The viability of irrigating mandarin trees with saline reclaimed water in a semi-arid Mediterranean region: a preliminary assessment

The effect of irrigation water quality was investigated in a commercial mandarin orchard during four growing seasons using fresh water (EC ≈ 1 dS m^?1), irrigators’ association water (EC = 1–3 dS m^?1) and reclaimed water (RW) (EC ≈ 3 dS m^?1). RW had higher concentration of macro- and micronutrients, especially potassium, and the phytotoxic elements, boron, sodium and chlorides. The microbiological load in the different irrigation water sources showed a high seasonal variability, and all water sources occasionally exceeded health standards to irrigate fruit trees. In the RW treatment, an increase in soil salinity and leaf boron concentration was observed. The nutritional contribution of RW was high, providing 24 and 15 % of the annual nitrogen and phosphorus (N and P₂O₅) fertilizer requirement for mandarin oranges, respectively, and RW treatment satisfied the entire potassium requirement (K₂O). An important fluctuation in the crop production was observed during the 4 years in the different water quality treatments. In general, quality parameters of mandarins were not affected. The results provide additional evidence that long-term effects must be studied to test sustainability when using RW irrigation on fruit trees.     

A model for computing date palm water requirements as affected by salinity

Irrigation of crops in arid regions with marginal water is expanding. Due to economic and environmental issues arising from use of low-quality water, irrigation should follow the actual crop water demands. However, direct measurements of transpiration are scant, and indirect methods are commonly applied; e.g., the Penman–Monteith (PM) equation that integrates physiological and meteorological parameters. In this study, the effects of environmental conditions on canopy resistance and water loss were experimentally characterized, and a model to calculate palm tree evapotranspiration ET_c was developed. A novel addition was to integrate water salinity into the model, thus accounting for irrigation water quality as an additional factor. Palm tree ET_c was affected by irrigation water salinity, and maximum values were reduced by 25 % in plants irrigated with 4 dS m^?1 and by 50 % in the trees irrigated with 8 dS m^?1. Results relating the responses of stomata to the environment exhibited an exponential relation between increased light intensities and stomatal conductance, a surprising positive response of stomata to high vapor pressure deficits and a decrease in conductance as water salinity increased. These findings were integrated into a modified ‘Jarvis–PM’ canopy conductance model using only meteorological and water quality inputs. The new approach produced weekly irrigation recommendations based on field water salinity (2.8 dS m^?1) and climatic forecasts that led to a 20 % decrease in irrigation water use when compared with current irrigation recommendations.     

Distribution and dynamics of soil water and salt under different drip irrigation regimes in northwest China

A 2-year experiment was carried out to investigate the effects of different drip irrigation regimes on distribution and dynamics of soil water and salt in north Xinjiang, China. Five treatments—F7 (0.24 dS m^?1 + Once every 7 days), B7 (4.68 dS m^?1 + Once every 7 days), S7 (7.42 dS m^?1 + Once every 7 days), F10 (0.24 dS m^?1 + Once every 10 days) and F3 (0.24 dS m^?1 + Once every 3 days)—were designed. For all treatments, additional 150-mm fresh water was applied on 10th November in 2009 (winter irrigation) to leach the accumulated salt. The results revealed that irrigation frequency and water quality had significant effects on the spatial distribution and change of soil water content, soil salt and the crop water consumption rate, but had a limited impact on the seasonal accumulative water consumption, and the cotton yield decreased with the decrease in irrigation frequency and water quality on the whole. During the cotton growing season, results showed that the salt mainly accumulated in the 0- to 60-cm soil layer, while the soil salt in 60- to 100-cm layer changed slightly, indicating that the drip irrigation could not leach the soil salt out of the root zone under the irrigation regimes. Therefore, salt leaching was necessary to maintain the soil water–salt balance and to prevent excessive salt accumulation in the root zone. After the 150-mm winter irrigation and subsequent thawing, soil salts were leached into the deeper layers (below 60 cm), and the soil salt content (SSC) (EC_1:5) in root zone in the next year was about 0.2 dS m^?1. Moreover, compared to 2009 season, the SSC within the root zone did not increase even the EC of the irrigation water was up to 7.42 dS m^?1. Additionally, it is important to note that the results were concluded based on the data of the 2-year experiment; further studies are need to optimize winter irrigation amount and assess the sustainability of saline water irrigation since long-term utilization of saline water may lead to soil degradation.     

