Evapotranspiration components and dual crop coefficients of coffee trees during crop production

Quantifying crop water consumption is essential for many applications in agriculture, such as crop zoning, yield forecast and irrigation management. The objective of this study was to determine evaporation (E), transpiration (T) and dual crop coefficients (Ke and Kcb) of coffee trees during crop production (3rd and 4th year of cultivation), conducted under sprinkler and drip irrigation and no irrigation, in Londrina, Paraná State, Brazil. Crop evapotranspiration (ET) was measured by weighing lysimeters cultivated with plants of cultivar IAPAR 59, E was measured by microlysimeters installed on the lysimeters and T was obtained by the difference between ET and E. The crop coefficient (Kc) was determined for the irrigated treatments as the ratio between ET and the reference evapotranspiration (ETo). Similarly, evaporation coefficient (Ke) and basal crop coefficient (Kcb) were determined as the ratio of E and T, respectively, to the value of ETo, which was estimated by the ASCE Penman-Monteith method on an hourly basis. The values of E and Ke varied due to atmospheric demand and water application method. Those factors, in addition to crop phenology and leaf area evolution, also influenced T and Kcb. Regardless irrigation treatment, the measured values of E represented 35% of ET, while T was 65% of ET. The recommended values of Ke were 0.46 and 0.26 for sprinkler and drip irrigation, respectively. The recommended values of Kcb were 0.52 and 0.82 for sprinkler-irrigated, and 0.5 and 0.65 for drip-irrigated treatments, varying as a function of daily ETo (ETo ≥ or <3 mm day⁻¹, respectively).     

Evaporation and canopy conductance of citrus orchards

Evaporation of citrus orchards has been widely studied, but differences in methodologies and management conditions have led to conflicting results, mainly due to differences in ground cover and soil evaporation. In this work the contribution of transpiration and soil evaporation has been studied in a drip-irrigated, clean cultivated mandarin (Citrus reticulata Blanco) orchard on a sandy soil in Southern Spain. Evapotranspiration (ET) was measured using eddy covariance while soil evaporation was determined with microlysimeters, during August 2000 and May 2001. Average ET was 2.6 mm day⁻¹ in August and 2.1 mm day⁻¹ in May. The crop coefficient (K_c) was 0.44 and 0.43 in 2000 and 2001, respectively. The coefficient of transpiration (K_p) was 0.30 in 2000 and 0.25 in 2001. The daily bulk canopy conductance (g_c) ranged from 1.2 to 2.2 (average 1.8) mm s⁻¹ in 2000 and from 1.2 to 2.7 (average 1.9) mm s⁻¹ in 2001. A model of daily canopy conductance as a function of intercepted radiation was derived and applied to calculate the transpiration of orchards with different values of ground cover (GC). The ratio of transpiration over reference ET of mandarin orchards is linearly related to ground cover (K_p = 0.7 GC). Calculated crop coefficients agree with values suggested by FAO for mature orchards (around 0.65) but are substantially lower than FAO values for young plantations.     

Soil water content and water balance in rainfed fields in Northeast Thailand

Northeast Thailand has a semi-humid tropical climate which is characterized by dry and rainy seasons. In order to stabilize crop production, it may be necessary to develop new water resources, such as soil moisture and groundwater, instead of rainfed resources. This is because rainfed agriculture has already been unsuccessfully tried in many areas of this region. In this study, we investigate the soil water content in rainfed fields in Khon Kaen in Northeast Thailand, where rice and sugarcane were planted, over a 1-year period that contained both dry and rainy seasons, and estimate the actual evapotranspiration (ET_a) using micrometeorological data. In addition, we assess the water balance from the results of the soil water content investigation and the actual evapotranspiration. Although the soil water content at depths above 0.6 m in both the lower and the sloping fields gradually decreased during the dry season, the soil water content at a depth of 1.0 m was under almost constant wet conditions. Two-dimensional profiles of the soil water content demonstrated that at the end of the dry season, the soil layers below a depth of 0.4 m showed a soil water content of more than 0.10-0.15 m³ m⁻³, thus suggesting that water was supplied to the sugarcane from those layers. The range in ET_a rates was almost the same as that in the previous study. The average ET_a rates were 3.7 mm d⁻¹ for the lower field and 4.2 mm d⁻¹ for the sloping field. In the dry season, an upward water flow of 373 mm (equivalent to a flux of 1.9 mm d⁻¹) was estimated from outside the profile. The source of this upward water flow was the sandy clay (SC) layer below a depth of 1 m. It was this soil water supply from the SC layer that allowed the sugarcane to grow without irrigation.     

