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.     

Consumptive water use and crop coefficients of irrigated sunflower

In semi-arid environments, the use of irrigation is necessary for sunflower production to reach its maximum potential. The aim of this study was to quantify the consumptive water use and crop coefficients of irrigated sunflower (Helianthus annuus L.) without soil water limitations during two growing seasons. The experimental work was conducted in the lysimeter facilities located in Albacete (Central Spain). A weighing lysimeter with an overall resolution of 250 g was used to measure the daily sunflower evapotranspiration throughout the growing season under sprinkler irrigation. The lysimeter container was 2.3 m × 2.7 m × 1.7 m deep, with an approximate total weight of 14.5 Mg. Daily ET _c values were calculated as the difference between lysimeter mass losses and lysimeter mass gains divided by the lysimeter area. In the lysimeter, sprinkler irrigation was applied to replace cumulative ET _c, thus maintaining non-limiting soil water conditions. Seasonal lysimeter ET _c was 619 mm in 2009 and 576 mm in 2011. The higher ET _c value in 2009 was due to earlier planting and a longer growing season with the maximum cover coinciding with the maximum ET _o period. For the two study years, maximum average K _c values reached values of approximately 1.10 and 1.20, respectively, during mid-season stage and coincided with maximum ground cover values of 75 and 88 %, respectively. The dual crop coefficient approach was used to separate crop transpiration (K _cb) from soil evaporation (K _e). As the crop canopy expanded, K _cb values increased while the K _e values decreased. The seasonal evaporation component was estimated to be about 25 % of ET _c. Linear relationships were found between the lysimeter K _cb and the canopy ground cover (f _c) for the each season, and a single relationship that related K _cb to growing degree-days was established allowing extrapolation of our results to other environments.     

The contribution of shallow groundwater by safflower (Carthamus tinctorius L.) under high water table conditions, with and without supplementary irrigation

Lysimetric experiments were conducted to determine the contribution made by groundwater to the overall water requirements of safflower (Carthamus tinctorius L.). The plants were grown in 24 columns, each having a diameter of 0.40 m and packed with silty clay soil. The four replicate randomized complete block factorial experiments were carried out using different treatment combinations. Six treatments were applied during each experiment by maintaining groundwater, with an EC of 1 dS m^?1, at three different water table levels (0.6, 0.8 and 1.10 m) with and without supplementary irrigation. The uptake of groundwater as a part of crop evapotranspiration was measured by taking daily readings of the water levels found in Mariotte tubes. The supplementary irrigation requirement for each treatment was applied by adding water (EC of 1 dS m^?1). The average percentage contribution from groundwater for the treatments (with and without supplementary irrigation under water table levels of 0.6, 0.8 and 1.10 m) were found to be 65, 59, 38% and 72, 70, 47% of the average annual safflower water requirement (6,466 m³ ha^?1). The increase in groundwater depths under supplementary irrigation treatments from 0.6 to 0.80 and 1.10 m caused seed and oil yield reductions of (7, 23.10%) and (48.23, 65.40%), respectively.     

Water use and the development of seasonal crop coefficients for Superior Seedless grapevines trained to an open-gable trellis system

Water consumption of table grapevines (Vitis vinifera cv. Superior Seedless) trained to a large open-canopy gable system was measured during six growing seasons (1999, 2001–2005) using 12 drainage lysimeters. The lysimeters (1.3 m³ each) were installed as part of a one-hectare vineyard in a semi-arid region in southern Israel. Water consumption of the lysimeter-grown vines (ET_c) was used as the basis for the calculation of irrigation applications in the vineyard. Three irrigation treatments, 80% (high), 60% (medium) and 40% (low) of ET_c of the lysimeter-grown vines, were applied in the vineyard. Reference evapotranspiration (ET_o) was calculated from regional meteorological data according to the Penman–Monteith equation. Seasonal curves for the crop coefficient (K _c) were calculated as K _c = ET_c/ET_o. Maximum ET_c values in different seasons ranged from 7.26 to 8.59 mm day⁻¹ and seasonal ET_c (from DOY 91 through DOY 304) ranged from 1,087 to 1,348 mm over the six growing seasons. Leaf area index (LAI) was measured monthly using the SunScan Canopy Analysis System. Maximum LAI ranged from 4.2 to 6.2 m² m⁻² for the 2002–2005 seasons. A second-order polynomial curve relating K _c to LAI (R² = 0.907, P < 0.0001) is proposed as the basis for efficient irrigation management. The effects of the irrigation treatments on canopy growth and yield are presented. The high ET_c and K _c values that were observed are explained by the wide canopy layout that characterize the large open-gable trellis system.     

