Long-term growth, water consumption and yield of date palm as a function of salinity

Actual measurements of water uptake and use, and the effect of water quality considerations on evapotranspiration (ET), are indispensable for understanding root zone processes and for the development of predictive plant growth models. The driving hypothesis of this research was that root zone stress response mechanisms in perennial fruit tree crops is dynamic and dependent on tree maturity and reproductive capability. This was tested by investigating long-term ET, biomass production and fruit yield in date palms (Phoenix dactylifera L., cv. Medjool) under conditions of salinity. Elevated salinity levels in the soil solution were maintained for 6 years in large weighing-drainage lysimeters by irrigation with water having electrical conductivity (EC) of 1.8, 4, 8 and 12 dS m⁻¹. Salinity acted dynamically with a long-term consequence of increasing relative negative response to water consumption and plant growth that may be explained either as an accumulated effect or increasing sensitivity. Sensitivity to salinity stabilized at the highest measured levels after the trees matured and began producing fruit. Date palms were found to be much less tolerant to salinity than expected based on previous literature. Trees irrigated with low salinity (EC = 1.8 dS m⁻¹) water were almost twice the size (based on ET and growth rates) than trees irrigated with EC = 4 dS m⁻¹ water after 5 years. Fruit production of the larger trees was 35-50% greater than for the smaller, salt affected, trees. Long term irrigation with very high EC of irrigation water (8 and 12 dS m⁻¹) was found to be commercially impractical as growth and yield were severely reduced. The results raise questions regarding the nature of mechanisms for salinity tolerance in date palms, indicate incentives to irrigate dates with higher rather than lower quality water, and present a particular challenge for modelers to correctly choose salinity response functions for dates as well as other perennial crops.     

Effects of salinity and fertigation practice on cotton yield and N recovery

The purpose of optimal water and nutrient management is to maximize water and fertilizer use efficiency and crop production, and to minimize groundwater pollution. In this study, field experiments were conducted to investigate the effect of soil salinity and N fertigation strategy on plant growth, N uptake, as well as plant and soil ¹⁵N recovery. The experimental design was a 3 × 3 factorial with three soil salinity levels (2.5, 6.3, and 10.8 dS m⁻¹) and three N fertigation strategies (N applied at the beginning, end, and in the middle of an irrigation cycle). Seed cotton yield, dry matter, N uptake, and plant ¹⁵N recovery significantly increased as soil salinity level increased from 2.5 to 6.3 dS m⁻¹, but they decreased markedly at higher soil salinity of 10.8 dS m⁻¹. Soil ¹⁵N recovery was higher under soil salinity of 10.8 dS m⁻¹ than those under soil salinity of 6.3 dS m⁻¹, but was not significantly different from that under soil salinity of 2.5 dS m⁻¹. The fertigation strategy that nitrogen applied at the beginning of an irrigation cycle had the highest seed cotton yield and plant ¹⁵N recovery, but showed higher potential loss of fertilizer N from the root zone. While the fertigation strategy of applying N at the end of an irrigation cycle tended to avoid potential N loss from the root zone, it had the lowest cotton yield and nitrogen use efficiency. Total ¹⁵N recovery was not significantly affected by soil salinity, fertigation strategy, and their interaction. These results suggest that applying nitrogen at the beginning of an irrigation cycle has an advantage on promoting yield and fertilizer use efficiency, therefore, is an agronomically efficient way to provide cotton with fertilizer N under the given production conditions.     

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.     

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.     

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

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

Soil salinity related to physical soil characteristics and irrigation management in four Mediterranean irrigation districts

