Influence of vertical sand column and supplemental irrigation on barley yield in arid soils affected by surface crust

A field experiment was conducted during the 1996/1997 season at the University of Jordan Research Station near Al-Muwaqqar village to investigate the effects of sand columns, sand column spacing, soil ridges, and supplemental irrigation on soil water storage, redistribution, and barley yields. The experimental site represents a typical Jordanian arid environmental soil suffering from surface crust formation overlaying impermeable material. In the 600-mm-depth soil profile, soil water storage was improved significantly by 59%, 45%, and 38% in the 1-m, 2-m, and 3-m sand column spacing treatments, respectively, compared with soil water storage in the control treatment (no sand columns). Sand columns increased the moisture stored in all four soil layers (0–150, 150–300, 300–450, and 450–600 mm). Moisture stored in the 450–600 mm soil layer increased significantly by about 188%, 147%, 88%, and 29% in the 1-m, 2-m, 3-m, and 4-m sand column spacing treatments, respectively, compared with moisture stored in the same soil layer of the control treatment. Increasing soil water storage also increased barley consumptive use significantly from 130 mm in the control treatment to an average of about 185 mm in sand column treatments. Without supplemental irrigation, barley grain and straw yields were negligible and almost zero. Barley yields in the control treatment, with 167 mm supplemental irrigation were low, being 0.19 ton/ha and 1.09 ton/ha of barley grain and straw, respectively. Sand columns increased barley grain and straw yields significantly compared with the control treatment to a maximum of 0.68 ton/ha and 3.97 ton/ha, respectively, with the 1-m sand column spacing. Soil ridges perpendicular to the land slope had no significant effect on increasing soil water storage due to lateral runoff and loss along the ridge. In general, sand columns minimize surface runoff and evaporation by allowing water to infiltration through the strong surface crust. Sand columns act as a sink for surface water, enhance subsurface lateral water movement, and reduce the possibility of surface crust formation in the vicinity of the sand column opening by preventing surface ponding. Received: 3 October 1997     

Effects of different ridge:furrow ratios and supplemental irrigation on crop production in ridge and furrow rainfall harvesting system with mulches

The ridge and furrow rainfall harvesting (RFRH) system with mulches is being promoted to increase water availability for crops for higher and stable agricultural production in many areas of the Loess Plateau in northwest China. In the system, plastic-covered ridges serve as rainfall-harvesting zones and stone-, straw- or film-mulched furrows serve as planting zones. To adopt this system more effectively, a field study (using corn as an indicator crop) was conducted to determine the effects of different ridge:furrow ratios and supplemental irrigation on crop yield and water use efficiency (WUE) in the RFRH system with mulches during the growing seasons of 1998 and 1999.The results indicated that the ridge:furrow ratios had a significant effect on crop yield and yield components. The 120:60 cm ridge and furrow (120 cm wide ridge and 60 cm wide furrow) system increased yield by 27.9%, seed weight per head by 14.8%, seed number per head by 7.4% and 1000-seed weight by 4.7%, compared with the 60:60 cm ridge and furrow (60 cm wide ridge and 60 cm wide furrow) system. No differences in WUE were found between the two ratio systems. For corn and winter wheat, the optimum ridge:furrow ratio seems to be 1:1 in the 300-mm rainfall area, 1:2 in the 400-mm rainfall area and 1:4 in the 500-mm rainfall area. The optimum ridge:furrow ratio seems to be 1:3 for millet in the 300-mm rainfall area, although it is unnecessary to adopt RFRH practice in regions with more than 400 mm rainfall. The most effective ridge size for crop production seems 60 cm in the Loess Plateau. Implementing supplemental irrigation in the RFRH system is also a useful way to deal with the temporal problem of moisture deficits. In the case of corn, supplemental irrigation at its critical growth stage can increase both grain yield and WUE by 20%. The combination of in situ RFRH system with supplemental irrigation practice will make the RFRH system more attractive.     

