Modernization and optimization of irrigation systems to increase water productivity

Population increase and the improvement of living standards brought about by development will result in a sharp increase in food demand during the next decades. Most of this increase will be met by the products of irrigated agriculture. At the same time, the water input per unit irrigated area will have to be reduced in response to water scarcity and environmental concerns. Water productivity is projected to increase through gains in crop yield and reductions in irrigation water. In order to meet these projections, irrigation systems will have to be modernized and optimised. Water productivity can be defined in a number of ways, although it always represents the output of a given activity (in economic terms, if possible) divided by some expression of water input. Five expressions for this indicator were identified, using different approaches to water input. A hydrological analysis of water productivity poses a number of questions on the choice of the water input expression. In fact, when adopting a basin-wide perspective, irrigation return flows often can not be considered as net water losses. A number of irrigation modernization and optimization measures are discussed in the paper. Particular attention was paid to the improvement of irrigation management, which shows much better economic return than the improvement of the irrigation structures. The hydrological effects of these improvements may be deceiving, since they will be accompanied by larger crop evapotranspiration and even increased cropping intensity. As a consequence, less water will be available for alternative uses.     

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.     

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.     

Effects of applied water and sprinkler irrigation uniformity on alfalfa growth and hay yield

This study was conducted to investigate the effects of applied water and sprinkler irrigation uniformity on alfalfa (Medicago sativa L.) growth and hay yield in a semi-arid region. Field experiments were carried out in 2006 in Varamin, Iran, on three plots of 25 m × 30 m. Each plot was subdivided into 25 subplots of 5 m × 6 m. Different irrigation depths and sprinkler water uniformities were obtained by various scenarios of sprinkler nozzle pressure. In each plot, applied water was measured at 250 points (125 points above and 125 points below canopy) and the soil water content of 40 cm deep below soil surface was monitored at 25 points, each in the center of a subplot, throughout the irrigation season. The results showed that sprinkler water and soil water content uniformity varied between 66-78 and 88-91%, respectively. The findings revealed that soil water content uniformity was around 20% higher than sprinkler water uniformity. The irrigation uniformity below the canopy was estimated to be 2.5% greater than above the canopy, and canopy-intercepted water could account for 11-15% of the total seasonal applied water. Evaluation showed that alfalfa leaf area index relies more heavily on farm water application uniformity than hay yield and crop height. The experimental results illustrated that water distribution in sprinkler irrigation systems has a direct effect on alfalfa growth, hay yield and water productivity such that the applied water reduction and the increased sprinkler water uniformity led to an increased alfalfa water productivity of 2.41 kg m⁻³.     

Long-term growth and yield responses of olive trees to different irrigation regimes

The aim of this work was to evaluate long-term effects of different irrigation regimes on mature olive trees growing under field conditions. A 9-year experiment was carried out. Three irrigation treatments were applied: no irrigation, water application considering soil water content (short irrigation), or irrigation without considering soil water reserves and applying a 20% of extra water as a leaching fraction (long irrigation). Leaf water content, leaf area, vegetative growth, yield and fruit characteristics (fruit size, pulp:stone ratio and oil content) were determined yearly. Results showed that growth parameters did not show significant differences as a consequence of applied water. Yield was increased in irrigated trees compared to non-irrigated ones, but little differences between short and long irrigation were observed, only when accumulated yield from 1998 to 2006 was considered. Irrigation did not cause significant differences in fruit size or pulp:stone ratio either. Irrigation regimes similar to those applied in this experiment, under environmental conditions with relatively high mean annual precipitation, does not increase growth, yield or fruit characteristics when compared to rain-fed treatment, and consequently, the installation of a irrigation system could be not financially profitable.     

