Search

25 Pags.- 6 Figs.- 2 Tabls. The definitive version is available at: http://www.sciencedirect.com/science/journal/03783774, Accumulated daily crop evapotranspiration (ETc) generally provides good estimates of cumulative soil water depletion between irrigation of well drained soils. If the canopy is wet due to fog, dew, or light rainfall, however, energy contribution to surface evaporation will reduce transpiration and hence soil water losses. When surface evaporation occurs, the ETc overestimates the soil water depletion by an amount approximately equal to the surface water evaporation. Moratiel et al. (2013) proposed a method to estimate the contribution of surface water to ETc based on the time of canopy drying. The first method assessment was done with California data, and this evaluation was conducted in the Ebro basin, Spain, to appraise the method in a higher latitude in area with a somewhat different climate. Differences between the California and Spain corrected models were less than 10% and depended mainly on the time of canopy drying. The comparison showed that the model is robust and useful to estimate the fraction (F) of ETc coming from the soil under dew, light rainfall, and fog conditions., Thanks are due to Ministry of Agriculture, Food and Environment for facilitating data collection.

45 Pags.- 10 Figs.- 6 Tabls. The definitive version is available at: http://www.sciencedirect.com/science/journal/03783774, Under sprinkler irrigation, local environmental conditions have an important influence on irrigation water losses, plant physiological changes and uniformity of irrigation, leading to different crop water production functions. We studied during three years the effect of irrigation depth on the plant growth, forage yield and N content, evapotranspiration and water use efficiency of an alfalfa (Medicago sativa L.) crop irrigated with a commercial solid-set sprinkler system in a semiarid Mediterranean climate. Six irrigation treatments were tested: 55%, 75%, 85%, 100%, 115% and 130% of the theoretical crop irrigation requirement (CIRt), calculated without considering water losses or non-uniformity. The seasonal irrigation amount applied at the 100% of CIRt ranged from 598 to 786 mm. The intercepted photosynthetically active radiation increased as the irrigation applied increased until the 115% of CIRt. Plant height at harvest linearly increased as the irrigation applied increased until the 130% of CIRt in two years. The maximum alfalfa forage yield was lower the first year (17 Mg ha−1) than in the two following years (20–22 Mg ha−1). The alfalfa forage yield increased linearly as the irrigation applied increased the first year of the experiment, but in the following two years this increase occurred until the irrigation applied was 115% of CIRt. The N content of alfalfa linearly decreased as the irrigation applied increased. The relationship between alfalfa forage yield and evapotranspiration was linear until the 115% of CIRt all years. The WUE of alfalfa was lower the first year of the experiment and was not affected by the irrigation applied in the rainiest year, but linearly increased as the irrigation applied increased up to 115% of CIRt in the other two years. Considering yield and quality (N content) of alfalfa forage and WUE, sprinkler irrigation with a solid-set system must be increased by 15% over the CIRt to optimize alfalfa forage production under the climatic conditions of the Ebro valley., This work was supported by the project AGL2010-21681-C03-01 (Ministerio de Economía y Competitividad) of Spanish Government.

44 Pags., 5 Tabls., 5 Figs. The definitive version is available at: http://www.sciencedirect.com/science/journal/00221694, Surface renewal (SR) analysis is an interesting alternative to eddy covariance (EC) flux measurements. We have applied two recent SR approaches, with different theoretical background, that from Castellví (2004), SRCas, and that from Shapland et al. (2012a, 2012b), SRShap. We have applied both models for sensible (H) and latent (LE) heat flux estimation over heterogeneous crop surfaces. For this, EC equipments, including a sonic anemometer CSAT3 and a krypton hygrometer KH20, were located in two zones of drip irrigated orchards of late and early maturing peaches. The measurement period was June to September 2009. The SRCas is based on similarity concepts for independent estimation of the calibration factor (, which varies with respect to the atmospheric stability. The SRShap is based on analysis of different ramp-dimensions, separating the ones that are flux-bearing from the others that are isotropic. According to the results obtained here, there was a high agreement between the 30-min turbulent fluxes independently derived by EC and SRCas. The SRShap agreement with EC was slightly lower. Estimation of fluxes determined by SRCas resulted in higher values (around 11% for LE) with respect to EC, similarly to previously published works over homogeneous canopies. In terms of evapotranspiration, the root mean square error (RMSE) between EC and SR was only 0.07 mm h-1 (for SRCas) and 0.11 mm h-1 (for SRshap) for both measuring spots. According to the energy balance closure, the SRCas method was as reliable as the EC in estimating the turbulent fluxes related to irrigated agriculture and watershed distribution management, even when applied in heterogeneous cropping systems., Ground cover fraction (GCF) is defined as the fraction of ground beneath the canopy covered or shaded by a crop near solar noon as observed from directly overhead. GCF is a useful variable that can be determined in a variety of experimental procedures performed at a field plot scale. GCF is usually measured in experimental field plots using ceptometers or digital imagery. The use of these techniques in the field requires the presence in situ of qualified workers and do not permit the continuous recording of GCF. Thus, only a small number of measured values of GCF are available along the season. A network of pyranometers located at the ground level and above canopy can be connected to a datalogger so a continuous series of global radiation values can be recorded for long periods of time without the presence of any staff. Continuous values of daily GCF can be worked out from those readings. This approach could be particularly useful at remote, unattended sites. Nevertheless, the feasibility of such measures must be evaluated as the main constraint is that the pyranometers must be placed nearby the plant rows to avoid possible damage by the machinery used in the farm. This work presents the daily GCF estimates from pyranometer readings (‘pyranometer‐driven’ method, GCFpyr) at two experiments: a) Experiment I, at a table grape grown under a net, from February 2007 to November 2009; b) Experiment II, at a late peach orchard, from May to September 2011. In the Experiment II measurements were taken for one full irrigated, ‘control’ tree and for one ‘deficit irrigation’ tree., The daily GCFpyr values were compared to measured values (‘reference’ method, GCFref) using either photographical techniques (table grape) or ceptometers (late peach). For computation of GCFpyr, solar radiation below and above the canopy was averaged for two time periods: a) two hours around solar noon; b) daytime period (8:00 to 18:00 Universal Time Coordinated, UTC). For both experiments, the results obtained with the ‘pyranometer‐driven’ method improved when the solar radiation was averaged for daytime periods. For the table grape vineyard (daytime averaging period), the ‘pyranometer‐driven’ method showed a good agreement with the GCFref values as shown by a mean estimation error (MEE) of 0.000, a root mean square error (RMSE) of 0.113, and an index of agreement (IA) of 0.967. For the peach orchard (daytime averaging period), the agreement of the ‘pyranometer‐driven’ method with the GCFref values was worse, particularly with the ‘deficit irrigation’ tree. MEE was 0.046 to 0.210, RMSE was 0.064 to 0.217, and IA was 0.863 to 0.232. The highest GCF attained, the larger measurement range for GCF (which involves a larger variability of sun angle above the horizon) and the presence of the net above the table grape, were the likely reasons for the better performance of GCFpyr in this crop. Further research is required to develop more appropriate calibration equations of GCFpyr taking into account the whole range of GCF variability., Work funded by the project Consolider CSD2006 – 00067 (Ministerio de Ciencia e Innovación, Spain).

In agricultural ecosystems the use of evapotranspiration (ET) to improve irrigation water management is generally widespread. Commonly, the crop ET (ETc) is estimated by multiplying the reference crop evapotranspiration (ETo) by a crop coefficient (Kc). Accurate estimation of ETo is critical because it is the main factor affecting the calculation of crop water use and water management. The ETo is generally estimated from recorded meteorological variables at reference weather stations. The main objective of this paper was assessing the effect of the uncertainty due to random noise in the sensors used for measurement of meteorological variables on the estimation of ETo, crop ET and net irrigation requirements of grain corn and alfalfa in three irrigation districts of the middle Ebro River basin. Five scenarios were simulated, four of them individually considering each recorded meteorological variable (temperature, relative humidity, solar radiation and wind speed) and a fifth scenario combining together the uncertainty of all sensors. The uncertainty in relative humidity for irrigation districts Riegos del Alto Aragón (RAA) and Bardenas (BAR), and temperature for irrigation district Canal de Aragón y Cataluña (CAC), were the two most important factors affecting the estimation of ETo, corn ET (ETc_corn), alfalfa ET (ETc_alf), net corn irrigation water requirements (IRncorn) and net alfalfa irrigation water requirements (IRnalf). Nevertheless, this effect was never greater than ±0.5% over annual scale time. The wind speed variable (Scenario 3) was the third variable more influential in the fluctuations (±) of evapotranspiration, followed by solar radiation. Considering the accuracy for all sensors over annual scale time, the variation was about ±1% of ETo, ETc_corn, ETc_alf, IRncorn, and IRnalf. The fluctuations of evapotranspiration were higher at shorter time scale. ETo daily fluctuation remained lower than 5 % during the growing season of corn and alfalfa. This estimation fluctuation in ETo, ETc_corn, ETc_alf , IRncorn, and IRnalf at daily time scale was within an acceptable range, and it can be considered that the sensor accuracy of the meteorological variables is not significant in the estimation of ETo.