Influence of irrigation frequencies and phosphate fertilization on actual evapotranspiration rate, yield and water use pattern of rajmash (Phaseolus vulgaris L.)

The hypothesis was tested, whether soil wetness and phosphorus status could regulate the evapotranspiration rate (ET_R), which is of special interest in the lower Gangetic Plain. Rajmash was grown during November-February of 2003-2004 and 2004-2005 on a sandy loam soil, and was irrigated when cumulative pan evaporation (CPE) attained the value of 33 mm (CPE₃₃); 44 mm (CPE₄₄) and 66 mm (CPE₆₆). Four levels of phosphate application were 0 kg P₂O₅ ha⁻¹ (P₀); 30 kg P₂O₅ ha⁻¹ (P₃₀); 60 kg P₂O₅ ha⁻¹ (P₆₀) and 90 kg P₂O₅ ha⁻¹ (P₉₀). Seed yield under CPE₃₃ was 1.37 Mg ha⁻¹ and reduced by 18% and 35%, respectively under CPE₄₄ and CPE₆₆. Continuous increasing trend in yield was recorded with an increase in phosphate level (PL). Irrespective of growth stages, similar trends were recorded for leaf area index (LAI). Maximum variation in LAI among the treatments was recorded at 60 days after sowing. On average, actual ET_R was 1.37 mm day⁻¹ under CPE₃₃ and declined by 13% and 16% under CPE₄₄ and CPE₆₆, respectively. Variation in ET_R under different PL was highest under CPE₃₃ and lowest under CPE₄₄. Except P₉₀, irrespective of PL, highest value of water use efficiency (WUE) was obtained under CPE₄₄. However, magnitude of net evapotranspiration efficiency (WUE_ET) and irrigation efficiency (WUE_I) attained the highest level under CPE₃₃ regime. All water use indices showed an increasing trend with the increase in phosphate level from 0 to 90 kg ha⁻¹. Impact of phosphorus on various parameters was pronounced under CPE₃₃.     

Yield and water-production functions of two durum wheat cultivars grown under different irrigation and nitrogen regimes

Wheat (Triticum durum L.) yields in the semi-arid regions are limited by inadequate water supply late in the cropping season. Planning suitable irrigation strategy and nitrogen fertilization with the appropriate crop phenology will produce optimum grain yields. A 3-year experiment was conducted on deep, fairly drained clay soil, at Tal Amara Research Station in the central Bekaa Valley of Lebanon to investigate the response of durum wheat to supplemental irrigation (IRR) and nitrogen rate (NR). Three water supply levels (rainfed and two treatments irrigated at half and full soil water deficit) were coupled with three N fertilization rates (100, 150 and 200 kg N ha⁻¹) and two cultivars (Waha and Haurani) under the same cropping practices (sowing date, seeding rate, row space and seeding depth). Averaged across N treatments and years, rainfed treatment yielded 3.49 Mg ha⁻¹ and it was 25% and 28% less than half and full irrigation treatments, respectively, for Waha, while for Haurani the rainfed treatment yielded 3.21 Mg ha⁻¹, and it was 18% and 22% less than half and full irrigation, respectively. On the other hand, N fertilization of 150 and 200 kg N ha⁻¹ increased grain yield in Waha by 12% and 16%, respectively, in comparison with N fertilization of 100 kg N ha⁻¹, while for cultivar Haurani the increases were 24% and 38%, respectively. Regardless of cultivar, results showed that supplemental irrigation significantly increased grain number per square meter and grain weight with respect to the rainfed treatment, while nitrogen fertilization was observed to have significant effects only on grain number per square meter. Moreover, results showed that grain yield for cultivar Haurani was less affected by supplemental irrigation and more affected by nitrogen fertilization than cultivar Waha in all years. However, cultivar effects were of lower magnitude compared with those of irrigation and nitrogen. We conclude that optimum yield was produced for both cultivars at 50% of soil water deficit as supplemental irrigation and N rate of 150 kg N ha⁻¹. However, Harvest index (HI) and water use efficiency (WUE) in both cultivars were not significantly affected neither by supplemental irrigation nor by nitrogen rate. Evapotranspiration (ET) of rainfed wheat ranged from 300 to 400 mm, while irrigated wheat had seasonal ET ranging from 450 to 650 mm. On the other hand, irrigation treatments significantly affected ET after normalizing for vapor pressure deficit (ET/VPD) during the growing season. Supplemental irrigation at 50% and 100% of soil water deficit had approximately 26 and 52 mm mbar⁻¹ more ET/VPD, respectively, than those grown under rainfed conditions.     

