Growth and physiological responses of Sporobolus robustus kunth seedlings to salt stress

Seedlings of S. robustus were exposed to increasing NaCl concentrations (0, 50, 100, 150, 200, 250, and 300?mM) for 50, 100, and 150 days, in greenhouse conditions. Total dry weight and salt tolerance index decreased gradually with increasing NaCl concentrations. The optimum growth of S. robustus (4.12 to 5.25?g?·?plant^?1) was obtained between 0 and 150?mM at 150 days after salt stress. Foliar chlorophyll a and total chlorophyll contents increased with NaCl concentration at 50 days after treatment. There was no significant effect of salinity on chlorophyll a, b and total chlorophyll contents at 100 and 150 days after treatment. Higher Na contents were found in the shoots as compared to the roots. The Na content increased, while K decreased with increasing NaCl concentrations, suggesting competitive inhibition between absorptions of Na and K as a consequence, the K/Na ratios in shoots and roots decreased with increasing salinity. The proline contents in S. robustus were more pronounced at 300?mM (2.02?µmol/g), 250?mM (2.64?µmol/g), and 200?mM NaCl concentrations (2.98?µmol/g) for 50, 100, and 150 days, respectively, as compared to the treatment without added NaCl. Overall, S. robustus could be considered as salt tolerant on the basis of their performance in biomass production, accumulation of Na, similar foliar chlorophyll a, chlorophyll b and total chlorophyll contents, and accumulation of proline with increasing salinity. The potential ability of S. robustus to accumulate significant amounts of Na makes this halophyte promising as a desalinization tool of salted soils.     

Combined effects of salinity and phosphorus availability on growth,gas exchange,and nutrient status of Catapodium rigidum

The combined effects of NaCl-salinity and phosphorus deficiency on biomass production, nutritional status, and photosynthetic activity were studied in Catapodium rigidum: an annual Poacea with fodder potential. Plants were grown in hydroponic conditions for 55 days under two phosphorus (P) supply: 5 (low) or 180?µmol KH₂PO₄ (sufficient), in the absence or presence of 100?mM NaCl. Obtained results demonstrated that both salinity and P deficiency treatments applied separately reduced substantially plant growth and CO₂ assimilation rate with a more marked impact of salt stress. Salinity has no substantial effect on both shoot P concentrations and phosphorus acquisition efficiency independently of P availability. The highest decrease in plant growth (?91%) was observed in plants simultaneously submitted to both stresses suggesting an additive effect of the two stresses and that P deficiency increased the susceptibility of C. rigidum to salinity. This may be linked to a significant decrease in potassium acquisition (?95%), K/Na selectivity ratio (?73%), stomatal conductance (?66%), CO₂ assimilation rate (?64%), and shoot water content (66%). Furthermore, plants cultivated under combined salinity and sufficient P supply displayed higher stomatal conductance, CO₂ assimilation rate, K/Na selectivity ratio, and plant growth than plants cultivated under combined effects of salinity and P deficiency. These results suggest that adding P to saline soils could be an alternative for alleviating the negative effects of salinity and may ameliorate salinity tolerance.     

Effects of salt treatment on growth,lipid membrane peroxidation,polyphenol content,and antioxidant activities in leaves of Sesuvium portulacastrum L.

Changes in growth, leaf contents of proline, oxidative stress-related parameters, and phenolic compounds, and antioxidant activities were investigated in the halophyte species Sesuvium portulacastrum L. under saline conditions. Rooted cuttings were individually cultivated in sandy soil. After five weeks of pre-treatment, seedlings were submitted during one month to different salt concentrations ranging from 0 to 800?mM NaCl. The plant growth was significantly improved by salt at 200–600?mM concentration. This trend was associated with (i) the stimulation of photosynthetic activity, (ii) the protection of membrane integrity (leaf MDA content 50% lower than the control), and (iii) higher total antioxidant activity, especially at 400?mM NaCl. At this salt concentration plants accumulated high contents of proline, polyphenols, antocyanins, and carotenoids. These compounds could be implied in the protection of the photosynthetic system and in the improvement of growth. Exposure to 800?mM NaCl impaired significantly photosynthesis, proline, polyphenol, antocyanin, and carotenoid accumulation. Yet, the strong antiradical activity (DPPH) observed at this extreme salinity might partly explain the plant survival. S. portulacastrum could be used in the rehabilitation and the stabilisation of saline or saline arid land. Additionally, under saline conditions, S. portulacastrum accumulate a large amount of proline and exhibits important antioxidant potentialities.     

