Yield and water use efficiency of cauliflower under varying irrigation frequencies and water application methods in Lower Gangetic Plain of India

A field study (1999-2000 to 2001-2002) was carried out to optimize the irrigation frequency and suitable water application methods for cauliflower with a view to increase curd yield (CY) and water use efficiency (WUE). Check Basin (CB), Each Furrow (EF) and Alternate Furrow (AF) methods were tested with three irrigation frequencies depending on the attainment of soil matric potential (Ψ_m) value at 0.2 m depth as: −0.03 MPa (F₁), −0.05 MPa (F₂) and −0.07 MPa (F₃). Maximum CY was recorded under F₁ and decreased by 10.4 and 31.4%, respectively under F₂ and F₃ frequencies. In contrast, WUE decreased by 9.3% from F₃ to F₁. Highest CY and WUE obtained under CB followed by EF and AF methods. Furrow application methods saved 12-24% irrigation water over CB method. Maximum soil water stress coefficient (K_s) recorded at curd development stage in comparison to other stages. Both seasonal evapotranspiration (ET_a) and yield-moisture stress index (Kys) recorded positive linear relationships with CY. Present study shows a crop response factor of 0.822 for cauliflower. In this region, cauliflower should be irrigated with check basin method at an interval of 8-10 days.     

Soil water dynamics and water use efficiency in spring maize (Zea mays L.) fields subjected to different water management practices on the Loess Plateau, China

Soil water supply is the main limiting factor to crop production across the Loess Plateau, China. A 2-year field experiment was conducted at the Changwu agro-ecosystem research station to evaluate various water management practices for achieving favorable grain yield (GY) with high water use efficiency (WUE) of spring maize (Zea mays L.). Four practices were examined: a rain-fed (RF) system as the control; supplementary irrigation (SI); film mulching (FM); and straw mulching (SM) (in 2008 only). The soil profile water storage (W) and the crop evapotranspiration (ET) levels were studied during the maize growing season, and the GY as well as the WUE were also compared. The results showed that mean soil water storage in the top 200 cm of the profile was significantly (P < 0.05) increased in the SI (380 mm in 2007, 411 mm in 2008) and SM (414 mm in 2008) compared to the FM (361 mm in 2007, 381 mm in 2008) and RF (360 mm in 2007, 384 mm in 2008) treatments. The soil water content was lower at the end of growing season than before planting in the 60-140 cm part of the profile in both the RF and FM treatments. Cumulative ET and average crop coefficiency (K_c) throughout the whole maize growing season were significantly (P < 0.05) higher in the SI (ET, 501 mm in 2007, 431 mm in 2008; K_c, 1.0 in 2007, 0.9 in 2008) treatment than in the other treatments. Both FM and SI significantly improved the GY. The WUE were increased significantly (23-25%; P < 0.05) under the FM treatment. It was concluded that both SI and FM are beneficial for improving the yield of spring maize on the Loess Plateau. However, FM is preferable because of the shortage of available water in the area.     

Evapotranspiration, seed yield and water use efficiency of drip irrigated sunflower under full and deficit irrigation conditions

Deficit irrigation occurrence while maintaining acceptable yield represents a useful trait for sunflower production wherever irrigation water is limited. A 2-year experiment (2003–2004) was conducted at Tal Amara Research Station in the Bekaa Valley of Lebanon to investigate sunflower response to deficit irrigation. In the plots, irrigation was held at early flowering (stage F1), at mid flowering (stage F3.2) and at early seed formation (stage M0) until physiological maturity. Deficit-irrigated treatments were referred to as WS1, WS2 and WS3, respectively, and were compared to a well-irrigated control (C). Reference evapotranspiration (ET_rye-grass) and crop evapotranspiration (ET_crop) were measured each in a set of two drainage lysimeters of 2 m × 2 m × 1 m size cultivated with rye grass (Lolium perenne) and sunflower (Helianthus annuus L., cv. Arena). Crop coefficients (K_c) in the different crop growth stages were derived as the ratio (ET_crop/ET_rye-grass).