Corn crop response under managing different irrigation and salinity levels

Non-uniformity of water distribution under irrigation system creates both deficit and surplus irrigation areas. Water salinity can be hazard on crop production; however, there is little information on the interaction of irrigation and salinity conditions on corn (Zea Mays) growth and production. This study evaluated the effect of salinity and irrigation levels on growth and yield of corn grown in the arid area of Egypt. A field experiment was conducted using corn grown in northern Egypt at Quesina, Menofia in 2009 summer season to evaluate amount of water applied, salinity hazard and their interactions. Three salinity levels and five irrigation treatments were arranged in a randomized split-plot design with salinity treatments as main plots and irrigation rates within salinity treatments. Salinity treatments were to apply fresh water (0.89 dS m⁻¹), saline water (4.73 dS m⁻¹), or mixing fresh plus saline water (2.81 dS m⁻¹). Irrigation treatments were a ratio of crop evapotranspiration (ET) as: 0.6ET, 0.8ET, 1.0ET, 1.2ET, and 1.4ET. In well-watered conditions (1.0ET), seasonal water usable by corn was 453, 423, and 380 mm for 0.89EC, 2.81EC and 4.73EC over the 122-day growing season, respectively. Soil salt accumulation was significantly increased by either irrigation salinity increase or amount decrease. But, soil infiltration was significantly decreased by either salinity level or its interaction with irrigation amount. Leaf temperature, transpiration rate, and stomata resistance were significantly affected by both irrigation and salinity levels with interaction. Leaf area index, harvest index, and yield were the greatest when fresh and adequate irrigation was applied. Grain yield was significantly affected in a linear relationship (r² ≥ 0.95) by either irrigation or salinity conditions with no interaction. An optimal irrigation scheduling was statistically developed based on crop response for a given salinity level to extrapolate data from the small experiment (uniform condition) to big field (non-uniformity condition) under the experiment constraints.     

Evaluation of FAO Penman-Monteith and alternative methods for estimating reference evapotranspiration with missing data in Southern Ontario, Canada

Grass reference evapotranspiration (ETo) is an important agrometeorological parameter for climatological and hydrological studies, as well as for irrigation planning and management. There are several methods to estimate ETo, but their performance in different environments is diverse, since all of them have some empirical background. The FAO Penman-Monteith (FAO PM) method has been considered as a universal standard to estimate ETo for more than a decade. This method considers many parameters related to the evapotranspiration process; net radiation (Rn), air temperature (T), vapor pressure deficit (Δe), and wind speed (U); and has presented very good results when compared to data from lysimeters populated with short grass or alfalfa. In some conditions, the use of the FAO PM method is restricted by the lack of input variables. In these cases, when data are missing, the option is to calculate ETo by the FAO PM method using estimated input variables, as recommended by FAO Irrigation and Drainage Paper 56. Based on that, the objective of this study was to evaluate the performance of the FAO PM method to estimate ETo when Rn, Δe, and U data are missing, in Southern Ontario, Canada. Other alternative methods were also tested for the region: Priestley-Taylor, Hargreaves, and Thornthwaite. Data from 12 locations across Southern Ontario, Canada, were used to compare ETo estimated by the FAO PM method with a complete data set and with missing data. The alternative ETo equations were also tested and calibrated for each location. When relative humidity (RH) and U data were missing, the FAO PM method was still a very good option for estimating ETo for Southern Ontario, with RMSE smaller than 0.53 mm day⁻¹. For these cases, U data were replaced by the normal values for the region and Δe was estimated from temperature data. The Priestley-Taylor method was also a good option for estimating ETo when U and Δe data were missing, mainly when calibrated locally (RMSE = 0.40 mm day⁻¹). When Rn was missing, the FAO PM method was not good enough for estimating ETo, with RMSE increasing to 0.79 mm day⁻¹. When only T data were available, adjusted Hargreaves and modified Thornthwaite methods were better options to estimate ETo than the FAO PM method, since RMSEs from these methods, respectively 0.79 and 0.83 mm day⁻¹, were significantly smaller than that obtained by FAO PM (RMSE = 1.12 mm day⁻¹).     