Physiologic response of six plant species grown in two contrasting soils and irrigated with brackish groundwater and RO concentrate

With declining availability of fresh surface water, brackish groundwater is increasingly used for irrigation in the arid and semi-arid southwestern United States. Brackish water can be desalinated by reverse osmosis (RO) but RO results in a highly saline concentrate. Disposal of concentrate is a major problem hindering augmentation of inland desalination in arid areas. The objective of this study was to determine the effect of texture and saline water irrigation on the physiology of six species (Atriplex canescens (Pursh) Nutt., Hordeum vulgare L., Lepidium alyssoides A. Gray, Distichlis stricta (L.) Greene, Panicum virgatum L., and ×Triticosecale Wittm. ex A. Camus [Secale?×?Triticum]). All species were grown in two contrasting soils and irrigated with the same volume of control water (EC 0.9?dS/m), brackish groundwater (4.1?dS/m), RO concentrate (EC 8.0?dS/m). Several plant physiological measurements were made during the growing season including height, number of stem nodes, average internodal length, number of leaves, leaf length, photosynthetic rates, stomatal conductance rates, transpiration rates, leaf temperatures, stem water potential, and osmotic potential. P. virgatum was the only species that showed significant decrease in plant height and growth with texture and irrigation water salinity. Except for A. canescens and L. alyssoides, number and length of leaves decreased with increasing salinity for all species. No significant differences were observed for photosynthetic, stomatal conductance, and transpiration rates by soil texture or irrigation water salinity. Stem water potential and osmotic potential did show some significant influence by soil texture and irrigation water salinity. Based on the results, RO concentrate can be reused to grow all six species in sand; however, growth of all species showed some limitations in clay. Local reuse of RO concentrate along desert margins with regular soil and environmental quality monitoring can accelerate implementation of inland desalination for sustaining food security.     

Mitigation of Salt Stress Negative Effects on Sweet Pepper Using Arbuscular Mycorrhizal Fungi (AMF), <Emphasis Type="Italic">Bacillus megaterium</Emphasis> and Brassinosteroids (BRs)

A study was conducted at the experimental farm of Faculty of Agriculture, Ain Shams University, Cairo, Egypt, during two successive summer seasons (2014 and 2015) to investigate the effects of arbuscular mycorrhizal fungi (Glomus irradicans 10% w/w), Bacillus megaterium (10?ml/pot) and brassinosteroids (24-EBL, C₂₈H₄₈O_6; 2?µM) on growth, nutrient absorption, chlorophyll, proline content, antioxidant enzymes activity and fruit yield of sweet pepper plants (Capsicum annuum L.) cv. Marconi. Plants were grown under three levels of salinity (0, 25 and 50?mM). The obtained results showed that plants grown under non-saline water (0?mM NaCl), with or without treatments, significantly gave the most vigorous vegetative growth and had the highest fruit yield compared with those grown under salt stress conditions. All anti-salinity treatments (Mycorrhiza, Bacillus and Brassinosteroids) improved growth when compared with untreated plants (control). Plants inoculated with mycorrhiza or treated with brassinosteroids showed better vegetative growth and shoot biomass (total fresh and dry weight per plant), chlorophyll a and b concentrations, antioxidant content expressed as total soluble phenols and proline concentrations at all studied salinity levels followed by plants inoculated with Bacillus megaterium compared with control plants which showed severe growth retardant especially under higher salt concentration (50?mM). Carotenoids concentration increased proportionally with the increase of salinity concentration. The maximum leaf relative water content (LRWC) and lowest values of membrane permeability (MP) were significantly observed with mychorhiza inoculated plants and brassinosteroid application respectively, followed by Bacillus inoculated plants. Antioxidant enzyme activity were highest in plants irrigated with moderate saline water (25?mM) than plants under high salinity irrigation water (50?mM) except polyphenol oxidase (PPO) as compared with unstressed plants (0?mM). Mycorrhizal inoculated plants accumulated higher K and lower Na and Cl followed by plants treated with brassinosteroids and then plants inoculated with Bacillus megaterium. Anti-salinity treatments positively enhanced fruit yield of sweet pepper plants under all salinity stress levels and the highest fruit yield were significantly observed with brassinosteroid application followed by mychorhiza inoculated plants and then Bacillus inoculated plants.     