31 Pags., 2 Tabls., 4 Figs. The definitive version is available at: http://cedb.asce.org/cgi/WWWdisplay.cgi?168575, Estimates of daily crop coefficient (Kc) for corn and irrigation scheduling were performed during 2009 and 2010 by means of two approaches: treatment I, computation of Kc using the FAO method; treatment II, computation of Kc from relative fraction of thermal units. Corn crop water requirements and irrigation gross depth for treatment I were about 25 to 33 % lower than that for treatment II in 2009 and 2010 respectively. However, the performance of the treatment II was better in terms of grain yield which was 9.2 Mg ha-1 (in 2009) and 9.4 Mg ha-1 (in 2010), about 37 and 29 % higher than that for treatment I. Water productivity was about 10 % higher for treatment II during 2009 and practically the same than that of treatment I for 2010. Due to the year-to-year variability the water productivity was about 25 % (treatment II) and 11 % (treatment I) for 2010 than for 2009. Finally, economic productivity for treatment II was 2162 $ ha-1 for both seasons, much higher than that for treatment I, 1575 (in 2009) and 1679 (in 2010) $ ha-1. These results confirm that the use of fraction of thermal units to estimate corn crop coefficient has improved the yield, and the water management of this crop under the conditions of this study. Because of the limitations of the study (only two years and one experimental plot), further evaluations under other conditions (climatic, cultivar, etc.) should be performed.

41 Pags.- 9 Tabls.- 3 Figs. The definitive version is available at: http://www.sciencedirect.com/science/journal/03783774, Nighttime sprinkler irrigation usually results in lower water losses and higher irrigation uniformity compared with daytime sprinkler irrigation due to lower wind speed. However, daytime sprinkler irrigation modifies the microclimatic conditions within the crop canopy which could result in improved crop growth. We studied during three years the effect of daytime and nighttime irrigation on the yield, N content, N uptake, water use efficiency, microclimate and canopy temperature of an alfalfa (Medicago sativa L.) crop irrigated with a solid-set sprinkler system in a semiarid Mediterranean climate. Two irrigation treatments were tested: daytime irrigation and nighttime irrigation. The same irrigation amount was applied in both treatments (552 to 757 mm year−1). The water losses of daytime irrigation (10%) tripled the water losses of nighttime irrigation (3%). In one year, daytime irrigation decreased the mean Christiansen coefficient of uniformity (CU) by 4% and the seasonal CU by 2%. Microclimatic and canopy temperature changes during sprinkler irrigation were higher for daytime irrigation as compared to nighttime irrigation. Daytime irrigation slightly reduced the soil water content of the surface layer (0–0.3 m). The actual seasonal crop evapotranspiration was slightly higher (+3.7%) in the daytime irrigation treatment compared to the nighttime irrigation treatment only in one of the years. The annual alfalfa forage yield (16 to 22 Mg ha−1), N content (3.16 to 3.38%), N uptake (514 to 740 kg ha−1) and water use efficiency (17.7 to 25.9 kg ha−1 mm−1) were not affected by the irrigation time of the day. Although nighttime sprinkler irrigation results in some water saving, daytime sprinkler irrigation of alfalfa can be performed if necessary., This work was supported by the project AGL2010-21681-C03-01 (Ministerio de Economía y Competitividad) of Spanish Government.

46 Pags., 3 Tabls., 10 Figs. The definitive version is available at: http://www.sciencedirect.com/science/journal/01681699, Software con manual de uso en: http://hdl.handle.net/10261/45608, This paper presents a real-time, on-farm irrigation scheduling software (RIDECO). The software was been designed for stone fruit orchards in the semiarid conditions of Spain. The characterization of stone fruit crop water requirements for the local conditions and under different irrigation strategies is presented. Meteorological data in the study area is collected daily from the SIAR public network of weather stations in an automated fashion. Subsequently, values of cumulative degree-days are computed to identify the stages of fruit growth and crop development. The software allows performing weekly irrigation schedules under standard, regulated deficit irrigation and water restriction conditions. The irrigation scheduling software stands as a valuable tool for on-farm water resources allocation planning. It can be used to forecast the irrigation water required to meet seasonal meteorological, agronomical and managerial scenarios in stone fruit orchards. RIDECO can also be used to plan deficit irrigation strategies in cases of severe water restrictions. The software can be parameterized to adjust to specific varieties and local farming conditions. A variety of graphs assist irrigation managers in their decisions., The authors sequence in this paper follows the “first-last-author-emphasis” norm. This research was funded by the Plan Nacional de I+D+i of the Government of Spain through grant RIDECO-CONSOLIDER CSD2006-00067.

49 Pags., 3 Tabls., 6 Figs. The definitive version is available at: http://link.springer.com/journal/271, Gross sprinkler evaporation losses (SELg) can be large and decrease irrigation application efficiency. However, it is not universally established how much of the SELg contributes to decrease the crop evapotranspiration during the sprinkler irrigation and how much are the net sprinkler losses (SELn). The components of SEL were the wind drift and evaporation losses (WDEL) and the water intercepted by the crop (IL). The gross WDEL (WDELg) and evapotranspiration (ET) were measured simultaneously in two alfalfa (Medicago sativa L.) plots, one being irrigated (moist, MT) and the other one not being irrigated (dry, DT). Catch can measurements, mass gains and losses in the lysimeters and micrometeorological measurements were performed to establish net WDEL (WDELn) during the irrigation and net IL (ILn) after the irrigation as the difference between ETMT and ETDT. Also, equations to estimate ILn and net sprinkler evaporation losses (SELn) were developed. ILn was strongly related to vapor pressure deficit (VPD). SELn were 8.3% of the total applied water. During daytime irrigations, SELn was 9.8% of the irrigation water and slightly less than WDELg (10.9%). During nighttime irrigations SELn were slightly greater than WDELg (5.4% and 3.7%, respectively). SELn was mainly a function of wind speed., This research was funded by the MCINN of the Government of Spain through grants AGL2007-66716-C03-01/02, AGL2010-21681-C03-01/03; the European Commission through grant QUALIWATER (INCO-CT-2005-015031) and by the FPI-MINECO PhD grant program.

39 Pag., 8 Fig., 4 Tabl. The definitive version is available at: http://www.sciencedirect.com/science/journal/15375110, The spatial variability of the wind in the Montesnegros Irrigation District (MID), in Spain, has been analysed. From a wind series (2004–2007) registered by a reference weather station, a windspeed >2 m s−1 was observed about 50% of the time. During these periods about 70% of the time it blew from the northwest (known as the Cierzo). Wind was monitored at the reference site and at 17 sites throughout the MID. Using regression a series of the local wind velocities for the irrigation seasons 2004–2007 were estimated from the reference station data. Wind exposure for 39% of the MID area was found to be similar to that of the reference site; 25% were less exposed and 36% considerably more exposed. The spatial variability of the wind was used to calculate the suitable time for irrigation (STI, %) using Ador-Sprinkler software. STI was simulated for different irrigation systems and strategies: standard – Christiansen’s uniformity coefficient (CUC) > 84% and wind drift and evaporation losses (WDEL) ≤ 20%, restrictive – CUC ≥ 90% and WDEL ≤ 15% and relaxed – CUC > 80% and WDEL ≤ 25%. At the reference site, STI varied from 50 to 56% of the total time during the irrigation season time for standard strategy, from 68 to 77% for the relaxed strategy and 8 to 30% for the restrictive strategy. Excluding the restrictive strategy, the least exposed sites averaged 14% greater STI than the most exposed sites., The sequence-determines-credit approach has been applied for the sequence of authors in this paper. This research was funded by the CICYT of the Government of Spain through grants AGL2004-06675-C03-03/AGR and AGL2007-66716-C03, by the Government of Aragón through grant PIP090/2005, and by the INIA and CITA through the PhD grants program.

42 Pags., 3 Tabls., 10 Figs. The definitive version is available at: http://www.springerlink.com/content/0342-7188/, The evapotranspiration (ET c) of a table grape vineyard (Vitis vinifera, cv. Red Globe) trained to a gable trellis under netting and black plastic mulching was determined under semiarid conditions in the central Ebro River Valley during 2007 and 2008. The netting was made of high-density polyethylene (pores of 12 mm2) and was placed just above the ground canopy about 2.2 m above soil surface. Black plastic mulching was used to minimize soil evaporation. The surface renewal method was used to obtain values of sensible heat flux (H) from high-frequency temperature readings. Later, latent heat flux (LE) values were obtained by solving the energy balance equation. For the May–October period, seasonal ET c was about 843 mm in 2007 and 787 mm in 2008. The experimental weekly crop coefficients (K cexp) fluctuated between 0.64 and 1.2. These values represent crop coefficients adjusted to take into account the reduction in ET c caused by the netting and the black plastic mulching. Average K cexp values during mid- and end-season stages were 0.79 and 0.98, respectively. End-season K cexp was higher due to combination of factors related to the precipitation and low ET o conditions that are typical in this region during fall. Estimated crop coefficients using the Allen et al. (1998) approach adjusting for the effects of the netting and black plastic mulching (K cFAO) showed a good agreement with the experimental K cexp values., Work funded by the project Consolider CSD2006 – 00067 (Ministerio de Ciencia e Innovación, Spain).

