Rice Evapotranspiration Research Articles

Temporal Upscaling of Rice Evapotranspiration Based on Canopy Resistance in a Water-Saving Irrigated Rice Field

AbstractAn important element of the hydrologic cycle, the hydrometeorological parameter of evapotranspiration (ET), is critical in the development of effective water resources planning and irrigation scheduling. The ET varies in response to changes in resistance at the canopy surface rc and soil moisture content θ, especially under water-saving irrigation (WSI) practices. Drawing on data collected by eddy covariance in WSI rice paddies in eastern China in 2015 and 2016, variations in ET were studied by calculating and analyzing hourly canopy resistance and daily canopy resistance . Discrepancies were noted between true daily ET with respect to the estimated daily ET at different periods [0700–1600 local time (UTC + 8)]. To estimate in the WSI rice fields, the mean value between 0900 and 1000 LT, and between 1000 and 1100 LT performed considerably better than for a single time. Seasonal estimated ET can be accurately calculated by interpolating at different time intervals, thereby achieving a greater correlation and consistency at 2-day intervals. Then a generalized two-segment line of variation was used to calculate , achieving good results and showing that in the absence of observational data, could be easily calculated through a simplified pattern of variability. In conclusion, an ET temporal upscaling method for a WSI paddy, based on variation in and values, was optimized and is recommended for local application. Future work will focus on temporal upscaling of ET by extrapolating remote sensing instantaneous estimates to daily values.

Geographical variations in gross primary production and evapotranspiration of paddy rice in the Korean Peninsula

The quantification of canopy photosynthesis and evapotranspiration of crops (ETc) is essential to appreciate the effects of environmental changes on CO2 flux and water availability in agricultural ecosystems and crop productivity. This study simulated the canopy photosynthesis and ET processes of paddy rice (Oryza sativa) based on the development of physiological modules (i.e., gross primary production [GPP] and ETc) and their incorporation into the GRAMI-rice model that uses remote sensing data. We also projected spatiotemporal variations in the GPP, ET, yield, and biomass of paddy rice at maturity using the updated GRAMI-rice model combined with geostationary satellite images to identify the relationships of canopy photosynthesis and ETc with crop productivity. GPP and ET data for paddy rice were obtained from three KoFlux sites in South Korea in 2015 and 2016. Vegetation indices were acquired from the Geostationary Ocean Color Imager (GOCI) of the Communication Ocean and Meteorological Satellite (COMS) from 2012 to 2017 and integrated into GRAMI-rice. GPP and ETc estimates using GRAMI-rice were in close agreement with flux tower estimates with Nash-Sutcliffe efficiency ranges of 0.40–0.79 for GPP and 0.49–0.62 for ETc. Also, GRAMI-rice was reasonably well incorporated with the COMS GOCI imagery and reproduced spatiotemporal variations in the GPP and ET of rice in the Korean peninsula. The current study results demonstrate that the updated GRAMI–rice model with the canopy photosynthesis and ETc modules is capable of reproducing spatiotemporal variations in CO2 assimilation and ET of paddy rice at various geographical scales and for regions of interest that are observable by satellite sensors (e.g., inaccessible North Korea).

Assessing recent impacts of climate change on design water requirement of Boro rice season in Bangladesh

Water requirement is sensitive to the impacts of climate change, especially in Bangladesh because of limited freshwater availability in the dry season, despite the fact that the country’s agriculture sector requires large quantities of water for the crop production. Hence, gaining a better understanding of changes in water requirements in Bangladesh during dry periods is important in the management of agricultural water resources. This study assesses the recent impacts of climate change on the design water requirement (DWR) of the Boro rice–growing season in Bangladesh using a frequency analysis over a 5-year period. The reference evapotranspiration (ETref), crop evapotranspiration (ETp), effective rainfall (ERF), and gross irrigation water requirements (GIWR) of Boro rice were estimated based on daily weather data for the period of 1984–2013 using the CROPWAT8.0 model. The results showed the significant decreasing trends of ETref in most of these Boro rice growth stages in all districts. The GIWR of Boro rice and its trends demonstrated significant spatial heterogeneity in the last three decades due to significant changes in the ERF and ETp. The DWR of Boro rice–growing season also supported the results of the GIWR, and the Weibull probability distribution function (PDF) is found to be an optimal PDF among eight PDFs for the estimation of DWR. Overall, the results indicate that a recent climate change does not only contribute to high water demands for the crop but also result in decrease water requirements due to variations in wind speed, sunshine hours, and relative humidity.