Lysimeter measured crop evapotranspiration (ET_crop) totaled 765 mm in 2003 and 882 mm in 2004 for total irrigation periods of 139 and 131 days, respectively. Daily ET_crop achieved a peak value of 13.0 mm day⁻¹ at flowering time (stage F3.2; 80–90 days after sowing) when LAI was >6.0 m² m⁻². Then ET_crop declined to 6.0 mm day⁻¹ during seed maturity phase. Average K_c values varied from 0.3 at crop establishment (sowing to four-leaf stage), to 0.9 at late crop development (four-leaf stage to terminal bud), to >1.0 at flowering stage (terminal bud to inflorescence visible), then to values <1.0 at seed maturity phase (head pale to physiological maturity). Measured K_c values were close to those reported by the FAO.

Average across years, seed yield at dry basis on the well-irrigated treatment was 5.36 t ha⁻¹. Deficit irrigation at early (WS1) and mid (WS2) flowering stages reduced seed yield by 25% and 14% (P < 0.05), respectively, in comparison with the control. However, deficit irrigation at early seed formation was found to increase slightly seed yield in WS3 treatment (5.50 t ha⁻¹). We concluded that deficit irrigation at early seed formation (stage M0) increased the fraction of assimilate allocation to the head, compensating thus the lower number of seeds per m² through increased seed weight. In this experiment, while deficit irrigation did not result in any remarkable increase in harvest index (HI), water use efficiency (WUE) was found to vary significantly (P < 0.05) among treatments, where the highest (0.83 kg m⁻³) and the lowest (0.71 kg m⁻³) values were obtained from WS3 and WS1 treatments, respectively. Finally, results indicate that irrigation limitation at early flowering (stage F1) and mid flowering (stage F3.2) should be avoided while it can be acceptable at seed formation (stage M0).     

Water resources and water use efficiency in the North China Plain: Current status and agronomic management options

Serious water deficits and deteriorating environmental quality are threatening agricultural sustainability in the North China Plain (NCP). This paper addresses spatial and temporal availability of water resources in the NCP, identifies the effects of soil management, irrigation timing and amounts, and crop genetic improvement on water use efficiency (WUE), and then discusses knowledge gaps and research priorities to further improve WUE. Enhanced irrigation and soil nutrient (mainly nitrogen) management are the focal issues in the NCP for enhancing WUE, which are shown to increase WUE by 10-25% in a wheat-maize double cropping system. Crop breeding has also contributed to increased of WUE and is expected to play an important role in the future as genetic and environmental interactions are understood better. Agricultural system models and remote sensing have been used to evaluate and improve current agronomic management practices for increasing WUE at field and regional scales. The low WUE in farmer's fields compared with well-managed experimental sites indicates that more efforts are needed to transfer water-saving technologies to the farmers. We also identified several knowledge gaps for further increasing WUE in the NCP by: (1) increasing scientific understanding of the effects of agronomic management on WUE across various soil and climate conditions; (2) quantifying the interaction between soil water and nitrogen in water-limited agriculture for improving both water and nitrogen-use efficiency; (3) improving irrigation practices (timing and amounts) based on real-time monitoring of water status in soil-crop systems; and (4) maximizing regional WUE by managing water resources and allocation at regional scales.     

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.     

A measure for the efficiency of water use and its determinants,a case study of small-scale irrigation schemes in North-West Province,South Africa

This paper analyses the efficiency with which water is used in small-scale irrigation schemes in North-West Province in South Africa and studies its determinants. In the study area, small-scale irrigation schemes play an important role in rural development, but the increasing pressure on water resources and the approaching introduction of water charges raise the concern for more efficient water use. With the data envelopment analysis (DEA) techniques used to compute farm-level technical efficiency measures and sub-vector efficiencies for water use, it was shown that under constant returns to scale (CRS) and variable returns to scale (VRS) specification, substantial technical inefficiencies, of 49% and 16%, respectively, exist among farmers. The sub-vector efficiencies for water proved to be even lower, indicating that if farmers became more efficient using the technology currently available, it would be possible to reallocate a fraction of the irrigation water to other water demands without threatening the role of small-scale irrigation. In a second step, Tobit regression techniques were used to examine the relationship between sub-vector efficiency for water and various farm or farmer characteristics. Farm size, landownership, fragmentation, the type of irrigation scheme, crop choice and the irrigation methods applied showed a significant impact on the sub-vector efficiency for water. Such information is valuable for extension services and policy makers since it can help to guide policies towards increased efficiency.     