Tuber yield, water and fertilizer productivity in early potato as affected by a combination of irrigation and fertilization

Excessive amounts of irrigation water and fertilizers are often utilized for early potato cultivation in the Mediterranean basin. Given that water is expensive and limited in the semi-arid areas and that fertilizers above a threshold level often prove inefficacious for production purposes but still risk nitrate and phosphorous pollution of groundwater, it is crucial to provide an adequate irrigation and fertilization management. With the aim of achieving an appropriate combination of irrigation water and nutrient application in cultivation management of a potato crop in a Mediterranean environment, a 2-year experiment was conducted in Sicily (South Italy). The combined effects of 3 levels of irrigation (irrigation only at plant emergence, 50% and 100% of the maximum evapotranspiration - ETM) and 3 levels of mineral fertilization (low: 50, 25 and 75 kg ha⁻¹, medium: 100, 50 and 150 kg ha⁻¹ and high: 300, 100 and 450 kg ha⁻¹ of N, P₂O₅ and K₂O) were studied on the tuber yield and yield components, on both water irrigation and fertilizer productivity and on the plant source/sink (canopy/tubers dry weight) ratio. The results show a marked interaction between level of irrigation and level of fertilization on tuber yield, on Irrigation Water Productivity and on fertilizer productivity of the potato crop. We found that the treatments based on 50% ETM and a medium level of fertilization represent a valid compromise in early potato cultivation management. Compared to the high combination levels of irrigation and fertilization, this treatment entails a negligible reduction in tuber yield to save 90 mm ha⁻¹ year⁻¹ of irrigation water and 200, 50 and 300 kg ha⁻¹ year⁻¹ of N, P₂O₅ and K₂O, respectively, with notable economic savings for farmers compared to the spendings that are usually made.     

Irrigation requirements and transpiration coupling to the atmosphere of a citrus orchard in Southern Brazil

Crop evapotranspiration (ETc) was measured as evaporative heat flux from an irrigated acid lime orchard (Citrus latifolia Tanaka) using the aerodynamic method. Crop transpiration (T) was determined by a stem heat balance method. The irrigation requirements were determined by comparing the orchard evapotranspiration (ETc) and T with the reference evapotranspiration (ETo) derived from the Penman-Monteith equation, and the irrigation requirements were expressed as ETc/ETo (Kc) and T/ETo (Kcb) ratios. The influence of inter-row vegetation on the ETc was analyzed because the measurements were taken during the summer and winter, which are periods with different regional soil water content. In this study, the average Kc values obtained were 0.65 and 0.24 for the summer and winter, respectively. The strong coupling of citrus trees to the atmosphere and the sensitivity of citrus plants to large vapor pressure deficits and air/leaf temperatures caused variations in the Kcb in relation to the ETo ranges. During the summer, the Kcb value ranged from 0.34 when the ETo exceeded 5 mm d⁻¹ to 0.46 when the ETo was less than 3 mm d⁻¹.     

Effects of nutrition systems and irrigation programs on tomato in soilless culture

A research has been carried out to determine the effects of nutrition systems and irrigation programs on soilless grown tomato plants under polyethylene covered unheated greenhouse conditions. Two nutrition systems (open and closed) and three irrigation programs (high, medium and low) based on integrated indoor solar radiation triggering thresholds (1 MJ m⁻² [0.4 mm], 2 MJ m⁻² [0.8 mm] and 4 MJ m⁻² [1.6 mm]) in both nutrition systems have been tested. Applied and discharged nutrient solution, evapotranspiration, total and marketable yield have been measured and water use efficiency has been calculated. The highest total yield has been obtained from the open system with respectively 11% and 7.2% increases in autumn and spring. Applied nutrient solution volume and seasonal ET have been modified between 47.8-180.4 l plant⁻¹ and 41.7-145.5 l plant⁻¹ respectively during both growing seasons. As average of two growing seasons, respectively 826.5 and 330.6 m³ ha⁻¹ nutrient solutions have been discharged from the greenhouse in the open and closed systems. WUE of treatments varied between 33-55 kg m⁻³ in autumn and 26-35 kg m⁻³ in spring. Highest WUE values have been determined in 4 MJ m⁻² and in the closed system in both growing seasons. Results showed that the closed system and infrequent irrigations increased water use efficiency while decreasing yield and discharged nutrient solution.     

