Foliar salt accumulation and injury in crops sprinkled with saline water

Summary Many crops accumulate salts through the leaves when they are wetted by sprinkler irrigation. This accumulation may cause foliar injury and decrease crop yield. This study was conducted to test the salt sensitivity of sprinkled alfalfa, barley, cauliflower, cotton, potato, safflower, sesame, sorghum, sugarbeet, sunflower and tomato. Plants were grown in a greenhouse in covered sand cultures that were trickle-irrigated with nonsaline nutrient solutions. Sprinkling with 15 and 30, and in the case of cotton and sunflower, 30 and 60 meq/l waters (9:1 NaCl:CaSO₄) was begun when plants were 1 to 3 months old and was continued for 4 to 7 weeks at a frequency of 1 h/day, 5 days/week. Except for sorghum, Na⁺ and Cl^– absorption through the leaves was essentially a linear function of salt concentration and duration of sprinkling. Most species absorbed Nat at approximately the same rate as Cl^–; however, in potato and sugarbeet Nat absorption exceeded Cl^–; and in barley and sesame Cl^–; exceeded Na¹. The mean rates of Na⁺ and Cl^–; absorption among species increased in the order: sorghum cotton = sunflower < cauliflower < sesame = alfalfa = sugarbeet < barley = tomato < potato = safflower. Susceptibility to leaf injury among species did not vary in strict relation to rates of salt absorption from 30 meq/l water. Potato and tomato readily absorbed Na⁺ and Cl^–; and quickly exhibited symptoms of leaf tip and margin necrosis. On the other hand, safflower, with one of the highest rates of salt absorption was only slightly injured by sprinkling. Barley readily absorbed salt, particularly Cl^–; and exhibited minor injury symptoms; whereas sesame and alfalfa had intermediate absorption rates but were somewhat more susceptible to injury. Sugarbeet was uninjured by sprinkling but absorbed appreciable amounts of Nat; whereas sorghum developed some necrosis along leaf edges but absorbed very little salt. Cauliflower, cotton, and sunflower absorbed salt slowly and exhibited almost no injury.Supervisory Plant Physiologist, Research Assistant, and Plant Physiologist     

Response of alfalfa (<Emphasis Type="Italic">Medicago sativa</Emphasis> L.) to diurnal and nocturnal saline sprinkler irrigations. II: shoot ion content and yield relationships

When using saline waters, sprinkling irrigation at night is a recommended practice to reduce evaporation, salt absorption by the wetted leaves and its negative effects on crops. We measured shoot ion concentrations (Cl⁻, Na⁺ and K⁺) and total dry matter (TDM) in alfalfa subject to diurnal and nocturnal saline sprinkler irrigations and established potential relationships among them. The work was carried out along the 2004–2006 growing seasons using EC waters from 0.5 to 5.6 dS m⁻¹. Saline sprinkling irrigations linearly increased shoot Cl⁻ and Na⁺ and decreased shoot K⁺. Even though daytime evaporation was much higher than nigh-time, shoot ion accumulation and TDM were similar in the diurnal and nocturnal irrigations. The salinity tolerance of alfalfa decreased in year 2006 due to increases in shoot Cl⁻ and, particularly, shoot Na⁺. The lower threshold for shoot Na⁺ (276 meq kg⁻¹) than for shoot Cl⁻ (726 meq kg⁻¹) shows that alfalfa is more sensitive to Na⁺ than to Cl⁻, and that Na⁺ accumulation is the preponderant cause of alfalfa yield decline after 3 years of sprinkling with saline waters.     