Influence of single and multiple water application timings on yield and water use efficiency in tomato (var. First power)

A greenhouse experiment was conducted at Japan International Research Center for Agriculture Science (JIRCAS), Okinawa Subtropical Station, Ishigaki, Japan with three multiple water application and two single water applications to study the effects of them on tomato yield, soil water content and water use efficiency. Multiple water application is a technique use to add the required amount of water during irrigation in multiple equal parts a day instead of one complete set (single water application) during the irrigation event. The multiple water application treatments were the day time (DT), day-night time (DNT) and night time (NT) while the single water application treatments were morning time (MT) and evening time (ET). In multiple water irrigation treatments the water was added to the soil into three equal parts. The supplied irrigation water was the same for all treatments and gradually increased with plant age to cover the crop water requirement during the growing season.The results revealed that multiple water application increased tomato yield by 5% over the highest yield of single water application. The DT treatment increased tomato yield by 5% and 15% compared to ET and MT treatments, respectively. For multiple water application, the DT was the best irrigation timing because it increases the tomato yield by 8% and 12% compared to DNT and NT, respectively. ET irrigation was better than MT irrigation for single water application. Multiple water application led to an increased in soil water content compared to single water application. By applying the same amount of water for all treatments, the DT treatment increased water use efficiency by 5-15% compared to ET and MT treatments of single water application. In conclusion, multiple water application is better than single water application and by choosing the proper irrigation timing, higher tomato yield resulting from efficient water management can be obtained.     

Effects of winter wheat row spacing on evapotranpsiration, grain yield and water use efficiency

A field study was conducted from 2002 to 2007 to investigate the influence of row spacing of winter wheat (Triticum aestivum L.) on soil evaporation (E), evapotranspiration (ET), grain production and water use efficiency (WUE) in the North China Plain. The experiment had four row spacing treatments, 7.5 cm, 15 cm, 22.5 cm, and 30 cm, with plots randomly arranged in four replicates. Soil E was measured by micro-lysimeters in three seasons and ET was calculated from measurements of soil profile water depletion, irrigation, and rainfall. The results showed that E increased with row spacing. Compared with the 30-cm row spacing (average E = 112 mm), the reduction in seasonal E averaged 9 mm, 25 mm, and 26 mm for 22.5 cm, 15 cm, and 7.5 cm row spacings, respectively. Crop transpiration (T) increased as row spacing decreased. The seasonal rainfall interception and seasonal ET were relatively unchanged among the treatments. In three out of five seasons, the four different treatments showed similar grain yield, yield components and WUE. We conclude that for winter wheat production in the North China Plain, narrow row spacing reduced soil evaporation, but had minor improvements on grain production and WUE under irrigated conditions with adequate nutrient levels.     

Canopy water use efficiency of winter wheat in the North China Plain

Canopy water use efficiency (W), the ratio of crop productivity to evapotranspiration (ET), is critical in determining the production and water use for winter wheat (Triticum aestivum L.) in the North China Plain, where winter wheat is a major crop and rainfall is scarce and variable. With the eddy covariance (EC) technique, we estimated canopy W of winter wheat at gross primary productivity (W_G) and net ecosystem productivity (W_N) levels from revival to maturing in three seasons of 2002/2003, 2003/2004 and 2004/2005 at Yucheng Agro-ecosystem Station. Meanwhile we also measured the biomass-based water use efficiency (W_B). Our results indicate that W_G, W_N and W_B showed the similar seasonal variation. Before jointing (revival-jointing), W_G, W_N and W_B were obviously lower with the values of 2.09-3.54 g C kg⁻¹, −0.71 to 0.06 g C kg⁻¹ and 1.37-4.03 g kg⁻¹, respectively. After jointing (jointing-heading), the winter wheat began to grow vigorously, and W_G, W_N and W_B significantly increased to 5.26-6.78 g C kg⁻¹, 1.47-1.86 g C kg⁻¹ and 6.41-7.03 g kg⁻¹, respectively. The maximums of W_G, W_N and W_B occurred around the stage of heading. Thereafter, W_G, W_N and W_B began to decrease. During the observed periods, three levels of productivity: GPP, NEP and aboveground biomass (AGB) all had fairly linear relationships with ET. The slopes of GPP-ET, NEP-ET and AGB-ET were 4.67-6.12 g C kg⁻¹, 1.50-2.08 g C kg⁻¹ and 6.87-11.02 g kg⁻¹, respectively. Generally, photosynthetically active radiation (PAR) and daytime vapor pressure deficit (D) had negative effects on W_G, W_N and W_B except for on some cloudy days with low PAR and D. In many cases, W_G, W_N and W_B showed the similar patterns. While there were still some obvious differences between them besides in magnitude, such as their significantly different responses to PAR and D on cloudy and moist days.     