Effect of soil matric potential on tomato yield and water use under drip irrigation condition

Field experiment was carried out to investigate the effect of soil matric potential (SMP) on tomato yield, evapotranspiration (ET), water use efficiency (WUE) and irrigation water use efficiency (IWUE) under drip irrigation condition in North China Plain. The experiment included five treatments, which controlled SMP at 0.2 m depth immediately under drip emitter higher than −10 (S1), −20 (S2), −30 (S3), −40 (S4) and −50 kPa (S5), respectively, after tomato plant establishment. The results showed that different SMP affected irrigation amount and tomato ET. Irrigation amount decreased from 185 mm (S1) to 83.6 mm (S5) in 2004, and from 165 mm (S1) to 109 mm (S5) in 2005, respectively. The ET decreased from 270 mm (S1) to 202 mm (S5) in both years. However, it was found that SMP did not affect the tomato yield significantly, for the range of SMP investigated. Both WUE and IWUE increased as SMP decreased. The maximum WUE (253 and 217 kg/ha mm) and IWUE (620 and 406 kg/ha mm) were for S5 in 2 years, whereas the minimum WUE (178 and 155 kg/ha mm) and IWUE 261 and 259 kg/ha mm) were for S1 in 2004 and 2005. Based on the above results, therefore, it is recommended that if the tomatoes are well irrigated (SMP is higher than −20 kPa) during establishment, controlling SMP higher than −50 kPa at 0.2 m depth immediately under drip emitter can be used as an indicator for drip irrigation scheduling during following period of tomato growth in North China Plain.     

Can soil bunds increase the production of rain-fed lowland rice in south eastern Tanzania?

Rain-fed lowland rice is by far the most common production system in south eastern Tanzania. Rice is typically cultivated in river valleys and plains on diverse soil types although heavy soil types are preferred as they can retain moisture for a longer period. To assess the effects of soil bunds on the production of rain-fed lowland rice, the crop was cultivated in bunded and non-bunded farmers’ plots under the common agronomic practices in the region, in three successive seasons on Grumic Calcic Vertisols (Pellic). For the three seasons and for the two plot types, crop transpiration was simulated with the BUDGET soil water balance model by using the observed weather data, soil and crop parameters. Comparison between the observed yields and the simulated crop transpiration yielded an exponential relationship with a determination factor of 0.87 and an RMSE of 0.15 tonnes ha⁻¹. With the validated soil water balance model crop yields that can be expected in bunded and non-bunded fields were subsequently simulated for wet, normal and dry years and various environmental conditions. Yield comparison shows that soil bunds can appreciably increase the production of rain-fed lowland rice in south eastern Tanzania in three quarters of the years (wet and normal years) when the soil profile is slow draining (K_SAT equal to or less than 10 mm day⁻¹). In normal years a minimum yield increase of 30% may be expected on those soil types. In wet years and when the soil hardly drains (drainage class of 0–5 mm day⁻¹), the yield may even double. In dry years the yield increase will be most of the time less than 10% except for plots with a percolation rate of 0–5 mm day⁻¹.     

In-season wheat root growth and soil water extraction in the Mediterranean environment of northern Syria

Wheat is the most important cereal crop in the semi-arid eastern Mediterranean region that includes northern Syria. Knowledge of wheat root depth and the vertical distribution during the winter growing season is needed for sound scheduling of irrigation and efficient use of water. This article reports evaluation of root development for three winter-grown bread (Triticum aestivum L.) and durum (Triticum turgidum L.) wheat under four soil water regimes (rainfed and full irrigation with two intermediate levels of 33 and 66% of full irrigation). Roots were sampled by soil coring to a depth of 0.75 m at four occasions during 2005-2006 growing season. Two distinct phases of root development were identified, a rapid downward penetration from emergence to end tillering phase, followed by a substantial root mass growth along the profile from tillering to mid-stem-elongation phase. Roots were detected as deep as 0.75 m during the initial rapid penetration, yet only 29% of the total seasonal root mass was developed. This downward penetration rate averaged 7 mm d⁻¹ and produced 10.8 kg ha⁻¹ d⁻¹ of root dry-biomass. The bulging of root mass from tillering to mid-stem-elongation coincided with vigorous shoot growth, doubling root dry-biomass at a rate of 52 kg ha⁻¹ d⁻¹, compared to the seasonal root growth rate of 18.3 kg ha⁻¹ d⁻¹. A second-degree equation described the total root dry-biomass as a function of days after emergence (r² = 0.85), whereas a simpler equation predicted it as a function of cumulative growing degree days (r² = 0.85). The final grain yield was a strong function of irrigation regimes, varying from 3.0 to 6.5 t ha⁻¹, but showed no correlation with root biomass which remained similar as soil water regimes changed. This observation must be viewed with care as it lacks statistical evidence. Results showed 90% of root mass at first irrigation (15 April) confined in the top 0.60-0.75 m soil in bread wheat. Presence of shallow restricting soil layers limited root depth of durum wheat to 0.45 m, yet total seasonal root mass and grain yield were comparable with non-restricted bread wheat. Most root growth occurred during the cool rainy season and prior to the late irrigation season. The root sampling is short of rigorous, but results complement the limited field data in literature collectively suggesting that irrigation following the rainy season may best be scheduled assuming a well developed root zone as deep as the effective soil depth within the top meter of soil.     