Soil water distribution, uniformity and water-use efficiency under alternate furrow irrigation in arid areas

Soil water distribution, irrigation water advance and uniformity, yield production and water-use efficiency (WUE) were tested with a new irrigation method for irrigated maize in an arid area with seasonal rainfall of 77.5–88.0 mm for 2 years (1997 and 1998). Irrigation was applied through furrows in three ways: alternate furrow irrigation (AFI), fixed furrow irrigation (FFI) and conventional furrow irrigation (CFI). AFI means that one of the two neighboring furrows was alternately irrigated during consecutive watering. FFI means that irrigation was fixed to one of the two neighboring furrows. CFI was the conventional method where every furrow was irrigated during each watering. Each irrigation method was further divided into three treatments using different irrigation amounts: i.e. 45, 30, and 22.5 mm water for each watering. Results showed that the soil water contents in the two neighboring furrows of AFI remained different until the next irrigation with a higher water content in the previously irrigated furrow. Infiltration in CFI was deeper than that in AFI and FFI. The time of water advance did not differ between AFI, FFI and CFI at all distances monitored, and water advanced at a similar rate in all the treatments. The Christiansen uniformity coefficient of water content in the soil (CU_s) was used to evaluate the uniformity of irrigated water distribution and showed no decrease in AFI and FFI, although irrigation water use was smaller than in CFI. Root development was significantly enhanced by AFI treatment. Primary root numbers, total root dry weight and root density were all higher in AFI than in the FFI and CFI treatments. Less irrigation significantly reduced the total root dry weight and plant height in both the FFI and CFI treatments but this was less substantial with AFI treatments. The most surprising result was that AFI maintained high grain yield with up to a 50% reduction in irrigation amount, while the FFI and CFI treatments all showed a substantial decrease of yield with reduced irrigation. As a result, WUE for irrigated water was substantially increased. We conclude that AFI is an effective water-saving irrigation method in arid areas where maize production relies heavily on repeated irrigation. Received: 16 October 1999     

Comparison of sprinkler,trickle and furrow irrigation efficiencies for onion production

In the Mesilla Valley of southern New Mexico, furrow irrigation is the primary source of water for growing onions. As the demand for water increases, there will be increasing competition for this limited resource. Water management will become an essential practice used by farmers. Irrigation efficiency (IE) is an important factor into improving water management but so is economic return. Therefore, our objectives were to determine the irrigation efficiency, irrigation water use efficiency (IWUE) and water use efficiency (WUE), under sprinkler, furrow, and drip irrigated onions for different yield potential levels and to determine the IE associated with the amount of water application for a sprinkler and drip irrigation systems that had the highest economic return.Maximum IE (100%) and economic return were obtained with a sprinkler system at New Mexico State University’s Agriculture Science Center at Farmington, NM. This IE compared with the 54–80% obtained with the sprinkler irrigation used by the farmers. The IEs obtained for onion fields irrigated with subsurface drip irrigation methods ranged from 45 to 77%. The 45% represents the nonstressed treatments, in which an extra amount of irrigation above the evapotranspiration (Et) requirement was applied to keep the base of the onion plates wet. The irrigation water that was not used for Et went to deep drainage water. The return on the investment cost to install a drip system operated at a IE of 45 was 29%. Operating the drip system at a IE of 79% resulted in a yield similar to surface irrigated onions and consequently, it was not economical to install a drip system. The IEs at the furrow-irrigated onion fields ranged from 79 to 82%. However, the IEs at the furrow-irrigated onion fields were high because farmers have limited water resources. Consequently, they used the concept of deficit irrigation to irrigate their onion crops, resulting in lower yields. The maximum IWUE (0.084 t ha⁻¹ mm⁻¹ of water applied) was obtained using the sprinkler system, in which water applied to the field was limited to the amount needed to replace the onions’ Et requirements. The maximum IWUE values for onions using the subsurface drip was 0.059 and 0.046 t ha⁻¹ mm⁻¹ of water applied for furrow-irrigated onions. The lower IWUE values obtained under subsurface drip and furrow irrigation systems compared with sprinkler irrigation was due to excessive irrigation under subsurface drip and higher evaporation rates from fields using furrow irrigation. The maximum WUE for onions was 0.009 t ha⁻¹ mm⁻¹ of Et. In addition, WUE values are reduced by allowing the onions to suffer from water stress.     