Irrigation strategies to improve the water use efficiency of wheat-maize double cropping systems in North China Plain

Water is the most important limiting factor of wheat (Triticum aestivum L.) and maize (Zea mays L.) double cropping systems in the North China Plain (NCP). A two-year experiment with four irrigation levels based on crop growth stages was used to calibrate and validate RZWQM2, a hybrid model that combines the Root Zone Water Quality Model (RZWQM) and DSSAT4.0. The calibrated model was then used to investigate various irrigation strategies for high yield and water use efficiency (WUE) using weather data from 1961 to 1999. The model simulated soil moisture, crop yield, above-ground biomass and WUE in responses to irrigation schedules well, with root mean square errors (RMSEs) of 0.029 cm³ cm⁻³, 0.59 Mg ha⁻¹, 2.05 Mg ha⁻¹, and 0.19 kg m⁻³, respectively, for wheat; and 0.027 cm³ cm⁻³, 0.71 Mg ha⁻¹, 1.51 Mg ha⁻¹ and 0.35 kg m⁻³, respectively, for maize. WUE increased with the amount of irrigation applied during the dry growing season of 2001-2002, but was less sensitive to irrigation during the wet season of 2002-2003. Long-term simulation using weather data from 1961 to 1999 showed that initial soil water at planting was adequate (at 82% of crop available water) for wheat establishment due to the high rainfall during the previous maize season. Preseason irrigation for wheat commonly practiced by local farmers should be postponed to the most sensitive growth stage (stem extension) for higher yield and WUE in the area. Preseason irrigation for maize is needed in 40% of the years. With limited irrigation available (100, 150, 200, or 250 mm per year), 80% of the water allocated to the critical wheat growth stages and 20% applied at maize planting achieved the highest WUE and the least water drainage overall for the two crops.     

交替隔沟灌溉对温室黄瓜生长及水分利用效率的影响

日光温室黄瓜生产中一直存在灌水量大,水分浪费严重等现象,针对这一问题,该试验以津育5号黄瓜（Cucumis sativus L）为试材,就交替隔沟灌溉和交替隔沟亏缺灌溉对日光温室黄瓜生长、灌溉水去向、水分利用效率和节水效果等的影响进行了研究。结果表明,交替隔沟灌溉减少了土壤水分的深层渗漏、土壤表面水分蒸发,植株蒸腾速率也略有下降,而植株光合作用没有受到明显影响,使同化产物有利于向果实分配,产量与对照持平,果实商品性和营养品质也有所提高。交替隔沟灌溉可节水37%～48%,作物水分利用效率提高47%～82%。此法简便易行,控漏减蒸效果明显,节水显著,在目前日光温室生产条件下极具推广应用价值。     

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

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

Seed yield and water use efficiency of canola (Brassica napus L.) as affected by high temperature stress and supplemental irrigation

The effects of high temperature stress and supplemental irrigation on seed yield and water use efficiency (WUE) of canola (Brassica napus L.) were studied in a field experiment conducted for 2 years. The experiment was a randomized complete block design arranged in split plot, conducted at Agricultural Research Station of Gonbad, Iran. It was arranged in two conditions, i.e. supplemental irrigation and rainfed. Two cultivars of canola (Hyola401 and RGS003) as subplots were grown at five sowing dates as main plots. The sowing dates were 9 November, 6 December, 5 January, 4 February and 6 March in 2005-2006 and 6 November, 6 December, 5 January, 4 February and 6 March in 2006-2007, to have a wide range of environmental conditions around flowering and seed filling periods, and to coincide reproductive stages of the crop with high temperature stress. Seed yield was improved due to field management practices, such as supplemental irrigation and optimum sowing date. Supplemental irrigation was an efficient practice to mitigate water stress, and to increase aboveground dry matter and seed yield. There was a strongly negative relationship between seed yield and air temperature during reproductive stages. Delay in sowing led to more rapid developmental of canola, decreased aboveground dry matter, leaf area index (LAI), harvest index (HI), WUE, and seed yield. Achieving a high aboveground dry matter was an essential prerequisite for high reproductive growth and a high seed yield. Greater seed yield and WUE at first sowing date were associated with greater LAI and aboveground dry matter, and lower temperatures during reproductive stages. The results support the view that WUE can be used as an indirect selection criterion for seed yield in genotypic selection.     

