Showing papers in "Irrigation Science in 2008"

ET mapping for agricultural water management: present status and challenges

Abstract: Evapotranspiration (ET) is an essential com- ponent of the water balance. Remote sensing based agrometeorological models are presently most suited for estimating crop water use at both field and regional scales. Numerous ET algorithms have been developed to make use of remote sensing data acquired by sensors on airborne and satellite platforms. In this paper, a literature review was done to evaluate numerous commonly used remote sensing based algorithms for their ability to estimate regional ET accurately. The reported estimation accuracy varied from 67 to 97% for daily ET and above 94% for seasonal ET indicating that they have the potential to estimate regional ET accurately. However, there are opportunities to further improving these models for accurately estimating all energy balance components. The spatial and temporal remote sensing data from the existing set of earth observing satellite platforms are not sufficient enough to be used in the estimation of spatially distributed ET for on-farm irri- gation management purposes, especially at a field scale level (*10 to 200 ha). This will be constrained further if the thermal sensors on future Landsat satellites are aban- doned. However, research opportunities exist to improve the spatial and temporal resolution of ET by developing algorithms to increase the spatial resolution of reflectance and surface temperature data derived from Landsat/ ASTER/MODIS images using same/other-sensor high resolution multi-spectral images.

Dry matter, harvest index, grain yield and water use efficiency as affected by water supply in winter wheat

Abstract: Food production and water use are closely linked processes and, as competition for water intensifies, water must be used more efficiently in food production worldwide. A field experiment with wither wheat (Triticum Aestivum L.), involving six irrigation treatments (from rain-fed to 5 irrigation applications), was maintained in the North China Plain (NCP) for 6 years. The results revealed that dry matter production, grain yield and water use efficiency (WUE) were each curvilinearly related to evapotranspiration (ET). Maximum dry matter at maturity was achieved by irrigating to 94% and maximum grain yield to 84% of seasonal full ET. A positive relationship was found between harvest index (HI) and dry matter mobilization efficiency (DMME) during grain filling. Moderate water deficit during grain filling increased mobilization of assimilate stored in vegetative tissues to grains, resulting in greater grain yield and WUE. Generally, high WUE corresponded with low ET, being highest at about half potential ET. At this location in NCP, highest WUE and grain yield was obtained at seasonal water consumption in the range 250–420 mm. For that, with average seasonal rainfall of 132 mm, irrigation requirements was in the range of 120–300 mm and due to the deep root system of winter wheat and high water-holding capacity of the soil profile, soil moisture depletion of 100–150 mm constituted the greater part of the ET under limited water supply. The results reveal that WUE was maximized when around 35% ET was obtained from soil moisture depletion. For that, seasonal irrigation was around 60–140 mm in an average season.

Effect of irrigation methods, management and salinity of irrigation water on tomato yield, soil moisture and salinity distribution

Abstract: The increasing demand for irrigation water to secure food for growing populations with limited water supply suggests re-thinking the use of non-conventional water resources. The latter includes saline drainage water, brackish groundwater and treated waste water. The effects of using saline drainage water (electrical conductivity of 4.2–4.8 dS m−1) to irrigate field-grown tomato (Lycopersicon esculentum Mill cv Floradade) using drip and furrow irrigation systems were evaluated, together with the distribution of soil moisture and salt. The saline water was either diluted to different salinity levels using fresh water (blended) or used cyclically with fresh water. The results of two seasons of study (2001 and 2002) showed that increasing salinity resulted in decreased leaf area index, plant dry weight, fruit total yield and individual fruit weight. In all cases, the growth parameters and yield as well as the water use efficiency were greater for drip irrigated tomato plants than furrow-irrigated plants. However, furrow irrigation produced higher individual fruit weight. The electrical conductivity of the soil solution (extracted 48 h after irrigation) showed greater fluctuations when cyclic water management was used compared to those plots irrigated with blended water. In both drip and furrow irrigation, measurements of soil moisture one day after irrigation, showed that soil moisture was higher at the top 20 cm layer and at the location of the irrigation water source; soil moisture was at a minimum in the root zone (20–40 cm layer), but showed a gradual increase at 40–60 and 60–90 cm and was stable at 90–120 cm depth. Soil water content decreased gradually as the distance from the irrigation water source increased. In addition, a few days after irrigation, the soil moisture content decreased, but the deficit was most pronounced in the surface layer. Soil salinity at the irrigation source was lower at a depth of 15 cm (surface layer) than that at 30 and 60 cm, and was minimal in deeper layers (i.e. 90 cm). Salinity increased as the distance from the irrigation source increased particularly in the surface layer. The results indicated that the salinity followed the water front. We concluded that the careful and efficient management of irrigation with saline water can leave the groundwater salinity levels unaffected and recommended the use of drip irrigation as the fruit yield per unit of water used was on average one-third higher than when using furrow irrigation.