Shifting planting date of Boro rice as a climate change adaptation strategy to reduce water use

Suitable adaptation strategies for dry season Boro rice cultivation under future climate change scenarios are important for future food security in Bangladesh. This study assessed the effect of shifting trans−/planting date of dry season Boro rice as an adaptation strategy, with focus on water requirements under future climate scenarios. Potential crop water requirement, effective rainfall and irrigation requirement to satisfy crop evapotranspiration of Boro rice were estimated using CropWat 8.0 for early, normal and late planting dates for 2050s and 2080s. Future climate scenarios were constructed using five global circulation model (GCM) outputs for RCP 4.5 and 8.5 by statistical downscaling and bias correction. Number of days exceeding the threshold temperatures (maximum of 35 °C and minimum of 25 °C) was counted for critical period of Boro rice to understand compatibility of the changed planting dates. Results indicate that late planting can substantially reduce irrigation demand by increasing rainfall availability during Boro growth duration, but the option is very limited due to both day- and night-time heat stress. An early planting, on the other hand, accounts for high water demand but ensures suitable temperature during the critical growth stages of the crop. The normal planting dates show the possibility of day-time heat stress. So, late planting of temperature-tolerant cultivars or early planting of high-yielding varieties would be recommended based on local water availability. However, adjustment of the planting date is currently limited because high temperature-tolerant cultivars are not available in the study region.

Simulating the effects of climatic fluctuations on rice irrigation water requirement using AquaCrop

Irrigation water requirement is influenced by climatic fluctuations which can be simulated using agro-meteorological models. This study investigates fluctuating irrigation water requirements for rice as affected by drought occurrences. Irrigation requirements were simulated by the AquaCrop model in paddy fields of Guilan in northern Iran. Model validation was done based on field measurements during two consecutive years of 2012 and 2013 in the study area. The reconnaissance drought index (RDI), based on cumulative values of precipitation and potential evapotranspiration, was used for drought monitoring for 1982–2014, in two time scales of 3- and 6-month. Also, irrigation water requirements (IWR) were calculated for this period. The normalized root mean square error (NRMSE) for simulating canopy cover, biomass, rice evapotranspiration and deep percolation by AquaCrop were obtained 7.0, 8.8, 18.45 and 26.6%, respectively. The contributions of crop evapotranspiration and deep percolation in IWR were 70.5% and 22.9%, respectively. There are more drought occurrences after 1994. A good correlation was obtained between simulated rice IWR and RDI of July (calculated with 3-month time scale) (R = -0.89). Maximum amounts of required irrigation water in wet, normal and dry years, were 6750, 8050 and 8760 m³ ha−1, respectively. Obtained relationship between rice IWR and RDI of July with a 3-month time scale can be used to allocate paddies irrigation water of the studied area at transplanting time based on seasonal forecasts of drought.

Estimation of crop evapotranspiration and crop coefficients of rice (Oryza sativa L.) under low land condition

An attempt has been made to estimate the crop evapotranspiration (ETc) and Kc under alternate wetting and drying method (AWD) of water management of rice (Oryza sativa L.) under lowland condition during 2013 and 2014 at Rajendranagar, Hyderabad. The average seasonal ETc was highest in continuous submergence (Cs) of 3-cm depth from transplanting to panicle initiation (PI) and 5-cm from PI to physiological maturity (PM) (657.8 mm) followed by AWD irrigation regimes of flooding to a water depth of 5-cm between15 DAT to PM and when ponded water level drops to 5-cm below ground level in field water tube (628 mm). The results suggested that the roots of rice were able to extract adequate amount of water to satisfy its ETc needs for 2-7 days in different treatments of AWD. The mean crop coefficient values worked out were 1.35, 1.59, 1.81 and 1.33 at initial establishment stage, vegetative and panicle initiation stage, at panicle development stage and at ripening and maturity stage.