Evapotranspiration and responses to irrigation of broccoli

In cold, semi-arid areas, the options for crop diversification are limited by climate and by the water supply available. Growing irrigated crops outside the main season is not easy, because of climatic and market constraints. We carried out an experiment in Albacete, Central Spain, to measure the water use (evapotranspiration, ET) of broccoli (Brassica oleracea L. var. italica Plenck) planted in late summer and harvested at the end of fall. A weighing lysimeter was used to measure the seasonal ET under sprinkler irrigation. Consumptive use reached 359 mm for a period of 109 days after transplanting. The crop coefficient (K_c) for broccoli was obtained and compared to the standard recommendations for normal planting dates. Dual crop coefficient computations of the lysimeter ET data indicated that evaporation represented 31% of seasonal ET. An analysis of the variation in daily K_c values at a time of full cover suggested that the use of a grass lysimeter as a reference ET (ET_o) was superior to using the ASCE Penman-Monteith (ASCE PM) equation at hourly time steps, which in turn caused less variability in K_c than when using the FAO-56 Penman-Monteith (FAO-56 PM) equation at daily time steps for the ET_o calculation. An additional experiment aimed at evaluating the yield response to applied irrigation water by the drip method (seven treatments, from 59 to 108% of ET_c) generated a production function that gave maximum yields of near 12 t ha⁻¹ at an irrigation level of 345 mm, and a water use efficiency of 3.37 kg m⁻³. It is concluded that growing broccoli in the fall season is a viable alternative for crop diversification, as the lower yields obtained here may be more than compensated for by the higher produce prices in autumn, at a time of the year where irrigation water demand for other crops is very low.     

Net irrigation requirements for Florida turfgrasses

A long-term (30 year) historical analysis of turfgrass monthly net irrigation requirements for southeast USA is analyzed and discussed in this paper. The process involved gathering weather data for ten locations in Florida plus one in Alabama, from 1980 through 2009, and data quality. Available weather data included maximum and minimum temperature, maximum and minimum relative humidity, wind speed, and rainfall. Solar radiation was estimated using the Hargreaves–Samani equation, and coefficients were calibrated for every location. Reference evapotranspiration (ET_os) was calculated using the ASCE-EWRI standardized reference evapotranspiration equation. Net irrigation was estimated using a daily soil–water balance. Variability in soil types and root depth was taken into account during the simulations, and three sets of monthly K _c values from the literature were applied from north through south Florida. Results showed that the calibrated Hargreaves–Samani adjustment coefficients varied from 0.14 in Tallahassee to 0.24 in Key West, with an inland average value of 0.15, and a coastal average value of 0.18. The calculated ET_os ranged from 1,296 mm year^?1 in Tallahassee to 1,658 mm year^?1 in Miami. The estimated net irrigation ranged from 423 mm year^?1 in Mobile, AL, to 1,063 mm year^?1 in Key West, FL. The number of irrigation events per year varied from 25 in Mobile to 161 in Key West. May and December were the months with the highest and lowest net irrigation requirements, respectively.     

Estimation of dwarf green bean water use under semi-arid climate conditions through ground-based remote sensing techniques

Determination of temporal and spatial distribution of water use (WU) within agricultural land is critical for irrigation management and could be achieved by remotely sensed data. The aim of this study was to estimate WU of dwarf green beans under excessive and limited irrigation water application conditions through indicators based on remotely sensed data. For this purpose, field experiments were conducted comprising of six different irrigation water levels. Soil water content, climatic parameters, canopy temperature and spectral reflectance were all monitored. Reference evapotranspiration (ET₀), crop coefficient K_c and potential crop evapotraspiration (ET_c) were calculated by means of methods described in FAO-56. In addition, WU values were determined by using soil water balance residual and various indexes were calculated. Water use fraction (WUF), which represents both excessive and limited irrigation applications, was defined through WU, ET₀ and K_c. Based on the relationships between WUF and remotely sensed indexes, WU of each irrigation treatments were then estimated. According to comparisons between estimated and measured WU, in general crop water stress index (CWSI) can be offered for monitoring of irrigated land. At the same time, under water stress, correlation between measured WU and estimated WU based on CWSI was the highest too. However, canopy-air temperature difference (T_c − T_a) is more reliable than others for excessive water use conditions. Where there is no data related to canopy temperature, some of spectral vegetation indexes could be preferable in the estimation of WU.     