Irrigated agriculture is threatened by soil salinity in numerous arid and semiarid areas of the Mediterranean basin. The objective of this work was to quantify soil salinity through electromagnetic induction (EMI) techniques and relate it to the physical characteristics and irrigation management of four Mediterranean irrigation districts located in Morocco, Spain, Tunisia and Turkey. The volume and salinity of the main water inputs (irrigation and precipitation) and outputs (crop evapotranspiration and drainage) were measured or estimated in each district. Soil salinity (EC_e) maps were obtained through electromagnetic induction surveys (EC_a readings) and district-specific EC_a-EC_e calibrations. Gravimetric soil water content (WC) and soil saturation percentage (SP) were also measured in the soil calibration samples. The EC_a-EC_e calibration equations were highly significant (P < 0.001) in all districts. EC_a was not significantly correlated (P > 0.1) with WC, and was only significantly correlated (P < 0.1) with soil texture (estimated by SP) in Spain. Hence, EC_a mainly depended upon EC_e, so that the maps developed could be used effectively to assess soil salinity and its spatial variability. The surface-weighted average EC_e values were low to moderate, and ranked the districts in the order: Tunisia (3.4 dS m⁻¹) > Morocco (2.2 dS m⁻¹) > Spain (1.4 dS m⁻¹) > Turkey (0.45 dS m⁻¹). Soil salinity was mainly affected by irrigation water salinity and irrigation efficiency. Drainage water salinity at the exit of each district was mostly affected by soil salinity and irrigation efficiency, with values very high in Tunisia (9.0 dS m⁻¹), high in Spain (4.6 dS m⁻¹), moderate in Morocco (estimated at 2.6 dS m⁻¹), and low in Turkey (1.4 dS m⁻¹). Salt loads in drainage waters, calculated from their salinity (EC_dw) and volume (Q), were highest in Tunisia (very high Q and very high EC_dw), intermediate in Turkey (extremely high Q and low EC_dw) and lowest in Spain (very low Q and high EC_dw) (there were no Q data for Morocco). Reduction of these high drainage volumes through sound irrigation management would be the most efficient way to control the off-site salt-pollution caused by these Mediterranean irrigation districts.     

Evaluating salinity distribution in soil irrigated with saline water in arid regions of northwest China

In arid and semi-arid regions, salinity is a serious and chronic problem for agriculture. A 3-year field experiment in the arid environment of Xinjiang, northwest China, was conducted to study the salinity change in soil resulting from deficit irrigation of cotton with non-saline, moderate saline and high saline water. The salinity profile distribution was also evaluated by an integrated water, salinity, and nitrogen model, ENVIRO-GRO. The simulated and observed salinity distributions matched well. Results indicated that after 3 years of cotton production, the average salinity in the 1.0-m soil profile was 336% and 547% of the original soil profile, respectively, for moderate saline and high saline water irrigation. If the practices continued, the average soil salinity (EC_e) in the 1.0-m soil profile would approach a steady level of 1.7, 10.8, and 14.7 dS m⁻¹, respectively, for the treatments receiving irrigation waters of 0.33, 3.62, and 6.71 dS m⁻¹. It was concluded that deficit irrigation of saline water in this region was not sustainable. Model simulation showed that a big flood irrigation after harvest can significantly reduce the salt accumulation in the soil profile, and that this practice was much more efficient for salinity control than applying the same extra amount of water during the growing season.     

Long term responses of olive trees to salinity

Water demand for irrigation is increasing in olive orchards due to enhanced yields and profits. Because olive trees are considered moderately tolerant to salinity, irrigation water with salt concentrations that can be harmful for many of fruit tree crops is often used without considering the possible negative effects on olive tree growth and yield. We studied salt effects in mature olive trees in a long term field experiment (1998-2006). Eighteen-year-old olive trees (Olea europaea L.) cv. Picual were cultivated under drip irrigation with saline water composed of a mixture of NaCl and CaCl₂. Three irrigation regimes (i. no irrigation; ii. water application considering soil water reserves, short irrigation; iii. water application without considering soil water reserves and adding a 20% more as a leaching fraction, long irrigation) and three salt concentrations (0.5, 5 or 10 dS m⁻¹) were applied. Treatments were the result of the combination of three salt concentrations with two irrigation regimes, plus the non-irrigated treatment. Growth parameters, leaf and fruit nutrition, yield, oil content and fruit characteristics were annually studied. Annual leaf nutrient analyses indicate that all nutrients were within the adequate levels. After 8 years of treatment, salinity did not affect any growth measurement and leaf Na⁺ and Cl⁻ concentration were always below the toxicity threshold of 0.2 and 0.5%, respectively. Annual and accumulated yield, fruit size and pulp:stone ratio were also not affected by salts. However, oil content increased linearly with salinity, in most of the years studied. Soil salinity measurements showed that there was no accumulation of salts in the upper 30 cm of the soil (where most of the roots are present) because of leaching by rainfall at the end of the irrigation period. Results suggest that a proper management of saline water, supplying Ca²⁺ to the irrigation water, using drip irrigation until winter rest and seasonal rainfall typical of the Mediterranean climate leach the salts from the first 0-60 cm depth, and growing a tolerant cultivar, can allow using high saline irrigation water (up to 10 dS m⁻¹) for a long time without affecting growth and yield in olive trees.     

