Determination of actual evapotranspiration and crop coefficients of broad bean (Vicia Faba L.) grown under field conditions in the jordan valley,jordan: Bestimmung der aktuellen evapotranspiration und pflanzenbestandskoeffizienten von bohnen (Vicia Faba L.) unter feldbedingungen im jordantal,jordanien

This study was conducted to determine actual evapotranspiration and crop coefficients at different growth stages of broad bean (Vicia faba L.) grown in an open field in the Jordan Valley, Jordan using a precise and accurate approach. The study involved 30-min fluxes measurements of energy budget components over broad bean crop using a complete setup of an Eddy Correlation (EC) system. The measurements were conducted during the three main crop growth stages namely initial, development, and midseason growth stages following the Food and Agriculture Organization of the United Nations (FAO) crop coefficient model for green harvested broad bean crop. The average crop coefficients during the initial (K_{C ini}), development (K_{C dev}) and midseason (K_{C mid}) growth stages were 0.37, 0.8 and 1.05, respectively. The measured weighted average crop coefficient over the entire growing season K_{C GS} was 9.5% lower than the FAO corresponding value.

Results showed that there was a clear decrease of (bulk) surface resistance (r_s) as crop canopy developed. Daily average r_s values were 855, 337, and 166?s/m for initial, development, and midseason growth stages, respectively. Moreover, r_s was found to be highly correlated to crop height (h_c). A simple linear relation between r_s and h_c with R² of 0.91 was found. This relation will enable future direct determination of crop evapotranspiration (ET_C) using Penman-Monteith equation without the need to calculate both grass reference evapotranspiration (ET_O) and crop coefficient (K_C) values.     

Performance Assessment of Chlorophyll Meter to Determine When to Irrigate Wheat under Different Soil Moisture Deficit Conditions: An Initial Study

ABSTRACT

Proper irrigation timing can minimize the negative impacts that reduce crop yields. Therefore, in an initial pot experimental study, we assessed the SPAD (Soil–Plant Analysis Development)-chlorophyll meter as a tool to determine proper irrigation timing of wheat under different soil water deficit conditions in a controlled-environment greenhouse. The treatments were controlled irrigation at 100% (T₁), 70% (T₂), 50% (T₃) and 30% (T₄) of soil water content at field capacity; and the growth stages were development, mid-season and late-season. SPAD readings were measured pre-irrigation events. The results indicated that the T₃ and T₂ achieved maximum grain yield per accumulated crop evapotranspiration, i.e. water productivity (0.82 and 0.76 kg m^?3), and were at par with T₁. Moreover, the SPAD readings had a high Pearson’s correlation coefficient with crop evapotranspiration (r = 0.95; P ≤ 0.001) and wheat grain yield (r = 0.90; P ≤ 0.001), indicating that SPAD reading could be used to reliably estimate when to irrigate wheat. Therefore, T₃ and T₂ SPAD readings were averaged to estimate a target limit at which irrigation should be applied. Accordingly, the target limit was defined as >44.76 for the development stage, >50.72 for the mid-season stage, and >37.64 for the late-season stage; readings below this target limit indicate that it is time to irrigate.     

Comparison of Different Methods of Estimating Saffron Yield Based on Soil Properties in Golestan Province

ABSTRACT

Evaluation of the relationship between soil properties and saffron yield estimation may contribute to agricultural planning in finding suitable lands for the growth of this valuable product. This study aimed to investigate the performance of artificial neural network (ANN), multiple linear regression (MLR), and adaptive neuro-fuzzy inference system (ANFIS) in terms of saffron yield estimation in some lands of Golestan province, Iran. To this end, 100 areas under saffron cultivation were selected. For rapid and low-cost saffron yield estimation, six different models were designed based on soil properties as inputs using MLR, ANN, and ANFIS methods. According to the results, ANN showed the highest accuracy (R² = 0.58–0.89) in estimating saffron yield as compared to MLR (R² = 0.41–0.47) and ANFIS (R² = 0.41–0.69) models. A comparison of the results obtained from the six models defined in these three methods indicated that Model 4 (R² _Reg = 0.45, R² _ANFIS = 0.57, R² _ANN = 0.87), with the inputs, organic phosphorus, potassium, and calcium carbonate, was the best model in terms of accuracy and speed in estimating saffron yield phosphorus. The RI indexes for ANN in the model were 50% and 34% relative to MLR and ANFIS, respectively, demonstrating the higher accuracy of ANN in saffron yield estimation. The study results can be used to identify lands suitable for saffron cultivation in the study area using organic phosphorus and organic matter levels in the soil.     