Role of irrigation and mulch on yield, evapotranspiration rate and water use pattern of tomato (Lycopersicon esculentum L.)

Irrigation management strategy invites the quantification of crop response to irrigation frequencies. Conventionally, mulches increase the yield and water use efficiency (WUE) to a great extent by augmenting the water status in the root zone profile. A field study was carried out during the winter season (November-March) of 2003-2004 and 2004-2005 at the Central Research Farm of Bidhan Chandra Krishi Viswavidyalaya (Latitude 22°58′N, Longitude 88°31′E and altitude 9.75 m amsl), Gayeshpur, India, to evaluate the effect of irrigation frequencies and mulches on evapotranspiration rate from tomato crop field as well as leaf area index (LAI), fruit yield and WUE of the crop. The experiment was laid out in a split-plot design where three irrigation treatments {rainfed (RF); CPE₅₀ and CPE₂₅ where irrigation was given at 50 and 25 mm of cumulative pan evaporation (CPE)} were kept in the main plots and the subplots contained four mulch managements {no mulch (NM), rice straw mulch (RSM), white polyethylene mulch (WPM) and black polyethylene mulch (BPM)}. Under CPE₂₅, tomato crop recorded significantly higher leaf area index (LAI) over CPE₅₀ and rainfed condition. LAI value under BPM was 9-30% more over other mulches. Maximum variation of LAI among different treatments was recorded at 60 days after transplanting (DAT). Fruit yield under CPE₂₅ was 39.4 Mg ha⁻¹; a reduction of 7 and 30% has been obtained under CPE₅₀ and RF condition. The use of mulch increased 23-57% yield in comparison to NM condition. Actual evapotranspiration rate (ET_R) was 1.82 mm day⁻¹ under CPE₂₅ and declined by 15 and 31% under CPE₅₀ and RF condition, respectively. The variation of ET_R among different mulches became more prominent under maximum water stressed (RF) condition, whereas the variation was negligible under CPE₂₅ frequency. Irrespective of mulching WUE was highest under moderately wet (CPE₅₀) soil environment. Among different mulches, BPM was responsible for attaining the highest WUE value (25.1 kg m⁻³), which declined by 22, 21 and 39% under WPM, RSM and NM, respectively.     

Water use efficiency and crop coefficients of dry season oilseed crops

Eastern India receives higher average annual rainfall (1000–2000 mm) but 80% of it occurs within the June–September (rainy season), whereas the winter season (November–March) is dry. Due to a shortage of soil moisture, most rainfed areas of the region remain fallow during the winter season and cultivation (mainly rice) is confined to the rainy season only (June–September). To explore the possibility of double cropping in the rainfed rice areas, three oilseed crops, viz., linseed (Linum usitatissimum L.), safflower (Carthamous tinctorious L.), mustard (Brassica juncea L.), were grown in a representative rainfed area of eastern India, i.e. Dhenkanal, Orissa, during the dry/winter season by applying irrigation water at phonological stages. Study revealed that with three supplemental irrigations, the highest WUE was achieved by safflower followed by linseed with the mean values being 3.04 and 2.59 kg ha⁻¹ mm⁻¹, respectively. Whereas, with one irrigation, the highest water use efficiency (WUE) was achieved for safflower (1.23 kg ha⁻¹ mm⁻¹) followed by linseed (0.93 kg ha⁻¹ mm⁻¹). Of the three crops studied, safflower withdrew maximum water followed by mustard and crops were shown to use 90–105 mm more water than linseed. With three irrigations, average maximum rooting depths were 1.66, 1.17 and 0.67 m for safflower, mustard and linseed, respectively, which were 13.5, 10.6 and 11.4% higher than for single irrigated crops because of more wet sub soils and decrease of soil strength. The crop growth parameters like leaf area, dry biomass were also recorded with different levels of irrigation. The research work amply revealed the potential of growing these low water requiring oilseed crops in rice fallow during dry/winter season utilizing limited irrigation from harvested rainwater of rainy season. Crop coefficients (K_c) of three winter season oilseed crops were derived using field water balance approach. Study showed that LAI was significantly correlated with K_c values with the R² values of 0.91, 0.89 and 0.94 in linseed, safflower and mustard, respectively. When LAI exceeded 3.0, the K_c value was 1 in safflower and mustard whereas in linseed corresponding LAI was 2.5. Study revealed that the K_c values for the development and mid season stage were slightly higher to that obtained by the procedure proposed by FAO, which might be due to local advection.     