Amelioration of salt stress by irrigation management in pepper plants grown in coconut coir dust

A long-term greenhouse experiment was conducted to study the effects of irrigation frequency and salinity on pepper fruit yield and quality in crops growing in coconut coir. Two salinity levels (4 mM NaCl, 2.6 dS m⁻¹ and 24 mM NaCl, 4.6 dS m⁻¹) were combined with four irrigation treatments (one irrigation event every two days (0.5), one irrigation event per day (1), four irrigation events per day (4), and eight irrigation events per day (8)) in a 2 × 4 factorial combination. The effect on fruit quality was evaluated at the early and late harvest seasons, corresponding with two different periods of fruit production (May and July). We found that above-ground total biomass and marketable fruit yield decreased in the salinized treatments. When salinized (24 mM NaCl) nutrient solution (NS) was applied, increasing the number of irrigation events to eight per day resulted in a decrease in the incidence of blossom-end rot and a corresponding increase in the marketable fruit yield. When control (4 mM NaCl) NS was applied, one irrigation event per day yielded as much marketable fruit as was produced with the highest irrigation frequency, and therefore increased water use efficiency, expressed as marketable fruit weight per L of NS applied. When NS containing 24 mM NaCl was used, there was an increase of Cl⁻ but not Na⁺ in the leaf tissue, with this increase reaching its maximum in the treatment involving eight irrigation events per day. Salinity decreased the Ca²⁺ concentration of the fruit only in the early harvest season of production. However, increasing irrigation frequency consistently resulted in higher Ca²⁺ concentration in the fruit. The effects of salinity on the morphological and organoleptic properties of the fruit were more pronounced in the late harvest season.     

Tolerance of young (Ceratonia siliqua L.) carob rootstock to NaCl

One-year-old carob (Ceratonia siliqua L.) rootstock was grown in fertilised substrate to evaluate the effects of NaCl salinity stress. The experiment consisted of seven treatments with different concentrations of NaCl in the irrigation water: 0 (control), 15, 30, 40, 80, 120 and 240 (mmol L⁻¹), equivalent to electrical conductivities of 0.0, 1.5, 2.9, 3.9, 7.5, 10.9 and 20.6 dS m⁻¹, respectively. Several growth parameters were measured throughout the experimental period. At the end of the experiment, pH, extractable P and K, and the electrical conductivity of the substrate were assessed in each salinity level. On the same date, the mineral composition of the leaves was compared. The carob rootstock tolerated 13.4 dS m⁻¹ for a period of 30 days but after 60 days the limit of tolerance was only 6.8 dS m⁻¹. Salt tolerance indexes were 12.8 and 4.5 for 30 and 60 days, respectively. This tolerance to salinity resulted from the ability to function with concentrations of Cl⁻ and Na⁺ in leaves up to 24.0 and 8.5 g kg⁻¹, respectively. Biomass allocation to shoots and roots was similar in all treatments, but after 40 days the number of leaves was reduced, particularly at the larger concentrations (120 and 240 mmol NaCl L⁻¹). Leaves of plants irrigated with 240 mmol NaCl L⁻¹ became chlorotic after 30 days exposure. However, concentrations of N, P, Mg and Zn in leaves were not affected significantly (P > 0.05) by salinity. Apparently, K⁺ and Ca²⁺ were the key nutrients affected in the response of carob rootstocks to salinity. Plants grown with 80 and 120 mmol L⁻¹ of NaCl contained the greatest K⁺ concentration. Na⁺/K⁺ increased with salinity, due to an elevated Na⁺ content but K⁺ uptake was also enhanced, which alleviated some Na⁺ stress. Ca²⁺ concentration in leaves was not reduced under salinity. Salinization of irrigation water and subsequent impacts on agricultural soils are now common problems in the Mediterranean region. Under such conditions, carob seems to be a salt as well as a drought tolerant species.     