Camelina water use and seed yield response to irrigation scheduling in an arid environment

Camelina sativa (L.) Crantz is a promising, biodiesel-producing oilseed that could potentially be implemented as a low-input alternative crop for production in the arid southwestern USA. However, little is known about camelina’s water use, irrigation management, and agronomic characteristics in this arid environment. Camelina experiments were conducted for 2 years (January to May in 2008 and 2010) in Maricopa, Arizona, to evaluate the effectiveness of previously developed heat unit and remote sensing basal crop coefficient (K _cb ) methods for predicting camelina crop evapotranspiration (ET) and irrigation scheduling. Besides K _cb methods, additional treatment factors included two different irrigation scheduling soil water depletion (SWD) levels (45 and 65 %) and two levels of seasonal N applications within a randomized complete block design with 4 blocks. Soil water content measurements taken in all treatment plots and applied in soil water balance calculations were used to evaluate the predicted ET. The heat-unit K _cb method was updated and validated during the second experiment to predict ET to within 12–13 % of the ET calculated by the soil water balance. The remote sensing K _cb method predicted ET within 7–10 % of the soil water balance. Seasonal ET from the soil water balance was significantly greater for the remote sensing than heat-unit K _cb method and significantly greater for the 45 than 65 % SWD level. However, final seed yield means, which varied from 1,500 to 1,640 kg ha^?1 for treatments, were not significantly different between treatments or years. Seed oil contents averaged 45 % in both years. Seed yield was found to be linearly related to seasonal ET with maximum yield occurring at about 470–490 mm of seasonal ET. Differences in camelina seed yields due to seasonal N applications (69–144 kg N ha^?1 over the 2 years) were not significant. Further investigations are needed to characterize camelina yield response over a wider range of irrigation and N inputs.     

Water pillow irrigation compared to furrow irrigation for soybean production in a semi-arid area

Field studies were done in 2003 and 2006 to evaluate the performance of water pillow (WP) irrigation as an alternative to furrow irrigation (FI) for soybean growth in semi-arid climatic conditions. There were four irrigation treatments: two of which (FI and WP_1.0) were full irrigation, in that the water deficit in the soil profile (0.9 m) was brought to field capacity in 10-day intervals. The other two treatments (WP_0.75 and WP_0.50) were deficit irrigation treatments, and received 75% and 50% of WP_1.0 irrigation amount. The highest seed yield was achieved with the WP_1.0 treatment. Irrigation water use efficiency (IWUE) and water use efficiency (WUE) were influenced significantly by the irrigation methods and levels (P ≤ 0.05). The highest values of WUE and IWUE were obtained by the WP_0.75 and WP_0.50 treatment, respectively, in both study years. However, the smallest irrigation amount resulted in lower total yield for the WP_0.50 treatment, and is not recommended. In conclusion, the WP_0.75 treatment is recommended for soybean production in order to attain higher values of IWUE and WUE, and to conserve water and maximize yield with the same volume of water.     

The comparison of advance and erosion of meandering furrow irrigation with standard furrow irrigation under varying furrow inflow rates

Meandering furrow irrigation (Gholam-gardeshi irrigation) is a modified form of furrow irrigation, which has being used in Iran, but to date, there is no study about the erosion of this method of irrigation. To measure the erosion of meandering furrow irrigation and to compare the results with standard furrow irrigation, two experimental fields with different soil textures and furrow inflow rates were used. The experiment utilized a randomized factorial design with three replications for each treatment. In both methods, the developed second order polynomial equation for the erosion, and advance equation were able to predict the field data with coefficients of determination of more than 0.94. The results showed that the velocity of advance, tail water runoff and erosion are significantly lower for meandering furrow irrigation as compared to standard furrow irrigation. As the furrow inflow rates increased, erosion and runoff in both irrigation methods increased significantly.     

Effect of tillage and furrow irrigation timing on efficiency of preplant irrigation