Regulated deficit irrigation improved fruit quality and water use efficiency of pear-jujube trees

Regulated deficit irrigation (RDI) was applied on field-grown pear-jujube trees in 2005 and 2006 and its effects on crop water-consumption, yield and fruit quality were investigated. Treatments included severe, moderate and low water deficit treatments at bud burst to leafing, flowering to fruit set, fruit growth and fruit maturation stages. Different deficit irrigation levels at different growth stages had significant effects on the fruit yield and quality. Moderate and severe water deficits at bud burst to leafing and fruit maturation stages increased fruit yield by 13.2-31.9% and 9.7-17.5%, respectively. Fruit yield under low water deficit at fruit growth and fruit maturation stages was similar to that of full irrigation (FI) treatment. All water deficit treatments reduced water consumption by 5-18% and saved irrigation water by 13-25% when compared to the FI treatment. During the bud burst to leafing stage, moderate and severe water deficits did not have effect on the fruit quality, but significantly saved irrigation water and increased fruit yield. Low water deficit during the fruit growth stage and low, moderate and severe water deficits during the fruit maturation stage had no significant effect on the fruit weight and fruit volume but reduced fruit water content slightly, which led to much reduced rotten fruit percentage during the post-harvest storage period. Such water deficit treatments also shortened the fruit maturation period by 10-15 d and raised the market price of the fruit. Fruit quality shown as fruit firmness, soluble solid content, sugar/acid ratio and vitamin C (V_C) content were all enhanced as a result of deficit irrigation. Our results suggest that RDI should be adopted as a beneficial agricultural practice in the production of pear-jujube fruit.     

Assessment of irrigation and environmental quality at the hydrological basin level: I. Irrigation quality

Irrigated agriculture notably increases crop productivity, but consumes high volumes of water and may induce off-site pollution of receiving water bodies. The objectives of this paper were to diagnose the quality of irrigation and to prescribe recommendations aimed at improving irrigation management and reducing the off-site pollution from a 15,500 ha irrigation district located in the Ebro River Basin (Spain). Three hydrological basins were selected within the district where the main inputs (irrigation, precipitation, and groundwater inflows) and outputs (actual crop's evapotranspiration, surface drainage outflows, and groundwater outflows) of water were measured or estimated during a hydrological year. The highest volume of water (I = 1400 mm/year) was applied in the basin with highly permeable, low water retention, flood irrigated soils where 81% of the total surface was planted with alfalfa and corn. This basin had the lowest consumptive water use efficiency (CWUE = 45%), the highest water deficit (WD = 5%) and the highest drainage fraction (DF = 57%). In contrast, the lowest I (950 mm/year), the highest CWUE (62%), and the lowest WD (2%) and DF (37%) were obtained in the basin with 60% of the surface covered with deep, high water retention, alluvial valley soils, where 39% of the cultivated surface is sprinkler irrigated and with only 48% of the surface planted with alfalfa and corn. We concluded that the three most important variables determining the quality of irrigation and the volume of irrigation return flows in the studied basins were (i) soil characteristics, (ii) irrigation management and irrigation system, and (iii) crop water requirements. Therefore, the critical recommendations for improving the quality of irrigation are to (i) increase the efficiency of flood-irrigation, (ii) change to pressurized systems in the shallow and highly permeable soils, and (iii) reuse of drainage water for irrigation within the district. These management strategies will conserve water of high quality in the main reservoir and will decrease the crop water deficits and the volume of irrigation return flows, therefore, minimizing the off-site pollution from this irrigation district.     