Water production functions of wheat (Triticum aestivum L.) irrigated with saline and alkali waters using double-line source sprinkler system

Expected yield losses as a function of quality and quantity of water applied for irrigation are required to formulate guidelines for the effective utilisation of marginal quality waters. In an experiment conducted during 2004-2006, double-line source sprinklers were used to determine the separate and interactive effects of saline and alkali irrigation waters on wheat (Triticum aestivum L.). The study included three water qualities: groundwater (GW; electrical conductivity of water, ECw 3.5 dS m⁻¹; sodium adsorption ratio, SAR 9.8 mmol L⁻¹; residual sodium carbonate, RSC, nil) available at the site, and two synthesized waters, saline (SW; ECw 9.4 dS m⁻¹, SAR 10.3 mmol L⁻¹; RSC nil) and alkali (AW; ECw 3.7 dS m⁻¹, SAR 15.1 mmol L⁻¹; RSC 9.6 meq. L⁻¹). The depths of applied SW, AW, and GW per irrigation ranged from 0.7 to 3.5 cm; the depths of applied mixtures of GW with either SW (MSW) or AW (MAW) ranged from 3.2 to 5 cm. Thereby, the water applied for post-plant irrigations using either of GW, SW or AW ranged between 15.2 and 34.6 cm and 17.1 and 48.1 cm during 2004-2005 and 2005-2006, respectively and the range was 32.1-37.0 and 53.1-60.0 cm for MSW or MAW. Grain yields, when averaged for two years, ranged between 3.08 and 4.36 Mg ha⁻¹, 2.57 and 3.70 Mg ha⁻¹ and 2.73 and 3.74 Mg ha⁻¹ with various quantities of water applied using GW, SW and AW, respectively, and between 3.47 and 3.75 Mg ha⁻¹ and 3.63 and 3.77 Mg ha⁻¹ for MSW and MAW, respectively. The water production functions developed for the two sets of water quality treatments could be represented as: RY = 0.528 + 0.843(WA/OPE) − 0.359(WA/OPE)² − 0.027ECw + 0.44 × 10⁻²(WA/OPE) × ECw for SW (R² = 0.63); RY = 0.446 + 0.816(OPE/WA) − 0.326(WA/OPE)² − 0.0124RSC − 0.55 × 10⁻⁴(WA/OPE) × RSC for AW (R² = 0.56). Here, RY, WA and OPE are the relative yields in reference to the maximum yield obtained with GW, water applied for pre- and post-plant irrigations (cm), and open pan evaporation, respectively. Crop yield increased with increasing amount of applied water for all of the irrigation waters but the maximum yields as obtained with GW, could not be attained even with increased quantities of SW and AW. Increased frequency of irrigation with sprinklers reduced the rate of yield decline with increasing salinity in irrigation water. The sodium contents of plants increased with salinity/alkalinity of sprinkled waters as also with their quantities. Simultaneous decrease in potassium contents resulted in remarkable increase in Na:K ratio.     

Salinity's influence on boron toxicity in broccoli: I. Impacts on yield, biomass distribution, and water use

