文献   

2.
Crop coefficient of sesame is necessary for the water requirement estimation in irrigation water planning and management. This study has been initiated to determine the crop coefficient (Kc) of sesame in a semi-arid climate. The relationships between Kc and ETp/Ep (pan evaporation) and leaf area index (LAI), growing degree-day (GDD) and days after sowing (DAS), were also investigated. The seasonal ETp for sesame in the study area with a 5 month growth period was 910 m. The mid-season and late-season Kc values for sesame were 1.08 and 0.64, respectively. These values are somewhat lower and higher than those for other oil seed crops. The Kc value for the initial stage was close to that obtained by the procedure proposed by Allen et al. [Allen, R.G., Smith, M., Pereira, L.S., Pruitt, W.O., 1997. Proposed revision to the FAO procedure for estimating evapotranspiration. In: The Second Iranian Congress on Soil and Water Issues, 15–17 February 1997. Tehran, I.R. of Iran, pp. 1–18]. The ratio of ETp/Ep varied between 0.49–1.0 from the beginning to the middle of the growing season which is a sign of mild local advection in the region. The maximum ratios of ETp/ET0 and ETp/Ep occurred at a LAI of 3.0. Furthermore, third-order polynomials were presented to predict the Kc values from days after sowing (DAS), percent days after sowing (%DAS) and growing degree-day (GDD).  相似文献   

3.
Based on evaporation from a 20 cm diameter pan placed above the crop canopy, sprinkler irrigation scheduling of winter wheat was studied in the North China Plain (NCP) in the 2001–2004 winter wheat seasons. Results showed that pan evaporation (E pan,C) was closely related to actual evapotranspiration (ET) measured using weighing lysimeters. The combined pan–crop coefficient (K c,pan), the ratio of ET to E pan,C, was closely related to leaf area index (LAI ) and plant height. Data from the 2002–2003 season were used to establish the relationships between K c,pan and LAI (method A) or plant height (method B), and used to determine the crop coefficient (method C). ET computed by the three methods was compared with measured ET using lysimeters in the 2001–2002 and 2003–2004 seasons. Mean relative error of estimated daily ET by the three methods ranged from 20 to 30%, and the relative error in cumulative ET in the experimental periods ranged from 1 to 19%. Among the three methods, results from methods A and B were not significantly different from each other (P > 0.01), and were closer to the lysimeter data than results from method C (P < 0.001). Method B, being easier to measure, was recommended for ET estimation in NCP.  相似文献   

4.
自动补水蒸发皿装置的原理及应用   总被引：1，自引：0，他引：1  
为了更好地利用蒸发皿的蒸发量指导农田灌溉,根据马氏瓶工作原理设计了一种简单、实用,价格低廉而且操控性强的恒水位蒸发皿装置,此装置在20 cm标准蒸发皿的基础上附加了一个自动补水装置.以20 cm标准蒸发皿的蒸发量为标准,对可进行自动补水的恒水位蒸发皿的水面蒸发过程进行了验证.通过大田冬小麦试验建立了水面蒸发过程与冬小麦同阶段耗水过程的关系.结果表明,设计开发的蒸发皿装置,具有较好的稳定性,组间测量值相对平均误差小于5%,超过5 d相对平均误差小于2%;其水面蒸发过程与20 cm标准蒸发皿的蒸发量具有显著的相关关系,相关系数高达0.99;华北地区优质高产冬小麦在拔节期、抽穗扬花期和灌浆成熟期的田间耗水量,与自动补水蒸发皿同阶段累计水面蒸发量的比值分别为1.09,1.31和1.16.因此,可以用该装置的水面蒸发量来指导农田灌溉,达到农作物优质、高效、高产的目的.  相似文献   