Magnetic treatment of irrigation water: Its effects on vegetable crop yield and water productivity

This study examines whether there are any beneficial effects of magnetic treatment of different irrigation water types on water productivity and yield of snow pea, celery and pea plants. Replicated pot experiments involving magnetically treated and non-magnetically treated potable water (tap water), recycled water and saline water (500 ppm and 1000 ppm NaCl for snow peas; 1500 ppm and 3000 ppm for celery and peas) were conducted in glasshouse under controlled environmental conditions during April 2007 to December 2008 period at University of Western Sydney, Richmond Campus (Australia). A magnetic treatment device with its magnetic field in the range of 3.5-136 mT was used for the magnetic treatment of irrigation water. The analysis of the data collected during the study suggests that the effects of magnetic treatment varied with plant type and the type of irrigation water used, and there were statistically significant increases in plant yield and water productivity (kg of fresh or dry produce per kL of water used). In particular, the magnetic treatment of recycled water and 3000 ppm saline water respectively increased celery yield by 12% and 23% and water productivity by 12% and 24%. For snow peas, there were 7.8%, 5.9% and 6.0% increases in pod yield with magnetically treated potable water, recycled water and 1000 ppm saline water, respectively. The water productivity of snow peas increased by 12%, 7.5% and 13% respectively for magnetically treated potable water, recycled water and 1000 ppm saline water. On the other hand, there was no beneficial effect of magnetically treated irrigation water on the yield and water productivity of peas. There was also non-significant effect of magnetic treatment of water on the total water used by any of the three types of vegetable plants tested in this study. As to soil properties after plant harvest, the use of magnetically treated irrigation water reduced soil pH but increased soil EC and available P in celery and snow pea. Overall, the results indicate some beneficial effect of magnetically treated irrigation water, particularly for saline water and recycled water, on the yield and water productivity of celery and snow pea plants under controlled environmental conditions. While the findings of this glasshouse study are interesting, the potential of the magnetic treatment of irrigation water for crop production needs to be further tested under field conditions to demonstrate clearly its beneficial effects on the yield and water productivity.     

Irrigation scheduling strategies for cotton to cope with water scarcity in the Fergana Valley, Central Asia

The Central Asian countries face high water scarcity due to aridity and desertification but excess water is often applied to the main irrigated crops. This over-irrigation contributes to aggravate water scarcity problems. Improved water saving irrigation is therefore required, mainly through appropriate irrigation scheduling. To provide for it, after being previously calibrated and validated for cotton in the Fergana region, the irrigation scheduling simulation model ISAREG was explored to simulate improved irrigation scheduling alternatives. Results show that using the present irrigation scheduling a large part of the applied water, averaging 20%, percolates out of the root zone. Several irrigation strategies were analyzed, including full irrigation and various levels of deficit irrigation. The analysis focused a three-year period when experiments for calibration and validation of the model were carried out, and a longer period of 33 years that provided for an analysis considering the probabilities of the demand for irrigation water. The first concerned a wet period while the second includes a variety of climatic demand conditions that provided for analyzing alternative schedules for average, high and very high climatic demand. Results have shown the importance of the groundwater contribution, mainly when deficit irrigation is applied. Analyzing several deficit irrigation strategies through the respective potential water saving, relative yield losses, water productivity and economic water productivity, it could be concluded that relative mild deficits may be adopted. Contrarily, the adoption of high water deficit that produce high water savings would lead to yield losses that may be economically not acceptable.     

Management trends and responses to water scarcity in an irrigation scheme of Southern Spain