Short-term daily forecasting of crop evapotranspiration of rice using public weather forecasts

Accurate forecasts of daily crop evapotranspiration (ETc) are essential for real-time irrigation management and water resource allocation. This paper presents a method for the short-term forecasting of ETc using a single-crop coefficient approach and public weather forecasts. Temperature forecasts with a 7-day lead time in 2013–2015 were retrieved and entered into a calibrated Hargreaves–Samani model to compute daily reference evapotranspiration (ET0) forecasts, while crop coefficient (Kc) empirical values were estimated from both observed ETc value and calculated ET0 values using the Penman–Monteith equation for the period of 2010–2012. Daily ETc forecasts of irrigated double-cropping rice were determined for three growing seasons during the period of 2013–2015 and were compared with ETc values measured by the weighing lysimeters at the Jiangxi experimental irrigation station in southeastern China. During the early rice season, the average mean absolute error (MAE) and root-mean-square-error (RMSE) values of ETc forecasts ranged from 0.95 to 1.06 mm day−1 and from 1.18 to 1.31 mm day−1, respectively, and the average correlation coefficient (R) ranged from 0.39 to 0.54; for late rice, the average MAE and RMSE values ranged from 1.01 to 1.09 mm day−1 and from 1.32 to 1.40 mm day−1, respectively, and the average R value ranged from 0.54 to 0.58. There could be three factors responsible for errors in ETc forecasts, including temperature forecast errors, Kc value errors and neglected meteorological variables in the HS model, including wind speed and relative humidity. In addition, ETc was more sensitive to changes in temperature than Kc. The overall results indicated that it is appropriate to forecast ETc with the proposed model for real-time irrigation management and water resource allocation.

Scale Effects of Water Saving on Irrigation Efficiency: Case Study of a Rice-Based Groundwater Irrigation System on the Sanjiang Plain, Northeast China

This research analyzed the scale effect of water saving in Bielahonghe (BLH) Basin, a rice-cultivating district on the Sanjiang Plain, Northeast China. Water budgets with different surface irrigation water supply ratios and water-saving measures were simulated with a semi-distributed water balance model. PFnws, representing the ratio of rice evapotranspiration to net water supply (the total amount of irrigation and precipitation minus the amount of water reused), was employed to assess the water use efficiency. Seven spatial scales (noted from S1 to S7), ranging from a single field (317.87 ha) to the whole basin (about 100,800 ha) were determined. PFnws values were quantified across scales and several water-saving measures, including water-saving irrigation regimes, canal lining, and a reduction of the surface water supply ratio (SWSR). The results indicated that PFnws increased with scale and could be calculated by a fitted power function (PFnws = 0.736Area0.033, R2 = 0.58). Furthermore, PFnws increased most prominently when the scale increased from S1 to S2. The water-saving irrigation regime (WSIR) had the most substantial water-saving effect (WSE) at S1. Specifically, PFnws improved by 21.2% at S1 when high-intensity WSIR was applied. Additionally, the WSE values of S3 and S5 were slightly higher than at other scales when the branch canal water delivery coefficient increased from 0.65 to 0.80 through canal lining. Furthermore, the PFnws at each scale varied with SWSR. Specifically, PFnws from S3 to S7 improved as SWSR decreased from 0.4 to 0.3 but remained approximately constant when SWSR decreased from 0.3 to 0.