Exogenously applied hexaconazole ameliorates salinity stress by inducing an antioxidant defense system in Brassica napus L. plants

The ability of hexaconazole (HEX) to ameliorate salinity stress was studied in canola plants (Brassica napus L.). Canola seedlings were subjected to sodium chloride (NaCl) treatment. A treatment with 200 mM NaCl reduced growth parameters, chlorophyll content and protein content as well as increased the proline (Pro) content in canola plants. In addition, NaCl stress increased the endogenous, nonenzymatic antioxidants and the activity of antioxidant enzymes, such as peroxidase (POX; EC 1.11.1.7), superoxide dismutase (SOD; EC 1.15.1.1) and catalase (CAT; EC 1.11.1.6). When these plants were treated with a combination of NaCl and 50 mg L⁻¹ HEX, the inhibitory effects of NaCl stress were decreased by increasing the root growth, shoot growth, dry weight (DW), chlorophyll content, protein content and antioxidant enzyme activity by ameliorating the salinity injury. These results suggested that HEX has an important role in the enhancement of plant antioxidant systems and resistance to salinity in canola plants.     

Response of<Emphasis Type="Italic">Tetranychus cinnabarinus</Emphasis> feeding on NaCl-stressed strawberry plants

The development and reproductive rates ofTetranychus cinnabarinus Boisduval (Acari: Tetranychidae), the carmine spider mite, were studied on two strawberry cultivars (Fragaria ×ananassa Duch.; ‘Camarosa’ and ‘Sweet Charlie’) at three NaCl concentrations, 1760, 2400 and 3040 mgl ⁻¹, and control. The effects of NaCl application on the contents of plant nutrients, chlorophyll, proline, peroxidase activity (POX) and proteins were assessed. On Camarosa,T. cinnabarinus had a faster development rate with applications of NaCl than without, except for female development at the highest salinity level. The total development time of females increased with the NaCl concentration, whereas total development time of males decreased. The oviposition period and female longevity on Camarosa was significantly longer in the control than with NaCl, whereas daily and total fecundity were significantly higher at all NaCl concentrations than in the control, except for total fecundity at the lowest salinity level. The total development time, oviposition period, female longevity, daily and total fecundity on Sweet Charlie did not differ significantly between NaCl salinity levels and the control. The intrinsic rate of natural increase (r _m ) on Camarosa and Sweet Charlie were significantly higher with NaCl than in the control. However, the contents of Na, Cl, P, chlorophyll, proline, POX and protein in the two strawberry cultivars changed depending on NaCl concentration. On the other hand, the K and N contents were not affected significantly by NaCl salinity. http://www.phytoparasitica.org posting Nov. 19, 2006.     