Effect of amount and timing of subsurface drip irrigation on corn yield

A field study was conducted at North Platte, Nebraska in 2007–2009, imposing eight irrigation treatments, ranging from dryland to fully irrigated. Four of the eight treatments allowed for various degrees of water stress only after tasseling and silking. In 2007, corn yield ranged from 8.9 Mg ha^?1 with a season total of 41 mm of irrigation water to 11.5 Mg ha^?1 for the fully irrigated treatment (264 mm of irrigation water). The treatment with the greatest reduction in irrigation water after tasseling and silking (158 mm) had a mean yield of 10.9 Mg ha^?1, only 0.6 Mg ha^?1 less than the fully irrigated treatment. In 2009, yields ranged from 12.6 to 13.5 Mg ha^?1. There were no significant yield differences between the irrigation treatments for several possible reasons: more in-season precipitation and cooler weather required less irrigation water; much of the irrigation water was applied after the most water-stress sensitive stages of tasseling and silking; and lower atmospheric demand allowed for soil water contents well below 50 % management allowed depletion (MAD) not to cause any yield losses.     

Wheat yield response to line source sprinkler irrigation and soil management practices on medium-textured shallow soils of arid environment

A field experiment was conducted for 3 years to evaluate the effect of deficit irrigation under different soil management practices on biomass production, grain yield, yield components and water productivity of spring wheat (Triticum estivum L.). Soil management practices consisted of tillage (conventional and deep tillage) and Farmyard manure (0 and 10 t ha^?1 FYM). Line source sprinkler laterals were used to generate one full- (ETm) and four deficit irrigation treatments that were 88, 75, 62 and 46 % of ETm, and designated as ETd₁, ETd₂, ETd₃, and ETd₄. Deep tillage significantly enhanced grain yield (14–18 %) and water productivity (1.27–1.34 kg m^?3) over conventional tillage. Similarly, application of FYM at 10 t ha^?1 significantly improved grain yield (10–13 %) and water productivity (1.25–1.31 kg m^?3) in comparison with no FYM. Grain yield response to irrigation varied significantly (5,281–2,704 kg ha^?1) due to differences in soil water contents. Water productivity varied from 1.05 to 1.34 kg m^?3, among the treatments in 3 years. The interactive effect of irrigation × tillage practices and irrigation × FYM on grain yield was significant. Yield performance proved that deficit irrigation (ETd₂) subjected to 75 % soil water deficit had the smallest yield decline with significant water saving would be the most appropriate irrigation level for wheat production in arid regions.     

Shallow groundwater use by Safflower (Carthamus tinctorius L.) in a semi-arid region

Two-year lysimeter experiments were conducted to determine groundwater contributions by safflower (Carthamus tinctorius L.) crop. The plants were grown in twenty columns each with a diameter of 0.40 m packed with Silty Clay soil. The experiments were carried out in a complete randomized blocks design with four replicates. In each experiment, five treatments were applied by maintaining groundwater salinity to a control treatment with EC 1 dS/m, while the groundwater salinity of the other treatments was 2, 5, 8 and 10 dS/m, and 0.8 m water table level, respectively. The use of groundwater as a part of crop evapotranspiration was characterized by using daily measurements of the water level in Mariotte tubes. The extra magnitude of irrigation water requirement for each treatment was applied by water with EC of 1 dS/m. The results of experiments showed that for different control treatments with 1 dS/m, 2, 5, 8 and 10 dS/m, the groundwater contributions were achieved as 59, 51, 38, 32 and 19% of the total plant water requirements, respectively.     