Inter-seasonal and cross-treatment variability in single-crop coefficients for rice evapotranspiration estimation and their validation under drying-wetting cycle conditions

A two-year experiment was conducted to investigate the inter-seasonal and cross-treatment variability in measured rice evapotranspiration (ETcMea), measured single-crop coefficients (KcMea), and treatment-specific calibrated coefficients (KcCal), under different drying-wetting cycles in a subtropical monsoon climate in East China. For each drying-wetting treatment, ETcMea was determined based on data collected in lysimeters, and KcMea was calculated from ETcMea, reference evapotranspiration, and soil moisture deficit coefficient. Following the single-crop coefficient method, KcCal was determined by matching KcMea. In 2012 and 2013, ETcMea varied from 459.5 to 486.7mm, and 544.5–605.1mm, respectively. Its inter-seasonal variability was larger than the cross-treatment variability. Stage-wise average KcMea were 1.07–1.17, 1.30–1.51, 1.49–1.54, and 1.17-1.29 in 2012, and 1.06–1.12, 1.31–1.49, 1.43–1.57, and 1.26–1.27 in 2013 during the initial, crop development, mid-season, and late season stages, respectively. Treatment-specific KcCal were calibrated as 1.09–1.20, 1.51–1.60, and 0.74–0.78 in 2012, and 1.05–1.14, 1.47–1.64, and 0.96–1.01 in 2013 for the initial, mid-season, and end-season stages, respectively. The inter-seasonal and cross-treatment variability in KcMea and KcCal was low. Each treatment-specific KcCal set performed similarly when rice ETc was calculated under different drying-wetting treatments. Cross validation indicated that large daily uncertainty in ETc estimation occurred when daily ETcMea was high, and uncertainty in seasonal ETc calculated using different treatment-specific KcCal sets ranged from 45.7 to 60.1mm (approximate to one irrigation). Calibrating KcCal using more data (season-specificKcCal or mixed treatment KcCal) would improve the accuracy of KcCal in ETc estimation.

Modeling plant density and ponding water effects on flooded rice evapotranspiration and crop coefficients: critical discussion about the concepts used in current methods

The aim of the study is to propose new modeling approaches for daily estimations of crop coefficient K c for flooded rice (Oryza sativa L., ssp. indica) under various plant densities. Non-linear regression (NLR) and artificial neural networks (ANN) were used to predict K c based on leaf area index LAI, crop height, wind speed, water albedo, and ponding water depth. Two years of evapotranspiration ET c measurements from lysimeters located in a Mediterranean environment were used in this study. The NLR approach combines bootstrapping and Bayesian sensitivity analysis based on a semi-empirical formula. This approach provided significant information about the hidden role of the same predictor variables in the Levenberg-Marquardt ANN approach, which improved K c predictions. Relationships of production versus ET c were also built and verified by data obtained from Australia. The results of the study showed that the daily K c values, under extremely high plant densities (e.g., for LAI max > 10), can reach extremely high values (K c > 3) during the reproductive stage. Justifications given in the discussion question both the K c values given by FAO and the energy budget approaches, which assume that ET c cannot exceed a specific threshold defined by the net radiation. These approaches can no longer explain the continuous increase of global rice yields (currently are more than double in comparison to the 1960s) due to the improvement of cultivars and agriculture intensification. The study suggests that the safest method to verify predefined or modeled K c values is through preconstructed relationships of production versus ET c using field measurements.

Rice evapotranspiration at the field and canopy scales under water-saving irrigation

