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7 Pags.- 5 Figs.- 4 Tabls., En este trabajo se recogen los resultados de tres años de ensayos de campo realizados en alfalfa regada por aspersión con un sistema de cobertura total en los que se ha analizado la respuesta productiva a la dosis de riego (55%, 70%, 85%, 100%, 115%, 130%) del requerimiento teórico de riego (CIR)) y al momento de riego (diurno o nocturno). La producción de forraje de alfalfa aumentó linealmente al aumentar el riego aplicado hasta el 115% del CIR. El contenido en N de la alfalfa disminuyó linealmente al aumentar el riego aplicado. La relación entre el forraje de alfalfa y la evapotranspiración fue creciente y lineal hasta el 115% del CIR. La eficiencia en el uso del agua de la alfalfa no fue afectada por el riego aplicado en el año más lluvioso, pero aumentó linealmente al aumentar el riego aplicado hasta el 115% del CIR los otros dos años. Considerando el rendimiento de la alfalfa y su calidad (contenido en N), el riego por aspersión con un sistema de cobertura total debe incrementarse en un 15% sobre el CIR para optimizar la producción de forraje de alfalfa en las condiciones climáticas del valle del Ebro. Las pérdidas de agua durante el riego diurno (10%) triplicaron las del riego nocturno (3%). Sin embargo, la uniformidad del riego solo disminuyó ligeramente con el riego diurno en uno de los tres años de ensayo. La producción anual de alfalfa (16 a 22 Tm ha-1), su contenido en N (3,16 a 3,38%) y la eficiencia en el uso del agua (17,7 a 25,9 kg ha-1 mm-1) no fueron afectados por el momento del riego. Aunque el riego nocturno de la alfalfa puede suponer un pequeño ahorro de agua (3,7% en uno de los años de estudio), el riego por aspersión de la alfalfa se puede realizar durante el día si es necesario. En aquellas explotaciones que cultiven maíz y alfalfa, en el caso de que sea necesario regar durante el periodo diurno debido a limitaciones del sistema de riego, la alfalfa debería ser el cultivo a regar durante dicho periodo diurno., Financiación de estos trabajos: Ministerio de Economía y Competitividad de España (AGL2010-21681-C03-01).

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.

10 Pags., 9 Tabls., 2 Figs., In agricultural ecosystems the use of evapotran- spiration (ET) to improve irrigation water management is generally widespread. Commonly, the crop ET (ET c ) is es- timated by multiplying the reference crop evapotranspiration (ET o ) by a crop coefficient ( K c ). Accurate estimation of ET o is critical because it is the main factor affecting the calcula- tion of crop water use and water management. The ET o is generally estimated from recorded meteorological variables at reference weather stations. The main objective of this pa- per was assessing the effect of the uncertainty due to ran- dom noise in the sensors used for measurement of meteo- rological variables on the estimation of ET o , crop ET and net irrigation requirements of grain corn and alfalfa in three irrigation districts of the middle Ebro River basin. Five sce- narios were simulated, four of them individually considering each recorded meteorological variable (temperature, relative humidity, solar radiation and wind speed) and a fifth sce- nario combining together the uncertainty of all sensors. The uncertainty in relative humidity for irrigation districts Rie- gos del Alto Arag ́ on (RAA) and Bardenas (BAR), and tem- perature for irrigation district Canal de Arag ́ on y Catalu ̃ na (CAC), were the two most important factors affecting the es- timation of ET o , corn ET (ET c corn ), alfalfa ET (ET c alf ), net corn irrigation water requirements (IRn corn ) and net alfalfa irrigation water requirements (IRn alf ). Nevertheless, this ef- fect 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 ET o , ET c corn , ET c alf , IRn corn , and IRn alf . The fluctua- tions of evapotranspiration were higher at shorter time scale. ET o daily fluctuation remained lower than 5 % during the growing season of corn and alfalfa. This estimation fluctu- ation in ET o , ET c corn , ET c alf , IRn corn , and IRn alf at daily time scale was within an acceptable range, and it can be con- sidered that the sensor accuracy of the meteorological vari- ables is not significant in the estimation of ET o .

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.