5.
The aim of this study carried out in Van, Turkey was to determine the most suitable irrigation frequencies and quantities in summer squash (Cucurbita pepo L. cv. Sakız) grown under field conditions. Irrigation quantities were based on pan evaporation (Epan) from a screened class-A pan. Irrigation treatments consisted of two irrigation intervals (I1: 5 days; I2: 10 days), and three pan coefficients (Kcp1: 0.45; Kcp2: 0.65 and Kcp3: 0.85). Plants were adequately watered from seed sowing to first fruit emergence, then, scheduled irrigations were initiated at 5- and 10-day intervals.Irrigation quantities applied to the treatments varied from 279 to 475 mm; seasonal plant water consumption or evapotranspiration (Et) of irrigation treatments varied from 336 to 539 mm; and the summer squash yield varied from 22.4 to 44.7 t ha−1. The highest total yield was obtained from I1Kcp3 treatment. However, Kcp2 treatments had the earliest yield. Treatments irrigated with higher amount of water generally gave lower irrigation water use efficiency (IWUE) values than others. Et/Epan ratios of treatments ranged from 0.12 to 1.16. Moreover, irrigation treatments had significant effects (P<0.01) on yield and there were significant positive linear relations among irrigation water, plant water consumption, fruit traits and yield.In conclusion, Kcp3 treatment with 5-day irrigation interval is recommended for summer squash grown under field conditions in order to get higher summer squash yield. However, if the irrigation water is scarce, it will be suitable to irrigate summer squash frequently using Kcp1 values.  相似文献   

6.
Actual evapotranspiration (ETc) of three mature sweet orange orchards (cv. Salustiana and Washington Navel on sour orange), under border irrigation and typical cultural practices was measured by the water balance method during 1981 to 1984. Soil water content was measured at 7 to 10 day intervals using a neutron meter and soil sampling of the 0–10 cm surface layer. Zero flux plane was calculated by measurements with mercury tensiometers. Irrigation water in these and other 5 similar orchards was measured by broad crested weirs. Rainfall and other climatic data for calculation of reference evapotranspiration by FAO's methods (ETo) were collected in a nearby meteorological station. Average yearly ETc ranged from 750 to 660 mm and mean monthly maximum was 3.7 and 3.2 mm/day in July for Salustiana and W. Navel orchards, respectively.ETo estimates for the different methods used were highly correlated (r 20.94). Monthly crop coefficients (Kc) based on pan evaporation ranged from 0.5–0.6 in spring and summer to 0.8 in autumn and were about 10% higher than those for Penman or radiation methods. Average annual Kc for the three plots studied was 0.64, 0.61 and 0.51, respectively, and correlated well (r 2=0.99) with tree ground cover. Irrigation efficiency was about 50% for orchards with soils with less water holding capacity and more applied water per irrigation and 70–80% in orchards with deeper soils or with a higher water holding capacity. Increasing irrigation frequency and applying smaller amounts of water per irrigation with good uniformity can improve on-farm irrigation efficiency.  相似文献   

7.
The objective of this study was to test an artificial neural network (ANN) for converting pan evaporation data (E p) to estimate reference evapotranspiration (ET0) as a function of the maximum and minimum air temperature. The conventional method that uses Pan coefficient (K p) as a factor to convert E p to ET0, is also considered for the comparison. The ANN has been evaluated under semi-arid conditions in Safiabad Agricultural Research Center (SARC) in the southwest of Iran, comparing daily estimates against those from the FAO-56 Penman–Monteith equation (PM), which was used as standard. The comparison shows that, the conventional method underestimated ET0 obtained by the PM method. The ANN method gave better estimates than the conventional method that requires wind speed and humidity data.  相似文献   