Impact of Exogenous Application of Salicylic Acid on Growth,Water Status And Antioxidant Enzyme Activity of Strawberry Plants (Fragaria vesca L.) Under Salt Stress Conditions

Irrigation with saline water can act as an alternate water resource and thus plays an important role in saving freshwater resources as well as promoting agriculture. Furthermore, salinity stress is considered one of the major abiotic stress factors, which strongly reduces crop productivity. In this context, the present work was conducted to examine the effect of exogenous salicylic acid (SA) application on salt stress tolerance of strawberry plants. For this purpose, strawberry plants (Fragaria vesca L.), three months old, were treated with three SA concentrations (0?mM, 0.25?mM and 0.5?mM), then subjected to 80?mM NaCl or not. After five weeks of treatment, growth responses, water status, photochemical efficiency and oxidative stress indicators were measured. The obtained results showed that irrigation with saline water negatively affected the growth parameters, the leaf water potential (LWP), the relative water content (RWC), the stomatal conductance (gs) and photochemical efficiency (Fv/Fm). While, the total protein content, the electrolyte leakage (EL), the malondialdehyde (MDA) and the hydrogen peroxide (H₂O₂) contents were increased in stressed plants compared to unstressed ones. Salt stress also leads to the activation of the antioxidant enzymes. However, the exogenous application of SA under salt stress conditions reduced the H₂O₂ accumulation, the electrolyte leakage and the MDA content. It has also improved the growth parameters, the LWP, the RWC, the gs, the Fv/Fm, the protein content and the antioxidant enzyme activities (POD, CAT and SOD) in the treated plants compared to those without SA application. Therefore, the beneficial effect of 0.25?mM SA on Fragaria vesca L. salinity tolerance may provide some practical basis for strawberry cultivation under saline conditions.

     

四翅滨藜主要渗透调节物质对NaCl胁迫累积的响应

采用盆栽沙培方法,研究四翅滨藜主要渗透调节物质对NaCl浓度和盐胁迫时间的响应。结果表明：① 胁迫时间对四翅滨藜叶片中脯氨酸、Na⁺、K⁺、Cl^-含量和K⁺/Na⁺有极显著影响。随着胁迫时间的延长,叶中脯氨酸、Na⁺含量增加,K⁺含量、K⁺/Na⁺下降,Cl-含量变化趋势较复杂;NaCl胁迫<40 d时,脯氨酸和Na⁺含量增加幅度相对较小,>40 d时均大幅增加。② NaCl浓度对四翅滨藜叶片中脯氨酸、Na⁺、K⁺、Cl^-含量和K⁺/Na⁺也有极显著影响。随着NaCl浓度的增加,叶中脯氨酸、Na⁺含量增加,K⁺含量、K⁺/Na⁺下降;高NaCl浓度处理下,脯氨酸和Na⁺含量增加幅度以及K⁺含量、K⁺/Na⁺下降幅度均较大。③ 四翅滨藜体内离子运输具有选择性。盐胁迫下,根向茎选择运输K⁺,将Na⁺滞留在根部;茎向叶选择运输Na⁺,抑制了K⁺向叶片的运输,使从根部运输的K⁺贮存在茎中;不同营养器官中K⁺/Na⁺从高到低依次为：茎>叶>根,并且都随着NaCl浓度的增加而降低。随着胁迫时间的延长,NaCl浓度对脯氨酸、K⁺、Na⁺及K⁺/Na⁺的影响逐渐放大,并且NaCl浓度与胁迫时间的交互作用也对以上指标（除K⁺外）有极显著影响,因此在研究盐分浓度对植物盐胁迫的影响时,应考虑时间因素及盐分浓度与胁迫时间的交互作用。
     

Effect of Azospirillum and Azotobacter Species on the Performance of Cherry Tomato under Different Salinity Levels