Over-canopy saline sprinkler irrigation of grapevines during different growth stages

Wetting plant foliage with saline irrigation increases the uptake of toxic ions Na⁺ and Cl⁻. Over three consecutive seasons, Colombard vines grafted on Ramsey rootstock were irrigated with saline water (EC 3.5 dS/m) by over-canopy sprinklers during any one of the first three of the four annual growth stages: bud burst to full bloom (treatment BB-FB), full bloom to veraison (treatment FB-V), and veraison to harvest (treatment V-H). At other times, vines received non-saline water (EC 0.5 dS/m) as did the control. Seasonal average soil salinities remained relatively constant over the trial. In contrast, the concentrations of Na⁺ and Cl⁻ in one-year old wood and grape juice more than doubled. In treatments FB-V and V-H the average yield over the three seasons was reduced by up to 15%. Results were compared with those obtained in an earlier study which was undertaken in the same vineyard with the same treatments applied via dripper. With drippers, the maximum reduction in the average yield over three seasons was 2%. Saline sprinkling caused rises in Na⁺ and Cl⁻ concentrations of fruit, leaf lamina and one-year-old wood that were at least 7-fold, 5-fold and 2-fold greater, respectively, than the rises caused by application of the same treatments with drip. Progressive seasonal rises in the concentrations of Na⁺ and Cl⁻ in these tissues were due in part to carryover of salt added in previous seasons; with saline sprinkling the magnitude of these carryovers was 4-fold greater than those with saline drip irrigation. With saline water, vignerons can reduce losses by using irrigation systems which do not wet the foliage.     

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.     

Response of Sultana vines (V. vinifera L.) on six rootstocks to NaCl salinity exposure and recovery

One-year-old Sultana (Vitis vinifera L.) vines, own-rooted and grafted on 41B, 110R, 140Ru, 1103P and SO₄ were grown in sand–perlite mixture (1:1) irrigated with half-strength nutrient solution containing 5, 25, 50 and 100 mM of NaCl. Growth, tissue mineral content and leaf gas exchange response to salt treatment and subsequent recovery were examined over a 70-day period. Shoot growth, leaf area and total dry weight were significantly reduced (P<0.05) at all salinity levels. Tissue salt content increased significantly with increasing salinity, Cl⁻ being always higher than Na⁺. Photosynthetic rate (P_n) and stomatal conductance (g_s) were greatly reduced by salinity and highly correlated with leaf Cl⁻ content. Own-rooted vines exhibited higher dry matter production and photosynthetic rates than grafted vines, despite the higher Cl⁻ and Na⁺ content. During recovery, vines previously treated with 50 and 100 mM NaCl exhibited photosynthetic rates and stomatal conductances similar to the control, although laminae Na⁺ and Cl⁻ content continued to increase. Our results showed that own-rooted ‘Sultana’ vines (V. vinifera) can cope better with high salinity followed by those grafted on 1103P, 140Ru, 110R, SO₄ and 41B rootstocks.     

Ameliorative effects of inoculation with the plant growth-promoting rhizobacterium Pseudomonas sp. DW1 on growth of eggplant (Solanum melongena L.) seedlings under salt stress

The objective of this work was to evaluate the effect of inoculation with the plant growth-promoting rhizobacterium Pseudomonas sp. DW1 on eggplant (Solanum melongena L.) growth, mineral uptake and activities of the antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) of plant leaves under salinity stress. The study was conducted in pot experiments using eggplant (S. melongena L., cv. Yinjia) and a coastal soil. The NaCl concentration of the coastal soil was 0.57 g (kg soil)⁻¹. Four NaCl levels were tested: 0.57, 1.0, 2.0, and 3.0 g NaCl (kg soil)⁻¹, by adding NaCl to soil, respectively. Pseudomonas-inoculated seeds had an increase in the germination percentage over its non-inoculated seeds under salinity. Salinity negatively affected growth of eggplant; however, plants inoculated with Pseudomonas sp. DW1 grew to a significantly greater extent than plants that were not treated with this bacterium. Salinity significantly decreased K⁺ concentration, increased Na⁺ concentration, and did not significantly decrease Ca²⁺ content in shoots of eggplants. Inoculating with Pseudomonas sp. DW1 increased shoot Ca²⁺ of eggplant compared to the non-inoculating eggplant plants under salinity. Inoculating treatments with Pseudomonas sp. DW1 had no effect on shoot Na⁺ concentration in 0.57 and 1 g (kg soil)⁻¹ NaCl, but there were significant decreases in inoculated treatments than in non-inoculated ones at 2 and 3 g (kg soil)⁻¹ NaCl. Salinity decreased SOD activities and increased POD activities, and inoculated Pseudomonas sp. DW1 had an increase effect on SOD activity in the leaves of eggplants. Alteration of mineral uptake and increase in the antioxidant enzyme activities may be two mechanisms for the alleviation of salt stress. Based on the results of the experiment reported herein, the use of the plant growth-promoting rhizobacterium treatment may provide a means of facilitating plant growth under salt stress.     