Crop water stress index is a sensitive water stress indicator in pistachio trees

Abstract: Regulated deficit irrigation (RDI) strategies, often applied in tree crops, require precise monitoring methods of water stress. Crop water stress index (CWSI), based on canopy temperature measurements, has shown to be a good indicator of water deficits in field crops but has seldom been used in trees. CWSI was measured on a continuous basis in a Central California mature pistachio orchard, under full and deficit irrigation. Two treatments—control, returning the full evapotranspiration (ETc) and RDI—irrigated with 40% ETc during stage 2 of fruit grow (shell hardening). During stage 2, the canopy temperature—measured continuously with infrared thermometers (IRT)—of the RDI treatment was consistently higher than the control during the hours of active transpiration; the difference decreasing after irrigation. The non-water-stressed baseline (NWSB), obtained from clear-sky days canopy–air temperature differential and vapour pressure deficit (VPD) in the control treatment, showed a marked diurnal variation in the intercept, mainly explained by the variation in solar radiation. In contrast, the NWSB slope remained practically constant along the day. Diurnal evolution of calculated CWSI was stable and near zero in the control, but showed a clear rising diurnal trend in the RDI treatment, increasing as water stress increased around midday. The seasonal evolution of the CWSI detected large treatment differences throughout the RDI stress period. While the CWSI in the well-irrigated treatment rarely exceeded 0.2 throughout the season, RDI reached values of 0.8–0.9 near the end of the stress period. The CWSI responded to irrigation events along the whole season, and clearly detected mild water stress, suggesting extreme sensitivity to variations in tree water status. It correlated well with midday leaf water potential (LWP), but was more sensitive than LWP at mild stress levels. We conclude that the CWSI, obtained from continuous nadir-view measurements with IRTs, is a good and very sensitive indicator of water stress in pistachio. We recommend the use of canopy temperature measurements taken from 1200 to 1500 h, together with the following equation for the NWSB: (T c − T a) = −1.33·VPD + 2.44. Measurements of canopy temperature with VPD < 2 kPa are likely to generate significant errors in the CWSI calculation and should be avoided.

Comparative study of Hargreaves’s and artificial neural network’s methodologies in estimating reference evapotranspiration in a semiarid environment

Abstract: The Penman–Monteith equation (PM) is widely recommended because of its detailed theoretical base. This method is recommended by FAO as the sole method to calculate reference evapotranspiration (ETo) and for evaluating other methods. However, the detailed climatological data required by the Penman–Monteith equation are not often available especially in developing nations. Hargreaves equation (HG) has been successfully used in some locations for estimating ETo where sufficient data were not available to use PM method. The HG equation requires only maximum and minimum air temperature data that are usually available at most weather stations worldwide. Another method used to estimate ETo is the artificial neural network (ANN). Artificial neural networks (ANNs) are effective tools to model nonlinear systems and require fewer inputs. The objective of this study was to compare HG and ANN methods for estimating ETo only on the basis of the temperature data. The 12 weather stations selected for this study are located in Khuzestan plain (southwest of Iran). The HG method mostly underestimated or overestimated ETo obtained by the PM method. The ANN method predicted ETo better than HG method at all sites.

Optimization model of an irrigation reservoir for water allocation and crop planning under various weather conditions

Abstract: This paper develops a non-linear programming optimization model with an integrated soil water balance, to determine the optimal reservoir release policies, the irrigation allocation to multiple crops and the optimal cropping pattern in irrigated agriculture. Decision variables are the cultivated area and the water allocated to each crop. The objective function of the model maximizes the total farm income, which is based on crop–water production functions, production cost and crop prices. The proposed model is solved using the simulated annealing (SA) global optimization stochastic search algorithm in combination with the stochastic gradient descent algorithm. The rainfall, evapotranspiration and inflow are considered to be stochastic and the model is run for expected values of the above parameters corresponding to different probability of exceedence. By combining various probability levels of rainfall, evapotranspiration and inflow, four weather conditions are distinguished. The model takes into account an irrigation time interval in each growth stage and gives the optimal distribution of area, the water to each crop and the total farm income. The outputs of this model were compared with the results obtained from the model in which the only decision variables are cultivated areas. The model was applied on data from a planned reservoir on the Havrias River in Northern Greece, is sufficiently general and has great potential to be applicable as a decision support tool for cropping patterns of an irrigated area and irrigation scheduling.

Daily evapotranspiration estimates from extrapolating instantaneous airborne remote sensing ET values

Abstract: In this study, six extrapolation methods have been compared for their ability to estimate daily crop evapotranspiration (ETd) from instantaneous latent heat flux estimates derived from digital airborne multispectral remote sensing imagery Data used in this study were collected during an experiment on corn and soybean fields, covering an area of approximately 12 × 22 km, near Ames, Iowa ETd estimation errors for all six methods and both crops varied from −57 ± 48% (MBE ± RMSE) to 260 ± 158% Extrapolated ETd values based on the evaporative fraction (EF) method better compared to eddy covariance measured ET values This method reported an average corn ETd estimate error of −03 mm day−1, with a corresponding error standard deviation of 02 mm day−1, ie, about 57 ± 48% average under prediction when compared to average ETd values derived from eddy covariance energy balance systems A solar radiation-based ET extrapolation method performed relatively well with ETd estimation error of 22 ± 101% for both crops An alfalfa reference ET-based extrapolation fraction method (ETrF) yielded an overall ETd overestimation of about 40 ± 100% for both crops It is recommended that the average daily soil heat flux not be neglected in the calculation of ETd when utilizing method EF These results validate the use of the airborne multispectral RS-based ET methodology for the estimation of instantaneous ET and its extrapolation to ETd In addition, all methods need to be further tested under a variety of vegetation surface homogeneity, crop growth stage, environmental and climatological conditions