Abiotic stress has a negative impact on plant physiology, influencing the overall growth and development of plant crops. Saline stress is one of the most serious environmental issues limiting crop plant production. Biofertilizers are reparative elements used in soil to increase tolerance to salinity and drought stress. We investigated the effect of salinity stress on qualitative and quantitative characteristics of cherry tomato plants (Lycopersicon esculentum cerasiforme) with biofertilizer application 0, 15 and 30 days after transplanting in this study. After different days of transplantation, different levels of salinity (0, 50, 100, and 150?mM) were used with biofertilizer (Azospirillum sp. and Azotobacter sp.) application (0, 15 and 30 days). The salinity (150?mM NaCl) significantly affected the studied variables, which were recorded with minimum levels of leaf area (52.42?cm²), root length (6.54?cm), fresh root weight (13.64?g), yield (6.52 tons/ha), leaf chlorophyll content (36.11?mg/m²) and maximum levels of total soluble solids (TSS, 8.87 °Brix). Control samples had higher leaf area (58.35?cm²), root length (15.23?cm), fresh root weight (17.86?g), yield (9.39 tons/ha), leaf chlorophyll content (44.09?mg/m²), and lower TSS (7.93 °Brix). Plants that received biofertilizer (15 days after transplanting) had higher plant height (73.41?cm), stem diameter (0.74?cm), leaf area (61.16?cm²), root length (15.35?cm), fresh root weight (18.38?g), root dry matter (60.41%), yield (10.43?t/ha), leaf chlorophyll content (42.55?mg/m²), fruit dry matter content (10.12?g), pH 4.52, and TSS (9.30 °Brix). The minimum plant height (51.33?cm), stem diameter (0.55?cm), leaf area (49.60?cm²), root length (7.04?cm), fresh root weight (12.76?g), root dry matter (42.16?g), yield (5.15 tons/ha), leaf chlorophyll content (35.18?mg/m²), fruit dry matter content (6.59?g), pH 4.27 and TSS (7.55 °Brix) were recorded in plants with no application of biofertilizer. The present study revealed that most growth and quality variables were negatively affected by salinity except for TSS, which showed positive effect with application of 150?mM of NaCl. Biofertilizer application at 15 days significantly influences the quantitative and qualitative attributes of cherry tomato under different levels of salinity.

     

Capillary barriers improve reclamation in drastically disturbed semiarid shrubland

Soils in arid climates affected by drastic disturbance do not recover without reclamation efforts, and saline-sodic conditions caused by development activities are especially problematic. To improve reclamation success, we created seeded depressions that held three types of sand capillary barriers in October 2013. Sand was placed above (mulch), below (capillary barrier), and encompassing (dual barrier) seeded native soil at ridge and depression sites near Wamsutter, WY, representative of natural gas extraction areas. We compared grass growth, salinity, and moisture among the treatments and under depressions without sand amendments (pit) and plots seeded by standard procedures (control). At the ridge site, the mulch treatment supported 249 stems?m^?2 in the seeded patches surviving to August 2014, compared with 110 and 89 stems?m^?2 in the pit and lower barrier treatments, respectively, less than 50 stems?m^?2 in the dual barrier treatments, and none in the control. The dual barrier and mulch treatments performed best at the depression site, with 40–50 stems?m^?2 in August compared with none in the other three treatments. Changes in soil moisture and salinity were variable, but indicate positive effects of capillary barriers. Capillary barriers led to reductions or smaller increases in salinity than in treatments without a capillary barrier. While mulch treatments effectively increased grass growth at both sites, the dual barriers only showed positive impact at the depression site, possibly due to adequate moisture. Sand is readily available in many regions, and scaling up from test plots may be achieved with existing equipment.     

Effects of spermidine and salinity stress on growth and biochemical response of paraquat‐susceptibe and ‐resistant goosegrass (Eleusine indica L.)

This study aimed to investigate the interaction effect of spermidine (Spd) and salinity stress on growth, photosynthetic rate, antioxidant system and free polyamines (PAs) contents of goosegrass (Eleusine indica L.) seedlings. E. indica was raised in a growth chamber under normal and toxic salt stress (100 mM of NaCl) and sprayed with 0 and 1.00 mM of Spd. The degree of growth inhibition caused by salt stress was lower in a paraquat‐resistant (R) biotype compared to a paraquat‐susceptible (S) biotype. Salt stress significantly elevated the accumulation of malondialdehyde, electrolyte leakage and proline and resulted in the degradation of chlorophyll; reduction in chlorophyll fluorescence; and a decrease in photosynthetic rate, relative water content and biomass. Spd‐treated plants maintained higher activities of antioxidant enzymes (catalase, superoxide dismutase and peroxidase), a greater rate of photosynthesis and lower osmotic pressure than untreated plants in the S biotype. Endogenous Spd content was reduced significantly in response to salt stress in both biotypes, but free PAs content in the S biotype was remarkably enhanced with exogenous Spd application under normal or salinity stress conditions. The result indicated that the S biotype was more sensitive to salinity than the R biotype; meanwhile, exogenous Spd maybe play an important role in protecting S biotype plants from salt stress.     