Comparative effects of chemical amendments on salt and NA leaching

Summary Efficiency of sodic soil reclamation is thought to vary with types of chemicals used. This study examined the effects of five inorganic (H₂SO₄, CaCl₂ · 2H₂O, CaSO₄ · 2H₂O, FeSO₄, Al₂(SO₄)₃) and two organic compounds (polyacrylamide, and trihydroxy glutaric acid) on the rate and the extent of salt and Na leaching in moderately Na-affected saline soils: Saneli silty clay loam (Vertic Torrifluvents, ESP=17.5%) and Glendale silty clay (Typic Torrifluvents, ESP=13.5%). Air-dry soil samples (<2mm) were packed in columns, and chemicals, except H₂SO₄, were incorporated into the surface 5 cm of the soils, and in selected cases, to 30 cm. H₂SO₄ was surface-applied. Application rates of the inorganic chemicals were 3.57 and 10.7 mmol(+) kg^-1 (2.5 and 7.5 Mg ha^-1 in gypsum equivalent weight) in the silty clay loam, and 8 and 24 mmol(+) kg^-1 in the silty clay, and the organic compounds were applied at rates of less than 620 kg ha^-1. The soils were then leached with simulated Rio Grande water (EC = 1.1 dS m^-1, SAR = 3.5) under continuous ponding. The tested inorganic compounds removed approximately equivalent amounts of exchangeable Na after approximately 35 cm of water application. However, the rate of water percolation (consequently the rate of salt leaching) from CaCl₂ treated columns, became progressively slow after about 20 cm of water intake. The combined effect of rapid electrolyte leaching and insufficient replacement of Na in the surface layer seemed to be responsible for the flow reduction. Gypsum and H₂SO₄ treatments provided lower ratios of sodicity to salinity in percolating solutions and relatively uniform hydraulic gradients throughout the soil depth. Incorporation of chemicals to the surface 30 cm did not alter performance, except in CaCl₂ treatments where water intake rates became even slower. The tested organic amendments improved initial water infiltration, but neither increased subsequent percolation rates nor improved salt and Na leaching. The fastest reclamation may be attained when chemicals are chosen and applied to yield an electrolyte concentration that is high enough to overcome Na effects at any depth of soil profiles throughout the leaching period.Contribution from Texas Agr. Expt. Sta. Texas A & M University System. This project was supported in part by the Binational Agricultural Research and Development (BARD) Fund and the Expanded Research Area Fund of the Texas Agricultural Experiment Station.     