华北地区设施茄子蒸散量估算模型及作物系数确定

构建华北地区设施茄子蒸散量估算模型,可为制定其优化灌溉制度提供理论依据。本研究设灌水定额15 mm(W1)、22.5 mm(W2)、30 mm(W3)和37.5 mm(充分灌溉, CK)4个处理,在设施茄子苗期、开花座果期和成熟采摘期土壤含水率分别达田间持水量的70%、80%和70%时进行灌溉,以保证土壤供水充足。基于修正后的Penman-Monteith方程,通过分析CK处理的作物系数与叶面积指数的关系,建立了基于气象数据与叶面积指数的蒸散量估算模型,利用W1、 W2和W3实测蒸散量对其进行验证。结果表明:修正后的Penman-Monteith方程可用于设施参考作物蒸散量的估算,W1、W2和W3蒸散量的实测值与新建模型的模拟值平均相对误差分别为17.81%、18.31%和17.97%。作物系数与叶面积指数呈显著线性关系,可通过叶面积指数确定作物系数。分析W1、W2、W3和CK处理的产量和水分利用效率(WUE)得出, W2与CK产量差异性不显著,而WUE差异性显著,较CK提高31.59%,表明W2兼顾产量和WUE。W2处理下茄子的作物系数,苗期为0.21～0.46,开花座果期为0.62～0.94,成熟采摘期为0.70～0.92。本研究认为,新建模型在估算设施茄子实际蒸散量上具有较好适用性,计算出的作物系数在节水灌溉条件下具有实际应用价值。     

Climate change impacts modeling on winter wheat yield under full and deficit irrigation in Myandoab-Iran

In this research, impact of climate change on wheat yield was simulated using SWAP in Myandoab, Iran. Field data of wheat in 2004–2005 and 2005–2006 periods were used for calibration and validation of the SWAP, respectively. The HadCM3 outputs, for A1B, A2 and B1 scenarios and 2046–2065 periods, were used in SWAP and wheat yield in mentioned period was compared with base period. Three irrigation levels, based on meeting 100, 70 and 50% of the crop ET demand, were used to study the climate change effects on wheat yield in full and deficit irrigation conditions. The results showed that temperature and reference evapotranspiration will increase in 2055s. Temperature increase cause to decrease crop growing period and crop evapotranspiration. The results showed that the negative impact of temperature increase has dominated to the positive impact of CO₂ concentration and the yield is reduced. For full irrigation situation, the reduction will be 24.1, 22.4 and 20.8% in A1B, A2 and B1, respectively. Reduction in yield can be related to the shorter maturity period of the crop. The results showed that under deficit irrigation, the yield is also decreased but this decrease rate of yield is higher in full irrigation.     

Yield and yield components of two irrigated red bean cultivars and some soil properties as influenced by wheat residues and nitrogen management

Crop residues are beneficial substances affecting crop production and soil properties. A field experiment was carried out to evaluate the effects of wheat (Triticum aestivum L.) residue rates (0, 25, 50 and 75%) combined with N levels (0, 34.5, 69, 103.5 kg ha^?1) on yield and yield components of two red common bean (Phaseolus vulgaris L.) cultivars and to monitor chemical soil parameters. The experiment was conducted at Research Center, College of Agriculture, Shiraz University, Shiraz, Iran for two years (2008–2009). The experiment was conducted as a split–split plot arranged in a randomized complete blocks design with three replications. The highest seed yield was obtained when 25–50% of residues were incorporated. The highest seed yield, seed weight per plant, 100-seed weight and seed number per pod were obtained with 103.5 kg N ha^?1 with no significant difference to 69 kg N ha^?1. Residue incorporation significantly increased soil organic carbon (SOC) as well as available K and P content. It is possible to sow red common bean as a double cropping by soil incorporation of 25–50% wheat residues with application of 69 kg N ha^?1.     