Candidate halophytic grasses for addressing land degradation: Shoot responses of Sporobolus airoides and Paspalum vaginatum to weekly increasing NaCl concentration

In many arid and semiarid regions worldwide, high levels of soil salinity is a key driver of land degradation, as well as a key impediment to re-establishing plant cover. Combating land degradation and erosion associated with soil salinity requires experimental determination of plant species that can grow in soils with high levels of salinity and can be used to re-establish plant cover. Herein, we evaluated the responses of untested candidate cultivars of two halophytic grass species to high soil salinity: alkali sacaton (Sporobolus airoides Torr.) and seashore paspalum (Paspalum vaginatum Swartz). We evaluated the growth responses of both species in a greenhouse under control (no-salt) and various levels of NaCl salinity (EC 8, 16, 24, 32, 40, and 48?dSm^?1) using Hoagland solution in a hydroponics system in a randomized complete block design trial. At all salinity levels, sacaton grass had a greater shoot height, shorter root length, lower shoot fresh and dry weights, and poorer color and general quality compared to seashore paspalum. The shoot fresh and dry weights of both grasses were greatest at the low to medium levels of salinity, with the greatest response observed at EC 16?dSm^?1. At the highest level, salinity significantly reduced shoot fresh and dry weights of both grasses. Because growth of both halophytic species exhibited high tolerance to salinity stress and were stimulated under low to medium levels of salinity, both species could be considered suitable candidates for re-establishing plant cover in drylands to combat desertification and land degradation associated with high levels of soil salinity.     

Growth and chemical composition of soybeans as affected by trifluralin and soil salinity

The combined effects of 0, 1 and 2 ppm trifluralin and five soil salinity levels (0.35, 2, 4, 6 and 8 mS/cm) on growth and chemical composition of soybeans [Glycine max (L.) Merr.] were studied in a glasshouse experiment. Analyses of variance indicated that the interaction of soil salinity and trifluralin was not significant for root and top dry weights and root nodulation. Root dry weight was not affected by trifluralin, whereas 2 ppm trifluralin significantly reduced top dry yield and root nodulation. Shoot and root yields and root nodulation were reduced with increasing soil salinity. Trifluralin at 1 ppm significantly decreased P concentration and at 2 ppm substantially increased N concentration. Moreover, there was a general trend of an increase in N concentration and a decrease in P concentration with salinity. The concentration and uptake of Cl and Na increased with increasing soil salinity. Probably large accumulations of Cl and Na and/or water stress caused by high salinity were responsible for growth reductions in salinized media.     

Rehabilitation of abandoned areas from a Mediterranean nature reserve by Salicornia crop: Influence of the salinity and shading