Effects of deficit irrigation scheduling on yields and soil water balance of irrigated maize

Abstract: This paper presents the findings of the effect of some selected deficit irrigation scheduling practices on irrigated maize crop in a sub-catchment in south western part of Tanzania. Field experiments, in which maize (TMV1-ST) variety was planted under total irrigation, were conducted during the dry seasons of 2004 and 2005. Surface irrigation method was used and the crop was planted in basins. The seasonal water applied ranged from 400 to 750 mm. Soil moisture content from both cropped and bare soils, leaf area index, dry matter, and grain yields were measured. The dry matter yield ranged between 6,966 and 12,672 kg/ha, and grain yields obtained were between 1,625 and 4,349 kg/ha. The results showed that deficit irrigation at any crop growth stage of the maize crop led to decrease in dry matter and grain yields, seasonal evapotranspiration and deep percolation. Deficit irrigation in any one growth stage of the maize crop only seems to affect grain production and no significant effect on biomass production, but deficit irrigation that spanned across two or more growth stages affect both biomass and grain production drastically. Crop water use efficiency (WUE) and Irrigation water use efficiency (IWUE) were strongly influenced by the number of growth stages in which deficit irrigations were applied and how critical the growth stages were to moisture stress rather than the amount of irrigation water applied. While maximum WUE was obtained under full irrigation, maximum IWUE was obtained in the deficit irrigation treatment at vegetative growth stage, which suggest that IWUE may be improved upon by practicing deficit irrigation at the vegetative growth stage of the maize crop.

Yield, water-use efficiencies and root distribution of soybean, chickpea and pumpkin under different subsurface drip irrigation depths and oxygation treatments in vertisols

Abstract: Most trickle irrigation in the world is surface drip yet subsurface drip irrigation (SDI) can substantially improve irrigation water use efficiency (IWUE) by minimizing evaporative loss and maximizing capture of in-season rainfall by the soil profile. However, SDI emitters are placed at depths, and in many soil types sustained wetting fronts are created that lead to hypoxia of the rhizosphere, which is detrimental to effective plant functioning. Oxygation (aerated irrigation water) can ameliorate hypoxia of SDI crops and realize the full benefit of SDI systems. Oxygation effects on yield, WUE and rooting patterns of soybean, chickpeas, and pumpkin in glasshouse and field trials with SDI at different emitter depths (5, 15, 25, and 35 cm) were evaluated. The effect of oxygation was prominent with increasing emitter depths due to the alleviation of hypoxia. The effect of oxygation on yield in the shallow-rooted crop vegetable soybean was greatest (+43%), and moderate on medium (chickpea +11%) and deep-rooted crops (pumpkin +15%). Oxygation invariably increased season-long WUE (WUEsl) for fruit and biomass yield and instantaneous leaf transpiration rate. In general, the beneficial effects of oxygation at greater SDI depth on a heavy clay soil were mediated through greater root activity, as observed by general increase in root weight, root length density, and soil respiration in the trialed species. Our data show increased moisture content at depth with a lower soil oxygen concentration causing hypoxia. Oxygation offsets to a degree the negative effect of deep emitter placement on yield and WUE of SDI crops.

Water use and yield responses of cotton to alternate partial root-zone drip irrigation in the arid area of north-west China

Abstract: A field experiment was carried out over 2 years to investigate the effect of partial root-zone irrigation applied using drip irrigation on the water use and yield of cotton (Gossypium hirsutum) in oasis fields of arid north-west China. Two irrigation treatments, i.e., conventional drip irrigation (CDI, both sides of plant row watered) or alternate drip irrigation (ADI, both sides of plant row alternatively watered) were applied under plastic mulch. Three irrigation levels (i.e., 15, 22.5, 30 mm during 2004 and 12, 18, 24 mm during 2005) were applied at each irrigation. Monitoring of soil water contents in the ADI treatment indicated a change in root-zone uptake in response to the irrigation method, although there existed some lateral soil water movement from the wetted side to the dry side after each watering. Stomatal conductance in ADI was lower than that of CDI when compared at the same irrigation level. Reduced stomatal conductance and water loss resulted in higher water use efficiency (WUE) in the ADI treatment. About 31-33% less total irrigation water was applied using the ADI method when compared to that of the CDI treatment with a similar seed cotton yield. ADI also yielded 11% more pre-frost seed cotton than CDI in 2005, indicating a better lint quality and higher price. These results suggest that ADI should be a useful water-saving irrigation method in arid oasis fields where cotton production is heavily dependent on irrigation and water resources are scarce.