During a sprinkler irrigation event some water is lost due to wind drift and evaporation (WDEL). After the irrigation event, plant-intercepted water is lost due to evaporation. The water lost causes microclimatic changes which could result in positive or negative plant physiological changes. We studied the microclimatic and physiological changes on two fields grown with maize (Zea mays L.) irrigated with a solid-set sprinkler system. The temperature and vapor pressure deficit (VPD) of the air were measured at the crop canopy level and above and below the canopy. Changes in maize canopy temperature, transpiration, and leaf water potential (LWP) were determined. Sprinkler irrigation during daytime strongly modified the microclimate where plants grow during the irrigation time and for a short period after the irrigation event finished. Daytime irrigation decreased air temperature by 3.3 to 4.4°C and VPD by 1.0 to 1.2 kPa at 0.5 m below the crop canopy height. The decrease was lower as the measurement height increased. Microclimatic changes during nighttime irrigation were minimal. Daytime irrigation reduced maize canopy temperature by 4 to 6°C and plant transpiration by 58%, and increased LWP from –1.2 and –1.4 MPa to –0.54 MPa. Transpiration reduction must be considered positive because it supposes a reduction of WDEL. The decrease in maize canopy temperature could be positive or negative, but the increase in LWP is a positive effect., This work was supported by the MCYT of Spain (AGL2004-06675-C03-02/AGR).

The final version is available at: http://cedb.asce.org/cgi/WWWdisplay.cgi?0880019, The effect of reduced corn evapotranspiration (ET) during solid-set sprinkler irrigation on application efficiency was analyzed on two subplots. During each irrigation event, one subplot was irrigated (moist treatment) while the other was not (dry treatment). ET (weighing lysimeter) and transpiration (heat balance method) rates were determined at each subplot before, during, and after the irrigations. During daytime irrigations, there was a significant decrease in ET (32 – 55%) and transpiration (58%) for the moist treatment. After the irrigations (1 – 2 h), ET significantly increased (34%) and transpiration decreased (20%). Gross wind drift and evaporation losses (WDELg) were found to be 19.3% of the applied water. Taking into account the ET changes during and after the irrigations, net sprinkler evaporation losses (SELn) were 14.4 – 17.5% of the applied water. During nighttime irrigations, changes in ET and transpiration were almost negligible, and SELn were slightly greater than WDELg (9.5 and 8.1%, respectively, of applied water). SELn was mainly a function of wind speed. Reduced ET and transpiration during daytime irrigations moderately increased solid-set sprinkler application efficiency., This work was supported by grant AGL-2004-06675-CO3-02 (PN I+D+I, Ministerio de Educación y Ciencia of Spain).

The final version is available at: http://www.sciencedirect.com/science/journal/01681923, The energy partitioning or Bowen ratio β at the surface, can be expressed as a function of a climatic factor C (which depends on the climatic characteristics through the climatological resistance ri) and of a surface factor S (which depends on the surface characteristics through the surface resistance rc). This paper explains an approach for estimating S and therefore β as a function of standard meteorological variables. The empirical approach is then validated by estimating the latent (λE) and sensible (H) heat flux. The experimental data were measured over grass at two semiarid locations in the Ebro river valley, NE Spain, with typical Mediterranean climates: at Mas Bove, using a Bowen ratio-energy balance method from 1991 to 1993, and at Zaragoza, using a weighing lysimeter from 1999 to 2000. Results show that the surface factor S depends on the square root of the absolute value of ri/ra (where ra is the aerodynamic resistance), with two locally calibrated empirical parameters. This result is valid for the largest possible range of situations (β values) throughout the day. Using three different hypotheses for computing ra, results for β (following Hypothesis 1) indicate a good level of performance by the model, although with a high degree of variability. The estimated latent heat flux λEest,1 tends to slightly underestimate the measured values. Under the semiarid conditions of the region, λEPM estimates obtained with the Penman–Monteith equation produce relative errors that are greater than those obtained with the proposed model once it has been calibrated. On average, sensible heat flux tends to be overestimated with the proposed method., This work was funded by the Spanish Ministry of Science and Technology under projects ENE2004-07619/ALT and REN2001-1630/CLI and, and by the Department of Universities and Research (Generalitat de Catalunya) under project 2001SGR-00306.

The definitive version is available at: http://www.sciencedirect.com/science/journal/03783774, In the last decade irrigation districts in the Ebro Valley of Spain have started to use database applications to enhance their management operations. Such applications often put more emphasis on administrative issues than on water management issues. A new irrigation district management software called “Ador” is presented in this paper. This database application has been designed to overcome limitations identified in an analysis of the software used in the study area. Ador can be used in irrigation districts independently of the type of irrigation system (surface, sprinkler or trickle) and the type of irrigation distribution network (open channel or pressurised). It can even be used in irrigation districts combining different types of irrigation systems and different types of irrigation distribution networks. The software can be used with minimum district information. The goals are to manage detailed information about district water management and to promote better on-farm irrigation practices. Ador is currently used to enhance management of 62 irrigation districts accounting for some 173,000 hectares in the Ebro Valley., National Plan for Research and Development of the Government of Spain (AGL2000-0151-P4-02). FEDER II of the European Union (2FD97-0547-C02). I3P program of the European Union. Oficina del Regante (Government of Aragón, FEOGA funds of the European Union).

The final editorial version is available at: http://www.sciencedirect.com/science/journal/03783774, The effects of years of extreme rainfall events on maize water-use under traditional flooding irrigation in a Mediterranean landplane were estimated through a simulation assessment; combining a weather generator with an agrohydrological simulation model. Two options: “Fully Irrigation” and “Deficit Irrigation” were considered in the simulations as the extreme water-management situations. Besides, a 2-m depth shallow water table and Free Drainage were considered as the typical extreme situations that can be found at the bottom of the simulated soil layer. Thirty “Dry” (DY) and “Wet” (WY) years were randomly selected from the weather generator output. The model SWAP was used to simulate the Relative Transpiration (RT), i.e. ratio between actual and maximum maize transpiration, Actual Maize Evapotranspiration (ETC), Percolated Water and Capillary Rising during wet and dry years and for each of the irrigation and bottom condition options. According to the modelling results, average mean RT is about 80% and 90% in dry and wet years, respectively. RT and ETC variability are very high under dry conditions although such variability is notably reduced if a suitable irrigation option is considered. Capillary rising can play a very important role during dry years in those places where irrigation is not enough, but water table is relatively shallower. On the other hand, a shallower water table can carry out RT reductions during wet years, due to water excess, although these negative effects are comparatively lower than those produced by rain scarcity. Besides, percolated water during wet years is very high, particularly in well irrigated farms.

The definitive version is available at: http://www3.interscience.wiley.com/journal/4125/home, This paper examines a model for estimating canopy resistance rc and reference evapotranspiration ETo on an hourly basis. The experimental data refer to grass at two sites in Spain with semiarid and windy conditions in a typical Mediterranean climate. Measured hourly ETo values were obtained over grass during a 4 year period between 1997 and 2000 using a weighing lysimeter (Zaragoza, northeastern Spain) and an eddy covariance system (Córdoba, southern Spain). The present model is based on the Penman-Monteith (PM) approach, but incorporates a variable canopy resistance rc as an empirical function of the square root of a climatic resistance r* that depends on climatic variables. Values for the variable rc were also computed according to two other approaches: with the rc variable as a straight-line function of r* (Katerji and Perrier, 1983, Agronomie 3(6): 513-521) and as a mechanistic function of weather variables as proposed by Todorovic (1999, Journal of Irrigation and Drainage Engineering, ASCE 125(5): 235-245). In the proposed model, the results show that rc/ra (where ra is the aerodynamic resistance) presents a dependence on the square root of r*/ra, as the best approach with empirically derived global parameters. When estimating hourly ETo values, we compared the performance of the PM equation using those estimated variable rc values with the PM equation as proposed by the Food and Agriculture Organization, with a constant rc = 70 s m-1. The results confirmed the relative robustness of the PM method with constant rc, but also revealed a tendency to underestimate the measured values when ETo is high. Under the semiarid conditions of the two experimental sites, slightly better estimates of ETo were obtained when an estimated variable rc was used. Although the improvement was limited, the best estimates were provided by the Todorovic and the proposed methods. The proposed approach for rc as a function of the square root of r* may be considered as an alternative for modelling rc, since the results suggest that the global coefficients of this locally calibrated relationship might be generalized to other climatic regions. It may also be useful to incorporate the effects of variable canopy resistances into other climatic and hydrological models., This work was funded by the Spanish Ministry of Science and Technology under project REN2001-1630/CLI and by the Department of Universities and Research (Generalitat de Catalunya) under project 2001SGR-00306- The second author was also supported by a fellowship from the High Council of Research and Development of the Autnomous Government of Aragon.