Effect of different safflower (Carthamus tinctorius L.)–bean (Phaseolus vulgaris L.) intercropping patterns on growth and yield under weedy and weed-free conditions

Two field experiments were carried out over two consecutive years (2010–2011) in the research field of the College of Agriculture, Shiraz University, Fars Province, southern Iran. The study was a factorial experiment based on a randomized complete block design with three replications: the first factor was the ratio of safflower (Carthamus tinctorius L. Pi cv.) to bean (Phaseolus vulgaris L. Saiad cv.) at five levels (safflower and bean sole cropping, and intercropping of safflower and bean at ratios of 1:3, 2:2 and 3:1); and the second factor was weed management at two levels: weed-free (complete weed control) and weedy (no weed control). The results showed that an intercropping system was the most appropriate method for decreasing the adverse effect of weeds on the performance of both crops. Intercropping was more suitable for weedy than weed-free conditions. According to the land equivalent ratio (LER) value, if the main crop was bean, the best intercropping treatment was one row of safflower and six rows of bean (S₁B₃) under both weedy and weed-free conditions. By contrast, if the main crop was safflower, the best treatment under weedy conditions was S₁B₃, whereas under weed-free conditions the best treatment was two rows of safflower and four rows of bean (S₂B₂). Overall, S₁B₃ can be introduced as the best intercropping method.     

Evaluation of pan coefficient equations for estimating reference crop evapotranspiration in the arid region

Reference evapotranspiration (ET₀) can be estimated on basis of pan evaporation data (E_pan), whose measurements have the advantage of low cost, simplicity of the measuring equipment, simple data interpretation and application as well as suitability for locations with limited availability of meteorological data. E_pan values were converted to ET₀ using the pan evaporation coefficient (K_pan). In this study, seven common K_pan equations were evaluated for prediction of ET₀ in the growing season (April to October) in arid region of Iran. The Cuenca approach was best suited compared to the standard FAO Penman–Monteith method (FAO-56 PM).     

滴灌夏玉米土壤水分与蒸散量SIMDualKc模型估算

为研究西北半干旱地区作物蒸腾和土壤蒸发规律,以及土壤蒸发量占蒸散量的比例(简称蒸发占比),开展2 a夏玉米滴灌控水试验,设置正常灌水(W1)、适度水分亏缺(W2)和中度水分亏缺(W3)3个灌水水平.采用W2实测土壤水分数据对SIMDualKc模型进行参数率定,并采用W1和W3实测土壤水分数据对模型进行验证;进一步基于SIMDualKc模型对不同水分供应的土壤水分胁迫系数、土壤蒸发量、植株蒸腾和蒸散量进行定量模拟分析.结果表明,SIMDualKc模型可以较好地模拟西北半干旱区滴灌夏玉米不同水分供应条件下的土壤水分动态变化过程,实测值与模型预测值有较好的一致性(R2＞0.88,RMSE＜5％);夏玉米生长期,模型能较好地估算不同水分供应的土壤水分胁迫系数、土壤蒸发量和植株蒸腾.土壤蒸发主要集中在生育前期,而生育中期较低,后期略微升高.植物蒸腾主要集中在快速生长期和生长中期,整个生育期呈先增大后减小的趋势.蒸散量随着土壤蒸发和植物蒸腾的变化而变化,前期主要受土壤蒸发的影响,快速生长期、生长中期和后期主要受植物蒸腾的影响.Wl～W3处理土壤蒸发量为78.1～100.2 mm,植株蒸腾为221.8～293.3 mm,蒸散量为299.3～383.0 mm,蒸发占比为24.1％～28.7％.研究可为西北半干旱地区制定合理的夏玉米滴灌制度和灌溉决策提供理论依据.     

Calibration of Hargreaves–Samani equation for estimating reference evapotranspiration in semiarid and arid regions

The Penman–Monteith (FAO-56 PM) equation is suggested as the standard method for estimating evapotranspiration (ET₀) by the International Irrigation and Drainage Committee and Food and Agriculture Organization (FAO). On the other hand, the Hargreaves–Samani (HS) equation is an alternative method compared with the FAO-56 PM equation. In the present study, the original coefficient C of the HS equation is calibrated based on the FAO-56 PM equation for estimating the reference ET₀ from 15 meteorological stations in central Iran (about 170,000 km²) under semiarid and arid conditions. After calibration, the new values for C are ranged from 0.0018 to 0.0037. The mean bias error (MBE), the root mean square error (RMSE), and the ratio of average estimations of ET₀ (R) values for all stations are ranged from 0.12 to 5.38, ?5.35 to 1.15 mm d^?1 and 0.64 to 1.28 for the HS equation and from 0.12 to 2.48, ?2.2 to 0.60 mm d^?1, and 1.00 to 1.05 for the calibrated Hargreaves–Samani equation (CHS), respectively. Results indicate that the average RMSE and MBE values are decreased by 40% and 66%, respectively. Relationships for calibrating the C coefficient on the basis of annual average of daily temperature range (ΔT) and wind speed (V) are proposed, calibrated, and validated. Hence, the CHS equation can be used for ET₀ estimates with acceptable accuracy instead of the FAO-56 PM method.     