8.
Irrigation is necessary in order to produce sugarcane in semiarid south Texas, but water supplies are becoming increasing limited. Drip and sprinkler irrigation systems offer more precise water control than conventional furrow irrigation, but are more expensive. This study was conducted to evaluate four different methods (pan evaporation (Epan), evapotranspiration (ET), auto-tensiometers, manual tensiometers) for determining the amount of irrigation water to apply, and three different frequencies of water application on sugarcane, in order to make the most efficient use of available water using subsurface drip irrigation. The study was conducted over three sugarcane seasons: the plant crop and two ratoon crops. The amount of water applied based on the different methods varied from year to year, with the ET method prescribing the most water in the first ratoon crop but the least amount in the second ratoon. This was probably caused mostly by differences in annual weather conditions. The more frequently water was applied, the larger amount any method tended to prescribe, since more frequent applications resulted in keeping the soil profile fuller, therefore providing less capacity to store rainfall when it occurred. Number of stress days as determined by calculating a stress coefficient based on ET and soil water balance indicated a large amount of stress in the first ratoon but almost none in the second ratoon crop. Direct soil water monitoring indicated much less stress than the calculated levels. Growth measurements and sugarcane yields showed that the highest water applications resulted in the best responses, regardless of the scheduling method used. All irrigation scheduling methods were effective, prescribing similar amounts of water for a given season. Direct measurement using tensiometers gives the most accurate assessment of field conditions, but is expensive and labor intensive. Automated tensiometers were not very reliable. Pan evaporation and ET are effective once they are properly calibrated by developing appropriate coefficients for a particular region. Pan evaporation has been used for a long time, but it is more difficult to obtain reliable data compared to ET data from automated weather stations.  相似文献   

9.
We address a need for a rapid technique to estimate the leaf area index (LAI) of pre-existing natural vegetation. This is required to determine the effects of agroforestry plantings on deep drainage from agricultural land. Previous work shows: (1) a relationship between the hydrologic ‘footprint’ of tree belts and their lineal leaf area (leaf area per metre of belt, LLA, m2 m−1), relative to the LAI of natural vegetation and (2) that the LAI of natural vegetation is related to plant-available soil moisture and climate. We evaluated relationships between LAI measured at 37 sites across southern Australia and (1) annual average rainfall, P; (2) annual average pan evaporation, E0; (3) ‘available rainfall’—annual average rainfall, P, minus annual average pan evaporation, E0; (4) a climate wetness index P/E0; (5) Specht's soil evaporative index, k = 0.0045 + 71.57/E0. P was the best indicator for the data set used, i.e. LAI = 0.003P + 0.41 (r2 = 0.80).  相似文献   

10.
Accurate reference evapotranspiration (ET0) data are essential to water resources project planning and farm irrigation scheduling. Evaporation pans are widely used to estimate reference ET0. Via the pan coefficient (K p), ET0 is estimated from evaporation pan data. Four common K p equations (Orang in Potential accuracy of the popular non-linear regression equations for estimating pan coefficient values in the original and FAO-24 tables, unpublished report, 1998; Allen and Pruitt in J Irrig Drain Eng 117(5):758–773, 1991; Cuenca in Irrigation system design: an engineering approach, p 133, 1989; Snyder in J Irrig Drain Eng 118(6):977–980, 1992) to calculate daily K p coefficients to estimate ET0 were evaluated using a 10-year mean climate dataset for a subtropical climate (north of Iran). Overall results showed that ET0 calculated using the daily K p values from Orang (Potential accuracy of the popular non-linear regression equations for estimating pan coefficient values in the original and FAO-24 tables, unpublished report, 1998) provided more accurate daily, monthly, and annual total estimates compared to the others equations.  相似文献   

11.
The reference crop evapotranspiration (ETr) for four areas in Saudi Arabia was estimated using five different methods: FAO-Penman, Jensen-Haise, Blaney & Criddle, pan evaporation, and calibrated FAO-Penman under local conditions (Penman-SA). Comparison was also made between the estimated ETr and the measured ETr of alfalfa grown in lysimeters in the Riyadh area. Regression analysis revealed that estimated ETr values were highly correlated with measured ETr values. In addition, linear regression relationships between ETr values estimated by the Penman-SA method and other methods were determined. The results of this study indicated that the calibrated Penman-SA method can be transferred successfully to other locations, and this method could be used for the estimation of ETr values in all areas in the southern region of Saudi Arabia. Received: 16 January 1998  相似文献   