49 Pags., 1 Tabl., 1 Fig. The definitive version is available at: http://ascelibrary.org/toc/jidedh/130/6, The development of a coupled crop model (Ador-Crop) and solid set sprinkler irrigation model (Ador-Sprinkler) is reported in this work. The crop model incorporates many of the features developed in the well-known CropWat model. Improvements include the use of thermal time and the input of daily ET0. The solid set sprinkler model applies ballistic theory to determine water distribution resulting from water droplets subjected to a wind vector. Regarding the validation of the coupled model (AdorSim), the plot of soil available water versus measured and simulated yield reduction resulted in similar features. AdorSim explained 25% of the variability in measured yield reduction. Most of the unexplained variability is due to the effect of nonwater-related factors affecting crop yield. In a companion paper, AdorSim is used to investigate optimum water management options in the middle Ebro basin in the NE of Spain., This research was sponsored by the Research and Development program of the Ministry of Science and Technology of the Government of Spain and the FEDER funds of The European Union, through grant 2FD97-0547, and by the CONSI+D of the Government of Aragón, through grant P028/2000. The International Agency of Cooperation (Government of Spain) awarded a research scholarship to F. Dechmi.

40 Pags., 2 Tabls., 9 Figs. The definitive version is available at: http://ascelibrary.org/toc/jidedh/130/6, In this work, applications of the coupled solid set sprinkler irrigation and crop model AdorSim introduced in the companion paper are presented. The sprinkler irrigation model is based on ballistic theory, while the crop model is based on CropWat. AdorSim was used to evaluate the effect of sprinkler spacing on seasonal irrigation water use (WU) and crop yield. The most relevant results were related to the characterization of advanced irrigation scheduling strategies. The differences in crop yield and WU derived from irrigating at different times of the day were estimated for two locations strongly differing in wind speed. Irrigation guidelines were established in these locations to relate gross water use and water stress induced yield reductions. Simulations were also applied to estimate adequate wind speed thresholds for irrigation operation. In the experimental conditions, thresholds of 2.0 - 2.5 m s-1 proved effective to control yield reductions and to minimize WU., This research was sponsored by the Research and Development program of the Ministry of Science and Technology of the Government of Spain and the FEDER funds of The European Union, through grant 2FD97-0547, and by the CONSI+D of the Government of Aragón, through grant P028/2000.

A field experiment was performed to study the effect of the space and time variability of water application on maize (Zea mays) yield when irrigated by a solid set sprinkler system. A solid set sprinkler irrigation layout, typical of the new irrigation developments in the Ebro basin of Spain, was considered. Analyses were performed (1) to study the variability of the water application depth in each irrigation event and in the seasonal irrigation and (2) to relate the spatial variability in crop yield to the variability of the applied irrigation and to the soil physical properties. The results of this research showed that a significant part of the variability in the Christiansen coefficient of uniformity (CU), and wind drift and evaporation losses were explained by the wind speed alone. Seasonal irrigation uniformity (CU of 88%) was higher than the average uniformity of the individual irrigation events (CU of 80%). The uniformity of soil water recharge was lower than the irrigation uniformity, and the relationship between both variables was statistically significant. Results indicated that grain yield variability was partly dictated by the water deficit resulting from the non-uniformity of water distribution during the crop season. The spatial variability of irrigation water depth when the wind speed was higher than 2 m s−1 was correlated with the spatial variability of grain yield, indicating that a proper selection of the wind conditions is required in order to attain high yield in sprinkler-irrigated maize.

17 Pags.- 1 Tabl.- 3 Figs. The definitive version is available at: http://www.sciencedirect.com/science/journal/01681923, Half-hour latent heat flux (LE) was measured over an early-maturing peach orchard (Prunus persica L.) by two different hygrometers: (1) infrared gas analyzer (IRGA) (LI-COR, model LI-7500) and (2) ultraviolet hygrometer (Campbell, KH20). A good agreement between LE obtained with the IRGA (LEIRGA) and the KH20 (LEKH20) hygrometers was observed. During rainy periods, LEIRGA and LEKH20 were not reliable due to failure of the instruments caused by water drops standing over the sensors heads. Filtering out rainy periods improved the similarity between LEIRGA and LEKH20: mean estimation error, 6.2Wm-2; root mean square error, 21.3Wm-2; and refined index of agreement, 0.919. Even though the IRGA hygrometer is generally recommended, when economic constraints exist, the KH20 hygrometer can be used with similar confidence., Work funded by the project Consolider CSD2006–00067 (Ministerio de Ciencia e Innovación, Spain).

28 Pags., 4 Tabls., 6 Figs. The definitive version is available at: http://www.sciencedirect.com/science/journal/03783774, Deficit irrigation strategies save water, but may enhance soil salinization and sodification when irrigated with low-quality waters. The objectives of this five-year study performed in the middle Ebro Basin (Spain) were to quantify these processes and assess their potential deleterious impact on the response of peach trees subjected to full irrigation (FULL), sustained deficit irrigation (SDI, irrigated at 62.5% of FULL) and regulated deficit irrigation (RDI, irrigated at 50% of FULL in Stage II of fruit development). In relation to FULL, water savings were 40% in SDI and 9% in RDI. Soil salinity (ECe), chloride concentration (Cle) and sodicity (SARe) measured in the saturation extract of 480 soil samples generally increased in the irrigation seasons, particularly in the more severe deficit irrigation strategy (SDI). These increases were counteracted by the leaching of salts induced by high leaching fractions (LF) and low water deficits (WD) attained during the non irrigation seasons. The changes in ECe, Cle and SARe measured between sampling dates were significantly correlated (p < 0.01) with WD and LF calculated for the periods between sampling dates. These parameters were therefore suitable to estimate the required irrigation depths for soil salinity and sodicity control. Peach trees were unaffected by the irrigation treatments, but yield productivity tended to decline above a threshold ECe of 4 dS m−1. Under the irrigation salinity (mean EC = 1.1 dS m−1) and the semiarid climatic characteristics of the study area, the three examined irrigation strategies proved to be sustainable in the five studied years., This work was financed by the CSD2006-00067 project (CONSOLIDER-INGENIO 2010).

8 Pags.- 4 Figs.- 2 Tabls., This paper evaluates the feasibility of using pyranometers for continuous estimation of ground cover fraction (GCF) at remote, unattended sites. Photographical techniques were used for measuring GCF (GCFref) at a table grape vineyard grown under a net. Daily pyranometer-driven GCF estimates (GCFpyr) were obtained from solar radiation measurements above and below the canopy. For GCFpyr computation, solar radiation was averaged for two hours around solar noon (midday periods) and for daylight periods (8:00 to 18:00 Universal Time Coordinated). GCFpyr and GCFref (daylight periods) showed a good agreement: mean estimation error, 0.000; root mean square error, 0.113; index of agreement, 0.967. The high GCF attained, the large measurement range for GCF and the presence of the net above the table grape were the likely reasons for the good performance of GCFpyr in this crop despite the short number of pyranometers used. Further research is required to develop more appropriate calibration equations of GCFpyr and for a more detailed evaluation of using a short number of pyranometers to estimate GCF., This work was funded by the Ministry of Scienceand Innovation, Spain (project Consolider CSD2006-00067).

4 Pags.

14 Págs., 5 Tabls., 11 Figs., During sprinkler irrigation some water is lost due to drift and evaporation. After irrigation, plant-intercepted water is lost due to evaporation. The water loss causes microclimatic changes, which may involve positive or negative plant physiological responses. We studied the changes in net photosynthesis of maize (Zea mays L.) and alfalfa (Medicago sativa L.) associated with irrigation with a solid-set sprinkler system. For each species, measurements were made simultaneously in two plots, one being irrigated and the other not being irrigated. Two automatic canopy chambers connected to two CO2 infrared gas analyzers were used. Sprinkler irrigation decreased air temperature (1.5°C on maize, 1.7°C on alfalfa), air vapor pressure deficit (VPD) (0.44 kPa for both crops) and canopy temperature (5.1°C on maize, 5.9°C on alfalfa). Sprinkler irrigation decreased maize net photosynthesis on 80% of the days and the mean reduction was 19%. Sprinkler irrigation increased alfalfa net photosynthesis on 36% of days, decreased it on 14% of days, and had no effect on half of the days. The decrease of maize net photosynthesis during sprinkler irrigation was linked to the high leaf wettability (water contact angles from 60–80°) and the decrease in temperature below the optimum range for photosynthesis. The higher hydrophobicity of alfalfa leaves (water contact angles >120°) and the wide range of optimum temperature for alfalfa photosynthesis may be the reasons why photosynthesis remained unaffected by sprinkler irrigation. The results suggest that daytime sprinkler irrigation with solid-set should be avoided for maize but can be used for alfalfa., This work was supported by the projects AGL2007-66716-C03-01 and AGL2010-21681-C03-01 (Ministerio de Economía y Competitividad) of Spanish Government. Y.F. Urrego-Pereira had a FPI grant of the Spanish government.