Production and water use in lettuces under variable water supply

The effects of a variable water supply on the water use, growth and yield of two crisphead and one romaine (i.e., Cos) lettuce cultivar were examined in a field experiment using a line source sprinkler system that produced a range of water regimes that occur in growers fields. Four locations at increasing distances from the main line were monitored through the season (i.e., from thinning to harvest, 28–63 days after planting (DAP)). These locations at the end of the season corresponded to: (1) rewatering to field capacity (FC); (2) watering with a volume 13% below that required in the field capacity treatment (0.87*FC); (3) 30% below FC (0.70*FC); and (4) 55% below FC (0.45*FC). A linear production function for dry matter accumulation and fresh weight vs. crop evapotranspiration (ET_c) was determined for lettuce during this period, giving a water use efficiency for dry matter of 1.86 g m^–2 mm^–1 and for fresh weight of 48 g m^–2 mm^–1 . For lettuce irrigated to field capacity, ET_c between thinning and harvest was 146 mm; maximum crop coefficients of 0.81–1.02 were obtained at maturity (55–63 DAP). For the three irrigation treatments receiving the largest water application, ET_c was higher in the Cos culivar than in the two crisphead lettuce cultivars which had similar ET_c. Plant fresh weight was more sensitive than dry weight to reduction in water supply. In the FC treatment, root length density and soil water extraction were greatest in the top 0–45 cm, and decreased rapidly below 45 cm depth. Soil water extraction by roots increased at lower depths when irrigation was reduced. Instantaneous rates of leaf photosynthesis and leaf water potential showed no response to the irrigation treatments in this study, despite differences in biomass production. Evaporation was determined to be the major component of ET_c for 45 of the 63 days of the growing season. The large loss of water by evaporation during mid-season and the apparent insensitivity of lettuce to the volume of irrigation during this period may provide an opportunity for reducing irrigation applications.     

Evapotranspiration and crop coefficients of irrigated biomass sorghum for energy production

New cultivars of sorghum for biomass energy production are currently available. This crop has a positive energy balance being irrigation water the largest energy consumer during the growing cycle. Thence, it is important to know the biomass sorghum water requirements, in order to minimize irrigation losses, thus saving water and energy. The objective of this study was to quantify the water use and crop coefficients of irrigated biomass sorghum without soil water limitations during two growing seasons. A weighing lysimeter located in Albacete (Central Spain) was used to measure the daily biomass sorghum evapotranspiration (ET_c) throughout the growing season under sprinkler irrigation. Seasonal lysimeter ET_c was 721 mm in 2007 and 691 mm in 2010. The 4 % higher ET_c value in 2007 was due to an 8 % higher evaporative demand in that year. Maximum average K _c values of 1.17 in 2007 and 1.21 in 2010 were reached during the mid-season stage. The average K _c values for the 2 years of study were K _c-ini: 0.64 and K _c-mid: 1.19. The seasonal evaporation component was estimated to be about 18 % of ET_c. The average basal K _c (K _cb) values for the two study years were K _cb-ini: 0.11 and K _cb-mid: 1.17. The good linear relationship found between K _cb values and the fraction of ground cover (f _c) and the excellent agreement found between Normalized Difference Vegetation Index and different biophysical parameters, such as K _cb and f _c, will allow monitoring and estimating the spatially distributed water requirements of biomass sorghum at field and regional scales.     

Almond agronomic response to long-term deficit irrigation applied since orchard establishment

This study assesses the long-term suitability of regulated (RDI) and sustained deficit irrigation (SDI) implemented over the first six growing seasons of an almond [Prunus dulcis (Mill.) D.A. Webb] orchard grown in a semiarid area in SE Spain. Four irrigation treatments were assessed: (i) full irrigation (FI), irrigated to satisfy maximum crop evapotranspiration (100% ET_c); (ii) RDI, as FI but receiving 40% ET_c during kernel-filling; (iii) mild-to-moderate SDI (SDI_mm), irrigated at 75–60% ET_c over the entire growing season; and (iv) moderate-to-severe SDI (SDI_ms), irrigated at 60–30% ET_c over the whole season. Application of water stress from orchard establishment did not amplify the negative effects of deficit irrigation on almond yield. Irrigation water productivity (IWP) increased proportionally to the mean relative water shortage. SDI_ms increased IWP by 92.5%, reduced yield by 29% and applied 63% less irrigation water. RDI and SDI_mm showed similar productive performances, but RDI was more efficient than SDI_mm to increase fruiting density and production efficiency (PE). We conclude that SDI_ms appears to be a promising DI option for arid regions with severe water scarcity, whereas for less water-scarce areas RDI and SDI_mm behaved similarly, except for the ability of RDI to more severely restrict vegetative development while increasing PE.     