Grapefruit response to variable salinity in irrigation water and soil

Summary Results are reported from a long-term field experiment designed to determine the effect of irrigation water salinity on the yield and water uptake of mature grapefruit trees. Treatments were started in 1970 and consisted of chloride concentrations in the irrigation water of 7.1, 11.4 and 17.1 meq/1 added as NaCl+CaCl₂ at a 1 : 1 weight ratio.For the last four years of the experiment, 1973 to 1976, yield was linearly related to the mean chloride concentration in the soil saturation extract weighted according to the distribution of water uptake with depth and time (Fig. 2, Table 1). There was a 1.45% (1.68 Mg/ha) yield reduction for each 1 meq/1 increase in chloride concentration above a threshold value of 4.5 meq/1. This corresponded to a 13.5% (14.7 Mg/ha) decrease per 1 mmho/cm increase in the electrical conductivity of the soil saturation extract above a threshold value of 1.2 mmho/cm.Total water uptake was reduced as salt concentration in the soil increased (Fig. 3, Table 2). In the high salinity treatment, root concentration in, and water uptake from, the lower portion of the root zone were decreased. The maximum electrical conductivity (ECe) measured at the bottom of the root zone was 7.90 mmho/cm similar to the values of EC, obtained by linear extrapolation to zero yield and also to zero water uptake.Salt accumulation in the soil depended on the quantity and salt concentration of the irrigation water, rainfall, and on the amount of leaching. SAR and the Na⁺ concentration of the soil remained low throughout the experiment (Table 3). No leaf symptoms of either Cl^– or Na⁺ injury were observed. The results indicate an osmotic — rather than a specific ion effect — of salinity on grapefruit yield.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. 1977 Series No. 197-E     

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.     

Combined effects of KNO3 and salinity on yield and chemical composition of lettuce and Chinese cabbage

Summary The effect of N and K nutrition on the salt tolerance of lettuce (Lactuca saliva L. cv. Saunas) and Chinese cabbage (Brassica campestris L., Pekinensis cv. Kazumi) was evaluated in three greenhouse experiments under a controlled aero-hydroponic system of cultivation. Three levels of KNO₃ (1, 5 and 10 mM) were tested in all the experiments with rapidly circulated saline and nonsaline nutrient solutions. Two experiments, carried out between January and March 1989, with lettuce (Exp. I) and Chinese cabbage plants (Exp. III), consisted of two salinity levels, EC = 1.75 and 6.0 dS m^–1, the former representing a nonsaline nutrient solution. In the third experiment with lettuce (Exp. II., conducted between March and May 1989), three saline nutrient solutions having EC levels of 4.7, 7.75 and 10.75 dS m^–1 were compared to the nonsaline solution. The nutrient solutions were salinized with NaCl and CaCl₂, in a 4:1 molar ratio. The highest yields of fresh weight of both crops were obtained from the 5 mM KNO₃ under both saline and non-saline conditions. The 10 mM treatment caused yield reduction in Chinese cabbage, probably due to a severe tipburn disorder. The relatively high fresh weight yield obtained at the lowest (1 mM) KNO₃ level can be explained by the positive effect of circulation velocity on nutrient uptake. The threshold salinity damage value for the vegetative yield of lettuce plants fed by 5 or 10 mM KNO₃ was approximately 5 dSm^–1 and the yield decreased by 6.5% per unit dS m^–1 above the threshold. No yield improvement due to the addition of KNO₃ occurred under highly saline conditions (Exp. II). The fresh weight of Chinese cabbage obtained from the saline 1 and 5 mM KNO₃ treatments was approximately 15% lower than the non-saline-treatment (Exp. III). Salinity increased tipburn and the effect was not altered by the addition of KNO₃. No significant interaction between nutrition (KNO₃ level) and salinity was found. The application of salts increased the concentration of Na and Cl in plant tissue and reduced the levels of N and K; the opposite occurred in plants fed by the medium and high levels of KNO₃.Contribution from Institute of Soils and Water, ARO, Volcani Center, PO Box 6, Bet Dagan 50250, Israel. No. 3092-E 1990 series     

Osmotic potentials of roots of onions and their rhizospheric soil solutions when irrigated with saline drainage waters

In the field experiments with onions in Hofuf, Saudi Arabia, the effect was investigated of irrigations with saline water having 2.3–8.0 mS cm^?1 on the Cl^? content of the soil close to the roots.Immediately after water application the rhizospheric soil contained 3–4.5 meq Cl^?/100 g, which was 3–5 times more than the remainder of the soil. After 4 days of water depletion 9–11 meq Cl^?/100 g were found in the rhizospheric soil, whereas the soil far from the roots contained only 0.5–1.5 meq Cl^?/100 g. The osmotic potentials of the rhizospheric soil solutions ranged from ?0.5 MPa to ?0.9 MPa after water application and from ?2.0 to ?3.0 MPa 4 days later. The differences in the salt contents of the rhizospheric soil were much lower than expected from the large differences in the salt concentrations of the irrigation water.     