Agronomic and socio-economic analysis of water management techniques for dry season cultivation of common bean in Malawi

A study was carried out in Malawi to compare agronomic and socio-economic aspects of different water management practices for two advanced bean lines. Four irrigation technologies and one control were studied in Chingale Area Development Program in Zomba District in southern Malawi. The technologies encompassed motorized pumps (MP), treadle pumps (TP), water cans, gravity-fed surface irrigation (GR) and a non-irrigated practice that used residual moisture. The study found that technologies that used <2 labour hours m^?3 were appropriate for such small-scale irrigation systems. The aggregated bean production labour cost and labourday thresholds were $893 ha^?1 and 2,978 LD ha^?1, respectively. An irrigation supply in the range of 7,000–10,000 m³ ha^?1 for the TP, MP and GR would be adequate. Assuming 20 irrigations season^?1, 400–600 m³ irrigation^?1 would be adequate, supplying 40–60 mm every 5–7 days. The study found that poor small-scale farmers in Malawi, particularly those using MPs, need fuel subsidies in order to offset operational costs. Basing on the findings in the study, we recommend further research on several bean lines in different agro-ecologies of Malawi using technologies that showed high yields, low labour efficiency and high water use productivity.     

Analysis of water application costs with a centre pivot system for irrigation of crops in Spain

The aim of this study was to present a methodology to analyse the main factors that influence annual water application costs in centre pivot irrigation systems and to determine the most cost-effective centre pivot design, given the variables of machine length, lateral pipe diameter, sprinkler type (LEPA and fixed and rotating spray plate sprinklers (FSPS and RSPS)), system capacity, application efficiency, and water and energy costs for the irrigation of crops such as maize under conditions in Spain. Annual water application costs were calculated as the sum of the investment (Ca), energy (Ce), water (Cw), and equipment maintenance costs (Cm). Parameters used to assess the influences on pivot design were system capacity S _c = 1.25 L s^?1 ha^?1; application efficiency Ea = 80% for FSPS, Ea = 85% for RSPS, and Ea = 90% for LEPA; water price P _w = 0.06 € m^?3 (0.081 US dollars); energy price En_e = 0.10 € kWh^?1 (0.135 US dollars); net annual crop irrigation water requirement N _n = 7,000 m³ ha^?1 year^?1; and net daily peak crop water requirement N _nmax = 7.63 mm d^?1 for maize. Results indicate that for plots smaller than 30 ha, the recommended pipeline diameter is 127.0 mm (5 in); for 30–40 ha, 168.3 mm (6 5/8 in); for 40–75 ha, 219.1 mm (8 5/8 in); and for 75–100 ha, 254.0 mm (10 in). A multidiameter pipe solution only slightly reduced water application costs in most cases studied. It was also determined that water costs and irrigation efficiency have a major influence on the total annual cost of water application; however, system capacity and energy price did not strongly affect total cost. For this reason, water application uniformity is very important and can be accomplished using a proper nozzle package and regular maintenance. The paper helps farmers determine the most cost-effective centre pivot design and management.     

Combining hydrological modeling and GIS approaches to determine the spatial distribution of groundwater recharge in an arid irrigation scheme

Accurate quantification of the rate of groundwater (GW) recharge, a pre-requisite for the sustainable management of GW resources, needs to capture complex processes, such as the upward flow of water under shallow GW conditions, which are often disregarded when estimating recharge at a larger scale. This paper provides (1) a method to determine GW recharge at the field level, (2) a consequent procedure for up-scaling these findings from field to irrigation scheme level and (3) an assessment of the impacts of improved irrigation efficiency on the rate of GW recharge. The study is based on field data from the 2007 growing season in a Water Users Association (WUA Shomakhulum) in Khorezm district of Uzbekistan, Central Asia, an arid region that is characterized by a predominance of cotton, wheat and rice under irrigation. Previous qualitative studies in the region reported irrigation water supplies far above the crop water requirements, which cause GW recharge. A field water balance model was adapted to the local irrigation scheme; recharge was considered to be a fraction of the irrigation water losses, determined as the difference between net and gross irrigation requirements. Capillary rise contribution from shallow GW levels was determined with the HYDRUS-1D model. Six hydrological response units (HRUs) were created based on GW levels and soil texture using GIS and remote sensing techniques. Recharge calculated at the field level was up-scaled first to these HRUs and then to the whole WUA. To quantify the impact of improved irrigation efficiency on recharge rates, four improved irrigation efficiency scenarios were developed. The area under cotton had the second highest recharge (895 mm) in the peak irrigation period, after rice with 2,514 mm. But with a low area share of rice in the WUA of <1 %, rice impacted the total recharge only marginally. Due to the higher recharge rates of cotton, which is grown on about 40 % of the cropped area, HRUs with a higher share of cotton showed higher recharge (9.6 mm day^?1 during August) than those with a lower share of cotton (4.4 mm day^?1). The high recharge rates in the cotton fields were caused by its water requirements and the special treatment given to this crop by water management planners due to its strategic importance in the country. The scenario simulations showed that seasonal recharge under improved irrigation efficiency could potentially be reduced from 4 mm day^?1 (business-as-usual scenario) to 1.4 mm day^?1 (scenario with maximum achievable efficiency). The combination of field-level modeling/monitoring and GIS approaches improved recharge estimates because spatial variability was accounted for, which can assist water managers to assess the impact of improved irrigation efficiencies on groundwater recharge. This impact assessment enables managers to identify options for a recharge policy, which is an important component of integrated management of surface and groundwater resources.     