Improvement of irrigation management in areas subjected to periods of water scarcity requires good knowledge of system performance over long time periods. We have conducted a study aimed at characterizing the behaviour of an irrigated area encompassing over 7000 ha in Southern Spain, since its inception in 1991. Detailed cropping pattern and plot water use records allowed the assessment of irrigation scheme performance using a simulation model that computed maximum irrigation requirements for every plot during the first 15 years of system operations. The ratio of irrigation water used to maximum irrigation requirements (Annual Relative Irrigation Supply, ARIS) was well below 1 and oscillated around 0.6 in the 12 years that there were no water supply restrictions in the district. The ARIS values varied among crops, however, from values between 0.2 and 0.3 for sunflower and wheat, to values approaching 1 for cotton and sugar beet. Farmer interviews revealed some of the causes for the low irrigation water usage which were mainly associated with the attempt to balance profitability and stability, and with the lack of incentives to achieve maximum yields in crops subsidized by the Common Agricultural Policy (CAP) of the European Union. The response to water scarcity was also documented through interviews and demonstrated that the change in crop choice is the primary reaction to an anticipated constraint in water supply. Water productivity (value of production divided by the volume of irrigation water delivered; WP) in the district was moderate and highly variable (around 2€ m⁻³) and did not increase with time. Irrigation water productivity (increase in production value due to irrigation divided by irrigation water delivered) was much lower (0.65€ m⁻³) and also, it did not increase with time. The lack of improvement in WP, the low irrigation water usage, and the changes in cropping patterns over the first 15 years of operation indicate that performance trends in irrigated agriculture are determined by a complex mix of technical, economic, and socio-cultural factors, as those that characterized the behaviour of the Genil-Cabra irrigation scheme.     

Effects of deficit irrigation on yield, water productivity, and economic returns of wheat

A field experiment was conducted for 3 consecutive years to study the effects of water deficit on yield, water productivity and net return of wheat. Yield attributes were affected by deficit irrigation treatments although they are not statistically different in all cases. The grain and straw yields were significantly affected by treatments. The highest grain yield was obtained with the no-deficit treatment. Differences in grain and straw yield among the partial- (single- or two-stage deficit) and no-deficit treatments are small and statistically insignificant in most cases. The highest water productivity and productivity of irrigation water were obtained in the alternate deficit treatment (T₇), where deficits were imposed at maximum tillering (jointing to shooting) and flowering to soft dough stages of growth period, followed by single irrigation at crown root initiation stage. Under both land- and water-limiting conditions, the alternate deficit strategy (T₇) showed maximum net financial return. The results will be helpful in policy planning regarding irrigation management for maximizing net financial returns from limited land and water resources.     

Soil water in relation to irrigation, water uptake and potato yield in a humid climate

Efficiently controlling soil water content with irrigation is essential for water conservation and often improves potato yield. Volumetric soil water content (θ_v) in relation to irrigation, plant uptake, and yield in potato hills and replicated plots was studied to evaluate four water management options. Measurements of θ_v using a hammer driven probe were used to derive a θ_v index representing the relative θ_v status of replicated plots positioned along a hill slope. Time series for θ_v were determined using time domain reflectometry (TDR) probes at 5 and 15 cm depths at the center, shoulder, and furrow locations in potato hills. Sap flow was determined using flow collars in replicated field plots for four treatments: un-irrigated, sprinkler, surface drip, and sub-surface drip irrigation (40 cm depth). Irrigated yields were high/low as the θ_v index was low/high suggesting θ_v excess was a production problem in the wetter portions of the study area. The diurnal pattern of sap flow was reflected in the θ_v fluctuation it induces at hill locations with appreciable uptake. Hill locations with higher plant uptake were drier as was the case for the 5 cm (dry) depth relative to the 15 cm (wet) depth and for locations in the hill (dry) relative to the furrow (wet). The surface drip system had the lowest water use requirement because it delivers water directly to the hill locations where uptake is greatest. The sub-surface drip system wetted the hill gradually (1-2 days). Measurement of the θ_v index prior to experimental establishment could improve future experimental design for treatment comparisons.     