Water use of spring wheat to raise water productivity

In semi-arid environments with a shortage of water resources and a risk of overexplotation of water supplies, spring wheat (Triticum aestivum L.) is a crop that can reduce water use and increase water productivity, because it takes advantage of spring rainfall and is harvested before the evaporative demands of summer. We carried out an experiment in 2003 at “Las Tiesas” farm, located between Barrax and Albacete (Central Spain), to improve accuracy in the estimation of wheat evapotranspiration (ETc) by using a weighing lysimeter. The measured seasonal ETc averages (5.63 mm day⁻¹) measured in the lysimeter was 417 mm compared to the calculated ETc values (5.31 mm day⁻¹) calculated with the standard FAO methodology of 393 mm. The evapotranspiration crop coefficient (Kc) derived from lysimetric measurements was Kc-mid: 1.20 and Kc-end: 0.15. The daily lysimeter Kc values were fit to the evolution linearly related to the green cover fraction (fc), which follows the crop development pattern. Seasonal soil evaporation was estimated as 135 mm and the basal crop coefficient approach was calculated in this study, Kcb which separates crop transpiration from soil evaporation (evaporation coefficient, Ke) was calculated and related to the green cover fraction (fc) and the Normalized Difference Vegetation Index (NDVI) obtained by field radiometry in case of wheat. The results obtained by this research will permit the reduction of water use and improvement of water productivity for wheat, which is of vital importance in areas of limited water resources.     

Evaluation of satellite evapotranspiration estimates using ground-meteorological data available for the Flumen District into the Ebro Valley of N.E. Spain

Accurate estimation of actual evapotranspiration (ET_a) is essential for effective local or regional water management. At a local scale, ET estimates can be made accurately considering a soil-plant-atmospheric system, if adequate meteorological-ground data or ET measurements are available. However, at a regional scale, ET_a values cannot be measured directly and the estimates are frequently subject to errors. Although it is possible to extrapolate to the regional scale from local (point) data of meteorological stations, the relative sparse coverage of ground estimate can make this problematic without some spatial analysis to demonstrate the similarity of the climate in the area. The introduction of remote sensing data and techniques offers alternatives both to estimate variables (i.e. radiation) and parameters (i.e. ET) with few spatial restrictions, thus, it provides potential advantages to the regional ET_a computation. In particular, the use of remote sensing procedures like the surface energy balance-based algorithms (SEB) have been successfully applied in different climates, enabling the estimation of ET_a at local and regional scales. A proper variation of the Surface Energy Balance Algorithm for Land (SEBAL) was applied to 4 years of data for the Flumen District in the Ebro Basin at the N.E. of Spain. Results obtained show that the remote sensing algorithm can provide accurate daily ET_a estimations as compared with lysimeter measurements of daily ET values for two crop plots: one with a reference grass and other with maize or wheat as function of the season. Also a comparison between ET_a and the reference and crop ET values applying the Penman-Monteith method was carried out. The comparison analysis consider an accepted error difference of 1.0 mm d⁻¹ (20% of error) for local scale, the ET_a values for the grass show a bias of 0.30 mm d⁻¹ against the ET_grass and a bias of 0.36 mm d⁻¹ against ET_o. Differences between ET_maize or ET_wheat and ET_a against their average showed an acceptable agreement for the field with s_diff ± 0.6 mm d⁻¹. For the crop fields at regional scale external causes associated to atmospheric and surface variations (i.e. land preparation) rather to the remote sensing algorithm made difficult to determine a percentage of error. Finally, ET_a values were obtained at regional scale and it was demonstrated that using the remote sensing improve significantly the crop ET estimations computed in the area using traditional methods.     