12.
Water requirements of olive orchards are difficult to calculate, since they are influenced by heterogeneous factors such as age, planting density and irrigation systems. Here we propose a model of olive water requirements, capable of separately calculating transpiration (E p), intercepted rainfall evaporation (E pd) and soil evaporation (E s) from the wet and dry fraction of the soil surface under localized irrigation. The model accounts for the effects of canopy dimension on E p and of the wetted soil surface fraction on E s. The model was tested against actual measurements of olive evapotranspiration (ET) obtained by the eddy covariance technique in a developing olive orchard during 3 years. The predicted ET and crop coefficients showed good agreement with the measured data. The model was then used to simulate the average water requirements of two mature orchards using 20-year meteorological datasets of Cordoba (Spain) and Fresno (CA, USA). Average annual ET of a 300 trees ha−1 orchard at Cordoba was 1,025 mm, while the same orchard at Fresno had an average ET of 927 mm. Transpiration losses were 602 mm at Cordoba and 612 mm at Fresno. Evaporation from the soil can have a large effect on olive ET; thus, olive crop coefficients (K c) are very sensitive to the rainfall regime.  相似文献   

13.
The aim of this study was to assess the magnitude of evaporation loss from the agricultural water reservoirs (AWRs) for irrigation at a regional scale and to analyze its impact on water storage efficiency. To this end, we identified the extant AWRs for irrigation in the Segura River Basin (SRB) in southeastern Spain, and calculated the water loss from each AWR per month and year. In order to accomplish this, we determined the monthly and yearly values of the pan coefficient, Kp, taking into account the geometric dimensions (area and depth) of the AWRs and local climate conditions through a function of air vapour pressure deficit (VPD). AWR areas were identified by interpreting aerial images, while climate conditions were assessed using daily meteorological data obtained from 74 automated agro-meteorological stations located in irrigated areas. Regional evaporation losses were estimated using aggregation GIS techniques. A total of 14,145 AWRs covering 4901 ha were identified, which represents 0.26 and 1.81% of the total area of SRB and the irrigated land, respectively. Results indicated that annual water loss at a basin scale reaches 58.5 × 106 m3, which corresponds to 1.404 m of water depth over the flooded area and to 8.3% of irrigation water use in the basin. This quantity is higher than the industrial demand and similar to the environmental demand, and is equivalent to 27% of the domestic water use in a region with approximately two million inhabitants. The method used, based on annual Kp, appears the most straightforward to assess regional evaporative losses from AWRs, and can be extended to other regions and climates, provided that the VPD-dependent function that gives the pan coefficient is available.  相似文献   

14.
入渗-覆膜开孔蒸发条件下砂夹层影响水、盐、热运动的方式和规律尚不清楚。通过不同埋深砂夹层土体室内入渗-蒸发试验,分析了3个不同埋深砂夹层和覆膜开孔影响下土体水、盐、热变化规律。试验结果表明,夹砂层土体在整个积水入渗过程中经历非线性、线性两个过程;砂夹层对水流有一定的阻滞作用,同时对盐分的淋洗不利;不同覆膜开孔率蒸发条件下,任意时刻剖面温度分布均为表层0cm最高,土体底部最低,25cm为土体温度变化的影响深度;25cm以上不同砂夹层埋深土体剖面温度梯度规律表现为T（5～10cm埋深）〉T（10～15cm埋深）〉T（20～25cm埋深）。  相似文献   