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.     

Evapotranspiration and water use of full and deficit irrigated cotton in the Mediterranean environment in northern Syria

Cotton (Gossypium hirsutum L.) is the most important industrial and summer cash crop in Syria and many other countries in the arid areas but there are concerns about future production levels, given the high water requirements and the decline in water availability. Most farmers in Syria aim to maximize yield per unit of land regardless of the quantity of water applied. Water losses can be reduced and water productivity (yield per unit of water consumed) improved by applying deficit irrigation, but this requires a better understanding of crop response to various levels of water stress. This paper presents results from a 3-year study (2004-2006) conducted in northern Syria to quantify cotton yield response to different levels of water and fertilizer. The experiment included four irrigation levels and three levels of nitrogen (N) fertilizer under drip irrigation. The overall mean cotton (lint plus seed, or lintseed) yield was 2502 kg ha⁻¹, ranging from 1520 kg ha⁻¹ under 40% irrigation to 3460 kg ha⁻¹ under 100% irrigation. Mean water productivity (WP_ET) was 0.36 kg lintseed per m³ of crop actual evapotranspiration (ET_c), ranging from 0.32 kg m⁻³ under 40% irrigation to 0.39 kg m⁻³ under the 100% treatment. Results suggest that deficit irrigation does not improve biological water productivity of drip-irrigated cotton. Water and fertilizer levels (especially the former) have significant effects on yield, crop growth and WP_ET. Water, but not N level, has a highly significant effect on crop ET_c. The study provides production functions relating cotton yield to ET_c as well as soil water content at planting. These functions are useful for irrigation optimization and for forecasting the impact of water rationing and drought on regional water budgets and agricultural economies. The WP_ET values obtained in this study compare well with those reported from the southwestern USA, Argentina and other developed cotton producing regions. Most importantly, these WP_ET values are double the current values in Syria, suggesting that improved irrigation water and system management can improve WP_ET, and thus enhance conservation and sustainability in this water-scarce region.     

Effects of irrigation using treated wastewater on table grape vineyards: dynamics of sodium accumulation in soil and plant

The effect of using treated wastewater for irrigation of table grapes (Vitis vinifera cv. Superior Seedless) was studied for six seasons. The experimental vineyard was grown on clay loam soil in a semi-arid area. Treated wastewater (5.83 meq L^?1 Na⁺) with (TWW + F) and without (TWW) fertilizer, and fresh water with fertilizer (FW + F, 2.97 meq L^?1 Na⁺), were each applied at three irrigation levels (80, 60 and 40 % of crop evapotranspiration before harvest). Root zone (0–60 cm soil depth) soil saturated paste extract Na⁺ concentrations and sodium adsorption ratio (SAR) values fluctuated over the years, but generally decreased in the order TWW > TWW + F > FW + F for each irrigation level. Both Na⁺ concentrations and SAR values developed faster and to a greater extent at higher irrigation. Adding fertilizer to TWW decreased Na⁺ and SAR only at the high irrigation level. Na⁺ concentrations in the trunk wood, bark and xylem sap of the TWW and TWW + F irrigated vines were significantly higher than those in the FW + F-irrigated vines. Leaf petiole Na⁺ content increased with time and its maximum value in TWW and TWW + F irrigated vines exceeded 6,500 mg kg^?1, threefold higher than in FW + F irrigated vines. We conclude that in clay soils under relatively high irrigation, Na⁺ may pose a greater potential risk to plants and soil rather than Cl^? or salinity per se. However, significant effects on yield were not recorded during this six-year study probably due to the high salinity tolerance of the ‘Paulsen’ rootstock used in the experiment.     