Research addressing the interactive effects of the dual plant stress factors, excess boron and salinity, on crop productivity has expanded considerably over the past few years. The purpose of this research was to determine and quantify the interactive effects of salinity, salt composition and boron (B) on broccoli (Brassica oleracea L.) fresh head yield, biomass distribution and consumptive water use. A greenhouse experiment was conducted using a sand-tank system in which salinity-B treatment solutions were supplemented with a complete nutrient solution. Chloride-dominated salinity and salinity characteristic of California's San Joaquin valley (SJV), or sulfate-dominated, were tested at ECw levels of 2, 12 and 19 dS m⁻¹. Each salinity treatment consisted of boron treatments of 0.5, 12 and 24 mg L⁻¹. Plant head yield and shoot biomass were significantly reduced by both salinity and boron. Moreover, there was a significant salinity-boron interaction where increased boron was relatively less detrimental under saline conditions. These results occurred regardless of the salt solution composition (chloride or SJV). We found that an ‘interactive model’ better described our growth response than did a ‘single stressor yield model’. Salinity and boron also affected the distribution of shoot biomass. Regardless of salt type, as salinity increased, the fraction of biomass as leaf tissue increased while the biomass fraction as stems and particularly heads, decreased. However, an increase in B at low or high salinity with the SJV composition, decreased the head biomass fraction. This was not observed at moderate salinity, nor on any plants treated with Cl-dominated salinity. Cumulative evapotranspiration (ET) was also reduced by increased salinity but water use efficiency (WUE) was not. WUE was reduced by increased boron, but only at the low and high salinity levels.     

Evapotranspiration, crop coefficient and growth of two young pomegranate (Punica granatum L.) varieties under salt stress

Pomegranate (Punica granatum L.) is a drought-hardy crop, suited to arid and semi-arid regions, where the use of marginal water for agriculture is on the rise. The use of saline water in irrigation affects various biochemical processes. For a number of crops, yields have been shown to decrease linearly with evapotranspiration (ET) when grown in salt-stressed environments. In the case of pomegranate, little research has been conducted regarding the effect of salt stress. Our study focused on the responses of ET, crop coefficient (K_c) and growth in pomegranate irrigated with saline water. Experiments were conducted using lysimeters with two varieties of pomegranate, P. granatum L. vars. Wonderful and SP-2. The plants were grown with irrigation water having an electrical conductivity (EC_iw) of 0.8, 1.4, 3.3, 4.8 and 8 dS m⁻¹. Plants were irrigated with 120% of average lysimeter-measured ET. Seasonal variation in ET, crop coefficient (K_c) and growth were recorded. Variation in daily ET was observed 1 month after initiation of the treatments. While significant seasonal ET variation was observed for the EC-0.8 treatment, it remained more stable for the EC-8 treatment. Salinity treatment had a significant effect on both daily ET (F = 131, p < 0.01) and total ET (F = 112.68, p = 0.001). Furthermore, the electrical conductivity of the drainage water (EC_dw) in the EC-8 treatment was five times higher than that of the EC-0.8 treatment in the peak season. Fitting the relative ET (ET_r) to the Maas and Hoffman salinity yield response function showed a 10% decrease in ET per unit increase in electrical conductivity of the saturated paste extract (EC_e) with a threshold of 1 dS m⁻¹. If these parameters hold true in the case of mature pomegranate trees, the pomegranate should be listed as a moderately sensitive crop rather than a moderately tolerant one. Fitting 30-day interval ET_r data to the Maas and Hoffman salinity yield response function showed a reduction in the slope as the season progressed. Thus using a constant slope in various models is questionable when studying crop-salinity interactions. In addition, both of the varieties showed similar responses under salt stress. Moreover, the calculated value of K_c is applicable for irrigation scheduling in young pomegranate orchards using irrigation water with various salinities.     

Strategies to decrease water drainage and nitrate emission from soilless cultures of greenhouse tomato

