Salih Aydemir

Exogenous application of mannitol and thiourea regulates plant growth and oxidative stress responses in salt-stressed maize (Zea mays L.)

Abstract The mechanism of growth amelioration in salt-stressed maize (Zea mays L. cv., DK 647 F1) by exogenously applied mannitol (M) and thiourea (T) was investigated. Maize seedlings were planted in pots containing perlite and subjected to 0 or 100 mM NaCl in full strength Hoaglands nutrient solution. Two levels of M (15 and 30 mM) or T (3.5 and 7.0 mM) were sprayed to the leaves of maize seedlings 10 days after germination. Salinity stress caused considerable reduction in plant dry biomass, chlorophyll content, and relative water content in the maize plants. However, it increased the activities of catalase (CAT; EC 1.11.1.6), superoxide dismutase (SOD; EC 1.15.1.1), and polyphenol oxidase (PPO; EC 1.10.3.1), and levels of hydrogen peroxide (H2O2) and electrolyte leakage, but it did not change peroxidase (POD; EC 1.11.1.7) activity. Foliar application of M or T was found to be effective in checking salt-induced shoot growth inhibition. Exogenously applied M or T reduced the activities of CAT, SOD, POD, and PPO in the salt-treated maize plants compared to those in the plants not fed with these organic compounds. Salinity increased Na+ contents but decreased those of K+, Ca2 +, and P in the leaves and roots of the maize plants. Foliar-applied M or T increased the contents of K+, Ca2 +, and P, but decreased that of Na+ in the salt-stressed maize plants with respect to those of the salt-stressed plants not supplied with mannitol or thiourea. Mannitol was found to be more effective than thiourea in improving salinity tolerance of maize plants in terms of growth and physiological attributes measured in the present study.

Quantification of soil features using digital image processing (DIP) techniques

A new thin section method is introduced which provides reliable, automated classification of mineral, non-mineral constituents (e.g. organic matter), non-crystalline, or poorly crystalline components (e.g. Fe–Mn oxides) and voids. A color image flatbed scanner scanned 10 soil thin section slides that contain the same features. Equal portions (about 6.3 cm 2 ) of each slide were imported into the Erdas Image Processing software (version 8.4) as 24 bit 3-band images. Images were classified with an unsupervised nearest neighbor classification method with several different processing steps. Five different classes were separated and quantified for each sample. Classified features were checked with 500 reference points under the petrographic microscope. Separation and identification was almost 100% for calcite, about 97% for void in all samples, but values decreased for sesquioxides, plasma, and quartz (96%, 96%, and 80%, respectively). Quantitative results of digital image processing based on pixel number of each class (aerial percentage) were compared with traditional point-counting method. Digital image processing results showed slightly lower values for voids, quartz, and sesquioxides, but higher values for plasma and almost equal quantity for calcite in all three samples when compared with the values of the point-counting method. This technique represents a significant improvement in quantitative soil micromorphology. Requirement of simple and inexpensive hardware and quick and routine identification and quantification of features (calcite, void, sesquioxides, and plasma) with much less error than other methods are two advantages of the proposed method to the earlier studies. D 2003 Elsevier B.V. All rights reserved.

The Use of Hyperspectral Visible and Near Infrared Reflectance Spectroscopy for the Characterization of Salt-Affected Soils in the Harran Plain, Turkey

The quality of lands may be degraded by the accumulation of salts in soils, which is typically measured as soil Electrical Conductivity (ECe). High-salinity soils developed in low elevation spots in the Harran Plain after the initiation of intensive irrigation and crop production on clayey soils under high evaporation. This study evaluated the feasibility of using hyperspectral Visible and Near Infrared Reflectance Spectroscopy (VNIRRS) as a potentially more cost-effective approach for the characterization of soil salinity. 150 locations were taken at 0–15 and 15–30 cm depths from an area of 1000 ha with salinity levels ranging from none to very high. Sieved soils were measured for ECe using saturation paste and also scanned by VNIRRS in both air dried and oven dry states. For spectral preprocessing, raw reflectance spectra were averaged over 10 nm and a continuum removal (CR) method was applied. Calibration models between spectra and ECe were based on Multiple Adaptive Regression Splines (MARS), Partial Least Square Regression (PLSR), and Classification and Regression Trees (CART, for groupings). The VNIRRS data were also combined with topographical parameters from digital elevation models to improve estimations. Results showed that the estimation quality of ECe varied depending on approaches used, with the best results using continuum removed spectra of oven dried samples using MARS after separating samples containing high amounts of gypsum (R2 = 0.86, RPD = 2.70). Topographical variables with VNIRRS data improved estimations up to 12%. CART analysis showed that soils could be categorized as saline and non-saline based on soil reflectance with 65% accuracy.