Summary A field study to determine the efficiency of preplant irrigating with furrow irrigation and the effects of tillage and fall or spring application of preplant irrigation on this efficiency was conducted during 1983, 1984, and 1985 at the Texas Agricultural Experiment Station, North Plains Research Field at Etter, Texas on a Sherm, silty clay loam soil. Sorghum residue from the previous crop was shredded, gravimetric soil samples were taken, and five tillage treatments were imposed in the fall. The tillage treatments consisted of various combinations of disking, chiselling, moldboard plowing, and disk bedding. A preplant irrigation was applied in the fall to half of each tillage plot and in the spring to the other half of each plot. Soil samples were taken from each plot one month after the spring preplant irrigation. Sorghum (Sorghum bicolor L. cv. NC 178) was planted and irrigated similarly on all plots during the growing season. On the average, 237 mm of water were required to irrigate the tillage treatments during fall preplant irrigation and 466 mm were required during spring preplant irrigation. The additional water requirement in the spring was associated with increased water uptake by non-wheel-track furrows. Treatments with chiselling required larger water application during spring preplant irrigation. All treatments had similar soil water contents at planting time. Neither timing of preplant irrigation nor type of tillage had any effect on sorghum grain yield. Therefore, fall preplant irrigation was considerably more efficient than spring preplant irrigation. Averaged over the three years do study and five tillage treatments storage efficiency was 26% for fall application and 17% for springtime.Contribution of the Texas Agricultural Experiment Station, Paper No. 21724     

Water use efficiency of winter-sown chickpea under supplemental irrigation in a mediterranean environment

Chickpea is one of the major legume crops grown in the West Asia and North Africa (WANA) region. It has considerable importance as a food, feed and fodder. Traditionally, it is sown in spring as a rainfed crop in the region, which has highly variable and often insufficient rainfall. It is, therefore, largely raised on residual moisture, which results in low and variable yields and discourages farmers from investing inputs in its production. In the early 1990s, a winter-sown chickpea technology was developed that outweighs spring-sown chickpea in terms of productivity, water use efficiency and other traits. Limited supplemental irrigation can, however, play a major role in boosting and stabilizing the productivity of both spring-sown and winter-sown chickpea. Therefore, we investigated the effect of supplemental irrigation and sowing date on yield and water use efficiency in winter-sown chickpea.An experiment was carried out over four cropping seasons (1997–2001) at ICARDA’s main station at Tel Hadya, Aleppo, northern Syria (mean annual rainfall 330 mm). A cold-tolerant chickpea cultivar with improved resistance to ascochyta blight (ILC 3279, released as Ghab 2 in Syria) was grown in rotation with wheat. The experiment included three sowing dates (late November, mid-January, and late February) and four levels of supplemental irrigation (SI): full SI, 2/3 SI, 1/3 SI, and no SI, i.e. rainfed. The plots were replicated three times in a split-plot design, with date of sowing being the main plot treatment. Soil water content was monitored at approximately at 7–14-day intervals using a neutron probe. Crop evapotranspiration was determined for each subplot during each time interval, from sowing to harvest, using the soil-water balance equation. Water use efficiency was determined as the ratio of crop yield per unit area to seasonal evapotranspiration.The results showed that chickpea yield per unit area increases with both earlier sowing and increased SI. However, water use efficiency under supplemental irrigation decreases with earlier sowing, due to the relatively large increase that occurs in the amount of evapotranspiration at early sowing dates. The study’s results indicated that a 2/3 SI level gives the optimum water use efficiency for chickpea under supplemental irrigation. Under rainfed conditions, however, it was found that sowing chickpea around mid-January resulted in the highest WUE. The analysis also proposed a function, based on regression, which relates winter-sown chickpea yield to water use and which is applicable under both supplemental and rainfed conditions.     

Effects of field length and management practices on dissolved organic carbon export in furrow irrigation

Farming practices, including tillage, cover cropping and residue management can have profound effects on the efficiency of irrigation practices. The effects of three field management practices (FMPs) standard tillage and winter-fallow (ST), standard tillage and winter-cover crop (STCC), and no-till and winter-fallow (NT) and two field lengths (122 and 366 m) on runoff and export of dissolved organic carbon (DOC) were investigated in a furrow-irrigated cropping system over two years. The residue cover was 40, 32 and 11% in 2007, and 58, 61 and 11% in 2008 for STCC, NT and ST, respectively. Furrow irrigation experiments were conducted prior to crop planting following the cover crop. The inflow was kept constant across all treatments, and infiltration and runoff were estimated using a volume balance model (VBM). The DOC concentration tended to increase with increasing field length, but did not differ among the FMPs. A threefold increase in field length increased infiltration by 40%, and decreased runoff by 60-90% and DOC export by 65-83%. In both years, infiltration was highest in STCC. In NT, infiltration was lowest in 2007, which was likely due to soil sealing, and intermediate among the three FMPs in 2008 perhaps due to the increase in residue cover in the second year. The DOC budget analysis showed that fields and FMPs acted as DOC sinks exporting less DOC than was applied in the irrigation water. The results suggest that longer furrows and STCC were greater DOC sinks compared to ST and shorter field practices. The VBM, as applied in this study to estimate infiltration and runoff, could be used to predict optimal field length to minimize runoff and promote DOC adsorption to soil within the constraints of water quality and availability and soil conditions.     