Effects of grapevine (Vitis vinifera L.) water status on water consumption, vegetative growth and grape quality: An irrigation scheduling application to achieve regulated deficit irrigation

Precision irrigation in grapevines could be achieved using physiologically based irrigation scheduling methods. This paper describes an investigation on the effects of three midday stem water potential (midday Ψ_S) thresholds, imposed from post-setting, over water use, vegetative growth, grape quality and yield of grapevines cv. Cabernet Sauvignon. An experiment was carried out on a vineyard located at the Isla de Maipo, Metropolitana Region, Chile, throughout the 2002/03, 2003/04 and 2004/05 growing seasons. Irrigation treatments consisted in reaching the following midday Ψ_S thresholds: −0.8 to −0.95 MPa (T1); −1.0 to −1.2 MPa (T2) and −1.25 to −1.4 MPa (T3) from post-setting to harvest. Results showed significant differences in grape quality components among treatments and seasons studied. In average, T3 produced smallest berry diameter (6% reduction compared to T1), high skin to pulp ratio (13% increment compared to T1) and significant increments in soluble solids and anthocyanins. Improvements in grape quality attributes were attributed to mild grapevine water stress due to significant reductions in water application (46% for T2 and 89% for T3 less in average, both compared to T1). This study found significant correlations between midday Ψ_S and berry quality components, no detrimental effects on yield by treatments were found in this study. This research proposes a suitable physiological index and thresholds to manage RDI and irrigation scheduling on grapevines to achieve high quality grapes on mild water stress conditions.     

Integrated effect of transplanting date, cultivar and irrigation on yield, water saving and water productivity of rice (Oryza sativa L.) in Indian Punjab: Field and simulation study

Individual effect of different field scale management interventions for water saving in rice viz. changing date of transplanting, cultivar and irrigation schedule on yield, water saving and water productivity is well documented in the literature. However, little is known about their integrated effect. To study that, field experimentation and modeling approach was used. Field experiments were conducted for 2 years (2006 and 2007) at Punjab Agricultural University Farm, Ludhiana on a deep alluvial loamy sand Typic Ustipsamment soils developed under hyper-thermic regime. Treatments included three dates of transplanting (25 May, 10 June and 25 June), two cultivars (PR 118 inbred and RH 257 hybrid) and two irrigation schedules (2-days drainage period and at soil water suction of 16 kPa). The model used was CropSyst, which has already been calibrated for growth (periodic biomass and LAI) of rice and soil water content in two independent experiments. The main findings of the field and simulation studies conducted are compared to any individual, integrated management of transplanting date, cultivar and irrigation, sustained yield (6.3-7.5 t ha⁻¹) and saved substantial amount of water in rice. For example, with two management interventions, i.e. shifting of transplanting date to lower evaporative demand (from 5 May to 25 June) concomitant with growing of short duration hybrid variety (90 days from transplanting to harvest), the total real water saving (wet saving) through reduction in evapotranspiration (ET) was 140 mm, which was almost double than managing the single, i.e. 66 mm by shifting transplanting or 71 mm by growing short duration hybrid variety. Shifting the transplanting date saved water through reduction in soil water evaporation component while growing of short duration variety through reduction in both evaporation and transpiration components of water balance. Managing irrigation water schedule based on soil water suction of 16 kPa at 15-20 cm soil depth, compared to 2-day drainage, did not save water in real (wet saving), however, it resulted into apparent water saving (dry saving). The real crop water productivity (marketable yield/ET) was more by 17% in 25th June transplanted rice than 25th May, 23% in short duration variety than long and 2% in irrigation treatment of 16 kPa soil water suction than 2-days drainage. The corresponding values for the apparent crop water productivity (marketable yield/irrigation water applied) were 16, 20 and 50%, respectively. Pooled experimental data of 2 years showed that with managing irrigation scheduling based on soil water suction of 16 kPa at 15-20 cm soil depth, though 700 mm irrigation water was saved but the associated yield was reduced by 277 kg ha⁻¹.     

Estimation of irrigation return flow from paddy fields considering the soil moisture

The objective of this study was to estimate irrigation return flow in irrigated paddy fields considering the soil moisture. The proposed model was applied to examine its feasibility with regard to the growing period of rice. Simulation results showed a good agreement between the observed and simulated values: root mean square error (RMSE) of 6.05-7.27 mm day⁻¹, coefficient of determination (R²) of 0.72-0.73, and coefficient of efficiency (E) of 0.54-0.55. The estimated average annual irrigation return flow during the period from 1998 to 2001 was 306.2 mm, which was approximately 25.7% of the annual irrigation amounts. Of this annual irrigation return flow, 14.1% was attributable to quick and 11.6% to delayed return flow. These results indicate that considerable amounts of irrigation water in the paddy fields were returned to streams and canals by surface runoff and groundwater discharge. The modeling assessment method proposed in this study can be used to manage agriculture water and estimate irrigation return flow under different hydrological and water management conditions.