Application of two amendments (gypsum and langbeinite) to reclaim sodic soil using sodic irrigation water

In this study, gypsum, a common amendment for sodic soil reclamation, was compared with langbeinite, a lesser used and known mineral. A column leaching experiment using sodic water was conducted on a sodic, non-saline soil (fine, montmorillonitic, thermic Ruptic Vertic Albaqualf) dominated by smectitic clays. Soil was amended with gypsum and langbeinite at rates equivalent to exchangeable Na at soil depths of 0.15 and 0.30 m. The soil water at depths of 0.75, 0.15, and 0.225 m and the effluent from each column were collected at intervals of 12 h and analysed for soluble bases. Sodium adsorption ratio (SAR) was calculated from soluble salts. Saturated hydraulic conductivity (Ksat) was calculated. At the end of the experiment, soil samples were removed from each column in 4 depth increments. Significantly less exchangeable Na and lower SAR of the soil water was found in the lower sections of the soil columns, and Ksat was greater for the amended treatments than for the control. High solubility of the langbeinite resulted in the highest Ksat value, with possible increase in electrolyte concentration and reduction of clay swelling and dispersion in the first 12 h. However, there was no significant difference in reclamation efficiency between equivalent rates of 2 amendments throughout the experiment. This experiment indicated that factors influencing the decision about using either amendment should be availability of the product, the seasonal fluctuation in price, required reclamation time, and the crop needs for Ca or Mg and K.

Mitigation effects of mycorrhiza on boron toxicity in wheat (Triticum durum) plants

Abstract A greenhouse study was conducted to investigate the effect of mycorrhiza on wheat (Triticum durum) boron (B) uptake under excessive B concentrations. Three levels of B (0, 3, and 6 mg B litre−1) were added to pots with or without mycorrhiza. Plant nutrients were added as Hoagland nutrient solution. In general, additions of B with or without mycorrhiza decreased wheat relative yield and increased shoot and root B concentrations. B concentrations in shoots ranged from 30.8 to 589 mg kg−1. The highest shoot B concentrations were with the highest B treatments (6 mg B litre−1), whereas the lowest concentrations were in the control (0 mg B litre−1). Mycorrhiza inoculation significantly improved relative yield of unstressed (control) plants, but those increases in relative yield of B‐stressed plants were not significant. In general, mycorrhiza inoculation decreased shoot and root B concentrations and uptake. Wheat growing at high B concentrations (6 and 3 mg B litre−1) with or without mycorrhiza showed leaf edge burning and necrosis compared with control treatments. The data suggested that mycorrhiza infection can prevent plants from an excessive concentration and uptake of B although that did not improve plant yield. Further evaluation is needed for the effects of mychorriza inoculation on B toxicity.

AMELIORATIVE EFFECT OF INDIGENOUS CALCITE ON SODIUM-SATURATED CLAY SYSTEMS

The role of calcium (Ca)-containing amendments in ameliorating the deleterious effects of sodium (Na) on soil hydraulic conductivity and infiltration rates has been extensively studied. Nevertheless, the effect of indigenous calcite itself on Na-saturated soil (clay) systems has not been clearly documented yet. The effect of calcite dissolution from different calcite (Wards standard 46-W-1435-PAC) containing columns and the ameliorative effects on Na-saturated clayey (SWy-1 montmorillonite) systems was examined from two different perspectives: i) leaching the columns with Na/Ca solutions of SAR 10 (sodium adsorption ratio), and ii) leaching the same columns again using deionized water (simulating the process in which rainfall percolates through Na-affected calcareous and noncalcareous soils). As the columns were leached with SAR 10 water, the SAR of the leachates decreased, and the pH increased considerably with the calcite dissolution. A higher level of carbon dioxide in the SAR 10 water drastically increased the effect of calcite in reducing exchangeable sodium percentage. When deionized water was applied to the columns, the pH values were about 10, and calcite dissolution was enhanced. With the calcite-containing columns, a linear relationship between electrical conductivity and hydraulic conductivity was found during the leaching with deionized water. As leaching continued, dispersion eventually subsided as Ca for Na exchange resulted in reduced exchangeable sodium percentage. Higher carbon dioxide concentrations of the extractant resulted in increased calcite dissolution and prevented clay dispersion. These results suggest that the dissolution of indigenous calcite alone may be sufficient to significantly change the composition of the soil solution, which results in improving the effectiveness of the soil to resist the negative impact of sodic conditions.