In the spring-summer season of 2005 and 2006, we explored the influence of three fertigation strategies (A-C) on the water and nitrogen use efficiency of semi-closed rockwool culture of greenhouse tomato conducted using saline water (NaCl concentration of 9.5 mol m⁻³). The strategies under comparison were the following: (A) crop water uptake was compensated by refilling the mixing tank with nutrient solution at full strength (with the concentrations of macronutrients equal or close to the corresponding mean uptake concentrations as determined in previous studies) and the recirculating nutrient solution was flushed out whenever its electrical conductivity (EC) surpassed 4.5 dS m⁻¹ due to the accumulation of NaCl; (B) the refill nutrient solution had a variable EC in order to maintain a target value of 3.0 dS m⁻¹; due to the progressive accumulation of NaCl, the EC and macronutrient concentrations of the refill nutrient solution tended to decrease with time, thus resulting in a progressive nutrient depletion in the recycling water till N-NO₃⁻ content dropped below 1.0 mol m⁻³, when the nutrient solution was replaced; (C) likewise Strategy A, but when EC reached 4.5 dS m⁻¹, crop water uptake was compensated with fresh water only in order to reduce N-NO₃⁻ concentration below 1.0 mol m⁻³ before discharge. In 2005 an open (free-drain) system (Strategy D), where the plants were irrigated with full-strength nutrient solution without drainage water recycling, was also tested in order to verify the possible influence of NaCl accumulation and/or nutrient depletion in the root zone on crop performance. In the semi-closed systems conducted following strategies A, B or C, the nutrient solution was replaced, respectively, 10, 14 and 7 times in 2005, and in 19, 24 and 14 times in 2006, when the cultivation lasted 167 days instead of 84 days in 2005. In both years, there were no important differences in fruit yield and quality among the strategies under investigation. Strategy C produced the best results in terms of water use and drainage, while Strategy B was the most efficient procedure with regard to nitrogen use. In contrast to strategies A and D, the application of strategies B and C minimized nitrogen emissions and also resulted in N-NO₃⁻ concentrations in the effluents that were invariably lower than the limit (approximately 1.42 mol m⁻³) imposed to the N-NO₃⁻ concentration of wastewater discharged into surface water by the current legislation associated to the implementation of European Nitrate Directive in Italy.     

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

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

Effect of stage-specific saline irrigation on greenhouse tomato production

In many water scarce areas, saline water has been included as an important substitutable resource in agricultural irrigation. It would be of practical use to investigate the effect of stage-specific saline irrigation on yield, fruit quality, and other growth responses of greenhouse tomato, to establish a proper irrigation management strategy for tomato production in these regions. Here, saline irrigations (3.33, 8.33, and 16.67 dS m⁻¹ NaCl solution) were applied during four growth stages of greenhouse tomato (L. esculentum Mill. cv. Zhongza No. 9) grown in the North China Plain, respectively. These include flowering and fruit-bearing stage (stage 1), first cluster fruit expanding stage (stage 2), second cluster fruit expanding stage (stage 3), and harvesting stage (stage 4). Compared with the following three stages, yield loss was most remarkable in stage 1 under all three salinity levels. Under irrigation practices using 3.33 dS m⁻¹ saline water in all four stages, 8.33 dS m⁻¹ saline water in latter three stages, and 16.67 dS m⁻¹ saline water in stage 4, yield reduction was not significant while fruit quality was improved. In conclusion, it is feasible to use stage-specific saline irrigation for tomato production in water scarce areas like North China Plain.     

Comparative affects of blending,intera/inter-seasonal cyclic uses of alkali and good quality waters on soil properties and yields of paddy and wheat

Degradation of soils irrigated with the ground waters having residual alkalinity constitutes a major threat to irrigated agriculture in semi-arid parts especially the South Asia. Paddy–wheat has come to stay as the major crop rotation in the afflicted areas, which is either irrigated solely with alkali waters (AW) or combined with good quality water supplies through canal networks. Therefore, to develop appropriate conjunctive use strategies for the latter situations, response of paddy and wheat was evaluated to the combined use of a good quality water (GW, EC_iw 0.5, RSC nil) and that having residual alkalinity (AW, EC_w 2.3 dS m⁻¹, RSC 11.3 mequiv L⁻¹, SAR_w 15 mmol L^0.5) for 6 years (1997–2003) in lysimeters (2.0 m deep, 0.9 m i.d., with drainage outlets at the bottom) filled in with a sandy loam soil (pH 7.8, ESP 5.3). Increase in soil pH (8.71), salinity (3.8 dS m⁻¹) and sodicity (ESP 27.3) as a consequence of irrigation with alkali water markedly affected the yields of both the crops. The sustainability yield index (SYI) was 0.522 and 0.793 for paddy and wheat, respectively, indicating the sensitivity of the former to the use of alkali water. Keeping the AW input to be similar through irrigations, the SYI for paddy with blending of GW and AW in the ratio of 2:1, 1:1 and 1:2 was 0.732, 0.708 and 0.678, respectively, when compared with 0.751, 0.729 and 0.701 under intera-seasonal cyclic uses. Similarly, the SYI of wheat ranged between 0.821–0.907 and 0.853–0.949 with blending and cyclic uses of the two waters, indicating thereby a yield advantage with the latter. When the two waters were rotated inter-seasonally, the dilution effects of monsoon rains helped to induce greater use of AW for paddy. The overall deterioration in soil properties under different modes was related to proportion of AW applied. It was concluded that the alternating good quality and alkali waters could be a better way to alleviate sodicity problems caused with the use of alkali water alone.     