In Reserva Natural de Castro Marim e Vila Real de Santo António (SE of Portugal), most of the salt marshes and saltpans are abandoned contributing to their degradation and, consequently, alteration of some ecological conditions. Rehabilitation of these areas by a Salicornia crop can contribute to their economic and environmental improvement by stimulation of biogeochemical processes and biomass commercialization. However, the development of agro-techniques adjusted to species and variable environmental conditions from Mediterranean are needed in order to improve the Salicornia crop. This study aimed to evaluate: i) potential use of seedlings from greenhouse in the field cultivation; and ii) survival, growth and yield of Salicornia under shading and different salinity conditions of the soils and irrigation waters. Autochthonous Salicornia species (S. ramosissima and S. patula) were tested. Germination tests under controlled conditions and in situ mesocosm assays were carried out. Assays were realized with a low density of seedlings from natural conditions and greenhouse, and soils and waters from estuary both with different salinities. Intermediate and high salinities (25–45?dS/m) affected only S. patula germination. In general, Salicornia growing in soils with low salinity had great fresh biomass accumulation independently of seedling source (from natural conditions and greenhouse) and/or growing season. The shading seems to improve the fresh biomass accumulation and yield. Under Mediterranean conditions, the transplantation of Salicornia from greenhouse to the field was a promising technique, independently of the salinity conditions. This study demonstrated that the abandoned and saline areas can be rehabilitated by a sustainable crop of Salicornia.     

Subsurface Drainage for Rehabilitation of Waterlogged Saline Lands: Example of a Soil in Semiarid Climate

In irrigated agriculture of arid and semiarid regions, soil salinity, coupled with waterlogging, is a serious problem. Provision of subsurface drainage seems to be a prerequisite for optimal crop production. A study was conducted to evaluate the long term (8-year) impact of a subsurface drainage system on soil properties and yields of wheat. The study was located in a severely affected, waterlogged, barren, sandy loamsaline soil (Comborthids). The subsurface drainage system was installed at a 1.75 m depth with three drain spacings (25, 50, and 75 m). The drains facilitated reclamation of the waterlogged saline land which had variations in salt removal with space and time. The removal of salts from the root zone varied initially with distance from the drain and with depth. However, after a few years, the variations were reduced and the land was reclaimed sufficiently to grow most of the crops of the region. Plots provided with a drain spacing of 75 m required more time for complete reclamation compared to plots provided with 25 m drain spacing. Leaching through subsurface drainage increased soil porosity, modulus of rupture, infiltration rate, organic carbon, available nitrogen, phosphorus, potassium, and available water, and decreased bulk density differently in the three drain spacings (20, 50, and 75 m). In the 75 m drain spacing plots, soil salinity (EC e ) and water content remained higher than in the 25 and 50 m drain spacing plots. Soil EC e and water content were less near the drains, were highest in areas midway between the drains, and the effects were more apparent in the summer season. Wheat grain yield decreased with increasing drain spacings in the initial years of reclamation. With the gradual improvement in soil salinity, yields from plots with a 75 m spacing reached those of the narrower drain spacing plots by the fourth year. It was concluded that by installing a subsurface drainage system in a monsoon climate, waterlogged saline soils can be reclaimed by the natural leaching that can take place from rainfall. The optimum yield can be attained with a drain spacing of 75 m, which is 50% more than the design spacing of 50 m. Faster reclamation and more yield were obtained with a 25 m drain spacing and was achieved at a higher cost for the more expensive drainage system.     

Ascorbic Acid Enhances Growth and Yield of Sweet Peppers (Capsicum annum) by Mitigating Salinity Stress

Salinity is a crucial problem which has affected crop productivity globally. Ascorbic acid is considered helpful against abiotic stresses due to its powerful antioxidant potential. In the pot experiment, salinity stress (0, 35, 70, and 105?mM) was applied to sweet peppers in split doses after 20 days of transplantation. To mitigate the adverse effects of salinity, ascorbic acid (0, 0.40, 0.80, and 1.20?mM) was applied as foliar spray after a 6-day interval during vegetative growth. Sweet pepper plants sprayed with distilled water (control) recorded maximum plant height (cm), leaf area (cm²), number of branches, stem diameter (mm), number of fruit plant^?1, fruit diameter (cm), yield plant^?1 (g), and chlorophyll content (mg 100?g^?1), while the maximum polyphenol oxidase (PPO) activity (unit mg protein^?1 min^?1) and ascorbate peroxidase (APX) activity (unit mg protein^?1 min^?1) were recorded in plants treated with 70?mM NaCl application. Salinity stress beyond 70?mM significantly reduced all the studied parameters. An ascorbic acid concentration of 1.20?mM significantly mitigated the negative effects of salt stress and recorded maximum plant height (cm), number of leaves plant^?1, leaf area (cm²), number of branches plant^?1, stem diameter (mm), number of fruit plant^?1, fruit diameter (cm), yield plant^?1 (g), chlorophyll content (mg 100?g^?1), PPO activity (unit mg protein^?1 min^?1), and APX activity (unit mg protein^?1 min^?1). Hence, a 1.20?mM concentration of foliar ascorbic acid could be used in saline conditions up to 70?mM of sodium chloride (NaCl) for better growth, productivity, and enzymatic activity of sweet peppers.