Effects of diluted Kraft pulp mill effluent on hybrid poplar and soil chemical properties

Irrigation with effluents can detrimentally affect soil physical and chemical properties and impact plant growth and development. Excessive irrigation can leach salts from the root zone; which can be accomplished by precipitation in some areas. This study was conducted to examine the effect of applications of Kraft pulp mill effluent (KPME) with and without distilled water (DW) to simulate precipitation would have on soil chemical properties and growth of hybrid poplar (Populus deltoides × P. petrowskyana L. cv. Walker). Distilled water (DW), KPME, and a 50% combination (v/v; COMB) of DW and KPME were applied at rates of 6 and 9 mm day⁻¹. COMB resulted in heights, biomasses, and leaf areas that were greater than those for KPME and comparable to those for DW. Diluted KPME treatments (i.e., COMB) still significantly increased soil electrical conductivity and sodium adsorption ratio compared to DW. Leachate collected from KPME 9 mm day⁻¹ had concentrations of HCO₃ ⁻, SO₄ ²⁻, Cl⁻, Ca²⁺, K⁺, and Mg²⁺ comparable to those collected from COMB 9 mm day⁻¹, but Na⁺ concentrations were three times higher in KPME than COMB 9 mm day⁻¹. Results indicate that precipitation or additional irrigation water could potentially provide the leaching necessary to prevent salt accumulation within the rooting zone; however, irrigating with saline or sodic effluents requires careful management.     

Salt effects on germination and seedling emergence of several vegetable crops and guayule

Summary Salt effects on seed germination and seedling emergence of several crops are evaluated to understand poor plant stands occurring in furrow-irrigated fields in saline areas. The test crops were carrot (Daucus carota L. cv. Imperator 58), chile pepper (Capsicum annuum L. cv. New Mexico 6-4), tomato (Lycopersicon esculentum M. cv. Rutgers), and guayule (Parthenium argentatum G. cv. 593). Seed germination was measured in petri-dishes containing saline solutions (0.8 to 32 dSm^–1 with a Na to Ca + Mg ratio of about 2 : 1); and seedling emergence in potted fine loamy sand subirrigated in a greenhouse with saline waters (0.8 to 7.6 dSm^–1 with SAR < 16). Seedling emergence through a thin layer of salted-loamy sand (having EC _e up to 46 dSm^–1) placed on emerging seedlings was also evaluated. Germination of tomato and carrot seeds began to decline at solution salinities of 12 and 18 dSm^–1, respectively, and was virtually zero at 23 dSm^–1, Chile pepper and guayule germinated well at 23 dSm^–1, Tomato had the highest emergence, and guayule the lowest, showing less than 20% when subirrigated at 2.2 dSm^–1, Seedling emergence which increased in the order of guayule, carrot, chile pepper and tomatoes did not quantitatively correlate with seed germination. However, it did correlate with the emergence through the thin layer of the salted-sand placed over emerging seedlings except in tomato. Salinity of the saturation extract of the surface 5 mm soil increased to 21 and 31 dSm^–1, in 7 days when subirrigated with water of 4.3 and 6.4 dSm^–1, respectively. Poor seedling emergence of guayule, carrots and, to some extent, chile pepper appeared to be caused by hypocotyl mortality associated with the salts accumulated at the soil surface, but not by reduced seed germination. The control of surface accumulated salts should be the target of management for improved emergence of these crops.Contribution from Texas Agric. Exp. Station. This project was supported in part by a grant from Binational Agricultural Research and Development (BARD) fund, the Expanded Research fund and the Latex Grant, USDA     