Drip irrigation of tea (Camellia sinensis L.): 1. Yield and crop water productivity responses to irrigation

The effects of drip irrigation on the yield and crop water productivity responses of four tea (Camellia sinensis (L.) O. Kuntze) clones were studied four consecutive years (2003/2004-2006/2007), in a large (9 ha) field experiment comprising of six drip irrigation treatments (labelled: I₁-I₆) and four clones (TRFCA PC81, AHP S15/10, BBK35 and BBT207) planted at a spacing of 1.20 m × 0.60 m at Kibena Tea Limited (KTL), Njombe in the Southern Tanzania in a situation of limited water availability. Each clone × drip irrigation treatment combination was replicated six times in a completely randomized design with 144 net plots each with an area of 72 m². Clone TRFCA PC81 gave the highest yields (range: 5920-6850 kg dried tea ha⁻¹) followed by clones BBT207 (5010-5940 kg dried tea ha⁻¹), AHP S15/10 (4230-5450 kg dried tea ha⁻¹) and BBK35 (3410-4390 kg dried tea ha⁻¹) and drip irrigation treatment I₂ gave the highest yields, ranging from 4954 to 6072 kg dried tea ha⁻¹) compared with those from other treatments (4113-5868 kg dried tea ha⁻¹). Most of these yields exceeded those (4200 kg dried tea ha⁻¹) obtained from overhead sprinkler irrigation system in Mufindi also Southern Tanzania, and Kibena Estate itself. Results showed that drip irrigation of tea not only increased yields but also gave water saving benefits of up to 50% from application of 50% less water to remove the cumulative soil water deficit (treatment I₂), and with labour saving of 85% for irrigation. The yield of dried tea per mm depth of water applied, i.e., “the crop water productivity” for drip irrigation of clones TRFCA PC81, BBT207 and BBK35, in 2003/2004 for instance, were 9.3, 8.5 and 7.1 kg dried tea [ha mm]⁻¹, respectively. The corresponding values in 2004/2005 were 2.7, 4.5 and 2.0 kg dried tea [ha mm]⁻¹ while the yield responses from clone AHP S15/10 were linear decreasing by 1 and 1.6 kg dried tea [ha mm]⁻¹ in 2003/2004 and 2004/2005, respectively. In 2005/2006 the crop water productivity from clones TRFCA PC81, AHP S15/10, BBK35 and BBT207 were 4.5, 0.4, 5.2 and 6.9 kg dried tea [ha mm]⁻¹, respectively with quadratic yield response functions to drip irrigation depth of water application. The results are presented and recommendations and implications made for technology-transfer scaling-up for increased use by large and smallholder tea growers.     

Evaluation of options for increasing yield and water productivity of wheat in Punjab, India using the DSSAT-CSM-CERES-Wheat model

The DSSAT-CSM-CERES-Wheat V4.0 model was calibrated for yield and irrigation scheduling of wheat with 2004–2005 data and validated with 13 independent data sets from experiments conducted during 2002–2006 at the Punjab Agricultural University (PAU) farm, Ludhiana, and in a farmer's field near PAU at Phillaur, Punjab, India. Subsequently, the validated model was used to estimate long-term mean and variability of potential yield (Y_p), drainage, runoff, evapo-transpiration (ET), crop water productivity (CWP), and irrigation water productivity (IWP) of wheat cv. PBW343 using 36 years (1970–1971 to 2005–2006) of historical weather data from Ludhiana. Seven sowing dates in fortnightly intervals, ranging from early October to early January, and three irrigation scheduling methods [soil water deficit (SWD)-based, growth stage-based, and ET-based] were evaluated. For the SWD-based scheduling, irrigation management depth was set to 75 cm with irrigation scheduled when SWD reached 50% to replace 100% of the deficit. For growth stage-based scheduling, irrigation was applied either only once at one of the key growth stages [crown root initiation (CRI), booting, flowering, and grain filling], twice (two stages in various combinations), thrice (three stages in various combinations), or four times (all four stages). For ET-driven irrigation, irrigations were scheduled based on cumulative net ETo (ETo-rain) since the previous irrigation, for a range of net ETo (25, 75, 125, 150, and 175 mm). Five main irrigation schedules (SWD-based, ET-driven with irrigation applied after accumulation of either 75 or 125 mm of ETo, i.e., ET75 or ET125, and growth stage-based with irrigation applied at CRI plus booting, or at CRI plus booting plus flowering stage) were chosen for detailed analysis of yield, water balance, and CWP and IWP. Nitrogen was non-limiting in all the simulations.Mean Y_p across 36 years ranged from 5.2 t ha⁻¹ (10 October sowing) to 6.4 t ha⁻¹ (10 November sowing), with yield variations due to seasonal weather greater than variations across sowing dates. Yields under different irrigation scheduling, CWP and IWP were highest for 10 November sowing. Yields and CWP were higher for SWD and ET75-based irrigations on both soils, but IWP was higher for ET75-based irrigation on sandy loam and for ET150-based irrigation on loam. Simulation results suggest that yields, CWP, and IWP of PBW343 would be highest for sowing between late October and mid-November in the Indian Punjab. It is recommended that sowing be done within this planting period and that irrigation be applied based on the atmospheric demand and soil water status and not on the growth stage. Despite the potential limitations recognised with simulation results, we can conclude that DSSAT-CSM-CERES-Wheat V4.0 is a useful decision support system to help farmers to optimally schedule and manage irrigation in wheat grown in coarse-textured soils under declining groundwater table situations of the Indian Punjab. Further, the validated model and the simulation results can also be extrapolated to other areas with similar climatic and soil environments in Asia where crop, soil, weather, and management data are available.     