The effects of crop load and irrigation rate in the oil accumulation stage on oil yield and water relations of ‘Koroneiki’ olives

The interactions between irrigation rates applied during the oil accumulation stage and crop load were studied in a six-year-old very-high-density Koroneiki (Olea europaea L.) orchard. Five irrigation rates, determined as thresholds of midday stem water potential, were applied from July 1st until harvest in 2008 and 2009 and from July 1st to the end of September in 2010. Oil yield increased with increasing crop load in all the irrigation treatments. Oil yield did not respond to increasing irrigation at very low crop load and the higher the crop load the higher the response to irrigation. There was no response to irrigation at the lowest crop loads, but the higher the irrigation rate the higher the oil yield at high crop loads. The predicted commercial oil yield at common fruit counts increased from 1.99 t/ha at the lowest irrigation rate to 3.06 t/ha at the highest irrigation rate. Stomatal conductance decreased with decreasing stem water potential but leveled off at 30–60 mmol m^?2 s^?1 at stem water potential values lower than ?4.0 MPa. High crop load increased stomatal conductance and decreased stem water potential relative to low crop load at low and medium irrigation rates. The effect of crop load on water relations became evident by the end of August and was well pronounced at the beginning of October. Physiological and irrigation water management implications related to the interactions between tree water status and crop load are discussed.     

Use of saline aquaculture wastewater to irrigate salt-tolerant Jerusalem artichoke and sunflower in semiarid coastal zones of China

In 2004 and 2005, the feasibility of agricultural use of saline aquaculture wastewater for irrigation of Jerusalem artichoke and sunflower was conducted in the Laizhou region using saline aquaculture wastewater mixed with brackish groundwater at different ratios. Six treatments with different electrical conductivities (EC) were included in the experiment: CK1 (rainfed), CK2 (irrigation with freshwater, EC of 0.02 dS m⁻¹), and saline aquaculture wastewater (EC of 39.2 dS m⁻¹) mixed with brackish groundwater (EC of 4.4 dS m⁻¹) at volumetric ratios of 1:1, 1:2, 1:3, and 1:4 with corresponding EC of 22.0, 16.1, 13.2, and 11.4 dS m⁻¹. Soil electrical conductivity (ECe) in the saline aquaculture wastewater irrigation treatments was significantly higher (P ≤ 0.05) than that in the rainfed or freshwater irrigation treatments, and the maximum value occurred in the 22.0 dS m⁻¹ treatment. The sodium adsorption ratio (SAR) ranged from 4.1 to 11.7 mmol^1/2 L^−1/2 and increased with decreasing salinity of irrigation water. The biomass of Jerusalem artichoke significantly decreased (P ≤ 0.05) when irrigated with saline aquaculture wastewater compared to the rainfed or freshwater irrigation treatments; however, the effect of salinity on root biomass was much smaller than the aerial parts. Concomitantly, the highest tuber yield of Jerusalem artichoke occurred in the 11.4 dS m⁻¹ treatment, while the highest seed yield of sunflower occurred in the rainfed treatment. Additionally, nitrogen and phosphorus concentrations of Jerusalem artichoke were significantly higher in the 11.4 dS m⁻¹ treatment than the other treatments. This study demonstrated that properly diluted saline aquaculture wastewater can be used successfully to irrigate Jerusalem artichoke with higher economic yield and nutrient removal, but not sunflower due to the difference in salt tolerance.     