Evapotranspiration (ET) is an important process of land surface water and thermal cycling, with large temporal and spatial variability. To reveal the effect of water-saving irrigation (WSI) on rice ET at different spatial scales and understand the cross spatial scale difference, rice ET under WSI condition at canopy (ETCML) and field scale (ETEC) were measured simultaneously by mini-lysimeter and eddy covariance (EC) in the rice season of 2014. To overcome the shortage of energy balance deficit by EC system, and evaluate the influence of energy balance closure degree on ETEC, ETEC was corrected as $${\text{ET}}_{\text{EC}}^{*}$$ by energy balance closure correction according to the evaporative fraction. Seasonal average daily ETEC, $${\text{ET}}_{\text{EC}}^{*}$$ and ETCML of rice under WSI practice were estimated as 3.12, 4.03 and 4.35 mm day−1, smaller than the values reported in flooded paddy fields. Daily ETEC, $${\text{ET}}_{\text{EC}}^{*}$$ and ETCML varied in a similar trends and reached the maximum in late tillering, then decreased along with the crop growth in late season. The value of ETEC was much lower than ETCML, and was frequently 1–2 h lagged behind ETCML. It indicated that the energy balance deficit resulted in underestimation of crop ET by EC system. The corrected value of $${\text{ET}}_{\text{EC}}^{*}$$ matched ETCML much better than ETEC, with a smaller RMSE (0.086 mm h−1) and higher R 2 (0.843) and IOA (0.961). The time lapse between $${\text{ET}}_{\text{EC}}^{*}$$ and ETCML was mostly shortened to less than 0.5 h. The multiple stepwise regression analysis indicated that net radiation (R n) is the dominant factor for rice ET, and soil moisture (θ) is another significant factor (p < 0.01) in WSI rice fields. The difference between ETCML and $${\text{ET}}_{\text{EC}}^{*}$$ ( $${\text{ET}}_{\text{CML}} - {\text{ET}}_{\text{EC}}^{*}$$ ) were significantly (p < 0.05) correlated with R n, air temperature (T a), and air vapor pressure deficit (D), and its partial correlation coefficients to R n and T a were slightly greater than D. Thus, R n, T a and D are important variables for understanding the spatial scale effect of rice ET in WSI fields, and for its cross scale conversion.

Atmospheric CO2 concentration effects on rice water use and biomass production.

Numerous studies have addressed effects of rising atmospheric CO2 concentration on rice biomass production and yield but effects on crop water use are less well understood. Irrigated rice evapotranspiration (ET) is composed of floodwater evaporation and canopy transpiration. Crop coefficient Kc (ET over potential ET, or ETo) is crop specific according to FAO, but may decrease as CO2 concentration rises. A sunlit growth chamber experiment was conducted in the Philippines, exposing 1.44-m2 canopies of IR72 rice to four constant CO2 levels (195, 390, 780 and 1560 ppmv). Crop geometry and management emulated field conditions. In two wet (WS) and two dry (DS) seasons, final aboveground dry weight (agdw) was measured. At 390 ppmv [CO2] (current ambient level), agdw averaged 1744 g m-2, similar to field although solar radiation was only 61% of ambient. Reduction to 195 ppmv [CO2] reduced agdw to 56±5% (SE), increase to 780 ppmv increased agdw to 128±8%, and 1560 ppmv increased agdw to 142±5%. In 2013WS, crop ET was measured by weighing the water extracted daily from the chambers by the air conditioners controlling air humidity. Chamber ETo was calculated according to FAO and empirically corrected via observed pan evaporation in chamber vs. field. For 390 ppmv [CO2], Kc was about 1 during crop establishment but increased to about 3 at flowering. 195 ppmv CO2 reduced Kc, 780 ppmv increased it, but at 1560 ppmv it declined. Whole-season crop water use was 564 mm (195 ppmv), 719 mm (390 ppmv), 928 mm (780 ppmv) and 803 mm (1560 ppmv). With increasing [CO2], crop water use efficiency (WUE) gradually increased from 1.59 g kg-1 (195 ppmv) to 2.88 g kg-1 (1560 ppmv). Transpiration efficiency (TE) measured on flag leaves responded more strongly to [CO2] than WUE. Responses of some morphological traits are also reported. In conclusion, increased CO2 promotes biomass more than water use of irrigated rice, causing increased WUE, but it does not help saving water. Comparability with field conditions is discussed. The results will be used to train crop models.