Irrigation scheduling of plastic greenhouse vegetable crops based on historical weather data

Irrigation scheduling based on the daily historical crop evapotranspiration (ET_h) data was theoretically and experimentally assessed for the major soil-grown greenhouse horticultural crops on the Almería coast in order to improve irrigation efficiency. Overall, the simulated seasonal ET_h values for different crop cycles from 41 greenhouses were not significantly different from the corresponding values of real-time crop evapotranspiration (ET_c). Additionally, for the main greenhouse crops on the Almería coast, the simulated values of the maximum cumulative soil water deficit in each of the 15 consecutive growth cycles (1988–2002) were determined using simple soil-water balances comparing daily ET_h and ET_c values to schedule irrigation. In most cases, no soil-water deficits affecting greenhouse crop productivity were detected, but the few cases found led us to also assess experimentally the use of ET_h for irrigation scheduling of greenhouse horticultural crops. The response of five greenhouse crops to water applications scheduled with daily estimates of ET_h and ET_c was evaluated in a typical enarenado soil. In tomato, fruit yield did not differ statistically between irrigation treatments, but the spring green bean irrigated using the ET_h data presented lower yield than that irrigated using the ET_c data. In the remaining experiments, the irrigation-management method based on ET_h data was modified to consider the standard deviation of the inter-annual greenhouse reference ET. No differences between irrigation treatments were found for productivity of pepper, zucchini and melon crops.     

The dual crop coefficient approach to estimate and partitioning evapotranspiration of the winter wheat–summer maize crop sequence in North China Plain

An accurate estimation of crop evapotranspiration (ET _c) is very useful for appropriate water management; hence, an accurate and user-friendly model is needed to support related irrigation decisions. In this view, a study was developed aimed at estimating the ET _c of winter wheat–summer maize crop sequence in the North China through eddy covariance measurements, to calibrate and validate the SIMDualKc model, to estimate the basal crop coefficients (K _cb) for both crops and to partition ET _c into soil evaporation and crop transpiration. Two years of field experimentation of that crop sequence were used to calibrate and validate the SIMDualKc model and to derive K _cb using eddy covariance measurements. Various indicators have shown the goodness of fit of the model, with estimated values very close to the observed ones and estimate errors close to 0.5 mm d^?1. The initial, mid-season and end basal crop coefficients for wheat were 0.25, 1.15 and 0.30, respectively, and those for maize were 0.15, 1.15 and 0.45, thus close to those proposed in FAO56 guidelines. The soil evaporation represented near 80 % of ET _c for the initial stages of winter wheat and summer maize and decreased to only 5–6 % during the mid-season period. Evaporation during the full crop season averaged 28 % for winter wheat and 40 % for summer maize. The importance of wetting frequency and crop ground coverage in controlling soil evaporation was evidenced.     

Evaluation of crop water stress index for LEPA irrigated corn

This study was designed to evaluate the crop water stress index (CWSI) for low-energy precision application (LEPA) irrigated corn (Zea mays L.) grown on slowly-permeable Pullman clay loam soil (fine, mixed, Torrertic Paleustoll) during the 1992 growing season at Bushland, Tex. The effects of six different irrigation levels (100%, 80%, 60%, 40%, 20%, and 0% replenishment of soil water depleted from the 1.5-m soil profile depth) on corn yields and the resulting CWSI were investigated. Irrigations were applied in 25 mm increments to maintain the soil water in the 100% treatment within 60–80% of the “plant extractable soil water” using LEPA technology, which wets alternate furrows only. The 1992 growing season was slightly wetter than normal. Thus, irrigation water use was less than normal, but the corn dry matter and grain yield were still significantly increased by irrigation. The yield, water use, and water use efficiency of fully irrigated corn were 1.246 kg/m², 786 mm, and 1.34 kg/m³, respectively. CWSI was calculated from measurements of infrared canopy temperatures, ambient air temperatures, and vapor pressure deficit values for the six irrigation levels. A “non-water-stressed baseline” equation for corn was developed using the diurnal infrared canopy temperature measurements as T _c–T _a = 1.06–2.56 VPD, where T _c was the canopy temperature (°C), Ta was the air temperature (°C) and VPD was the vapor pressure deficit (kPa). Trends in CWSI values were consistent with the soil water contents induced by the deficit irrigations. Both the dry matter and grain yields decreased with increased soil water deficit. Minimal yield reductions were observed at a threshold CWSI value of 0.33 or less for corn. The CWSI was useful for evaluating crop water stress in corn and should be a valuable tool to assist irrigation decision making together with soil water measurements and/or evapotranspiration models. Received: 19 May 1998     

Mapping and assessing water use in a Central Asian irrigation system by utilizing MODIS remote sensing products