15.
For sustainable sunflower production in semi-arid sub-tropical regions, it is essential to increase its water use efficiency. Field studies were conducted for three years on deep alluvial loamy sand (Typic Ustipsamment) and sandy loam (Typic Ustochrept) soils at Punjab Agricultural University, Ludhiana, India, to evaluate the interactive effects of three irrigation regimes (irrigation water to net open pan evaporation ratios, I1, I2, I3) on sunflower yield in relation to tillage (conventional tillage, CT, and deep-tillage, DT) and mulching (no mulch, M0, and residue mulch, M1).Both deep tillage and mulch significantly increased crop yield irrespective of soil type and year. Increase in mean achene yield across soils during three years with DT over CT varied between 10 and 16% and that with mulch over no mulch by 8 to 17%.Deep tillage and/or mulching helped the crop in efficient utilization of water by increasing leaf area index (LAI) and the depth and density of rooting. Irrigation and tillage interacted for their effects on yield on loamy sand, as the crop responded to higher level of irrigation with CT than with DT. On loamy sand, mean achene yield increased with increase in water supply up to IW/PE = 1.5 in a dry year and upto IW/PE = 1.2 in relatively wetter years. On sandy loam, mean yield response to irrigations was observed upto IW/PE = 1.0 in all the three years.Regression analysis of relative yield against water supply during the three years on both the soils, showed that for 80% relative yield the crop required 105 cm water in CTM0, 90 cm in CTM or DTM0 and only 80 cm in DTM. The study suggests that deep tillage or straw mulch may be used to achieve higher water use efficiency in sunflower on coarse textured soils in semi-arid, sub-tropical regions.  相似文献   

16.
Summary The effect of different frequencies of irrigation on the leaf water relations and dry matter production of the West Coast Tall coconut palms (Cocos nucifera L.) was studied during two growing seasons. Irrigation was applied in amounts of 60 mm at a ratio of irrigation water to cumulative pan evaporation (I/E) of 1.0, 0.75, 0.50 and 0.0. Measurements were made of stomatal resistance, leaf water potential and epicuticular wax content, and vegetative and reproductive dry matter production. Irrigation treatments resulted in a four-to five-fold increase in the soil water deficit at I/E ratios of 0.5 and 0.0 as compared to 1.0. Coconut palms experienced severe moisture stress at an irrigation level of 0.50, resulting in a greater stomatal resistance (111%) and epicuticular wax content (32%) and reduced transpiration rate (10%), leaf water potential (68%), and reproductive dry matter production (22%), compared with well watered palms. Based on the relationship between the soil water deficit and the stomatal resistance, the critical soil water deficit for irrigation scheduling was deduced to be 110 mm. However vegetative dry matter production was reduced at much lower soil water deficits than this value.  相似文献   

17.
Accurate estimation of reference evapotranspiration (ET0) is important for water resources engineering. Therefore, a large number of empirical or semi-empirical equations have been developed for assessing ET0 from numerous meteorological data. However, records of such weather variables are often incomplete or not always available for many locations, which is a shortcoming of these complex models. Therefore, practical and simpler methods are required for estimating the ET0. In this study, the efficiency of a wavelet regression (WR) model in estimating reference evapotranspiration based on only Class A pan evaporation is examined. The results of the WR model are compared with those of three pan-based equations, namely the FAO-24 pan, Snyder ET0 and Ghare ET0 equations and their calibrated versions. Daily Class A pan evaporation data from the Fresno and Bakersfield stations of the United States Environmental Protection Agency in California, USA, are used in the study. The WR model estimates are compared against those of the FAO-56 Penman–Monteith equation. Results showed that the WR model is capable of accurately predicting the ET0 values as a product of pan evaporation data.  相似文献   

18.
Measurement of evaporation (E) rate from various natural surfaces is known as the key element in any hydrological cycle and hydrometeorological studies. Due to the shortage of pan evaporation (E P) data, the estimation of E P for such studies seems necessary. The main aim of this paper was to estimate daily E P using artificial neural network (ANN) and multivariate non-linear regression (MNLR) methods in semi-arid region of Iran. Five different ANN and MNLR models comprising various combinations of daily meteorological variables, that is, relative humidity (RH), air temperature (T), solar radiation (SR), wind speed (U) and precipitation (P) were developed to evaluate degree of effect of each of these variables on E P. The comparison of models estimates showed that the ANN 5 model characterized by Delta-Bar-Delta learning algorithm and Sigmoid activation function which uses all input parameters (T, U, SR, RH, P) performed best in prediction of daily E P. The sensitivity analysis revealed that the estimated E P data are more sensitive to T and U, respectively. A comparison of the model performance between ANN and MNLR models indicated that ANN method presents the best estimates of daily E P.  相似文献   