Calibration of Hargreaves–Samani and Priestley–Taylor equations in estimating reference evapotranspiration in the Northwest of Iran

Accurate estimation of reference evapotranspiration (ET_o) is essential for water resources management and irrigation systems scheduling, especially in arid and semiarid regions such as Iran. In the present research, constant coefficients of Hargreaves–Samani (C_H–S) and Priestley–Taylor (C_P–T) equations were locally calibrated to estimate the ET_o based on the FAO–Penmen–Monteith (PM) method as standard method. For this purpose, meteorological data of eight synoptic stations located in the northwest of Iran were used during the period of 1997–2008. The outcomes showed that the values of C_H–S and C_P–T were 0.0026 (instead of 0.0023) and 1.68 (instead of 1.26), respectively. Also, at stations with high wind speed, the values of calibrated coefficients of C_H–S and C_P–T were maximum. Then, the estimated ET_o values using adjusted C_H–S and C_P–T coefficients were compared to the obtained actual ET_o values by PM method using root mean square error and mean bias error indices. The results indicated that the new calibrated H–S and P–T equations have good agreement with the PM method for estimation of the ET_o. Moreover, the equation of Ravazzani et al. was calibrated in the studied region. It was concluded that in general, the mentioned equation was shown better performance than original H–S equation.     

蒸渗仪测定滴灌枣树不同时间尺度下腾发强度特征

为精确测定、准确模拟阿克苏地区滴灌枣树腾发过程,基于大型称重式蒸渗仪测定枣树全生育期逐时及逐日腾发强度（ET）,利用水量平衡方程、PM公式及经典统计原理,分析不同时间尺度下叶面积指数（LAI）、气象因素[温度（I）、风速（V）、净辐射（R_n）]、表层土壤含水率（W）与枣树腾发强度的相关关系并建立预测模型。结果表明：枣树日内腾发强度呈单峰型变化趋势,夜间变化幅度较小且腾发贡献率低。枣树全生育期逐日腾发强度变化呈先增大后减小的趋势,花期的腾发强度最大,为4.42 mm·d^-1;全生育期腾发总量为640.83 mm,其中花期和果实生长发育期耗水量占比较大,分别为38.61%和32.72%。在小时和日时间尺度上,影响腾发强度的主要因素不完全相同,且影响程度有所差异。综合考虑各影响因素,以萌芽期、花期、果实发育期为基础,分别建立以小时、日尺度下估算腾发强度的经验模型ET₁（h）=0.153+0.004T+0.012V+0.176R_n+0.002W+0.067LAI、ET₂（d）=-3.325+0.081T+0.163R_n+0.069W+2.089LAI,拟合度R²均在0.7以上,以果实发育期与成熟期数据对模型进行检验,纳什效率系数分别达0.63、0.80。经偏相关检验,冠层净辐射（R_n）对两种尺度的腾发强度均影响最显著,因此以枣树全生育期数据量为基础,仅建立冠层净辐射（R_n）与腾发强度的回归模型ET₁（h）=-0.063 3R_n²+0.361 2R_n—0.003 7、ET₂（d）=-0.018 3R_n²+0.684 7R_n–1.642 1,R²分别为0.704 7与0.743 6,可满足缺少数据支撑情况下的腾发过程估算。这些模型明确了阿克苏地区滴灌枣树腾发机制及影响程度,可为水分管理精准化提供计算基础。     

Increasing saffron (Crocus sativus L.) corm size through the mycorrhizal inoculation,humic acid application and irrigation managements

Corm size is the most important factor in production of replacement corms and flower yield of saffron. The aim of this study was to investigate the effect of nutrition and irrigation managements on saffron corms characteristics in the experimental field of Faculty of Agriculture, Ferdowsi University of Mashhad, Iran, in 2013–2015. The experiment was carried out as split-split plot based on a Randomized Complete Block Design with 18 treatments and three replications. Experimental factors were: 1- superabsorbent (SA) [application and no-application of superabsorbent (non-SA)], 2- irrigation intervals [irrigation every 2, 3 and 4 weeks] and 3- nutrition management [humic acid, mycorrhiza (Glomus intraradices) and control]. The results showed that the highest total weight of replacement corms per clone in sum of two years was obtained in non-SA application, two weeks irrigation intervals and humic acid treatment. The corm/tunic weight ratio decreased by increasing the irrigation intervals and this index in two weeks irrigation intervals was 31% more than four weeks irrigation intervals. Application of nutritional treatments increased the number of saffron replacement corms per clone in all of the weight categories (0-3, 3–6, 6–9 and more than 9 g) on averaged 5, 40, 36 and 25%, respectively compared with control treatment in both years. Results showed that the replacement corms yield in large weight groups was on average 34% higher in the second year than the first year. Finally, application of SA, organic and bio fertilizers and four weeks irrigation intervals improved most of criteria and yield of saffron replacement corms.     