Water use, crop coefficients, and irrigation management criteria for camelina production in arid regions

Camelina sativa (L.) Crantz is an oilseed crop touted as being suitable for production in the arid southwestern USA. However, because any significant development of the crop has been limited to cooler, rain-fed climate-areas, information and guidance for managing irrigated-camelina are lacking. This study measured the crop water use of a November-through-April camelina crop in Arizona using frequent measurements of soil water contents. The crop was grown under surface irrigation using five treatment levels of soil water depletion. The seed yields of treatments averaged 1,142 kg ha⁻¹ (8.0% seed moisture) and were generally comparable with camelina yields reported in other parts of the USA. Varying total irrigation water amounts to treatments (295–330 mm) did not significantly affect yield, whereas total crop evapotranspiration (ET_c) was increased for the most frequently irrigated treatment. However, total ET_c for the camelina treatments (332–371 mm) was markedly less than that typically needed by grain and vegetable crops (600–655 mm), which are commonly grown during the same timeframe in Arizona. The camelina water-use data were used to develop crop coefficients based on days past planting, growing degree days, and canopy spectral reflectance. The crop coefficient curves, along with information presented on camelina soil water depletion and root zone water extraction characteristics will provide camelina growers in arid regions with practical tools for managing irrigations.     

Comparison and selection of furrow irrigation models

The capability of hydrodynamic, zero-inertia, kinematic-wave and volume-balance models to predict advance and recession phases in furrow irrigation were compared against two sets of field data, providing a wide range of soil conditions and field slopes. The input parameters required for each model were studied, and a simple sensitivity analysis was performed for field slope, furrow geometry, roughness coefficient, infiltration constants, time step, and discharge. The accuracy of the models' predictions depends on the precision of the measurements and the estimation of the input parameters. Excellent prediction of the advance and recession phases were obtained with hydrodynamic, zero-inertia and kinematic-wave models. Those models therefore are preferred in design and management in furrow irrigation.     

Evaluation of surge flow furrow irrigation for onion production in a semiarid region of Ethiopia

The study was conducted to evaluate surge irrigation against continuous irrigation in terms of irrigation and water use efficiencies to produce onion. It was carried out at Mekelle Agricultural Research Center, Ethiopia on 70 m long and 0.6 m center–center spacing furrows of 0.26% average slope on a clay soil. The treatments consisted of factorial combination of two discharges (Q ₁ = 1 l/s and Q ₂ = 2 l/s) and three-cycle ratios (CR₁ = 1/3, CR₂ = 1/2, and C = 1 for continuous irrigation). Surge flow treatments advanced faster than the respective continuous flow treatments with surge flow treatment SF₂₁ being the fastest. The best value of application efficiency (60%) was achieved for SF₁₁ and the least (46%) for CF₂. The maximum (87%) and minimum (68%) values of distribution uniformity were obtained for cycle ratios CR₁ and C, respectively. Storage efficiency was highest (89%) for CF₂ and lowest (78%) for SF₁₂. Onion yield was significantly affected (p < 0.05) by the interaction effect, the highest (14,400 kg/ha) and the lowest (13,363 kg/ha) yields were obtained for SF₁₁ and SF₂₁, respectively. The maximum irrigation water use efficiency (2.27 kg/m³) was observed for SF₁₁ and the minimum (1.68 kg/m³) for CF₂. Surge irrigation was found to be a promising irrigation practice for onion production in the study area as it saves water, reduces irrigation period, and increases the crop yield.     