Salinity's influence on boron toxicity in broccoli: II. Impacts on boron uptake, uptake mechanisms and tissue ion relations

Limited research has been conducted on the interactive effects of salinity and boron stresses on plants despite their common occurrence in natural systems. The purpose of this research was to determine and quantify the interactive effects of salinity, salt composition and boron on broccoli (Brassica oleracea L.) performance, particularly, element accumulation, ion interactions and boron uptake processes. A greenhouse experiment was conducted using a sand tank system where salinity-B treatment solutions were supplemented with a complete nutrient solution. Chloride-dominated salinity and salinity characteristic of California's San Joaquin valley (SJV), or sulfate-dominated, were tested at ECw (electrical conductivity of the irrigation water) levels of 2, 12 and 19 dS m⁻¹. Each salinity treatment consisted of boron treatments of 0.5, 12 and 24 mg L⁻¹. Salinity, regardless of salt composition, reduced shoot boron concentration at very high boron concentration (24 mg L⁻¹). However, increased salinity increased shoot boron concentration when external boron concentration was low (0.5 mg L⁻¹). Tissue Ca, Mg, Na, K, S and Cl concentrations were also affected by salinity level, chloride or sulfate salinity composition, and in some cases by substrate boron concentration. Calcium concentrations in shoots were greater for chloride-treated salinity as compared to SJV salinity-treated plants; magnesium concentrations trended opposite and were greater in those treated with SJV salinity. Chloride and sodium shoot concentrations both increased with salinity. Shoot chloride was greater with chloride substrate salinity and shoot sodium was greater with SJV substrate salinity. Using stable isotope analysis of solutions to separate transpiration from evapotranspiration (ET), we found that boron uptake and accumulation in the shoot was not simply the product of mass flow (solution concentration × cumulative transpiration), and the vast majority of the water lost from the tank system was by transpiration (>90%) regardless of treatment. Under low substrate boron, the levels of boron in broccoli shoots could be not accounted for by simple passive uptake and transport in the transpiration stream, which suggests that some energy-dependent process was also occurring. However, under high boron treatments, broccoli plants exhibited a mechanism that restricted boron uptake, transport and accumulation in the shoot.     

Carbon and nitrogen cycling in a tropical Brazilian soil cropped with sugarcane and irrigated with wastewater

Carbon (C) and nitrogen (N) dynamics in agro-systems can be altered as a consequence of treated sewage effluent (TSE) irrigation. The present study evaluated the effects of TSE irrigation over 16 months on N concentrations in sugarcane (leaves, stalks and juice), total soil carbon (TC), total soil nitrogen (TN), NO₃⁻-N in soil and nitrate (NO₃⁻) and dissolved organic carbon (DOC) in soil solution. The soil was classified as an Oxisol and samplings were carried out during the first productive crop cycle, from February 2005 (before planting) to September 2006 (after sugarcane harvest and 16 months of TSE irrigation). The experiment was arranged in a complete block design with five treatments and four replicates. Irrigated plots received 50% of the recommended mineral N fertilization and 100% (T100), 125% (T125), 150% (T150) and 200% (T200) of crop water demand. No mineral N and irrigation were applied to the control plots. TSE irrigation enhanced sugarcane yield but resulted in total-N inputs (804-1622 kg N ha⁻¹) greater than exported N (463-597 kg N ha⁻¹). Hence, throughout the irrigation period, high NO₃⁻ concentrations (up to 388 mg L⁻¹ at T200) and DOC (up to 142 mg L⁻¹ at T100) were measured in soil solution below the root zone, indicating the potential of groundwater contamination. TSE irrigation did not change soil TC and TN.