19.
Summary Mature Salustiana orange trees under drip irrigation were subjected to deficit irrigation during three years. The water applied (including effective rainfall) in the five irrigation treatments was: (A) 60% of the evaporation of a Class A pan over irrigated grass (Control treatment); B) and C 80% and 60% of control, during the whole year, respectively; (D) 60% of control during the flowering and fruit set period; (E) 60% of control during the fruit maturation period. During the rest of the year, treatments D and E received the same amount of water as the control. There were four replicates in a completely randomized block design. Irrigation frequency was the same for all treatments. Crop evapotranspiration (ET) was estimated by the water balance method using a neutron moisture meter. ET for the control treatment was about 840 mm/year and it was reduced in the deficit treatments. Irrigation treatments affected both yield and fruit quality although the effects varied between years according to the season's rainfall. Fruit number was not affected by the irrigation treatments, therefore differences in yield were due to effect on average fruit weight. Compared to the control treatment, treatments B and C decreased yield significantly (p = 0.05) by 5% and 15%, respectively, and increased the total soluble solids and acids content of the fruit juice. Water deficit in the flowering and fruit set period (treatment D) decreased yield by 4%, acids content of the juice and peel thickness. Treatment E produced fruit of lower quality with thicker peel and more acids than the control. Treatments did not affect juice and pulp content, maturity index of fruits nor maturation time. The effects of the irrigation treatments on the water status of the trees, fruit set and abscission and their implications on irrigation scheduling are also discussed.  相似文献   

20.
A study of losses from field channels under arid region conditions   总被引：1，自引：0，他引：1  
In arid regions, water losses from unlined small field channels are usually high due to seepage and evaporation from open surfaces. These losses are often neglected by many project planners and engineers. A theoretical analysis has been developed to modify the equation usually used to determine the water losses based on the ponding method, where the channel longitudinal slope was considered in the analysis. A field investigation has been carried out in sandy soil to determine and evaluate the water losses for three different types of channels. They are: earthen-uncompacted channel, compacted channel bed and channel lined by jute mats coated with bitumen emulsion on both faces. The last two cases are relatively low-cost, need less skillful labour than lining by cement and are more suitable for temporary field channels. Manning's coefficient was determined for each case. The results show that the process of compating the channel bed reduced the rate of seepage by a considerable value and that lining of field channels by prefabricated bitumen jute mats caused a significant reduction in the seepage rate. The results also show that the evaporation from open surfaces caused a considerable loss and should be considered when studying water losses from irrigation channels in arid regions. Abbreviations A = channel surface area ⋅ Ac = channel cross section-area ⋅ b = channel bed width ⋅ d = observed difference in Class-A pan ⋅ h1 = original water depth in the canal ⋅ h2 = canal water depth after a certain time ⋅ k = constant ⋅ L = canal length ⋅ n = Manning's coefficient ⋅ p = average wetted perimeter ⋅ qevap = evaporation losses rate ⋅ qs = canal seepage losses rate ⋅ qt = total losses from the canal ⋅ Q = canal discharge ⋅ R = penetration resistance ⋅ Rh = hydraulic radius of the channel ⋅ s = channel longitudinal slope ⋅ t = time ⋅ Ve = volume of water lost by evaporation ⋅ vm = channel mean velocity ⋅ vs = channel surface velocity ⋅ Vs = volume of water lost by seepage ⋅ Vt = total volume of water lost ⋅ w = water surface width of the canal ⋅ y1 = downstream water depth at time zero ⋅ y2 = downstream water depth after a time t ⋅ z = canal side slope Received: 6 October 1995  相似文献   

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