En el riego por aspersión parte del agua emitida por los aspersores se pierde por evaporación y arrastre (WDEL) durante el riego. Asimismo, tras el riego el agua interceptada por el cultivo se evapora. Estas pérdidas de agua modifican el microclima en el que crecen las plantas provocando cambios fisiológicos en las mismas. La eficiencia de aplicación del agua de riego está determinada tanto por las pérdidas de agua como por la uniformidad del riego y la respuesta productiva del cultivo. En este trabajo se ha analizado: 1) los cambios microclimáticos y fisiológicos y la eficiencia de aplicación en el riego por aspersión del maíz (Zea mays L.) en un sistema de pívot central, 2) el efecto del riego por aspersión sobre la fotosíntesis del maíz y la alfalfa (Medicago sativa L.), y 3) la relevancia del momento de riego y de las pérdidas de agua en el rendimiento del maíz regado con un sistema de aspersión de cobertura total. La magnitud y duración de los cambios microclimáticos [temperatura del aire y déficit de presión de vapor (VPD)] y fisiológicos (temperatura de la cubierta vegetal y transpiración) del maíz debidos al riego por aspersión con pívot central se midieron en 2008 en una parcela comercial en Valfarta (Huesca, España). Dichas variables se midieron simultáneamente en tres tramos del pívot y en una zona situada a 270 m regada con anterioridad. Se estudiaron 34 eventos de riego, en 7 de los cuales se midió la transpiración de las plantas. Durante el riego se redujo temperatura del aire (1,8-2,1 ºC), el VPD (0,53-0,61 kPa), la temperatura de la cubierta vegetal (3,1-3,8 ºC) y la transpiración del maíz (0,22-0,28 mm h-1), siendo mayor la reducción en los días más secos y calurosos. Los cambios empezaron antes de pasar el brazo del pívot por la zona de medida (0,6-2,1 h) y se prolongaron tras el paso del mismo (0,8-2,4 h), si bien fueron menores. La duración total de los cambios microclimáticos disminuyó con la distancia hasta el centro del pívot pero la duración de los cambios fisiológicos fue similar en los diferentes tramos del brazo del pívot. La reducción de la transpiración debida al riego fue mayor cuanto más cerca del centro del pívot y representó entre el 5 y el 7% del agua de riego aplicada. Las WDEL fueron el 13% (tramo 2), 11% (tramo 4) y 10% (tramo 5) del agua aplicada. Considerando la reducción de la transpiración, las pérdidas netas por evaporación del sistema de riego oscilaron entre el 11 y 13% del agua aplicada, sin diferencias relevantes a lo largo del brazo del pívot. La fotosíntesis neta del maíz y la alfalfa regados con un sistema de aspersión de cobertura fija se midieron en dos experimentos diferentes (maíz: 2009 y 2010; alfalfa: 2009, 2010 y 2011). Para cada especie las medidas se realizaron simultáneamente en dos parcelas, una se estaba regando y la otra no. Se utilizaron dos cámaras automáticas conectadas a dos analizadores de CO2 por infrarrojos. El riego redujo la temperatura del aire (1,5 ºC en maíz, 1,7 ºC en alfalfa), el VPD (0,44 kPa en ambos cultivos) y la temperatura de la cubierta vegetal (5,1 ºC en maíz, 5,9 ºC en alfalfa). El riego por aspersión disminuyó la fotosíntesis neta del maíz en el 80% de los días siendo la reducción media del 19%. El riego por aspersión incrementó la fotosíntesis neta de la alfalfa en el 36% de los días y la disminuyó en el 14% de los días, no afectando a la misma en la mitad de los días. La reducción de la fotosíntesis neta del maíz durante el riego por aspersión fue causada por la alta mojabilidad de las hojas (¿120º) y su amplio rango de temperatura óptima para la fotosíntesis fueron las causas de que la fotosíntesis no se viera afectada negativamente por el riego por aspersión. El riego por aspersión durante el día debe ser evitado en el maíz. En los años 2009 y 2010 se estudió la relevancia del momento de riego (diurno o nocturno) y de las pérdidas de agua (añadiéndolas o no a la dosis de riego) sobre el rendimiento del maíz. La parcela experimental se dividió en 12 sectores de riego independientes, cada uno formado por cuatro aspersores en un marco de 18m x 18m. El riego por aspersión diurno tuvo mayores WDEL (16-22%) que el riego nocturno (3-9%). La uniformidad del riego (CU) fue similar para los riegos diurnos y nocturnos en 2009 (84%) pero en 2010 fue menor para los riegos diurnos (78%) que para los riegos nocturnos (84%). El riego diurno disminuyó un 9% el rendimiento del maíz en 2010, el año en el que el CU disminuyó. El aumento de la dosis de riego con las pérdidas de agua incrementó el potencial mátrico del suelo pero no el rendimiento del maíz. La menor uniformidad en el riego diurno parece ser una razón relevante para la reducción del rendimiento. Los sistemas de aspersión de cobertura fija para el maíz deben estar diseñados para minimizar el riego diurno y permitir una alta uniformidad del riego diurno (>84%).

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).

1 fichero .pdf (18 Pags.) copia de la presentación original de los autores en Seminario del 11-04-2014., La ET de una superficie engloba la transpiración de las plantas y la evaporación directa de agua del suelo o interceptada. Distintos métodos para medir LE (= ET) real. Comúnmente se basan en el balance de energía. Rn = H + G + LE. El método de covarianza de torbellinoses uno de los pocos que miden H y LE independientemente. Es el método más comúnmente empleado como alternativa a la lisimetría de pesada.

5 Pags., 5 Figs., 3 Tabls., El riego por aspersión nocturno es más eficiente que el riego diurno porque las pérdidas por evaporación y arrastre (PEA) son menores y la uniformidad del riego es mayor. El agua que se evapora durante el riego por aspersión modifica el microclima en el que se desarrollan las plantas, lo que afecta a su fisiología. En trabajos anteriores se observó una reducción del rendimiento del maíz cuando se riega de día por lo que se han analizado las razones agronómicas de dicho descenso del rendimiento. Durante dos años se estudió la relevancia del momento de riego (diurno o nocturno) y de las PEA (añadiéndolas o no en el riego aplicado) en el rendimiento del maíz. En 2010 la uniformidad del riego diurno fue menor, reduciéndose el rendimiento del maíz en un 9%. Sin embargo, en 2009 la uniformidad del riego diurno fue similar al nocturno, reduciéndose el rendimiento del maíz solo un 5%. El incremento del agua de riego aplicada añadiendo las PEA aumentó la humedad del suelo pero no el rendimiento del maíz. El riego diurno disminuyó la fotosíntesis del maíz en el 80% de los días estudiados, siendo la reducción media de un 19%. Las razones agronómicas del descenso del rendimiento del maíz cuando se riega por aspersión de día en nuestras condiciones de clima y suelo son principalmente la menor uniformidad del riego y la disminución de la fotosíntesis. Si bien la uniformidad del riego puede aumentarse modificando el marco entre aspersores, la disminución de la fotosíntesis es inevitable, por lo que en la medida de lo posible se debe evitar el riego por aspersión del máiz durante el día., Agradecimiento al MCYT por la financiación de estos trabajos (AGL2004-06675-C03/AGR, AGL2007-667 16-C03, AGL2OIO-2 1681-C03-O1).