A step towards new irrigation scheduling strategies using plant-based measurements and mathematical modelling

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

Comparative study of conventional and artificial neural network-based ETo estimation models

Abstract: Accurate estimation of reference crop evapotranspiration (ETo) is required for several hydrological studies and thus, in the past, a number of ETo estimation methods have been developed with different degree of complexity and data requirement. The present study was carried out to develop artificial neural network (ANN) based reference crop evapotranspiration models corresponding to the ASCE’s best ranking conventional ETo estimation methods (Jensen et al. ASCE Manual and Rep. on Engrg. Pract. no. 70, 1990). Among the radiation methods, FAO-24 radiation (or Rad) method for arid and Turc method for humid region, and among the temperature methods, FAO-24 Blaney–Criddle (or BC) method were studied. The ANN architectures corresponding to the above three less data-intensive methods were developed for four CIMIS (California Irrigation Management Information System) stations, namely, Davis, Castroville, Mulberry, and West Side Field station. The comprehensive ANN architecture developed by Kumar et al. (J Irrig Drain Eng 128(4):224–233, 2002) corresponding to Penman–Monteith (PM) ETo for Davis was also tried for the other three stations. Daily meteorological data for a period of more than 10 years (01 January 1990 to 30 June 2000) were collected from these stations and were used to train, test, and validate the ANN models. Two learning schemes, namely, standard back-propagation with learning rate of 0.2 and standard back-propagation with momentum having learning rate of 0.2 and momentum term of 0.95 were considered. ETo estimation performance of the ANN models was compared with the FAO-56 PM method. It was found that the ANN models gave better closeness to FAO-56 PM ETo than the best ranking method in each category (radiation and temperature). Thus these models can be used for ETo estimation in agreement with climatic data availability, when not all required climatic variables are observed.

Response of sweet orange cv ‘Lane late’ to deficit irrigation in two rootstocks. I: water relations, leaf gas exchange and vegetative growth

Abstract: The influence of a deficit-irrigation (DI) strategy on soil–plant water relations and gas exchange activity was analysed during a 3-year period in mature ‘Lane late’ (Citrus sinensis (L.) Osb.) citrus trees grafted on two different rootstocks, ‘Cleopatra’ mandarin (Citrus reshni Hort. ex Tanaka ) and ‘Carrizo’ citrange (C. sinensis L., Osbeck × Poncirus trifoliata L.). Two treatments were applied for each rootstock: a control treatment, irrigated at 100% ETc (crop evapotranspiration) during the entire season, and a DI treatment, irrigated at 100% ETc, except during Phase I (cell division) and Phase III (ripening and harvest) of fruit growth, when complete irrigation cut-off was applied. Under soil water deficit, the seasonal variations of soil water content suggested that ‘Cleopatra’ mandarin had a better root efficiency for soil water extraction than ‘Carrizo’ citrange. Moreover, in all years, trees on ‘Cleopatra’ reached a lower water-stress level (midday xylem water potential values (Ψmd) > −2 MPa), maintaining a better plant water status during the water-stress periods than trees on ‘Carrizo’ (Ψmd < −2 MPa). Similarly, net CO2 assimilation rate (A) was higher in trees on ‘Cleopatra’ during the water-stress periods. In addition, the better plant water status in trees on ‘Cleopatra’ under DI conditions stimulated a greater vegetative growth compared to trees on ‘Carrizo’. From a physiological point of view, ‘Cleopatra’ mandarin was more tolerant of severe water stress (applied in Phases I and III of fruit growth) than ‘Carrizo’ citrange.

Integrating satellite-based evapotranspiration with simulation models for irrigation management at the scheme level

Abstract: Improvements in irrigation management are urgently needed in regions where water resources for irrigation are being depleted. This paper combines a water balance model with satellite-based remote-sensing estimates of evapotranspiration (ET) to provide accurate irrigation scheduling guidelines for individual fields. The satellite-derived ET was used in the daily soil water balance model to improve accuracy of field-by-field ET demands and subsequent field-scale irrigation schedules. The combination of satellite-based ET with daily soil water balance incorporates the advantages of satellite remote-sensing and daily calculation time steps, namely, high spatial resolution and high temporal resolution. The procedure was applied to Genil–Cabra Irrigation Scheme of Spain, where irrigation water supply is often limited by regional drought. Compared with traditional applications of water balance models (i.e. without the satellite-based ET), the combined procedure provided significant improvements in irrigation schedules for both the average condition and when considering field-to-field variability. A 24% reduction in application of water was estimated for cotton if the improved irrigation schedules were followed. Irrigation efficiency calculated using satellite-based ET and actual applied irrigation water helped to identify specific agricultural fields experiencing problems in water management, as well as to estimate general irrigation efficiencies of the scheme by irrigation and crop type. Estimation of field irrigation efficiency ranged from 0.72 for cotton to 0.90 for sugar beet.