Integrating remote sensing, census and weather data for an assessment of rice yield, water consumption and water productivity in the Indo-Gangetic river basin

Crop consumptive water use and productivity are key elements to understand basin water management performance. This article presents a simplified approach to map rice (Oryza sativa L.) water consumption, yield, and water productivity (WP) in the Indo-Gangetic Basin (IGB) by combining remotely sensed imagery, national census and meteorological data. The statistical rice cropped area and production data were synthesized to calculate district-level land productivity, which is then further extrapolated to pixel-level values using MODIS NDVI product based on a crop dominance map. The water consumption by actual evapotranspiration is estimated with Simplified Surface Energy Balance (SSEB) model taking meteorological data and MODIS land surface temperature products as inputs. WP maps are then generated by dividing the rice productivity map with the seasonal actual evapotranspiration (ET) map. The average rice yields for Pakistan, India, Nepal and Bangladesh in the basin are 2.60, 2.53, 3.54 and 2.75 tons/ha, respectively. The average rice ET is 416 mm, accounting for only 68.2% of potential ET. The average WP of rice is 0.74 kg/m³. The WP generally varies with the trends of yield variation. A comparative analysis of ET, yield, rainfall and WP maps indicates greater scope for improvement of the downstream areas of the Ganges basin. The method proposed is simple, with satisfactory accuracy, and can be easily applied elsewhere.     

Evaluation on the irrigation and fertilization management practices under the application of treated sewage water in Beijing, China

Irrigation and fertilization management practices play important roles in crop production. In this paper, the Root Zone Water Quality Model (RZWQM) was used to evaluate the irrigation and fertilization management practices for a winter wheat–summer corn double cropping system in Beijing, China under the irrigation with treated sewage water (TSW). A carefully designed experiment was carried out at an experimental station in Beijing area from 2001 to 2003 with four irrigation treatments. The hydrologic, nitrogen and crop growth components of RZWQM were calibrated by using the dataset of one treatment. The datasets of other three treatments were used to validate the model performance. Most predicted soil water contents were within ±1 standard deviation (S.D.) of the measured data. The relative errors (RE) of grain yield predictions were within the range of −26.8% to 18.5%, whereas the REs of biomass predictions were between −38% and 14%. The grain nitrogen (N) uptake and biomass N uptake were predicted with the RE values ranging from −13.9% to 14.7%, and from −11.1% to 29.8%, respectively. These results showed that the model was able to simulate the double cropping system variables under different irrigation and fertilization conditions with reasonable accuracy. Application of RZWQM in the growing season of 2001–2002 indicated that the best irrigation management practice was no irrigation for summer corn, three 83 mm irrigations each for pre-sowing, jointing and heading stages of winter wheat, respectively. And the best nitrogen application management practice was 120 kg N ha⁻¹ for summer corn and 110 kg N ha⁻¹ for winter wheat, respectively, under the irrigation with TSW. We also obtained the alternative irrigation management practices for the hydrologic years of 75%, 50% and 25%, respectively, in Beijing area under the conditions of irrigation with TSW and the optimal nitrogen application.     