The effect of salinity on water productivity of wheat under deficit irrigation above shallow groundwater

Saline groundwater is often found at shallow depth in irrigated areas of arid and semi-arid regions and is associated with problems of soil salinisation and land degradation. The conventional solution is to maintain a deeper water-table through provision of engineered drainage disposal systems, but the sustainability of such systems is disputed. This shallow groundwater should, however, be seen as a valuable resource, which can be utilised via capillary rise (i.e. sub-irrigation). In this way, it is possible to meet part of the crop water requirement, even where the groundwater is saline, thus decreasing the need for irrigation water and simultaneously alleviating the problem of disposing of saline drainage effluent. Management of conditions within the root zone can be achieved by means of a controlled drainage system.A series of lysimeter experiments have permitted a detailed investigation of capillary upward flow from a water-table controlled at shallow depth (1.0 m) under conditions of moderately high (5 mm/day) evaporative demand and with different levels of salinity. Experiments were conducted on a wheat crop grown in a sandy loam soil. Groundwater salinity was held at values from 2 to 8 dS/m while supplementary (deficit) irrigation was applied at the surface with salinity in the range 1-4 dS/m.Our experiments show that increased salinity decreased total water uptake by the crop, but in most treatments wheat still extracted 40% of its requirement from the groundwater, similar to the proportion reported for non-saline conditions. Yield depression was limited to 30% of maximum when the irrigation water was of relatively good quality (1 and 2 dS/m) even with saline groundwater (up to 6 dS/m). Crop water productivity (grain yield basis) was around 0.35 kg/m³ over a wide range of salinity conditions when calculated conventionally on the basis of total water use, but was generally above 1.0 kg/m³ if calculated on the basis of irrigation input only.     

Evaluation of surface irrigation as a function of water infiltration in cultivated soils in the Nile Delta

As sources of irrigation water are decreasing, efficient use of surface irrigation is essential. The purpose of this study is to determine if partially-wetted furrow irrigation has more efficient water storage and infiltration than traditional border irrigation in an alluvial clay soil under cultivated grape production. The two irrigation components considered were wet (WT) and dry (DT) treatments, at which water was applied when available soil water reached 65 % and 50 %, and the traditional border irrigation control. Empirical power form equations were obtained for measured advance and recession times along the furrow length during the irrigation stages of advance, storage, depletion and recession. Coefficient of variation (CV) was 5.2 and 9.5 % for WT and DT under furrow irrigation system comparing with 7.8 % in border, respectively. Water was deeply percolated as 11.9 and 19.2 % for wet and dry furrow treatments respectively, compared with 12.8 % for control, with no deficit in the irrigated area. Partially-wetted furrow irrigation had greater water-efficiency and grape yield than dry furrow and traditional border irrigation, where application efficiency achieved as 88.1 % for wet furrow irrigation that achieved high grape fruit yield (30.71 Mg /ha). The infiltration (cumulative depth, Z and rate, I) was functioned to opportunity time (t ₀ ) in minute for WT and DT treatments as: Z _WT ?=?0.528?t ₀ ^0.6, Z _DT ?=?1.2?t ₀ ^0.501, I _WT ?=?19?t ₀ ^?0.4, I _DT ?=?36?t ₀ ^?0.498. Empirical power form equations were obtained for measured advance and recession times along the furrow length during the irrigation stages of advance, storage, depletion and recession. The irrigation parameters and coefficients, and soil water distribution have been also evaluated.     

Corn crop response under managing different irrigation and salinity levels

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

Uptake of shallow groundwater by cotton: growth stage,groundwater salinity effects in column lysimeters

A 3-year column lysimeter experiment was conducted with cotton (Gossypium hirsutum L.) to determine the influence of shallow groundwater salinity on groundwater uptake. Nonsaline (0.3 dS m⁻¹) irrigation water was applied at 7-day intervals throughout the growing season, with the cotton allowed to use stored soil water and groundwater as root water uptake permitted. Groundwater salinities ranging from 0.3 dS m⁻¹ electrical conductivity (EC_w) to 30.8 dS m⁻¹ were evaluated. Water for leaching was applied following harvest each year in amounts adequate to produce a nonsaline soil profile at the beginning of each year. Equations were developed to describe relationships between day of year, growth stage or growing degree days and shallow groundwater uptake. Groundwater contributed about 30 to 42% of seasonal total evapotranspiration (ET) in treatments with groundwater salinity ≤ 20 dS m⁻¹ but declined to 12 to 19% of total ET at higher salinity levels.     