Effect of timing of a deficit-irrigation allocation on corn evapotranspiration, yield, water use efficiency and dry mass

Water regulations have decreased irrigation water supplies in Nebraska and some other areas of the USA Great Plains. When available water is not enough to meet crop water requirements during the entire growing cycle, it becomes critical to know the proper irrigation timing that would maximize yields and profits. This study evaluated the effect of timing of a deficit-irrigation allocation (150 mm) on crop evapotranspiration (ETc), yield, water use efficiency (WUE = yield/ETc), irrigation water use efficiency (IWUE = yield/irrigation), and dry mass (DM) of corn (Zea mays L.) irrigated with subsurface drip irrigation in the semiarid climate of North Platte, NE. During 2005 and 2006, a total of sixteen irrigation treatments (eight each year) were evaluated, which received different percentages of the water allocation during July, August, and September. During both years, all treatments resulted in no crop stress during the vegetative period and stress during the reproductive stages, which affected ETc, DM, yield, WUE and IWUE. Among treatments, ETc varied by 7.2 and 18.8%; yield by 17 and 33%; WUE by 12 and 22%, and IWUE by 18 and 33% in 2005 and 2006, respectively. Yield and WUE both increased linearly with ETc and with ETc/ETp (ETp = seasonal ETc with no water stress), and WUE increased linearly with yield. The yield response factor (ky) averaged 1.50 over the two seasons. Irrigation timing affected the DM of the plant, grain, and cob, but not that of the stover. It also affected the percent of DM partitioned to the grain (harvest index), which increased linearly with ETc and averaged 56.2% over the two seasons, but did not affect the percent allocated to the cob or stover. Irrigation applied in July had the highest positive coefficient of determination (R²) with yield. This high positive correlation decreased considerably for irrigation applied in August, and became negative for irrigation applied in September. The best positive correlation between the soil water deficit factor (Ks) and yield occurred during weeks 12-14 from crop emergence, during the “milk” and “dough” growth stages. Yield was poorly correlated to stress during weeks 15 and 16, and the correlation became negative after week 17. Dividing the 150 mm allocation about evenly among July, August and September was a good strategy resulting in the highest yields in 2005, but not in 2006. Applying a larger proportion of the allocation in July was a good strategy during both years, and the opposite resulted when applying a large proportion of the allocation in September. The different results obtained between years indicate that flexible irrigation scheduling techniques should be adopted, rather than relying on fixed timing strategies.     

Particle-size effects on soil temperature, evaporation, water use efficiency and watermelon yield in fields mulched with gravel and sand in semi-arid Loess Plateau of northwest China

Gravel and sand mulch is an effective practice in conserving soil and moisture. However, the proportion of different particle size in this kind of mulch layer is an important factor to be considered in order to obtain optimal results from this practice. From 2005 to 2007, a series of experiments including one with watermelon were conducted in the semi-arid Loess Plateau of northwest China to determine the influence of particle size and its proportion in mulch layer on soil temperature, evapotranspiration, water use efficiency (WUE) and watermelon (Citrullus lanatus L.) yield. The treatments in no-watermelon experiments included particle sizes classified as <0.3, 0.3-1, 1-2, 2-4, 4-6, 6-8 and 8-10 cm mesh size or various rates of 2-6 cm pebble accounting for 0, 10, 20, 30, 40, 50, 60 and 70% with 30% 1-2 cm gravel-sand in mulch layer (as well as correspondingly decreasing sand proportions). The watermelon experiment included three particle sizes, 0.3-1, 1-2 and 2-6 cm. Soil temperature at 8:00 h was highest for the 1-2 cm treatment, and the daily average temperature at 14:00 h was highest for the 0.3-1 cm treatment. Soil temperature decreased with particle size increasing due to porosity enlarging. The relationship between soil temperature and particle size followed a quadratic or cubic curve. Soil temperature was increased by gravel-sand mulch plus plastic film. The increment of soil temperature was larger especially for 1-4 cm particle size. In the gravel-sand mulch layer having different size particles, the greater percentage being of 2-6 cm pebbles, increases porosity, and lowers soil temperature, and causes more evaporation. The results of the watermelon experiment showed that soil moisture before seeding would not affect the yield during the years of using gravel mulch. Watermelon yield and WUE were higher for 1-2 and 0.3-1 cm treatments than 2-6 cm treatments in later experiments during 2006 and 2007. In conclusion, 2-6 cm large size particles would not account for much in gravel-sand mulching layer. It would be better if the percentage of 2-6 cm particles was less than 30%.     