Evapotranspiration in a rice paddy field over 13 crop years

Evapotranspiration (ET) in rice paddy fields has been studied over the past half-century, but despite that long history of rice ET study, not much is known about their inter-annual variation. This study investigates ET in rice paddy fields during the growing season for 13 years (2002-2014) at one of the longest flux monitoring sites in Japan. The cumulative ET estimated for each growing season (120 days after transplanting) was 419±45 SD (standard deviation) mm/season (3.5 mm d−1), which increased to 534±64 mm/season (4.4 mm d−1) when energy balance was forced to close. This study determined that ET was correlated with meteorological conditions defined by potential evaporation (EP), and the inter-annual variability of seasonal ET/EP (coefficient of variation (CV) = 4.6%) was less than half the variability of ET (CV = 10.7%). For most years, the seasonal ET was reasonably estimated as the product of EP and the overall average ET/EP (=0.89), including years that experienced both extremely warm and cold summers. However, the errors in estimation were relatively large for 2008 (which experienced high precipitation) and 2012 (which was characterized by an extremely low leaf area index). Although the seasonal ET/EP was relatively invariable among years, both the seasonal trends of ET and ET/EP greatly differed between years. The inter-annual variability in ET/EP was particularly high at the ripening stage (defined as 91-120 days after transplanting). The ET/EP at this stage was well correlated to precipitation, and the variation was possibly caused by evaporation from intercepted rainfall. The variation in ET/EP associated with precipitation at the ripening stage accounted for 21% of the inter-annual variation of seasonal ET/EP.

Modeling rice evapotranspiration under water-saving irrigation by calibrating canopy resistance model parameters in the Penman-Monteith equation

A canopy-resistance-based Penman-Monteith (PM) model’s performance in estimating rice evapotranspiration (ET) under water-saving irrigation (WSI) condition at hourly and daily intervals was evaluated. To improve the performance of Jarvis-type canopy-resistance model in calculating rice ET under water-saving irrigation condition with Penman-Monteith (PM) model, a term of effective leaf area index was used to reflect the influence of canopy coverage condition, and field capacity was replace by saturated soil moisture (θs) in soil water response functions due to the specific field moisture condition in WSI rice fields. Two years of hourly rice ET measured using eddy covariance (EThEC) with energy balance closure adjustment served to calibrate (2014 data) and validate (2015 data) a canopy-resistance-based PM model. Results indicate that the PM model’s output (EThsim) with calibrated canopy resistance model parameters closely matched measured EThEC, with a regression slope, intercept, coefficient of determination (R2), root mean squared error (RMSE) and index of agreement (IOA) of 1.001, 0.010mmh−1, 0.942, 0.057mmh−1 and 0.985, respectively for validation data set in 2015, better than the results calculated by model with parameters calibrated for general paddy field. The improved PM model performed well not only in a dense canopy condition (LAI>3) but also for a sparse canopy (LAI<3). The model also performed well both in sunny and cloudy days of each rice growth stages. A more detailed analysis indicated that EThsim tended to overestimate or underestimate EThEC in varied degrees at noon time or during the transition period from day to night. These differences between EThsim and EThEC associated with the variation of net radiation (Rn), soil heat flux (G0), and soil moisture (θ). Additionally, the PM model calibrated on hourly dataset, performed well in calculating the daily ET directly under WSI for 2014 (R2=0.973, RMSE=0.237mmd−1, IOA=0.993) and 2015 (R2=0.961, RMSE=0.302mmd−1, IOA=0.990). Therefore, the PM model calibrated using the hourly data was capable of accurately estimating both hourly and daily ET for rice under WSI condition.