Net changes of main ions in the soil profile of irrigated field plots in central Spain

Implementation of improved irrigation schedules in some semiarid zones improve water efficiency and can be recommended where occasional periods of heavy rainfall may remove some of the accumulated salts. We hypothesized, however, that the leaching pattern of the main ions may differ regarding their potential contribution to the total salt discharge. The experiment was conducted near Madrid in Spain on a typical Xerofluvent soil with sandy-loam texture in the first 0.5 m. For 4 years, a traditional crop rotation of corn–wheat–corn–oat (Zea mays L.–Triticum aestivum L.–Zea mays L.–Avena sativa L.) was planted and two irrigation treatments (traditional and improved) were applied only to the corn. In an experimental set-up of 24 plots, samples of the soil solutions were extracted 61 times during the experiment at soil depths of 0.4, 0.9 and 1.4 m. During the experiment, drainage volume was estimated in plots under the two irrigation schedules. Main ions in the soil solution were SO₄²⁻, Cl⁻, Ca²⁺, Na⁺ and HCO₃⁻. These solutes accounted for 88% of total salt discharge under the two irrigation treatments. Two main patterns of salt leaching were observed. For most main ions, except HCO₃⁻, the input to discharge ratio was lower than one. Also for HCO₃⁻ , the irrigation treatment did not affect the leaching pattern (higher input than discharge under the two irrigation treatments). Improved irrigation schedules can be implemented without increasing the total salt load, but attention should be paid to specific leaching patterns of individual ions.     

Rice growth and yield respond to changes in water depth and salinity stress

Depth of standing water in rice paddy fields is an important agronomic parameter in the management of irrigation-related salinity problems. It was hypothesized that reductions in the yield of rice under salinity stress can be ameliorated by adjusting the water depth. This study was designed to determine the interactive effects of salinity and water depth on seedling establishment and grain yield in rice. Plants were grown in a greenhouse and irrigated with nutrient solutions amended with NaCl and CaCl₂ (5:1 molar concentrations). Treatments were three salt levels with electrical conductivities at 0.9, 3.3 and 6.0 dS m⁻¹ and six water depths at 4, 7, 10, 13, 16 and 20 cm. The effects of both salinity and water depth were significant on plant growth and yield. However, there was no interaction between the effects of salinity and water depth. Reductions in seedling establishment and grain yield with increases of salinity and water depth resulted from a simple combination of the two different stresses on plants. Highly significant negative correlations were identified between water depth and seedling establishment and also between water depth and grain yield when data were combined across salt levels. Generally, plants performed better with respect to seedling establishment and grain yield in shallow water (i.e. <10 cm) than in deep water (i.e. >10 cm). Under salt stress, the effect of water depth was significant for panicle number, but not significant for panicle weight. The loss of grain yield under salt stress with the increases of water depth was mainly due to reduction in fertile tiller number. We suggest that water depth be lowered during the initiation and growth of productive tillers. However, the practice by lowering water depth must be incorporated with appropriate field management such as the increase of irrigation frequency, precision leveling, and effective weed control methods.     

Effects of fixed partial root-zone drying irrigation and soil texture on water and solute dynamics in calcareous soils and corn yield