Relationship between stable carbon isotope discrimination and water use efficiency under regulated deficit irrigation of pear-jujube tree

To investigate the relationship between stable carbon isotope discrimination (Δ) of different organs and water use efficiency (WUE) under different water deficit levels, severe, moderate and low water deficit levels were treated at bud burst to leafing, flowering to fruit set, fruit growth and fruit maturation stages of field grown pear-jujube tree, and leaf stable carbon isotope discrimination (Δ_L) at different growth stages and fruit stable carbon isotope discrimination (Δ_F) at fruit maturation stage were measured. The results indicated that water deficit had significant effect on Δ_L at different growth stages and Δ_F at fruit maturation stage. As compared with full irrigation, the average Δ_L at different growth stages and Δ_F at fruit maturation stage were decreased by 1.23% and 2.67% for different water deficit levels, respectively. Δ_L and Δ_F among different water deficit treatments had significant difference at the same growth stage (P < 0.05). Under different water deficit conditions, significant relationships between the Δ_L and WUE_i (photosynthesis rate/transpiration rate, P_n/T_r), WUE_n (photosynthesis rate/stomatal conductance of CO_2, P_n/g_s), WUE_y (yield/crop water consumption, Y/ET_c) and yield, or between the Δ_F and WUE_y and yield were found, respectively. There were significantly negative correlations of Δ_L with WUE_i, WUE_n, WUE_y and yield (P < 0.01) at the fruit maturation stage, or Δ_L with WUE_i and WUE_n (P < 0.01) over whole growth stage, respectively. Δ_F was negatively correlated with WUE_y, WUE_n and yield (P < 0.05), but positively correlated with ET_c (P < 0.01) over the whole growth stage. Thus Δ_L or Δ_F can compare WUE_n and WUE_y, so the stable carbon isotope discrimination method can be applied to evaluate the water use efficiency of pear-jujube tree under the regulated deficit irrigation.     

Reductions in water use following rehabilitation of a flood-irrigated area on the Murray River in South Australia

Water use was monitored during rehabilitation of flood-irrigated farms in the lower Murray River of South Australia. Ten irrigation offtakes at six farms were monitored over a period of two years during the rehabilitation process. Full rehabilitation consisted of improved inlet structures, flow metering, elimination of water leaks, laser levelling of paddocks, and construction of re-use systems to recycle excess surface irrigation runoff. Partial rehabilitation consisted of the same improvements with the exception of the re-use system. The mean water use per watering of 0.61 ± 0.08 Ml/ha for the fully rehabilitated farm was approximately one third of that for non-rehabilitated farms (1.89 ± 0.15 Ml/ha) and two thirds of that for partially rehabilitated farms (0.99 ± 0.07 Ml/ha). These differences were statistically significant at the 95% confidence level. A large improvement in efficiency of water use was achieved by upgraded water delivery infrastructure and laser levelling of paddocks. Considerable improvement in water use efficiency was also gained, however, only by installation of re-use systems. It is expected that the overall rehabilitation of irrigation infrastructure will result in a significant reduction of water extracted from the river for flood irrigation in this region. Further longer term monitoring is required to confirm this.     

Effect of timing of first and last irrigation on the yield and water use efficiency in cotton

With increasing concern about declining water resources, there is increasing thrust in improving water management in farming systems to improve water use efficiency. The present investigation was undertaken to determine the optimum timing for the first and last irrigation of cotton on the basis of meteorological approach for scheduling irrigations. The experiment was conducted in a split plot design with three timings of first irrigation as main-plots and three timing of last irrigation as sub-plots. Delay of first irrigation from 28 days after sowing (DAS) to 42 DAS, irrespective of last irrigation, resulted in an increase of 8, 14 and 17% in seed cotton yield during first, second and third year, respectively. The corresponding increases due to delay in the last irrigation from 130 to 170 DAS were 14, 32 and 8%, respectively. On the basis of 3 years average, application of first and last irrigation at optimum time (after 42 and 170 days after sowing) resulted in an increase of 36% in seed cotton yield without involving any additional cost. Water expense efficiency (WEE) increased by 54%.