The effects of irrigation methods with effluent and irrigation scheduling on water use efficiency and corn yields in an arid region

A great challenge for the agricultural sector is to produce more food from less water, particularly in arid and semi-arid regions which suffer from water scarcity. A study was conducted to evaluate the effect of three irrigation methods, using effluent versus fresh water, on water savings, yields and irrigation water use efficiency (IWUE). The irrigation scheduling was based on soil moisture and rooting depth monitoring. The experimental design was a split plot with three main treatments, namely subsurface drip (SSD), surface drip (SD) and furrow irrigation (FI) and two sub-treatments effluent and fresh water, which were applied with three replications. The experiment was conducted at the Marvdasht city (Southern Iran) wastewater treatment plant during 2005 and 2006. The experimental results indicated that the average water applied in the irrigation treatments with monitoring was much less than that using the conventional irrigation method (using furrows but based on a constant irrigation interval, without moisture monitoring). The maximum water saving was obtained using SSD with 5907 m³ ha⁻¹ water applied, and the minimum water saving was obtained using FI with 6822 m³ ha⁻¹. The predicted irrigation water requirements using the Penman-Monteith equation (considering 85% irrigation efficiency for the FI method) was 10,743 m³ ha⁻¹. The pressure irrigation systems (SSD and SD) led to a greater yield compared to the surface method (FI). The highest yield (12.11 × 10³ kg ha⁻¹) was obtained with SSD and the lowest was obtained with the FI method (9.75 × 10³ kg ha⁻¹). The irrigation methods indicated a highly significant difference in irrigation water use efficiency. The maximum IWUE was obtained with the SSD (2.12 kg m⁻³) and the minimum was obtained with the FI method (1.43 kg m⁻³). Irrigation with effluent led to a greater IWUE compared to fresh water, but the difference was not statistically significant.     

Effect of saline water irrigation and manure application on the available water content, soil salinity, and growth of wheat

Good water management combined with appropriate soil management is necessary for sustainable crop production in drylands. A pot culture experiment was conducted using sand dune soil under greenhouse conditions to evaluate the response of wheat (Triticum aestivum L.) to the application of farmyard manure (FYM) or poultry manure (PM), and irrigation with water at two salinity levels (0.11 and 2.0 dS m⁻¹) and two irrigation intervals (daily and every second day). The manure was applied at a rate of 20 Mg ha⁻¹. The soil water content, measured 1 h before every irrigation, showed that soil treated with PM retained more water than that treated with FYM, while the control (no manure) contained the least water. FYM treatment resulted in 78 and 21% higher dry matter yield compared to the control and PM treatments, respectively, under daily irrigation using good-quality water. The increase was 29 and 55%, respectively, when saline water was used for daily irrigation. A similar trend was observed with the alternate day irrigation treatment; FYM gave the highest dry matter yield. The number of tillers and plant height showed that FYM was better than PM, which in turn was better than the control under irrigation with good-quality water regardless of the irrigation interval. When water of the highest salinity was used for irrigation, FYM was still always the best, but the control was now better than the PM treatment. The electrical conductivity of the soil measured at the end of the experiment was slightly higher with PM, as compared to the FYM and control treatments. A significant interaction between irrigation water quality and manure application was observed, affecting plant growth. PM aggravated the adverse affect of saline water on plant growth by increasing soil salinity.     