Artificial neural network estimation of reference evapotranspiration from pan evaporation in a semi-arid environment

Abstract: The objective of this study was to test an artificial neural network (ANN) for converting pan evaporation data (Ep) to estimate reference evapotranspiration (ET0) as a function of the maximum and minimum air temperature. The conventional method that uses Pan coefficient (Kp) as a factor to convert Ep 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.

Evaluation of partial root-zone drying for potential field use as a deficit irrigation technique in commercial vineyards according to two different pipeline layouts

Abstract: The use of partial root-drying (PRD) irrigation implies doubling pipelines instead of using a conventional single pipeline. However, pipelines can be spaced a short distance apart (e.g. 1 m) along the vine row (“D” layout) or joined with cable ties and laid as a single pipeline (“S” layout). Pipelines in “S” configuration are laid under the vine row, and in “D” at both sides of the vine row. These two different layouts can change the wetted soil zone and affect grapevine response to irrigation. The focus of this study was therefore on establishing the role of pipeline layout in vine-grape (cv. ‘Tempranillo’) response under semi-arid conditions in which PRD is managed as a deficit irrigation technique. Six irrigation treatments were applied, which resulted from the combination of Control (C, full irrigation), PRD and seasonal sustained deficit irrigation (SSDI), and “S” and “D” pipeline layouts. SSDI and PRD were irrigated to 50% C throughout the irrigation season, and C irrigation was scheduled according to a crop water balance technique. Midday stem water potential (Ψstem) and leaf conductance (gl) indicated that, on the whole, PRD treatments had a slightly higher water status than SSDI treatments, but a substantially lower status than C treatments. Use of the “D” pipeline layout significantly reduced Ψstem in both PRD and SSDI treatments and in some instances for Control conditions, too. Berry yield, vine intercepted radiation, leaf abscisic acid (ABA) and gl were highly correlated with Ψstem. Differences in water status between PRD-S and SSDI-S, according to a sub-surface irrigation test, seemed to be more related to changes in soil evaporation losses and irrigation efficiency than to any intrinsic PRD effect. PRD-S accounted for water savings equivalent to 10% according to the ratio between applied water and grape production for the SSDI-S treatment, whereas PRD-D berry yield was not significantly different from that associated with the SSDI-S treatment. In conclusion, under the growing conditions of this experiment, PRD-S offered the possibility of slightly improving water conservation when irrigation was applied to the soil surface.

Emitter discharge variability of subsurface drip irrigation in uniform soils: effect on water-application uniformity

Abstract: Emitter discharge of subsurface drip irrigation (SDI) decreases as a result of the overpressure in the soil water at the discharge orifice. In this paper, the variation in dripper discharge in SDI laterals is studied. First, the emitter coefficient of flow variation CVq was measured in laboratory experiments with drippers of 2 and 4 L/h that were laid both on the soil and beneath it. Additionally, the soil pressure coefficient of variation CVhs was measured in buried emitters. Then, the irrigation uniformity was simulated in SDI and surface irrigation laterals under the same operating conditions and uniform soils; sandy and loamy. CVq was similar for the compensating models of both the surface and subsurface emitters. However, CVq decreased for the 2-L/h non-compensating model in the loamy soil. This shows a possible self-regulation of non-compensating emitter discharge in SDI, due to the interaction between effects of emitter discharge and soil pressure. This resulted in the irrigation uniformity of SDI non-compensating emitters to be greater than surface drip irrigation. The uniformity with pressure-compensating emitters would be similar in both cases, provided the overpressures in SDI are less than or equal to the compensation range lower limit.

Response of sweet orange cv ‘Lane late’ to deficit-irrigation strategy in two rootstocks. II: Flowering, fruit growth, yield and fruit quality

Abstract: We evaluated the effects of a deficit-irrigation (DI) strategy in mature ‘Lane late’ sweet orange (Citrus sinensis (L.) Osb.) trees grafted on two different drought-tolerant rootstocks, ‘Cleopatra’ mandarin (Citrus reshni Hort. ex Tanaka) and ‘Carrizo’ citrange (Citrus sinensis (L.) Osbeck x Poncirus trifoliata L.). Two treatments were applied: a control treatment, irrigated at 100% of crop evapotranspiration (ETc) during the entire season, and a DI treatment, irrigated at 100% ETc, except during phases I (initial fruit-growth period,) and phase III (final fruit-growth period, ripening, harvest), when no irrigation was applied. Flowering, fruit abscission and fruit growth of trees on ‘Carrizo’ were more affected by DI than on ‘Cleopatra’. Deficit irrigation reduced yield in both rootstocks due mainly to a decrease in the number of fruits. The phase most sensitive to drought stress was phase I. Moreover, DI altered fruit quality depending on the period when drought stress was applied. Fruit quality was modified by DI: total soluble sugars and titratable acidity increased when a severe drought stress occurred only in phase III but only increased the peel/pulp ratio if it occurred only in phase I. The quality of fruits from trees on ‘Carrizo’ under DI was affected more than that of fruits from trees on ‘Cleopatra’. Under DI in semi-arid regions ‘Cleopatra’ mandarin can mitigate more the negative effects of drought stress on yield and fruit quality than ‘Carrizo’ citrange.