Optimization of furrow irrigation schedules,designs and net return to water

A seasonal furrow irrigation model consisting of irrigation scheduling and kinematic-wave-based hydraulic submodels was modified to incorporate an economic optimization submodel. The model used a systematic simulation technique to optimize furrow irrigation schedules and designs assuming 80% irrigation adequacy at cutoff time. The irrigation schedules and designs were optimized for the homogeneous and heterogeneous infiltration under the mean and observed ET_o (grass reference crop ET) conditions. The optimal management allowable depletion (MAD) level changed with the variation in ET_o condition, and with the consideration of spatial and temporal (seasonal) variability in infiltration characteristics. Irrigation design changed with both infiltration conditions and MAD level. Infiltration variability did not influence the bean yield. However, the return to water decreased when spatial variability in infiltration conditions was considered. Using mean ET_o resulted in slightly higher yield and net return to water as compared to using observed ET_o. A small variation in daily mean ET_o values with respect to daily observed ET_o values caused a change in both irrigation schedules and designs. Therefore, mean ET_o cannot be used to forecast irrigation schedules and designs at the beginning of crop season. The net return to water increased (1.7 to 3.6%), and the seasonal inflow, losses, and bean yield decreased in the case of variable interval scheduling (holding MAD constant) as compared to the fixed interval scheduling (MAD varies).     

Simulation of furrow irrigation practices (SOFIP): a field-scale modelling of water management and crop yield for furrow irrigation

Because of the spatial and temporal variabilities of the advance infiltration process, furrow irrigation investigations should not be limited to a single furrow irrigation event when using a modelling approach. The paper deals with the development and application of simulation of furrow irrigation practices (SOFIP), a model used to analyse furrow irrigation practices that take into account spatial and temporal variabilities of the advance infiltration process. SOFIP can be used to compare alternative furrow irrigation management strategies and find options that mitigate local deep-percolation risks while ensuring a crop yield level that is acceptable to the farmer. The model is comprised of three distinct modelling elements. The first element is RAIEOPT, a hydraulic model that predicts the advance infiltration process. Infiltration prediction in RAIEOPT depends on a soil moisture deficit parameter. PILOTE, a crop model, which is designed to simulate soil water balance and predict yield values, updates the soil moisture parameter. This parameter is an input of a parameter generator (PG), the third model component, which in turn provides RAIEOPT with the data required to simulate irrigation at the scale of an N-furrow set. The study of sources of variability and their impact on irrigation advance, based on field observations, allowed us to build a robust PG. Model applications show that irrigation practices must account for inter-furrow advance variability when optimising furrow irrigation systems. The impact of advance variability on deep percolation and crop yield losses depends on both climatic conditions and irrigation practices.     

Micro-catchment water harvesting potential of an arid environment

Micro-catchment water harvesting (MCWH) requires development of small structures across mild land slopes, which capture overland flow and store it in soil profile for subsequent plant uses. Water availability to plants depends on the micro-catchment runoff yield and water storage capacity of both the plant basin and the soil profile in the plant root zone. This study assessed the MCWH potential of a Mediterranean arid environment by using runoff micro-catchment and soil water balance approaches. Average annual rainfall and evapotranspiration of the studied environment were estimated as 111 and 1671 mm, respectively. This environment hardly supports vegetation without supplementary water. During the study period, the annual rain was 158 mm in year 2004/2005, 45 mm in year 2005/2006 and 127 mm in year 2006/2007. About 5000 MCWH basins were developed for shrub raising on a land slope between 2 and 5% by using three different techniques. Runoff at the outlets of 26 micro-catchments with catchment areas between 13 and 50 m² was measured. Also the runoff was indirectly assessed for another 40 micro-catchments by using soil water balance in the micro-catchments and the plant basins. Results show that runoff yield varied between 5 and 187 m³ ha⁻¹ for various rainfall events. It was between 5 and 85% of the incidental rainfall with an average value of 30%. The rainfall threshold for runoff generation was estimated about 4 mm. Overall; the soil water balance approach predicted 38-57% less water than micro-catchment runoff approach. This difference was due to the reason that the micro-catchment runoff approach accounted for entire event runoff in the tanks; thus showed a maximum water harvesting potential of the micro-catchments. Soil water balance approach estimated water storage in soil profile and did not incorporate water losses through spillage from plant basins and deep percolation. Therefore, this method depicted water storage capacity of the plant basins and the root zone soil profile. The different between maximum water harvesting potential and soil-water storage capacity is surplus runoff that can be better utilized through appropriate MCWH planning.     