Declining trends of water requirements of dry season Boro rice in the north-west Bangladesh

The drought prone North-West Bangladesh is vulnerable to the impacts of climate change, particularly because of less water availability in the dry period and high water requirement for crop production. Improved understanding of recent changes in crop water demand in the dry season is important for the water resources management in the region. A study was carried out to determine the potential impacts of recent climate change during last three decades on trends of water requirements of Boro rice. The reference crop evapotranspiration (ETo), potential crop water requirement (∑ETC), effective rainfall during the crop growing period (ER), potential irrigation requirement for crop evapotranspiration (∑ETC−ER) and net irrigation requirement of Boro rice were estimated using observed daily climate data in the CropWat model for the period of 1980 to 2013 for four North-West districts. Significant decreasing trends of ETo were observed in most of the dry months due to increasing relative humidity and decreasing wind-speed and sun-shine hours. The results showed decreasing trends of potential crop water requirement, i.e. the total crop evapotranspiration (∑ETC), of Boro rice due to decreasing reference crop evapotranspiration and shorter crop growing periods. The variations in trends of potential irrigation requirement for crop evapotranspiration (∑ETC−ER) found among different districts, are mainly linked to variations in trends of changes in effective rainfall. The net irrigation requirement of Boro rice has decreased, by 11% during the last three decades at an average rate of −4.4mmyear−1, instead of decreasing effective rainfall, mainly because of high rate of decrease of crop evapotranspiration (−5.9mmyear−1). Results indicate that a warming climate does not always result in higher agricultural water use and that climate change can also result in reduced water demands because of changes in humidity, wind-speed and sun-shine hours.

Validation of dual-crop coefficient method for calculation of rice evapotranspiration under drying–wetting cycle condition

Based on data collected from rice fields under drying–wetting cycle condition, the procedure of dual-crop coefficient (K cd) approaches was calibrated and validated to reveal its feasibility and improve its performance in rice evapotranspiration (ET c) estimation. It was found that K cd based on FAO-recommended basal crop coefficients (K cb) underestimated dual-crop coefficients in monsoon climate region in East China. The recommended coefficient (K cp) value of 1.2 was not high enough to reflect the pulse increase of rice ET c after soil wetting. The K cb values were calibrated as 1.52 and 0.63 in midseason and late season, and the K cp value was adjusted as 1.29 after soil wetting in rice field under drying–wetting cycle condition. The dual-crop coefficient curves based on locally calibrated K cbCal and K cpCor matched well with the measured crop coefficients and performed well in calculating rice evapotranspiration from paddy fields under drying–wetting cycle condition. So it can be concluded that the procedure of dual-crop coefficient method is feasible in rice ET c estimation, and locally calibrated K cb and K cp can improve its performance remarkably.

Effects of Irrigation and Nitrogen Fertilization on Rice Physiological Characters and Yield and Quality

The effects of irrigation model and Nitrogen (N) fertilization on rice evapotranspiration and yield were studied in an experiment of pool culture with in rain-proof shelter. Results showed that irrigation model and nitrogen fertilization had significantly influence on rice growth and photosynthetic capacity and yield and quality. Compared with the conventional irrigation, the plant height, rice water consumption, water requirement intensity and valid panicle number decreased and while water use efficiency, grain number perspike and seed setting rate in creased under control irrigation. With the in cement of N application rates, rice water consumption, water requirement intensity, effect panicle number and grain number per spikein creased, while setting-seed rate and 1000-grain weight decreased. Use the controllable irrigation technology, which had obvious effects of yield and quality on rice with the raise of N fertilizer rate. The yield reached 11489 kg/hm2 and 10126 kg/hm2 when the treatments was with 180 kg/Nhm2 and 270 kg/Nhm2, which was significantly higher than the treatment of CIN1and C2N1. The determination results showed that the palatability value of C1N2 was highest to 79.3, the cooking quality was improved. Then analyzed water and nitrogen fertilizer, yield and water use efficiency were highest at 180 kg/hm2 of N applied. We concluded that control irrigation model combined with suitable N application rate (180 kg/hm2) could benefit for rice production by reducing cost and gaining high yield.