Seed composition is influenced by irrigation regimes and cultivar differences in soybean

Abstract: In the midsouth USA, soybean is produced either under irrigated or non-irrigated conditions. The objective of this experiment was to show the utility of supplemental irrigation as an alternative to full-season and non-irrigation to achieve high yield and high seed composition. The effects of irrigation and cultivar differences on soybean yield and seed composition were conducted. Two cultivars (Dwight and Freedom) and three irrigation regimes (full-season irrigation, FS; reproductive stage/supplemental irrigation, RI; and non-irrigation, NI) were used. Protein percentage was higher in Dwight under FS and RI than NI. In Freedom, protein percentage was higher under NI than under FS and RI. Under NI, Freedom had higher protein percentage than Dwight, especially in 2004, but lower oil in 2003 and 2004. Cultivars showed significant differences in fatty acids. Yield in Freedom under FS and RI was not significantly different. Nitrogen fixation was substantially higher under NI conditions. The results indicate that irrigation management and cultivar selection significantly affect seed composition and yield. Protein increase in Freedom under non-irrigated conditions may benefit producers for high protein seed under dry-land conditions. Supplemental irrigation at the reproductive stage may be a possible alternative for full season irrigation for the cultivar Freedom.

Use of thermal units to estimate corn crop coefficients under semiarid climatic conditions

Abstract: Two crop coefficient equations were derived as a function of fraction of thermal units from lysimeter measured corn evapotranspiration (ETc-lys) during 1997 and 1998, and reference evapotranspiration obtained from: (a) lysimeter measurements (Kcmes) or FAO Penman-Monteith (ETo-PM) estimates (Kcest-PM). For validation, corn evapotranspiration (ETc-est) was estimated in 2005 and 2006 from ETo-PM and: (a) the equation for Kcmes with (ETc-est-lyslc) or without (ETc-est-lys) locally calibrated ETo-PM; (b) the equation for Kcest-PM; and (c) the FAO approach (ETc-est-FAO). The ETc-est_lys estimates showed the lowest bias (0.09 mm day−1); the ETc-est-PM and ETc-est-FAO, the highest (0.50-0.51 mm day−1). However, the root mean square error (RMSE, 1.23–1.27 mm day−1) and the index of agreement (IA, around 0.94) of the ETc-est-lys, ETc-est-lyslc and ETc-est-PM were similar. Therefore, ETc-est-lys is recommended although the ETc-est-lyslc was similarly accurate. The ETc-est-PM is less recommended due to poorer bias and systematic mean square error, and a general underestimation except for low corn ET values. For real time irrigation scheduling, the ETc-est-FAO should be avoided as RMSE (1.35 mm day−1), IA (0.93) and bias were slightly worse, corn ET was overestimated but for high values, and the length of the four phenological stages must be known in advance.

Water stress imposed on muskmelon (Cucumis Melo L.) with subsurface and surface drip irrigation systems under semi-arid climatic conditions

Abstract: In 2005 and 2006, a study was conducted to determine the effect of subsurface and surface drip irrigation systems and to determine optimum irrigation water using six different irrigation levels imposed on muskmelon (Cucumis Melo L. cv. Ananas F1) under semi-arid climatic conditions. Irrigation treatments received 0, 25, 50, 75, 100, and 125% of class A pan evaporation rates. In 2005, average yield from subsurface and surface drip irrigation systems ranged from 16.2 (I 0) to 31.1 (I 75) t ha−1 and from 16.2 (I 0) to 43.8 (I 75) t ha−1, respectively. While in 2006, fruit yields for the same systems ranged from 8.2 (I 0) to 40.4 (I 75) t ha−1 and from 8.2 (I 0) to 38.9 (I 100) t ha−1. Regression analysis of the yield data indicated no significant (P > 0.05) difference between years and irrigation systems. The highest muskmelon yields from subsurface and surface drip irrigation systems were obtained at 83 and 92% of class A pan. Bigger fruits were obtained with optimum irrigation amounts for both of the irrigation systems. However, there was no clear indication of irrigation water amounts on total soluble solid and flesh thickness of muskmelon fruits.

CFD and digital particle tracking to assess flow characteristics in the labyrinth flow path of a drip irrigation emitter

Abstract: It is necessary to have a comprehensive understanding of the flow mechanisms within drip irrigation emitters to design emitters that have a high anti-clogging performance. The use of computational fluid dynamics (CFD) to research the flow characteristics is appropriate because the labyrinth flow path is narrow and its boundary is complex. In this paper, a CFD for numeric model was developed for numerical simulation of the velocity distribution and turbulence intensity distributions within labyrinth emitters. A two-dimensional digital particle-tracking velocimetry (2D-DPIV) visual display system of the full flow fields was also constructed using plain laser inducement fluorescence velocity measurement technology, custom-made fluorescent particles and a plane model of the emitters. The object lens of a microscope was fitted to a conventional charge coupled device (CCD) camera to overcome the contradiction problems between the image viewing area and resolution power within the flow path. The measured turbulence and velocity distribution characteristics within the labyrinth flow path were in good agreement with the calculated CFD results. This enabled the optimal emitter design patterns to be determined based on the hydraulic characteristics and clogging resistance in the labyrinth flow path.