Energy and water balance measurements for water productivity analysis in irrigated mango trees, Northeast Brazil

Crop water parameters, including actual evapotranspiration, transpiration, soil evaporation, crop coefficients, evaporative fractions, aerodynamic resistances, surface resistances and percolation fluxes were estimated in a commercial mango orchard during two growing seasons in Northeast Brazil. The actual evapotranspiration (E_a) was obtained by the eddy covariance (EC) technique, while for the reference evapotranspiration (E₀); the FAO Penman–Monteith equation was applied. The energy balance closure showed a gap of 12%. For water productivity analysis the E_a was then computed with the Bowen ratio determined from the eddy covariance fluxes. The mean accumulated E_a for the two seasons was 1419 mm year⁻¹, which corresponded to a daily average rate of 3.7 mm day⁻¹. The mean values of the crop coefficients based on evapotranspiration (K_c) and based on transpiration (K_cb) were 0.91 and 0.73, respectively. The single layer K_c was fitted with a degree days function. Twenty percent of evapotranspiration originated from direct soil evaporation. The evaporative fraction was 0.83 on average. The average relative water supply was 1.1, revealing that, in general, irrigation water supply was in good harmony with the crop water requirements. The resulting evapotranspiration deficit was 73–95 mm per season only. The mean aerodynamic resistance (r_a) was 37 s m⁻¹ and the bulk surface resistance (r_s) was 135 s m⁻¹. The mean unit yield was 45 tonne ha⁻¹ being equivalent to a crop water productivity of 3.2 kg m⁻³ when based on E_a with an economic counterpart of US$ 3.27 m⁻³. The drawback of this highly productive use of water resources is an unavoidable percolation flux of approximately 300 mm per growing season that is detrimental to the downstream environment and water users.     

Crop evapotranspiration of chilli in the tropics

Abstract

The rate of crop evapotranspiration though can be predicted theoretically but the actual field study would give a more accurate data. Result from a simple lysimeter study showed that the daily rate of actual crops evapotranspiration, ETa of chilli (Capsicum annum) under the tropical condition was in the range between 4.94–7.72 mm. Their actual crop evapotranspiration/ reference crop evapotranspiration ratio, ETa/ETo ratio was between 0.94 to 1.76 depending on the growth stages of the crops. The estimated monthly value of ETo using Blaney‐Criddle was about 5 mm/day.     

Evaluation of water schemes for peanut,using CSM-CROPGRO-Peanut model

Drought stress is an important factor limiting the yield potential of peanut. In order to determine the effect of different irrigation scenarios on peanut production, field experiments were conducted in 2011 and 2012 growing seasons using factorial design with three replicates. On the other hand, the crop simulation models can be useful to predict crop yields and to investigate the impact of drought stress on plant growth and development. In this study, the Cropping System Model–Crop Growth (CSM-CROPGRO)-Peanut model was employed for the simulation of seed yield, pod yield, biomass, soil water balance components and water productivity for peanut in Astaneh-Ashrafiyeh, Iran. Results showed that the model was able to reasonably simulate seed yield, pod yield and final biomass for different irrigation scenarios (RMSEn < 20%, R² > 0.8 and d > 0.8). According to the results, irrigation depth and interval were important factors affecting yield and biomass. In general, model error increased as the amount of water applied decreased. The least amount of water applied (40 mm) resulted in yield reductions by 76%, 70% and 67% of the greatest amount of water applied (480 mm) for seed yield, pod yield and final biomass, respectively. For each irrigation interval, larger irrigation depth led to lower water productivity (WP) of irrigation (WP_I), but higher WP based on evapotranspiration (WP_ET) and transpiration (WP_T).The average amounts of WP_I, WP_ET, WP_T based on seed yield were 1.2, 0.63 and 1.01 kg m^?3, respectively.     