45 Pags., 8 Figs., 6 Tabls. The definitive version is available at: http://link.springer.com/journal/271, The quantification of transpiration and corresponding basal crop coefficients is crucial for appropriate irrigation scheduling of drip-irrigated crops. Besides basal crop coefficients already published, there is the announcing need for setting values for the new growing practices such as cropping under netting. In this paper, measurements of unstressed table grape transpiration and basal crop coefficients under netting have been taken. Vineyards of two seedless cultivars (Crimson and Autumn Royal) were trained on an overhead trellis system which permitted the ground cover to reach values up to 90 %. Two campaigns of mid-season measurements were performed using one of the heat pulse techniques available (that known as the T max approach). Obtained values for average seasonal daily transpiration ranged between 3.9 and 4.4 mm day−1, for both cultivars, depending on the period considered. Weekly averages of the basal crop coefficients, from mid-May to end-September, ranged from 0.47 to 0.87. A polynomial equation was fit to the measured basal crop coefficients as a function of fraction of thermal units. After further validation for other cultivars with different cumulative thermal requirements, this equation could be considered helpful for farmers as a practical estimate of the table grape basal crop coefficient under the netting., Work funded by the project Consolider CSD2006 – 00067 (Ministerio de Ciencia e Innovación, Spain).

18 Pags., 6 Tabls., 7 Figs. Available online at www.inia.es/sjar, Fruit production development is resulting in large commercial orchards with improved water management standards. While the agronomic and economic benefits of regulated deficit irrigation (RDI) have long been established, the local variability in soils and climate and the irrigation system design limits its practical applications. This paper uses a case study approach (a 225 ha stone fruit orchard) to unveil limitations derived from environmental spatial variability and irrigation performance. The spatial variability of soil physical parameters and meteorology in the orchard was characterized, and its implication on crop water requirements was established. Irrigation depths applied during 2004- 2009 were analysed and compared with crop water requirements under standard and RDI strategies. Plant water status was also measured during two irrigation seasons using stem water potential measurements. On-farm wind speed variability amounted to 55%, representing differences of 17% in reference evapotranspiration. During the study seasons, irrigation scheduling evolved towards deficit irrigation; however, the specific traits of RDI in stone fruits were not implemented. RDI implementation was limited by: 1) poor correspondence between environmental variability and irrigation system design; 2) insufficient information on RDI crop water requirements and its on-farm spatial variability within the farm; and 3) low control of the water distribution network, This research was funded by the Plan Nacional de I+D+i of the Government of Spain through grant RIDECO-CONSOLIDER CSD2006-00067 and by CSIC through the grant PIE 2007-2009.

9 Pags., 6 Tabls., 3 Figs., Daytime sprinkler irrigation with a solid-set system can result in higher water losses, lower uniformity, and lower maize (Zea mays L.) yield compared with nighttime irrigation. We studied the relevance of irrigation time (daytime or nighttime) and water losses (compensating them or not in the irrigation applied) for the growth and yield of maize during 2 yr. The seasonal average sprinkler water losses compensated ranged from 14 to 19% for daytime irrigation and from 5 to 11% for nighttime irrigation. The average Christiansen coefficient of uniformity (CU) was similar for daytime and nighttime irrigation in 2009 (84%) but lower for daytime irrigation (78%) than nighttime irrigation (84%) in 2010. Daytime irrigation decreased the maize grain yield by 9% in the year that the CU was reduced. Increasing the water applied to compensate the water losses increased the soil matric potential but did not increase maize yield. The lower irrigation uniformity for daytime sprinkler irrigation compared with nighttime sprinkler irrigation seems to be a relevant reason for the yield reduction. Solid-set sprinkler irrigation systems for maize should be designed to minimize daytime irrigation or to allow a high daytime irrigation uniformity (>84%)., This work was supported by the project AGL2007-66716-C03-01 (Ministerio de Economía y Competitividad of Spain).

The definitive version is available at: http://www.sciencedirect.com/science/journal/00221694, This paper reports the evaluation of three geostatistical interpolation methods (ordinary kriging, cokriging and modified residual kriging) to interpolate long-term mean total annual reference evapotranspiration (AETO) and long-term mean total annual precipitation (APRE) in a mountainous region, where the stationarity hypothesis probably do not hold for the whole region, but do hold locally. AETO and APRE estimates and estimation errors were evaluated at validation stations. Estimates and computed estimation error variances (used as indicators of estimation uncertainty) were also obtained at 1913 5 km grid points. In general, estimates at validation stations were in good agreement with observed values for all interpolation methods, although modified residual kriging estimates of APRE were slightly worse than those obtained by the other two methods. Based on mean absolute error (MAE) and mean squared error (MSE) at validation stations, no method ranked clearly above other for interpolation of AETO. At grid points, AETO estimation uncertainty was improved by cokriging by about 11.5% and 8.4% compared with ordinary kriging and modified residual kriging, respectively. Likewise, cokriging was superior for interpolation of APRE in terms of MAE and MSE obtained at validation stations. At grid points, cokriging reduced estimation uncertainty by 18.7% and 24.3 % compared with ordinary kriging and modified residual kriging, respectively, whereas modified residual kriging in general did not improve ordinary kriging results. Computed estimation error variance values indicated that modified residual kriging would reduce estimation uncertainty in areas where very few weather stations are available for interpolation., This research was funded by the Ministerio de Educaci6n y Ciencia (project CICYT-514 and a grant to the author) and the Ministerio de Agricultura (INIA, project SC93-059-061), Government of Spain. I

38 Pags., 8 Figs., 6 Tabls. The definitive version is available at: http://www.springerlink.com/content/0342-7188/, The evapotranspiration (ETc) of sprinkler-irrigated rice was determined for the semiarid conditions of NE Spain during 2001, 2002 and 2003. The surface renewal method, after calibration against the eddy covariance method, was used to obtain values of sensible heat flux (H) from high-frequency temperature readings. Latent heat flux values were obtained by solving the energy balance equation. Finally, lysimeter measurements were used to validate the evapotranspiration values obtained with the surface renewal method. Seasonal rice evapotranspiration was about 750–800 mm. Average daily ETc for mid-season (from 90 to 130 days after sowing) was 5.1, 4.5 and 6.1 mm day-1 for 2001, 2002 and 2003, respectively. The experimental weekly crop coefficients fluctuated in the range of 0.83–1.20 for 2001, 0.81–1.03 for 2002 and 0.84–1.15 for 2003. The total growing season was about 150–160 days. In average, the crop coefficients for the initial (Kcini), midseason (Kcmid) and late-season stages (Kcend) were 0.92, 1.06 and 1.03, respectively, the length of these stages being about 55, 45 and 25 days, respectively., This work was funded through project AGL- 2000-1775-C03-02 (Plan Nacional de I?D, Spanish Ministry of Science and Technology).

43 Pag., 7 Fig., 5 Tabl. The definitive version is available at: http://www.sciencedirect.com/science/journal/03783774, Irrigation water use in private landscapes represents an increasing share of total water use in semiarid areas. In this work, 102 households located in the Montecanal neighbourhood (Zaragoza, Spain) were analysed. Research took advantage of the dual water supply network (separate indoor and irrigation water networks). The analysis was based on bi-monthly water billing records for the period 2005–2007. The total household landscape area (93 m2) and the area occupied by turf, trees and shrubs were derived from aerial photographs. A method based on reference evapotranspiration was used to estimate net landscape irrigation requirements. The total average water use was 0.80 m3 household−1 day−1, with irrigation water use amounting to 46% of the total water use. Average air temperature largely determined irrigation water use (the correlation coefficient was 0.958). Overirrigation was common in the three years of study, with the average irrigation water application (IWA) being much higher than the Net Irrigation Requirements (1359 and 555 mm, respectively). Only 34% of the households showed adequate irrigation, while 6% of the households underirrigated their landscape areas. In the rest of the households (60%), overirrigation was observed. Significant time correlations were found for IWA and for an adequacy index, suggesting that landowners applied their inadequate irrigation criteria in a consistent way. Local private landscape irrigation performance was found to be very poor, probably owing to low water cost and over-the-average household income., This research was funded by the Ebro Watershed Authority (Confederación Hidrográfica del Ebro) and by the National Research, Development and Innovation Plan of the Government of Spain (Plan Nacional de I + D + i) through grants AGL2007-66716-C03 and CSD2006-00067.

38 Pag., 4 Tabl., 7 Fig. The definitive version is available at: http://www.sciencedirect.com/science/journal/03783774, The evapotranspiration of hedge-pruned olive orchards (Olea europaea L. cv. Arbequina) was measured under the semiarid conditions of the middle Ebro River Valley in a commercial olive orchard (57 ha) during 2004 and 2005. No measured ETc values for this type of olive orchards have previously been reported. An eddy covariance system (krypton hygrometer KH20 and 3D sonic anemometer CSAT3, Campbell Scientific) was used. The eddy covariance measurements showed a lack of the energy balance closure (average imbalance of 26%). Then sensible and latent heat (LE) flux values were corrected using the approach proposed by Twine et al. (2000) in order to get daily measured olive evapotranspiration (ETc) and crop coefficient (Kc) values. The highest measured monthly ETc averages were about 3.1–3.3 mm day−1, while the total seasonal ETc during the irrigation period (March–October) was about 585 mm (in 2004) and 597 mm (in 2005). Monthly Kc values varied from about 1.0 (Winter) to 0.4–0.5 (Spring and Summer). These Kc values were similar to Kc values reported for round-shape canopy olive orchards, adjusted for ground cover, particularly during late Spring and Summer months when differences among measured and published Kc values were about less than 0.1., Work funded by the project CAO-01-AR-04 (Instituto Nacional de Investigación Agraria, Spain).