     

Tillage and herbicide treatments with inter‐row cultivation influence weed densities and yield of three industrial crops

Field experiments were conducted in northern Greece in 2003 and 2004 to evaluate effects of tillage regimes (moldboard plowing, chisel plowing, and rotary tilling), cropping sequences (continuous cotton, cotton‐sugar beet rotation, and continuous tobacco) and herbicide treatments with inter‐row hand hoeing on weed population densities. Total weed densities were not affected by tillage treatment except that of barnyardgrass (Echinochloa crus‐galli), which increased only in moldboard plowing treated plots during 2003. Redroot pigweed (Amaranthus retroflexus) and black nightshade (Solanum nigrum) densities were reduced in continuous cotton, while purple nutsedge (Cyperus rotundus), E. crus‐galli, S. nigrum, and johnsongrass (Sorghum halepense) densities were reduced in tobacco. A. retroflexus and S. nigrum were effectively controlled by all herbicide treatments with inter‐row hand hoeing, whereas E. crus‐galli was effectively reduced by herbicides applied to cotton and tobacco. S. halepense density reduction was a result of herbicide applied to tobacco with inter‐row hand hoeing. Yield of all crops was higher under moldboard plowing and herbicide treatments. Pre‐sowing and pre‐emergence herbicide treatments in cotton and pre‐transplant in tobacco integrated with inter‐row cultivation resulted in efficient control of annual weed species and good crop yields. These observations are of practical relevance to crop selection by farmers in order to maintain weed populations at economically acceptable densities through the integration of various planting dates, sustainable herbicide use and inter‐row cultivation; tools of great importance in integrated weed management systems.     

Effect of salinity on tissue nutrient contents of the four dryland tree species of Indus flood plains

Salinity is a common issue of semi-arid and arid lands rendering them unfit for agriculture. Saline wastelands can be converted into productive ecosystems by rehabilitating them with salt tolerant native tree species. The objective of this work was to study the effect of NaCl salinity on tissue nutrient contents of the four dryland tree species. Saplings were grown in pots under nonsaline and high salinity conditions. After eighteen weeks the plants were harvested and their tissue nutrient contents were analyzed. Results revealed that all species accumulated high amounts of Na⁺ under saline conditions, while concentrations of N, P and Mg²⁺ decreased in their tissues. Concentrations of K⁺ and Ca²⁺ showed more variable trend in various tissues in response to increase in soil salinity. Na⁺: K⁺ ratios of roots (1.57), stems (1.27), and leaves (1.66) of salinized Salvadora oleoides plants were lowest among all the four species. Root Na⁺: K⁺ ratio of salinized plants was significantly higher for Prosopis cineraria (7.10), while these ratios for stem (1.85) and leaf (3.42) were highest for Tamarix aphylla. Plants of P. cineraria showed lowest Stem-Na⁺/root-Na⁺ ratio (0.30) when subjected to salinity. Results showed that salinity induces nutrient deficiency in all species. Salinity tolerance of these species can be attributed to their ability to (i) restrict translocation of Na⁺ from roots to stem; (ii) keeping low tissue Na⁺: K⁺ ratios; and (iii) selectivity of K⁺ and Ca²⁺ over Na⁺, and can be used for the screening of salt-tolerant ecotypes for the rehabilitation of saline wastelands.