Effects of water quality and frequency of irrigation on growth and yield of barley (Hordeum vulgare L.)

A field trial on a loamy sand soil was carried out to study the effect of three irrigation waters with different qualities on growth and yield of ‘Gesto’, a barley (Hordeum vulgare L.) cultivar. Three irrigation water quality treatments (canal irrigation water, drainage water, and mixed canal and drainage waters at 1:1 ratio) were imposed with two irrigation frequencies (I and 2 week intervals). In addition, nitrogen and phosphorus fertilizers were applied at different rates. Barley grain and straw yields were significantly decreased under the use of drainage water (EC 10.7–16.7 dS m⁻¹), attributed mainly to reduction in the number of spikes per plant and grain weight. The mixed irrigation water (EC 6.8–9.9 dS m⁻¹) produced high seedling emergence and good vegetative growth, which was followed by high grain and straw yields. These yields were not significantly different from those under fresh canal irrigation water (EC 2.8–3.9 dS m⁻¹). Thus, mixed water could be another alternative for irrigation under similar experimental conditions especially with high rates of nitrogen (250–350 kg ha⁻¹) and phosphorus (90 kg ha⁻¹) fertilization at weekly irrigation intervals, which could eventually save more fresh irrigation canal water for other cultivated crops.     

Nitrogen fixation in a white clover-grass pasture irrigated with saline groundwater

Nitrogen (N₂) fixation in an irrigated white clover-grass sward was estimated using the ¹⁵N isotope dilution technique following the addition of K¹⁵NO₃ at 0.5 gN m^–2 and 80 atom % ¹⁵N in a field study during the 1990–91 season. Two water salinity treatments (channel water; EC_w = 0.07 and groundwater; 2.4 dS m^–1) and four irrigation frequencies were included in a factorial design with four replicates. The channel water treatments were irrigated when pan evaporation minus rainfall equalled 50 mm, whereas the groundwater treatments were irrigated at deficits of 40, 50, 65 or 80 mm. Cumulative dry matter of the clover was significantly less in treatments irrigated with saline groundwater compared to channel water at day 164, and soil salinities (EC_e) increased on average from 2.3 to 5.07 dS m^–1. In contrast, salinity of the irrigation water had no effect on the cumulative yield of grass. Cumulative dry matter of the grass and clover were not affected by groundwater irrigation frequency. Total N accumulation by the grass did not differ significantly between treatments. However, total N accumulation in white clover was significantly less (P < 0.05) in all treatments irrigated with groundwater compared to channel water. Neither the N concentrations of the grass nor the clover differed significantly between the salinity treatments. Salinity and irrigation frequency had no effect on the proportion of clover N (P_atm) derived from N₂ fixation. The values of P_atm were high throughout, and increased progressively from 0.78 at day 39 to 0.91 at day 164 (P < 0.01). However, the yield of fixed N was lower in clover when watered with groundwater compared to channel water (P < 0.01). Thus low to moderate soil salinity did not affect the symbiotic dependence of clover, but the yield of biologically-fixed N was depressed through a reduction in the dry matter yield of the legume.     

Effect of saline irrigation on germination and growth parameters of barley (Hordeum vulgare L.) in a pot experiment