2 Pags., References. Ver además: http://hdl.handle.net/10261/10364

Corn (Zea mays L.) transpiration during daytime solid-set sprinkler irrigation was analyzed on two neighbouring subplots to determine the effect of the transpiration reduction on water application efficiency. During each irrigation event, one subplot was irrigated (moist treatment) while the other was not (dry treatment). Transpiration rates were determined at each subplot by the heat balance method (Dynamax Flow4 System) before, during and after the irrigations. During irrigations, there was a significant decrease in transpiration (60 %) for the moist treatment. Within the first hour after irrigation, transpiration rates were also smaller for the moist treatment, but the reduction was lower (17 %). It was found a significant correlation between the transpiration reduction and the decrease of water vapor deficit during, and after the irrigation event. Leaf water potential during the irrigation increased (about 61 %) for the moist treatment, which suggests that the reduction of transpiration was not due to stomata closure but to smaller water vapor gradient between the plant and the surrounding atmosphere., This work was supported by grant AGL-2004-06675-CO3-02 (PN I+D+I, Ministerio de Educación y Ciencia of Spain).

The final version is available at: http://www.sciencedirect.com/science/journal/03783774, Cultivation of paddy rice in semiarid areas of the world faces problems related to water scarcity. This paper aims at characterizing water use in a set of paddies located in the central Ebro basin of Spain using experimentation and computer simulation. A commercial field with six interconnected paddies, with a total area of 5.31 ha, was instrumented to measure discharge and water quality at the inflow and at the runoff outlet. The soil was classified as a Typic Calcixerept, and was characterised by a mild salinity (2.5 dS m 1) and an infiltration rate of 5.8 mm day-1. The evolution of flow depth at all paddies was recorded. Data from the 2002 rice growing season was elaborated using a mass balance approach to estimate the infiltration rate and the evolution of discharge between paddies. Seasonal crop evapotranspiration, estimated with the surface renewal method, was 731 mm (5.1 mm day-1), very similar to that of other summer cereals grown in the area, like corn. The irrigation input was 1,874 mm, deep percolation was 830 mm and surface runoff was 372 mm. Irrigation efficiency was estimated as 41%. The quality of surface runoff water was slightly degraded due to evapoconcentration and to the contact with the soil. During the period 2001-2003, the electrical conductivity of surface runoff water was 54% higher than that of irrigation water. However the runoff water was suitable for irrigation. A mechanistic mass balance model of inter-paddy water flow permitted to conclude that improvements in irrigation efficiency can not be easily obtained in the experimental conditions. Since deep percolation losses more than double surface runoff losses, a reduction in irrigation discharge would not have much room for efficiency improvement. Simulations also showed that rice irrigation performance was not negatively affected by the fluctuating inflow hydrograph. These hydrographs are typical of turnouts located at the tail end of tertiary irrigation ditches. In fact, these are the sites where rice has been historically cultivated in the study area, since local soils are often saline-sodic and can only grow paddy rice taking advantage of the low salinity of the irrigation water. The low infiltration rate characteristic of these saline-sodic soils (an experimental value of 3.2 mm day-1 was obtained) combined with a reduced irrigation discharge resulted in a simulated irrigation efficiency of 60%. Paddy rice irrigation efficiency can attain reasonable values in the local saline-sodic soils, where the infiltration rate is clearly smaller than the average daily rice evapotranspiration., This research was funded by the Plan Nacional de I+D+i of the Government of Spain, through grant AGL2000-1775. Olga Pérez Coveta received a scholarship from the Plan Nacional de Formación de Personal Investigador of the Government of Spain.

Nighttime sprinkler irrigation usually results in lower wind drift and evaporation losses (WDELs) and better irrigation uniformity compared with daytime irrigation. However, daytime sprinkler irrigation modifies the microclimatic conditions within the crop canopy which could result in improved crop growth. We studied the effect of daytime and nighttime irrigation on the growth and yield of maize (Zea mays L.) irrigated with a solid-set sprinkler system. Two irrigation treatments were tested: daytime irrigation (starting at 1000 Greenwich Mean Time, GMT) and nighttime irrigation (starting at 2200 GMT). The same irrigation amount was applied in both treatments. The irrigation amount was determined as the difference between the crop evapotranspiration (ETc) and the effective precipitation. The WDELs of daytime irrigation were twice the nighttime irrigation WDELs. Daytime irrigation decreased the mean Christiansen coefficient of uniformity (CU) by 5 to 7% and the seasonal CU by 4%. Daytime irrigation caused a 10% reduction in maize grain yield, mostly due to a reduction in biomass production. The lower soil matric potential found with daytime irrigation late in the season indicated that a progressive water stress occurred that was due to less water availability and was caused by the higher WDEL for daytime irrigation. Even though positive microclimatic changes have been reported with daytime sprinkler irrigation, the results of our study indicate that they cannot compensate the negative effects caused for the crop by less water reaching the soil root zone because of increased WDEL and by poorer irrigation uniformity.

The definitive editor version is available at: http://link.springer.com/journal/271 http://www.springerlink.com/content/h7270424k3j76459/, 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 almost as 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., This research has been funded through projects HID96-1295-C04-04 and AGL-2004-06675-CO3-02 (Spanish Ministry of Education), and PIP090/2005 (Regional Government of Aragón).

The definitive version is available at: http://www.sciencedirect.com/science/journal/03783774, In this paper, a contribution to the design of collective pressurized irrigation networks in solid-set sprinkler irrigated windy areas is presented. The methodology is based on guaranteeing minimum on-farm performance, using a historical hourly wind speed database and a ballistic solid-set irrigation simulation model. The proposed method was applied to the Montesnegros Irrigation District (central Ebro basin, Spain). The district irrigates an area of 3,493 ha using an on-demand schedule. The average wind speed in the area is 2,8 m s-1. An analysis of district water records showed that farmers often reduce water demand when the wind speed is high, but their irrigation decision making is limited by the capacity of the irrigation network and by the unpredictable character of local winds. Simulations were performed for eleven irrigation seasons, two triangular sprinkler spacings (18x18 and 18x15 m), and two sprinkler models. The percentage of monthly suitable time for irrigation was determined for four management strategies. The first one was based on a wind speed threshold (3 m s-1), while the other three were based on three levels (standard, relaxed and restrictive) of two irrigation performance parameters: the Christiansen Uniformity Coefficient (CU) and the Wind Drift and Evaporation Losses (WDEL). The thresholds for the standard strategy were CU ≥ 84% and WDEL ≤ 20%. The suitable time for the first strategy (56%) was always lower than for the standard and the relaxed strategies (with respective average values of 75 and 86%), and higher than for the restrictive strategy (30%). In order to design the collective network, the hydrant operating time was equalled to the suitable time for irrigation. The differences in the cost of the collective network plus the on-farm equipment were particularly relevant between the restrictive strategy and the other three. Differences in suitable operating time were clear between sprinkler spacings, and less evident between sprinkler models. The application of the proposed methodology may be limited by the availability of historical wind speed records and CU estimates for different combinations of sprinkler models, sprinkler spacings and wind speed., CICYT of the Government of Spain (grant AGL2004-06675-C03-03/AGR) Government of Aragón (grant PIP090/2005)

The definitive version is available at: http://www.sciencedirect.com/science/journal/01681923, The performance of surface renewal (SR) analysis for estimating sensible (H) and latent (λE) heat fluxes has been analysed over a sprinkler irrigated rice. Similarity principles were not fully met during the experiment and the (H + λE) measured values with the eddy covariance did not close the surface energy balance. H and λE estimates using SR analysis were reliable and provided a reasonable energy-balance closure. The Bowen ratio was also estimated using SR analysis. Good estimates were obtained though mainly under unstable atmospheric conditions., This study was supported by projects REN2001/CLI1630, TRANSCLA and AGL2000-1775-C03-02.

[1] This paper describes two approaches for estimating sensible heat flux, using surface renewal and similarity concepts. One approach depends on a temperature structure function parameter and is valid in the inertial sublayer. The other approach depends on the temperature standard deviation and operates when measurements are made above the canopy top, either in the roughness or inertial sublayer. The approaches were tested over grass, rangeland grass, wheat, grape vineyard, and nectarine and olive orchards. It is shown that the free convection limit expression for the standard deviation method holds for slightly unstable conditions. When surface homogeneity and fetch requirements are not fully met in the field, the results show that the equations based on surface renewal principles are more robust and accurate than equations exclusively based on similarity backgrounds. It is likely that the two methods are less sensitive to site-specific adjustment of the similarity relationships unless the canopy is rather heterogeneous. Under unstable conditions, the free convection limit equation, which depends on the temperature standard deviation, can provide online sensible heat flux estimates using affordable battery-powered data logger with temperature data as the only input. The approach performed well when measuring above the canopy in the roughness and inertial sublayers, thus suggesting that the method is useful for long-term monitoring over growing vegetation.