Evaluation of pan coefficient for reference crop evapotranspiration for semi-arid region

Abstract: Pan coefficient (Kpan) is the important factor for computation of reference evapotranspiration (ETo) from pan evaporation (Epan). In this paper, the approaches proposed by Cuenca (Irrigation system design: an engineering approach. Prentice-Hall, Englewood Cliffs, 1989), Snyder (J Irrig Drain Eng 118(6):977–980, 1992), Orang (Potential accuracy of the popular non-linear regression equations for estimating pan coefficient values in the original and FAO-24 tables. Unpublished Report, Calif. Dept. of Water Resources, Sacramento, 1998), Raghuwanshi and Wallender (J Irrig Drain Eng 118 (6):977–980, 1998) and Pereira et al. (Agric Water Manage 76:75–82, 1995) were evaluated for a semi-arid region. By comparing with the FAO 56 Penman-Monteith (F-PM) method the Snyder (J Irrig Drain Eng 118(6):977–980, 1992, 1992) approach was best suited for the semi-arid region.

Optimizing yield, water requirements, and water productivity of aerobic rice for the North China Plain

Abstract: Water resources for agriculture are rapidly declining in the North China Plain because of increasing industrial and domestic use and because of decreasing rainfall resulting from climate change. Water-efficient agricultural technologies need to be developed. Aerobic rice is a new crop production system in which rice is grown in nonflooded and nonsaturated aerobic soil, just like wheat and maize. Although an estimated 80,000 ha are cultivated with aerobic rice in the plain, there is little knowledge on obtainable yields and water requirements to assist farmers in improving their management. We present results from field experiments with aerobic rice variety HD297 near Beijing, from 2002 to 2004. The crop growth simulation model ORYZA2000 was used to extrapolate the experimental results to different weather conditions, irrigation management, and soil types. We quantified yields, water inputs, water use, and water productivities. On typical freely draining soils of the North China Plain, aerobic rice yields can reach 6–6.8 t ha−1, with a total water input ranging between 589 and 797 (rainfall = 477 m and water application = 112–320 mm). For efficient water use, the irrigation water can be supplied in 2–4 applications and should aim at keeping the soil water tension in the rootzone below 100–200 kPa. Under those conditions, the amount of water use by evapotranspiration was 458–483 mm. The water productivity with respect to total water input (irrigation plus rainfall) was 0.89–1.05 g grain kg−1 water, and with respect to evapotranspiration, 1.28–1.42 g grain kg−1 water. Drought around flowering should be avoided to minimize the risk of spikelet sterility and low grain yields. The simulations suggest that, theoretically, yields can go up to 7.5 t ha−1 and beyond. Further research is needed to determine whether the panicle (sink) size is large enough to support such yields and/or whether improved management is needed.

Crop coefficient for drip-irrigated cotton in a Mediterranean environment

Abstract: A 3-year study was conducted in the eastern Mediterranean region of northern Syria to develop crop coefficient, K c, for drip-irrigated short-season cotton (Gossypium hirsutum L.). Two sets of K c curves were determined, the generalized K c published by the UN’s Food and Agriculture Organization (FAO) that was adjusted for local climate, and the locally developed K c as the ratio of measured cotton evapotranspiration to calculated reference evapotranspiration. The adjusted FAO K c curves were the same for the 3 years. However, the locally developed K c curves not only differed among the 3 years, but also from the adjusted FAO K c. During the mid-season stage, the adjusted FAO K c was 24% higher than the locally developed value of 1.05. Variations in locally developed K c values were caused by normal year-to-year variations in irrigation timing and amount, suggesting sensitivity of K c that cautions against the use of locally developed K c based on limited data (i.e., a single season). On the season, the overestimation of crop evapotranspiration by using adjusted FAO K c was substantial and equivalent to 150 mm water or about two additional irrigations per season. Results caution against blind application of published FAO K c curve, suggesting some local or regional calibration for increased accuracy.

Evolving strategies for crop planning and operation of irrigation reservoir system using multi-objective differential evolution

Abstract: In this paper multi-objective differential evolution (MODE) approach is proposed for the simultaneous evolution of optimal cropping pattern and operation policies for a multi-crop irrigation reservoir system. In general, farming community wants to maximize total net benefits by irrigating high economic value crops over larger area, which may also include water-intensive crops and longer duration crops. This poses a serious problem under water-scarce conditions and often results in crop failure. Under varying hydrological conditions, the fixed cropping pattern with conventional operating rule curve policies may not yield economically good results. To provide flexible policies, a nonlinear multi-objective optimization model is formulated. To achieve robust performance by handling interdependent relationships among the decision variables of the model, the recent MODE technique is adopted to solve the multi-objective problem. The developed model is applied for ten-daily reservoir operation to a case study in India. The model results suggest that changes in the hydrologic conditions over a season have considerable impact on the cropping pattern and net benefits from the irrigation system. Towards this purpose, the proposed MODE model can be used to evolve different strategies for irrigation planning and reservoir operation policies, and to select the best possible solution appropriate to the forecasted hydrologic condition.