The effect of saline irrigation was investigated on germination and growth parameters of six barley (Hordeum vulgare L.) cultivars in a pot experiment. The crop germination decreased between 24–35% with irrigation water having EC of 9.26 dS m⁻¹, 28–47% with water EC of 13.4 dS m⁻¹ and 30–53% with water EC of 16.28 dS m⁻¹ among various cultivars. The sequence of reduction in germination was Hassawi > Gusto > Madini > M. Khariji > Qassimi. Plant height and total number of plant tillers decreased significantly with increasing irrigation-water salinity. Plant height ranged between 39.43 cm (Qassimi cultivar) with water EC of 3.00 dS m⁻¹ to 1.97 cm (Gusto) with water EC of 16.28 dS m⁻¹ whereas the range for total number of plant tillers per pot was 77.00 (Qassimi) with irrigation EC of 3.00 dS m⁻¹ to 9.67 (Gusto) with irrigation EC of 16.28 dS m⁻¹. The trend of reduction in plant height for different cultivars was Gusto > Qassimi > Hassawi > Madini > M. Khariji whereas for plant tillers, the sequence was Gusto < Hassawi < M. Khariji < Qassimi < Madini. Greenmatter and drymatter yield decreased significantly with increasing irrigation water salinity. The greenmatter yield ranged between 138.67 g per pot (Madini) with water EC of 3.00 dS m⁻¹ to 11.40 g per pot (Gusto) with water EC of 16.28 dS m⁻¹. A similar trend was found for drymatter yield. The trend of reduction in yield among various cultivars (both greenmatter and drymatter) was Gusto > Hassawi > M. Khariji > Qassimi > Madini. Overall sequence of salt tolerance for different barley cultivars was Madini > Qassimi > M. Khariji > Hassawi > Gusto. A comparison of cultivars indicated that irrigation waters with EC 13.40 dS m⁻¹ and above reduced crop germination and greenmatter production to a significant level. In conclusion, there exists a lot of potential for a reasonable production of barley as forage crop with irrigation water having salinity up to 9.26 dS m⁻¹ provided 15% extra water above crop-water requirement is applied as leaching requirements to control soil salinity.     

On the magnitude and dynamics of eddy covariance system residual energy (energy balance closure error) in subsurface drip-irrigated maize field during growing and non-growing (dormant) seasons

We investigated the magnitude and dynamics of the eddy covariance system (ECS) residual energy (energy balance closure error) for a subsurface drip-irrigated maize (Zea mays L.) field in 2005 and 2006 growing and non-growing (dormant) seasons. The corrections for coordinate rotation, oxygen, frequency, and Webb–Pearman–Leuning corrections improved the slope of the total convective energy (latent heat + sensible heat) with respect to the net available energy (from 0.68 to 0.84), but the data filtering (for horizontal and frictional wind speeds higher than 2 m s^?1 and lower than 0.2 m s^?1) had little effect on the slope. Also, the number of data points available for the analyses was reduced by 53 % after filtering. Overall, the daytime residual energy varied between ?100 and 200 W m^?2 during the dormant seasons and between ?500 and 600 W m^?2 during the growing seasons. Most of the nighttime residual energy ranged within ±40 W m^?2 during the calendar year in 2005 and within ?60 and 20 W m^?2 in 2006. During nighttime, the total convective energy is vertically distributed with respect to (R _n ? G), indicating that the total convective energy is independent of the variations in (R _n ? G). Secondly, it was observed that nighttime residual energy did not show any seasonal variation patterns throughout the two consecutive years and confined mostly within a narrow range of ±40 W m^?2, showing no dependency on seasonal changes in surface conditions. The maximum variation in residual energy was usually around frictional wind speed of 0.3–0.5 m s^?1 (varying between ?150 and 300 W m^?2) and then decreasing to a range of ±100 W m^?2 at higher frictional wind speeds. On average, the residual energy decreased by about 33 W m^?2 (after the intercept) for every 1.0 m s^?1 increase in frictional wind speed, whereas the residual energy decreased by about 4 W m^?2 (after the intercept) for every 1.0 m s^?1 increase in horizontal wind speed. Similar diurnal residual energy distribution patterns, with different magnitudes, were observed during growing and dormant seasons. Even though a slight decrease in residual energy was observed with increase in leaf area index (LAI) in both growing seasons, LAI did not have considerable influence on the seasonal variation in the residual energy. The residual energy was also evaluated by separating the data into morning and afternoon hours. We observed that the root-mean-squared difference value is slightly greater for the morning data than the afternoon, indicating greater residual energy in the morning hours due to weaker turbulent mixing than the afternoon. Overall, significant reduction in the available evapotranspiration data after applying a series of corrections possess challenges in terms of utilization of ECS for in-season irrigation management and crop water requirement determinations that needs to be further researched and addressed.     

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.