26 Pags., 3 Tabls., 6 Figs. The definitive version is available at: http://www.ingenieriadelagua.com/2004/rev_1.asp, La evapotranspiración del arroz (ETarroz) bajo riego por aspersión se determinó mediante el método de la renovación de la superficie aplicado a distintas alturas de medida en el valle medio del Ebro (Zaragoza) en 2001 y 2003. Los valores semihorarios de flujo de calor latente (LE) determinados en las diferentes alturas fueron significativamente diferentes entre sí (a = 0.95). Estas diferencias no fueron sistemáticas; a escala diaria, se produjeron con una incertidumbre similar a la de otros métodos micrometeorológicos (alrededor del 10 %). Los valores diarios de ETarroz fueron relativamente altos debido al riego frecuente que necesita este cultivo. En 2003, más caluroso, fueron algo mayores que en 2001, con valores estacionales de 799 mm en 2001 y 812 mm en 2003. La fase inicial del cultivo fue muy larga (50-60 días), mientras que las fases de crecimiento, máximo desarrollo y final fueron de unos 20, 50 y 20-30 días, respectivamente. Los valores de coeficiente de cultivo (Kc) en la fase inicial fueron aproximadamente de 0.90, con oscilaciones importantes causadas por los frecuentes precipitaciones y riegos. Durante la fase de máximo desarrollo, los valores de Kc fluctuaron entre 1.10 y 1.15; durante la fase final, los valores se aproximaron a 0.90. Aún deben resolverse diversos problemas agronómicos para este cultivo y sistema de riego. Por ello, estos valores de ETarroz y Kc deben considerarse con precaución. Son convenientes campañas posteriores de medidas para confirmar o mejorar estos resultados., Este trabajo ha sido financiado con el proyecto AGL-2000-1775-C03-02, del Plan Nacional de I+D (Ministerio de Ciencia y Tecnología).

[1] The eddy covariance technique for measuring surface fluxes is often not affordable outside experimental research institutes. Therefore knowledge of the performance of alternative methods for determining surface fluxes is valuable. The performance of surface renewal (SR) analysis and the flux variance (FV) method for estimating sensible heat flux has been evaluated in an experiment carried out over a heterogeneous canopy (olive orchard, 50% ground cover) at a semiarid climate in a windy area. Measurements were made at a single level close to the canopy top. SR analysis was accurate under both stable and unstable conditions. The FV method also showed a good performance under unstable conditions, but it was uncertain near neutral conditions and was not applicable under stable conditions.

The definitive version is available at: http://www.sciencedirect.com/science/journal/03783774 http://dx.doi.org/10.1016/j.agwat.2005.01.015, Wind drift and evaporation losses (WDEL) represent a relevant water sink in sprinkler irrigation, particularly in areas with strong winds and high evaporative demand. The objectives of this paper include: 1) Characterize WDEL under day and night operation conditions for solid-set and moving lateral configurations; 2) Propose adequate predictive equations; and 3) Prospect the effect of sprinkler irrigation on the meteorological variables and on the estimates of reference evapotranspiration. A total of 89 catch can irrigation evaluations were performed in both irrigation systems and under day and night conditions. Different predictive equations of WDEL were proposed for combinations of the two irrigation systems and the two operation times. The equations were selected based on their capability to explain and predict WDEL. Most equations use wind speed alone as an independent variable, although some use relative humidity or combinations of both variables plus air temperature. In the semi-arid meteorological conditions of Zaragoza (Spain), the average WDEL for the solid-set were 15.4 % and 8.5 % during day and night irrigations, respectively. For the experimental moving lateral, losses amounted to 9.8 % during the day and 5.0 % during the night. The effect of sprinkler irrigation on the meteorological variables was moderate, with small increases in relative humidity (3.9 %) and decreases in air temperature (0.5 ºC) during the irrigation event and a few minutes afterwards. Consequently, reference evapotranspiration, estimated by the Penman-Monteith method, decreased during the irrigation event by 0.023 mm h-1 on the average. This decrease represents 2.1 % of WDEL, suggesting that the WDEL do not significantly contribute to satisfy crop water requirements, and therefore constitute a consumptive water loss., This research was funded by the CONSI+D of the Government of Aragón (Spain) through grant P028/2000 and by the Plan Nacional de I+D+I of the government of Spain through grant AGL2004-06675-C03-03/AGR.

The definitive version is available at: http://www.sciencedirect.com/science/journal/03783774 http://dx.doi.org/10.1016/j.agwat.2003.12.003, A comparison between experimental and simulated data, considering the Priestley-Taylor (PT) and Penman-Monteith (PM) Reference-Evapotranspiration (ET0) approaches was carried out. Experimental data, obtained from an irrigation assessment, conducted during the 1995 and 1996 maize growth-seasons at Zaragoza, Spain, was compared to the mechanistic-model SWAP simulation-results, considering each of the ET0 calculation approaches in the model input. Soil hydraulic properties, meteorological data, seeding and harvest dates, crop water management and other experimental data were used as SWAP input. As corresponding to the windy and dry conditions found in many Mediterranean landplanes, PT ET0 values were significantly lower than PM ET0 calculations. Furthermore, simulated actual evapotranspirations considering the PT approach (PT-ETc) were lower than those found in the simulations that consider the PM approach (PM-ETc). Correspondingly, simulated drainage flux and soil water contents were higher when the PT ET0 approach was used. The correlation coefficients between simulated and measured actual maize evapotranspirations and soil water contents were statistically significant, but the same for both ET0 calculation approaches. Mean and median differences between actual and simulated maize water-use were not statistically different from zero for both considered ET0 calculation approaches. Experimental data variability was significantly higher than simulated variability. The comparisons among the evaluated irrigation options, made with the experimental water-use data, lead almost to the same conclusions than those achieved from the simulated maize water-use. Considering PM-ETc rather than PT-ETc yields no statistical difference in the modeling-based conclusions. According to the obtained results, the PT approach could be used under Mediterranean conditions for comparative assessments aimed to support irrigation decision-making.

The definitive version is available at: http://www.sciencedirect.com/science/journal/03783774, This study evaluates the Hargreaves (HARG) equation for estimation of monthly ET0 under the semiarid conditions of the middle Ebro River Valley (NE Spain). First, the Hargreaves equation was compared against measured lysimeter ET0 values at Zaragoza for the period May 1997–October 2000. The average of estimated values was only 5.6% above the average of measured values. Later, the Hargreaves equation was compared against the FAO Penman–Monteith equation for monthly ET0 estimation at nine locations. These locations can be grouped as non-windy (Alcañiz, Daroca and Tamarite) and windy (Almudévar, Ejea, Gallocanta, Monflorite, Sariñena and Zaragoza). Simple linear regression and error analysis statistics suggest that agreement between the two estimation methods was quite good for the windy locations. Average errors ranged between 2 and 5% for Almudévar, Ejea, Sariñena and Zaragoza, and between 7 and 10% for Gallocanta and Monflorite where some underestimation was observed. However, the agreement between the Hargreaves and FAO Penman–Monteith equations was lower for the non-windy locations. In this case, the Hargreaves equation overestimated ET0 and average errors varied between 14 and 20%. According to these results, it is proposed that, under the semiarid conditions of this study, no local calibration would be required for windy locations (those where monthly average windspeeds above 2.0 m s−1 are frequent), while a value of 0.0020 instead of the original 0.0023 should be used in the Hargreaves equation for non-windy locations. Further research should be undertaken to evaluate whether these results can be extended to other semiarid regions of the world., Research funded by projects HID96-1295-C04-04 (Water Resources Program, Spanish Ministry of Education), 2FD97-0547-C02-01 (FEDER Program), P028/200 and P030/2000 (Government of Aragón), and 1999-PH-31-I, 2001-PH-02 and 2002-PH-04-I (Confederación Hidrográfica del Ebro).

The definitive version is available at: http://www.sciencedirect.com/science/journal/03783774, The performance of the surface renewal method to estimate latent heat fluxes (LE) over a wheat crop was evaluated by comparison against values of LE measured independently using a weighing lysimeter. High-frequency temperature readings were taken at 1.5 m above ground from 29 April to 7 June 2000 over a 0.7–0.8 m high wheat crop. Surface renewal analysis was applied for two time lags r (0.75 and 0.25 s) to estimate half-hour sensible heat flux (H) and, subsequently, LE by solving the energy balance equation, using concurrent measurements of net radiation and soil heat flux. When H was estimated using sensor measurement height (z) in the computations, indices of agreement (IA) between lysimeter and surface renewal LE were above 0.94 and relative errors varied between 8.5 and 14.9% for time lag r=0.75 s for all analyzed days but 7 June. Results were slightly poorer for time lag r=0.25 s. When z−hc or z−d (hc being the crop height and d being the zero plane displacement) were used instead of z to compute H, surface renewal LE estimates slightly improved, particularly for the z−d case. The improvement was particularly noticeable for 7 June. The use of z−hc or z−d was thus more appropriate for these measurements, with the result that it was not necessary to calibrate the weighing factor α, as required by the standard surface renewal method. Unfortunately, although of similar magnitude than those reported for other micrometeorological methods, surface renewal errors found in this paper were biased and LE was underestimated. Further research and testing of the surface renewal method is therefore required to remove biases from the estimates of LE., This work was funded by the project HID96-1295-C04-04 (Ministry of Education, Government of Spain).