Water dynamics and salt distribution in the soil were studied under Fixed Partial Root zone Drying irrigation (FPRD) conditions in corn fields in Northern Greece. FPRD irrigation technique was applied without deficit treatment in two calcareous soils, a sandy clay loam and a sandy loam. Soil water content was recorded in the vertical profile of 0.6 m with the use of capacitance sensors in the row and interrow positions of plants. Salt built-up was monitored to the depth of the root zone, bi-weekly, by measuring electrical conductivity (EC_e) and the concentrations of soluble cations Ca²⁺, Mg²⁺, Na⁺ and K⁺ of the saturation extract on irrigated and non irrigated interrow positions. Soil moisture distribution and salt built-up in soil were used to evaluate the potentials and constraints of FPRD efficiency to sustain plant growth and crop production as a low cost drip irrigation technique. The results indicated that FPRD application on both soils was capable of supplying sufficient amounts of water on plant row. Soil analyses showed that salts accumulated to high levels in the soil surface and decreased in depth at the non irrigated interrow positions. Spatial and temporal variability of salt movement and distribution in the soil profile of 0.6 m were ascribed to soil textural differences. The development and yield of corn plants for both soils reached the usual standards for the area with a minor decrease in the sandy loam soil.     

Nitrogen leaching during sprinkler irrigation of a Dutch clay soil

Short-circuiting, which is vertical movement of free water through large continuous pores in an unsaturated soil matrix, was measured in the field in large columns from a cracked Dutch clay soil. The columns had been fertilized with chemical nitrogen fertilizer at a rate of 80 kg N ha^?1. Sprinkler irrigation (with an average intensity of 18 mm h^?1 and applied quantities varying from 8 mm to 22 mm) resulted in strong nitrogen leaching from the columns. Losses, which averaged 30%, resulted from mass-flow due to short-circuiting. Redox measurements suggested that no denitrification occurred. Application of only 6 mm of water slightly reduced nitrogen losses to approximately 15%. Losses could be reduced to 8% by applying the fertilizer to a wet soil surface which had just been sprinkled, and by sprinkling again the next day. In that way, the fertilizer grains dissolve and nitrogen diffuses into the surface soil, allowing less nitrogen movement along the soil surface towards the vertical cracks during the next sprinkling.     

Salt sensitivity of cowpea at various growth stages

Summary The relative salt tolerance of cowpea (Vigna unguiculata (L.) Walp. cv. California Buckeye No. 5) at different stages of growth was determined in a greenhouse. Plants were grown in sand cultures that were irrigated four times daily with modified half-strength Hoagland's solution. Salination with NaCl and CaCl₂ (2:1 molar ratio) provided seven treatment solutions with osmotic potentials (_s) ranging from –0.05 to –1.05 MPa (electrical conductivities of 1.4 to 28 dS/m). Salt stress was imposed for 20 days beginning at either 7, 27, or 52 days after planting. The three 20-day stages are referred to here as vegetative, flowering, and pod filling stages. Pod and seed yields from plants stressed during either the vegetative, flowering, or pod-filling stages indicated that cowpea was the most sensitive to salinity during the vegetative stage and became less sensitive the later plants were stressed. Seed yield was reduced 50% at _s =–0.45, –0.76, and –0.88 MPa for plants salinized during the vegetative, flowering, and pod-filling stages, respectively. Salinity reduced seed yield by reducing seed number; it had little, if any, effect on the weight of individual seeds. Vegetative growth was significantly reduced by salt stress during all three stages but the effect was much less when stress was imposed during the last two stages than during the first stage.     

Response of two varieties of lentil to soil salanity

Two varieties of lentil were grown in tanks filled with clay, and were irrigated with waters containing three different levels of salinity. Salinity affected the germination and survival of the seedlings; the pre-dawn leaf-water potential and maximum osmotic adjustment; the development of leaf area, dry matter and number of flowers, and, finally, the yield.Lentil has a high water-use efficiency, about 2 kg m⁻³ under non-saline conditions, much higher than legumes such as broadbean and soybean. The crop, however, is much more salt sensitive and can only be grown on non-saline soils. At an EC_e of 2 dS/m, the limit between non-saline and slightly saline soils, the yield reduction is about 20% and at an EC_e of 3 dS/m it is 90–100%.The salt tolerance classification, made after a greenhouse experiment with nutritive solutions, was not confirmed by the experiments reported here.