Plant response to evapotranspiration and soil water sensor irrigation scheduling methods for papaya production in south Florida

An irrigation study was conducted to determine the effects of implementing different irrigation practices on growth and yields of papaya plants in south Florida. Treatments included using automated switching tensiometers based on soil water status, irrigation based on ET calculated from historic weather data and a set schedule irrigation regime. The study consisted of two trials (2006-2007 and 2008-2009). Water volumes applied, plant height and diameter, leaf gas exchange, leaf petiole nutrient levels, fruit yields and fruit total soluble solids were measured throughout the study. For both trials, significantly more water was applied in the set schedule irrigation treatment than in all other treatments; historic ET and soil water based treatments received only about 31-36% of the water applied in the set schedule irrigation. Trunk diameter and plant height per unit water volume applied values for the set schedule treatment were significantly lower than those from all other treatments during both trials. The set schedule treatment in both trials also had the lowest crop production water use efficiency (CP-WUE); CP-WUE values among all other treatments were generally not significantly different from each other. Soil water and historic ET-based irrigation methods were identified as more sustainable practices compared to set schedule irrigation due to the lower water volumes applied while maintaining plant nutrient content, growth, photosynthetic rates, and fruit yields for this production system.     

Assessing basin irrigation and scheduling strategies for saving irrigation water and controlling salinity in the upper Yellow River Basin, China

Water saving in irrigation is a key concern in the Yellow River basin. Excessive water diversions for irrigation waste water and produce waterlogging problems during the crop season and soil salinization in low lands. Supply control and inadequate functionality of the drainage system were identified as main factors for poor water management at farm level. Their improvement condition the adoption of water saving and salinity control practices. Focusing on the farm scale, studies to assess the potential for water savings included: (a) field evaluation of current basin irrigation practices and further use of the simulation models SRFR and SIRMOD to generate alternative improvements for the surface irrigation systems and (b) the use of the ISAREG model to simulate the present and improved irrigation scheduling alternatives taking into consideration salinity control. Models were used interactively to define alternatives for the irrigation systems and scheduling that would minimize percolation and produce water savings. Foreseen improvements refer to basin inflow discharges, land leveling and irrigation scheduling that could result in water savings of 33% relative to actual demand. These improvements would also reduce percolation and maintain water table depths below 1 m thereby reducing soil salinization.     

Evaluation of the influence of irrigation methods and water quality on sugar beet yield and water use efficiency

Rapid urbanization and industrialization have increased the pressure on limited existing fresh water to meet the growing needs for food production. Two immediate responses to this challenge are the efficient use of irrigation technology and the use of alternative sources of water. Drip irrigation methods may play an important role in efficient use of water but there is still limited information on their use on sugar beet crops in arid countries such as Iran. An experiment was conducted to evaluate the effects of irrigation method and water quality on sugar beet yield, percentage of sugar content and irrigation water use efficiency (IWUE). The irrigation methods investigated were subsurface drip, surface drip and furrow irrigation. The two waters used were treated municipal effluent (EC = 1.52 dS m⁻¹) and fresh water (EC = 0.509 dS m⁻¹). The experiments used a split plot design and were undertaken over two consecutive growing seasons in Southern Iran. Statistical testing indicated that the irrigation method and water quality had a significant effect (at the 1% level) on sugar beet root yield, sugar yield, and IWUE. The highest root yield (79.7 Mg ha⁻¹) was obtained using surface drip irrigation and effluent and the lowest root yield (41.4 Mg ha⁻¹) was obtained using furrow irrigation and fresh water. The highest IWUE in root yield production (9 kg m⁻³) was obtained using surface drip irrigation with effluent and the lowest value (3.8 kg m⁻³) was obtained using furrow irrigation with fresh water. The highest IWUE of 1.26 kg m⁻³ for sugar was obtained using surface drip irrigation. The corresponding efficiency using effluent was 1.14 kg m⁻³. Irrigation with effluent led to an increase in the net sugar yield due to an increase in the sugar beet root yield. However, there was a slight reduction in the percentage sugar content in the plants. This study also showed that soil water and root depth monitoring can be used in irrigation scheduling to avoid water stress. Such monitoring techniques can also save considerable volumes of irrigation water and can increase yield.     

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.