31 Pags., 2 Tabls., 6 Figs. The definitive version is available at: http://www.sciencedirect.com/science/journal/00221694, This paper reports a study undertaken to evaluate the feasibility of the surface renewal method to accurately estimate long-term evaporation from the playa and margins of an endorreic salty lagoon (Gallocanta lagoon, Spain) under semiarid conditions. High-frequency temperature readings were taken for two time lags (r) and three measurement heights (z) in order to get surface renewal sensible heat flux (HSR) values. These values were compared against eddy covariance sensible heat flux (HEC) values for a calibration period (25–30 July 2000). Error analysis statistics (index of agreement, IA; root mean square error, RMSE; and systematic mean square error, MSEs) showed that the agreement between HSR and HEC improved as measurement height decreased and time lag increased. Calibration factors α were obtained for all analyzed cases. The best results were obtained for the z=0.9 m (r=0.75 s) case for which α=1.0 was observed. In this case, uncertainty was about 10% in terms of relative error (RE). Latent heat flux values were obtained by solving the energy balance equation for both the surface renewal (LESR) and the eddy covariance (LEEC) methods, using HSR and HEC, respectively, and measurements of net radiation and soil heat flux. For the calibration period, error analysis statistics for LESR were quite similar to those for HSR, although errors were mostly at random. LESR uncertainty was less than 9%. Calibration factors were applied for a validation data subset (30 July–4 August 2000) for which meteorological conditions were somewhat different (higher temperatures and wind speed and lower solar and net radiation). Error analysis statistics for both HSR and LESR were quite good for all cases showing the goodness of the calibration factors. Nevertheless, the results obtained for the z=0.9 m (r=0.75 s) case were still the best ones., This research was funded by the Confederación Hidrográfica del Ebro (Spanish Ministry of Environment) and EPTISA, an Engineering Services private company.

7 Pags., 4 Tabls., 6 Figs., Geostatistical techniques were used to describe and map the spatial distribution of crenate broomrape populations parasitizing broad bean over 6 yr (from 1985 to 1990). In the first year, the spatial distribution was random, but from 1986 to 1989, crenate broomrape populations were clearly aggregated. The crenate broomrape infection severity (IS: number of emerged broomrape m−2) increased every year, from an average of 0.45 in 1985 to 29.4 in 1989, with a slight decrease the following year (IS = 27.4). Spherical functions provided the best fit because the cross-validation criteria were accomplished in all study cases. Kriged estimates were used to draw contour maps of the populations. About 34.3, 43.3, and 74.3% of the field plot surface exhibited an IS ≥ 1 (economic threshold) in 1985, 1986, and 1987, respectively, and nearly 100% of the area exceeded the economic threshold from 1988 to 1990; 1985 and 1986 were key years for control of the parasitic weed population. The percentage of infested area at different IS intervals in each year's map obtained by kriging was used to estimate the percentage of yield losses in each infested area (YA) with the equation: YA = A * Ymax * (1 − IS * 0.124), where A is the infested area at a given IS interval and Ymax is the expected broomrape-free broad bean yield. Yield losses under different IS intervals were compared with yield loss attributable to a uniform distribution of crenate broomrape. Results showed that yield loss assuming a uniform distribution of crenate broomrape was clearly overestimated, which is important to avoid overuse of herbicides., This work has been partially supported by a FEDER projecr (1FD97-0049) and the Spanish Scientific and Technological Committee (AGF99-0878).

33 Pags., 8 Tabls., 7 Figs. The definitive version is available at: http://link.springer.com/journal/271, Latent (LE) and two sets of sensible (H) heat fluxes (H ec and H t 2) were measured with an eddy covariance system (sonic anemometer, krypton hygrometer, two fine-wire thermocouples) over grass (6 days, summer 1997) and wheat (7 days, late spring 1999) in NE Spain. The objective was to evaluate a method to correct eddy covariance underestimation due to horizontal sensor displacement, based upon the similarity of covariance loss for both LE and H. First, this assumption was examined by regression analyses of measured lysimeter LE (LE lys ) versus eddy covariance LE (LE ec ) and H ec versus H t 2. In general, regression slopes of LE and H were broadly similar, although this similarity depended upon the atmospheric stability conditions. For grass, LE ec was significantly lower than LE lys , while for wheat there was a close agreement between LE lys and LE ec . Ratios of horizontal sensor displacement to measurement sensor height above zero plane displacement (s:z d ) were about 0.36–0.40 for grass and 0.11 for wheat. A further regression analysis was performed to compare LE lys with corrected eddy covariance LE (LE ecv ) values. That correction significantly improved eddy covariance LE values measured over grass but only in some cases, mostly under unstable (near to neutral) atmospheric conditions. It can be concluded that low s:z d ratios (less than 0.1) are preferable to reduce loss in covariance of LE. If the use of higher s:z d ratios cannot be avoided, the Villalobos method may reduce the expected loss in covariance but only under limited conditions. In these situations other solutions to reduce loss in covariance should be investigated further., This work has been funded by the project HID96-1295-C04-04 (Ministry of Education, Government of Spain).

The definive version is avalaible at: http://www.springerlink.com/content/0920-4741/, This paper presents the results of the interpolation of annual precipitation over a regular grid performed in Aragón (Spain). The main objective was the quantification of the improvement in estimation uncertainty by including elevation in the interpolation and by using base 10 logarithms of both annual precipitation and elevation versus the original values. Long-term annual precipitation (APRE) was available at 182 weather stations. Elevation above sea level (ELEV) was available at those stations and at 1913 additional points over a regular 5 km grid. The spatial variability of APRE, ELEV and their base 10 logarithms (LAPRE and LELEV, respectively), and the spatial correlation between APRE and ELEV, APRE and LELEV, LAPRE and ELEV, and LAPRE and LELEV were described by gaussian direct- and cross-semivariogram models with nugget effects. Geostatistical interpolation methods, ordinary kriging and cokriging, were used to estimate APRE and LAPRE at the 1913 additional elevation points. Estimates of LAPRE were transformed back to APRE values. Cokriging estimates were in general higher than kriging ones, mainly at points of high elevation. The average percent difference among cokriging and kriging estimates was 9–12%. Cokriging estimates obtained with the different sample data sets were in general terms similar. However, at points of high elevation, cokriging with ELEV as the auxiliary variable seemed to overestimate annual precipitation. Estimation error standard deviations (EESD) also were computed in each interpolation point. For all points, the EESD obtained using LAPRE values were lower than those obtained using APRE values, being the average percent differences of –38 to –42%. Likewise, for all interpolation points, cokriging EESD were lower than kriging ones. Using LAPRE and LELEV values, the average percent difference among cokriging and kriging EESD was –11.0%, with minimum and maximum percent differences of –6.7 and –35.8%, respectively., This research was funded by the Ministerio de Educaci6n y Ciencia, Government of Spain, through the project CICYT-514 and a grant to the author.

The definitive version is available at: http://www.sciencedirect.com/science/journal/00221694, An investigation of the application of multivariate geostatistics for analysis of regional evapotranspiration is reported. The focus of the research was analysis and modeling of the spatial correlation between evapotranspiration and elevation above sea level. The main goal was to investigate whether the use of cokriging could improve the accuracy of evapotranspiration estimates over a regular grid by including elevation in the estimation procedure. A total of 11 study cases for each of four different climatic regions (Willamette Valley, North Central, South Central and East) within the state of Oregon were analyzed. Long-term monthly (February to November) averages of daily reference evapotranspiration (ETr) and values of annual ETr were available at 199 locations within the regions. Values of elevation were available at the 199 locations and at 8570 additional locations spaced at approximately 5 km intervals on a grid. Experimental direct- and cross-semivariograms were computed to describe the spatial variability of ETr and elevation, and their correlation. Experimental direct-semivariograms for ETr showed best fit with isotropic spherical models with small nugget effects. Experimental direct-semivariograms for elevation showed best fit with isotropic models with nugget effects and two nested structures (spherical and gaussian) for the Willamette Valley region, one structure (spherical) for the North Central region, and two nested structures (spherical and linear) for the South Central and East regions. The experimental cross-semivariograms showed best fit with isotropic spherical models. Monthly and annual ETr values were estimated at 8570 locations situated at an approximately 5 km grid spacing using kriging and cokriging in conjunction with the previously fitted direct- and cross-semivariograms. Kriging and cokriging estimation error standard deviations were computed for each study case at all locations. ETr estimates and estimation error standard deviations were plotted as contour maps. Maximum, minimum and average kriging and cokriging estimates of ETr were in general agreement, although minimum and average values tended to be lower for cokriging. However, contour lines of cokriged ETr more closely reflected the elevation features of the climatic regions. Maximum and average estimation errror standard deviations were lower for cokriging, although minimum values were very similar for both kriging and cokriging. Average cokriging standard deviations decreased by about 20–30% in the Willamette Valley and North Central regions and by 5–13% in the South Central and East regions. These differences between regions were due to the lower correlation coefficients between ET, and elevation observed in the latter two regions. Contour maps of standard deviations showed cokriging had a more uniform distribution of estimation errors than kriging, for which errord tended to decrease in the vicinity of the sample ET, points at the weather stations. Errors increased along regional borders for both kriging and cokriging, although maximum estimation error values were lower for cokriging., The authors thank the Office of International Cooperation and Development (U.S. Department of Agriculture), the Oregon State University Agricultural Experiment Station and the Diputación General of Aragón (Spain) for their financial support.