Effects of a suspended shade cloth cover on water quality of an agricultural reservoir for irrigation

Water availability and quality are two fundamental factors for agriculture in arid and semi-arid regions. This study evaluates the effects of a water-permeable, Suspended Shade Cloth Cover (SSCC), on the quality of water stored in an on-farm Agricultural Water Reservoir (AWR). Water quality (water temperature, electrical conductivity, chlorophyll-a concentration, dissolved oxygen concentration and water turbidity) and environmental (evaporation, rainfall, wind speed and solar radiation) parameters were measured over a 2-year period in a typical AWR located in south-eastern Spain. In the first year, the AWR remained uncovered and the behaviour was quasi-isothermal. In the second year, installing a SSCC induced a thermal gradient in the water that reached a maximum temperature difference of 12 °C during summer. The lack of turbulence under the cover and the reduction in photosynthesis (95% reduction of chlorophyll-a) reduced the concentration of dissolved oxygen to 1.5 mg L⁻¹, and turbidity from 40 NTU at installation to less than 1 NTU. The positive balance between rainfall and evaporation during the second year reduced the electrical conductivity of the water by 8.2%. The improvement in water quality associated with the installation of a SSCC increases the efficiency of drip irrigation systems by reducing the water filtering requirements, the likelihood of emitter clogging, and the risk of irrigation-induced salinity.     

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.     

Deficit irrigation in maize for reducing agricultural water use in a Mediterranean environment

Research on crop response to deficit irrigation is important to reduce agricultural water use in areas where water is a limited resource. Two field experiments were conducted on a loam soil in northeast Spain to characterize the response of maize (Zea mays L.) to deficit irrigation under surface irrigation. The growing season was divided into three phases: vegetative, flowering and grain filling. The irrigation treatments consisted of all possible combinations of full irrigation or limited irrigation in the three phases. Limited irrigation was applied by increasing the interval between irrigations. Soil water status, crop growth, above-ground biomass, yield and its components were measured. Results showed that flowering was the most sensitive stage to water deficit, with reductions in biomass, yield and harvest index. Average grain yield of treatments with deficit irrigation around flowering (691 g m⁻²) was significantly lower than that of the well-irrigated treatments (1069 g m⁽²). Yield reduction was mainly due to a lower number of grains per square metre. Deficit irrigation or higher interval between irrigations during the grain filling phase did not significantly affect crop growth and yield. It was possible to maintain relatively high yields in maize if small water deficits caused by increasing the interval between irrigations were limited to periods other than the flowering stage. Irrigation water use efficiency (IWUE) was higher in treatments fully irrigated around flowering.     

Wheat water productivity and yield in a cool highland environment: Effect of early sowing with supplemental irrigation

The Central Anatolian Plateau of Turkey is a typical cool highland rainfed wheat area with an annual rainfall of 300–500 mm. Due to suboptimal seasonal rainfall amounts and distribution, wheat yields in the region are low and fluctuate substantially over seasons. Delayed sowing due to late rainfall affects early crop establishment before winter frost and causes substantial reduction in yield. A 4-year field study (1998/1999 to 2001/2002) was carried out at Ankara Research Institute of Rural Services to assess the impact of early sowing with supplemental irrigation (SI) and management options during other dry spells on the productivity of a bread wheat cultivar, “Bezostia”. Treatments included early sowing with 50 mm irrigation and normal sowing with no irrigation as main plots. Four spring (SI) levels occupied the sub-plots. These are rainfed (no-irrigation), full irrigation to sature crop water requirements and two deficit irrigation levels of 1/3 and 2/3 at the full irrigation treatments.Results showed that early establishment of the crop, using 50 mm of irrigation water at sowing, increased grain yield by over 65% and adding about 2.0 t/ha to the average rainfed yield of 3.2 t/ha. Early sowing with SI allowed early crop emergence and development of good stand before being subjected to the winter frost. As a result, the crop used rainwater more efficiently. Additional supplemental irrigation in the spring also increased yield significantly. Grain yields of 5120, 5170 and 5350 kg/ha were obtained by applying 1/3, 2/3 and full SI, respectively. The mean productivity of irrigation water given at sowing was 3.70 kg/m³ with maximum value of 4.5 kg/m³. Water productivity of 1/3, 2/3 and full SI were 2.39, 1.46 and 1.27 kg/m³, respectively, compared to rainwater productivity of 0.96 kg/m³.