Study of different climatic conditions to assess the role of solar radiation in reference crop evapotranspiration equations

This study aims to assess radiation-based models versus the FAO Penman–Monteith (FPM) model to determine the best model using linear regression under different weather conditions. The reference evapotranspiration was estimated using 22 radiation-based methods and was compared with the FPM. The results showed that the Stephens method estimates the reference evapotranspiration better than other methods in the most provinces of Iran (nine provinces). However, the values of R² were more than 0.9930 for 24 provinces of Iran. The radiation-based methods estimated the reference evapotranspiration near the Caspian Sea better than other regions. The most precise methods were the Berengena–Gavilan, Modified Priestley–Taylor, and Priestley–Taylor methods for the provinces ES (center of Iran), GI and GO (north of Iran) and the Stephens–Stewart method for IL (west of Iran). Finally, a list of the best performance of each method has been presented to use other regions and next research steps according to the values of mean, maximum, and minimum temperature, relative humidity, solar radiation, elevation, sunshine, and wind speed. The best weather conditions to use radiation-based equations are 23.6–24.6 MJ m^?2 day^?1, 12–20°C, 18–24°C, 5–13°C, and <180 hour month^?1 for solar radiation, mean, maximum, and minimum temperature, and sunshine, respectively.     

日光温室覆膜滴灌条件下樱桃西红柿耗水规律

为了给温室膜下滴灌灌溉制度的制定提供参考,通过大型称重式蒸渗仪实测覆膜滴灌条件下樱桃西红柿蒸腾量,分析了温室微环境气象条件及水面蒸发量的变化规律,计算了日光温室春夏茬樱桃西红柿在覆膜滴灌条件下不同生育阶段的耗水强度、作物系数及蒸发皿系数。结果表明：日光温室覆膜滴灌条件下,樱桃西红柿在不同生育阶段的耗水强度、作物系数和蒸发皿系数分别为：苗期0.22 mm/d、0.09、0.10;开花坐果期1.65 mm/d、0.48、0.65;盛果期2.56 mm/d、1.56、1.76;盛果后期1.90 mm/d、1.12、2.06;该研究建立了温室樱桃西红柿累计耗水量与水面蒸发量累积值、温室温度累计值之间函数关系,为合理地制定温室作物灌溉制度提供了一定依据。     

用FAO-56作物系数法推求控制灌溉条件下晚稻作物系数及验证

根据国家“863”节水农业重大专项试验资料，利用FAO-56推荐的分段单值法和双值法构建了控制灌溉条件下晚稻的作物系数曲线，分析了调整灌溉或降雨后的最大作物系数值对双值法水稻作物系数计算结果的影响，并根据2004年实测资料对研究结果进行了验证。结果表明：控制灌溉条件下，晚稻分蘖期、拔节孕穗期、抽穗开花期及乳熟期的作物系数实测值分别为1.14、1.49、1.43和1.12。分段单值法得到初始生长期、生育中期和后期的作物系数分别为1.1、1.39和0.79。降雨频繁阶段或灌溉阶段，对最大作物系数作调整后，减小了双值法作物系数计算值与实测值的误差。验证结果表明，2004年晚稻累积蒸发蒸腾量模拟值与实测值的相对误差为12.42%～16.24%，以基于调整后的双值法作物系数的晚稻蒸发蒸腾量模拟结果与实测值最为接近。     

额济纳绿洲草地蒸散系数研究

联合国粮农组织推荐的蒸散计算方法中,蒸散系数是计算实际蒸散必不可少的参数。本文从蒸散系数的定义出发,在2005年额济纳绿洲生长季连续观测的基础上,运用波文比能量平衡法计算额济纳绿洲草地的实际蒸散量,利用FAO 56Penman-Monteith模型计算草地的参考蒸散,将实际蒸散与参考蒸散相除即得到额济纳绿洲草地的蒸散系数。通过研究发现:生长季草地的蒸散量(ETc)为446.96mm,从生长季初期开始,草地的蒸散量开始增加,在6月后半月达到最大值6.724mm/d,此后蒸散量开始快速下降,在生长季末期达到最低值1.215mm/d;蒸散系数(Kc)呈现出与蒸散量(ETc)相同的变化趋势,自生长季初期开始蒸散系数快速上升,在6月后半月达到生长季最大值0.623,之后随着草地生长减缓,蒸散系数快速下降,直至生长季末期草地停止生长。对额济纳绿洲草地蒸散系数的计算可以为该地区准确估算草地生态需水量提供依据。