Construction, installation, and performance of two repacked weighing lysimeters

Abstract: Weighing lysimeters are the standard method for directly measuring evapotranspiration (ET). This paper discusses the construction, installation, and performance of two (1.52 m × 1.52 m × 2.13-m deep) repacked weighing lysimeters for measuring ET of corn and soybean in West Central Nebraska. The cost of constructing and installing each lysimeter was approximately US $12,500, which could vary depending on the availability and cost of equipment and labor. The resolution of the lysimeters was 0.0001 mV V −1 , which was limited by the data processing and storage resolution of the datalogger. This resolution was equivalent to 0.064 and 0.078 mm of ET for the north and south lysimeters, respectively. Since the percent measurement error decreases with the magnitude of the ET measured, this resolution is adequate for measuring ET for daily and longer periods, but not for shorter time steps. This resolution would result in measurement errors of less than 5% for measuring ET values of ≥3 mm, but the percent error rapidly increases for lower ET values. The resolution of the lysimeters could potentially be improved by choosing a datalogger that could process and store data with a higher resolution than the one used in this study.

Spatially distributed monthly reference evapotranspiration derived from the calibration of Thornthwaite equation: a case study, South of Iran

Abstract: The Penman-Monteith equation is the most common method for estimating reference crop evapotranspiration (ETo). Using this method reqiures many different meteorological data, yet few stations with adequate meteorological data may exist in a region. Setting up a station that records the required data for Penman-Monteith equation is expensive. Alternatively, the Thornthwaite equation is a simpler method for estimating ETo since it is a temperature-based method. In this study, the Thornthwaite equation was spatially calibrated based on the Penman-Monteith method (as the standard and reference method to compute ETo) for every month of the year, using the meteorologica data of seven synoptic weather stations in Fars province, and seven synoptic stations outside the Fars province. The Thornthwaite equation using effective temperature that has been introduced recently in other studies was used (Camargo et al. in Revista Brasileira de Agrometeorologica 7:251–257, 1999). For this purpose a calibration coefficient k must be determined. The results of the spatial and temporal calibration of the new approach using the Thornthwaite equation showed that for each station different k values should be used monthly. Generally, the k values fluctuated between 0.55 and 1.12, and the mean RMSE for all stations was less than 1 mm day−1, which showed good and reliable agreement between the ETo estimations obtained from the Penman-Monteith and calibrated Thornthwaite equations. Depending on the geographical location of each station, spatial distribution maps of monthly k values were created for the study area using the inverse distance weighting (IDW) interpolation method. It is therefore possible to estimate monthly ETo using the appropriate k map and the Thornthwaite equation for different regions of study area instead of using the Penman-Monteith method. This case study showed that the same analysis might be used for the other parts of the country or any part of the world and would result in efficient scheduling of water resources for agriculture.

Water integration by plants root under non-uniform soil salinity

Abstract: Soil salinity over root zone usually demonstrates temporal and spatial variations. By changing irrigation management practices it is possible to change both the frequency of salinity fluctuations and its distribution over the root zone. The objective of this study was to experimentally investigate how plants integrate soil salinity over its rooting depth when irrigated with saline water. Consequently, detailed experiments with alfalfa were conducted in some lysimeters containing packed loamy sand soil. The target soil salinities were created by changing quantity and quality of applied saline water. Results indicated that the uptake rate preliminary reacts to soil salinity. But at given water content and salinity, the “evaporative demand” and “root activity” become more important to control the uptake pattern. The obtained results also indicate that root activity is inconstant during the stress period. By increasing salinity, the activity of that part of the root system is also increased. Thus, most water is taken from the less saline part and the uptake at other parts with higher salinities never stops. Consequently, the reduced uptake in one compartment resulting from high salinity is not only compensated from other parts with less salinities, but also from the same increment by increasing root activity.

Factors affecting the economic benefits of sprinkler uniformity and their implications for irrigation water use

Abstract: Adoption of more uniform sprinkler systems involves a trade off between increased capital expenditure on equipment and the benefits associated with reduced water application when application is uniform. An empirical analysis of the economics of lettuce production, grown using sprinkler systems under the windy conditions of the Swan Coastal plain in Western Australia is presented, where the yield response to water exhibits eventual declining marginal productivity. A range of sprinkler designs that have been field-tested for performance were examined. The optimal per-crop water application for the least efficient system was up to double the application rate of the most efficient system. However, the economic analysis demonstrates that there are clear incentives for adopting more water-efficient systems despite the higher capital cost, because of the yield depressing effect of over-watering. Sensitivity analysis demonstrates substantially poorer incentives for improving irrigation efficiency when yield relationships follow a Mitscherlich functional form.