Spatial and temporal patterns of water depletion in the irrigated land of Khorezm, a region located in Central Asia in the lower floodplains of the Amu Darya River, were mapped and monitored by means of MODIS land products. Land cover and land use were classified by using a recursive partitioning and regression tree with 250 m MODIS Normalized Difference Vegetation Index (NDVI) time series. Seasonal actual evapotranspiration (ET_act) was obtained by applying the Surface Energy Balance Algorithm for Land (SEBAL) to 1 km daily MODIS data. Elements of the SEBAL based METRIC model (Mapping Evapotranspiration at high Resolution and with Internalized Calibration) were adopted and modified. The upstream–downstream difference in irrigation was reflected by analyzing agricultural land use and amounts of depleted water (ET_act) using Geographical Information Systems (GIS). The validity of the MODIS albedo and emissivity used for modeling ET_act was assessed with data extracted from literature. The r ² value of 0.6 indicated a moderate but significant association between ET_act and class-A-pan evaporation. Deviations of ET_act from the 10-day reference evapotranspiration of wheat and cotton were found to be explainable. In Khorezm, seasonal maximum values superior to 1,200 and 1,000 mm ET_act were estimated for rice and cotton fields, respectively. Spatio-temporal comparisons of agricultural land use with seasonal ET_act disclosed unequal water consumption in Khorezm. Seasonal ET_act on agricultural land decreased with increasing distance to the water intake points of the irrigation system (972–712 mm). Free MODIS data provided reliable, exhaustive, and consistent information on water use relevant for decision support in Central Asian water management.     

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.     

Foliar and yield response of Santa rosa plum to saline water spray

Summary Canopies of 22-year-old Santa Rosa plum trees irrigated with mini-sprinklers below the canopy with nonsaline (0.3 dS/m) water were sprayed weekly during one irrigation season with water having six levels of salinity (0.3, 1.1, 2.1, 3.3, 4.5, and 6.8 dS/m) to evaluate the extent of leaf injury, foliar absorption of Cl and Na, and yield response. Recognizable leaf injury was caused by spray water containing 29 mol/m³ of chloride and 15 mol/m³ of sodium. Severe leaf damage occurred when the leaf chloride and sodium concentrations exceeded 300 and 125 mmol/kg (dry weight), respectively. These concentrations were higher than those causing foliar damage on other trees in the same orchard which had been irrigated below the canopy with water having the same salinity as that sprayed on the canopy. No residual foliar injury was observed during the irrigation season following the year when the spray treatments were applied. Fruit yield measured six weeks after treatments were initiated was unaffected. In the following 2 years, yield was reduced by the highest salinity levels, even though the salt spray treatments were not continued and no foliar injury was visible.     

Growth and yield responses of almond (Prunus amygdalus) to trickle irrigation

Growth and yield responses of developing almond trees (Prunus amygdalus, Ruby cultivar) to a range of trickle irrigation amounts were determined in 1985 through 1987 (the fifth through seventh year after planting) at the University of California's West Side Field Station in the semi-arid San Joaquin Valley. The treatments consisted of six levels of irrigation, ranging from 50 through 175% of the estimated crop evapotranspiration (ET_c), applied to a clean-cultivated orchard using a line source trickle irrigation system with 6 emitters per tree. ET_c was estimated as grass reference evapotranspiration (ET₀) times a crop coefficient with adjustments based upon shaded area of trees and period during the growing season. Differential irrigation experiments prior to 1984 on the trees used in this study significantly influenced the initial trunk cross-section area and canopy size in the 50% ET_c treatment and 125% ET_c treatment. In these cases, treatment effects must be identified as relative effects rather than absolute. The soil of the experimental field was a Panoche clay loam (nonacid, thermic, Typic Torriorthents). The mean increase in trunk cross-sectional area for the 3-year period was a positive linear function (r ² = 0.98) of total amounts of applied water. With increases in water application above the 50% ET_c treatment, nut retention with respect to flower and fertile nut counts after flowering, was increased approximately 10%. In 1985 and 1987, the nut meat yields and mean kernel weights increased significantly with increasing water application from 50% to 150% ET_c. Particularly in the higher water application treatments, crop consumptive use was difficult to quantify due to uncertainty in estimates of deep percolation and soil water uptake. Maintenance of leaf water potentials higher than –2.3 MPa during early nut development (March through May) and greater than –2.5 MPa the remainder of the irrigation season (through August) were positively correlated with sustained higher vegetative growth rates and higher nut yields.