Evapotranspiration and grain yield of upland rice as affected by water deficit

ABSTRACT To achieve an accurate phenotyping for drought tolerance, it is important to control water stress levels and timing. This study aimed to determine water use by upland rice plants during periods of irrigation withholding and its relationship with grain yield in order to increase the efficiency of this phenotyping. Two experiments were carried out in a randomized block design in which six water treatments (irrigation withholding for periods of 2, 4, 6, 8, 10 and 12 days) were compared, with four replicates. In the first experiment, treatments were applied at the R3 stage (panicle exsertion) and, in the second, at the R5 stage (beginning of grain filling). The amount of water evapotranspired was determined by the difference between the soil water storage at the beginning and at the end of irrigation withholding periods, from the surface to 80-cm depth. Evapotranspiration of upland rice from R3 stage was higher compared to that observed from R5 stage, when subjected to similar irrigation withholding periods in both growth stages. Rice grain yield is more sensitive to irrigation withholding imposed from R5 stage than from R3 stage.

Water Requirement Components of some Egyptian Rice Varieties in North Nile Delta

Twoexperiments were conducted at Sakha Agriculture Research Station, during the two successive summer growing seasons of 2012 and 2013 to estimate and analysis water requirements components for some Egyptian rice varieties (Oryza sativa L); namely cvs. Giza 178, Sakha 102 and Sakha 104 and to evaluate and compare the estimated rice crop evapotranspiration (ETc) values computed using Hargreaves, Penmen-Monteith and Class A pan methods used for (ETc) with the measured actual rice evapotranspiration (ETa) using micro- paddy lysimeter used for (ETa) to evaluate the best method for estimating the reference evapotranspiration which suitable with North Nile Delta conditions. Results showed that evaporation (E) is the highest component of total rice water requirements (WR) during the whole growing season stages for cv. Giza 178 with an average 39.8%, followed by cvs. Sakha 102 and Sakha 104 with an average 38.3 and 38.2%, respectively. However, Transpiration (T) is the lowest part of WR for cvs. Giza 178, Sakha 102 and Sakha 104 with an average 21.0, 20.1 and 21.4%, respectively. For percolation (P) is major for Sakha 102 and Sakha 104 varieties with an average of 41.6 and 40.4%, respectively. Meanwhile, the lowest value of P (39.2%) was lost from Giza 178. Mean values of ETa for cv. Giza 178, Sakha 102 and Sakha 104 were 6.1, 6.0 and 6.0 mm day-1,respectively. Although mean values of the estimated rice crop evapotranspiration resulted from Hargreaves, Penmen-Monteith and Class A pan methods were underestimated actual rice evapotranspiration, but Hargreaves and Penmen-Monteith methods performed best for North Delta, Egypt because of the least amount of error and least percentage deviation between ETa and ETc. Crop water productivity (CWP) were 0.85, 0.86, and 0.87 Kg m-3 for rice cvs. Giza 178, sakha 102, and Saka 104, respectively. Also results indicated that the values of crop water use efficiency (CWUE) of rice for cvs. Giza 178, Sakha 102 and Sakha 104 were 1.53, 1.55 and 1.46 Kg m-3 respectively. So, Hargreaves and Penmen-Monteith methods could be recommended for saving irrigation water with planting rice cv. Giza 178, which gave higher water productivity.

Estimation of Potential Evapotranspiration at Botanga Irrigation Scheme in the Northern Region of Ghana

Climatic parameters such as temperature, rainfall, wind speed, relative humidity and sunshine hours were used to assess reference evapotranspiration and potential crop evapotranspiration of selected crops. The Penmann Monteith method for calculation of Reference Evapotranspiration, which has been incorporated in CROPWAT software, was used. Test crops included rice, tomato and pepper, which were part of the major crops cultivated in the Botanga irrigation scheme. Research findings indicated that temperature (r = 0.653) played a crucial role in assessing reference evapotranspiration and potential evapotranspiration. Temperature was lowest during the months from July to September due to lower solar radiation and higher rainfall. The potential crop evapotranspiration of rice, tomato and pepper were 697, 533 and 427 mm/season respectively. Rice growers will require more water for irrigation to ensure higher production due to its high evapotranspiration rate. DOI: http://dx.doi.org/10.5755/j01.erem.70.4.7752