Regulation of growth and some key physiological processes in salt-stressed maize (Zea mays L.) plants by exogenous application of asparagine and glycerol

Abstract Maize seedlings were subjected to concentrations of 0 and 100mMof NaCl in Hoagland’s nutrient solution medium in plastic pots containing perlite. Two levels of asparagine (5 and 10 mM) and glycerol (20 and 40 mM) were sprayed onto the leaves of maize seedlings 10 days after germination. Saline stress caused considerable decline in total dry mass, chlorophyll content and relativewater content in the maize plants. It increased the activities of superoxide dismutase, catalase and polyphenol oxidase as well as electrolyte leakage, but did not alter the activity of non-specific peroxidise. Foliar application of asparagine or glycerol was found to be effective in checking shoot growth inhibition under NaCl stress. Exogenously applied asparagine or glycerol reduced superoxide dismutase, non-specific peroxidase and polyphenol oxidase activities in salt-stressed maize plants compared to those not treated with these organic compounds. Salinity increased Na+ contents but reduced those of K+, Ca2+ and P in the roots of the used genotype of maize. Foliar application of asparagine or glycerol increased the contents of K+, Ca2+ and P, but it reduced that of Na+ in salt-stressed maize plants as compared to those of the salt-stressed plants not supplied with glycerol or asparagine. Glycerol was more effective than asparagine in improving salinity tolerance of maize plants in terms of growth and physiological attributes measured in the present study

Exchangeable Sodium Accumulation with Irrigation in Soils under Turfgrass

Abstract Many municipal water supplies in southeast Texas have a relatively high level of Na+ and a low total of dissolved solids. Most soils of this area are dominated by smectitic clays that respond to wetting by swelling, especially when wetted with high Na+ waters of low salinity. This study assessed the degree of Na+ accumulation in southeast Texas soils under irrigated turfgrass and tested models predicting Na accumulation. The Ap, E, and Bt horizons of 18 turf soils in 10 municipal water districts were studied. Irrigation water sodicity (SARiw) and salinity (ECiw) were strongly correlated with soil sodicity (SARe) and salinity (ECe). The SARiw was found to be the best single variable to model soil Na accumulation, but exchangeable Na also increased as a function of years of irrigation. The multiple‐regression equation: SARe=− 5.16+0.53 SARiw+4.04 ln (yr) (R2=0.86) best predicted SARe to a depth of 30 cm. In the first 10 years, the rate of increase of SARe would increase rapidly, then it would gradually increase after about 10 years and would probably reach equilibrium after 15‐year irrigation.

Determination of Zinc Phytoavailability in Soil by Diffusive Gradients in Thin Films

Assessment of zinc (Zn) phytoavailability by the newly developed technique of diffusive gradients in thin films (DGT) has started gaining more importance because of some advantages over routine soil extractants. A greenhouse study was conducted to determine Zn phytotoxicity thresholds and the phytoavailability of Zn to sorghum sudan (Sorghum vulgare var. sudanese) grass by DGT, compared with calcium chloride (CaCl2) extraction. Treatments were five Zn levels and two soil pH (6.5 and 6). To obtain various amounts of Zn phytoavailability, soils having two different pH values were amended with zinc sulfate (ZnSO4) at rates of 0, 150, 300, 600, and 1200 mg Zn kg−1. Control soil (pH = 6.5) was treated with predetermined elemental sulfur to create different soil pH values (6). Shoot and root Zn concentrations ranged from 27 to 827 mg kg−1 and 101 to 2858 mg kg−1, respectively. In general, the Zn concentrations in shoots and roots were increased by increasing Zn concentrations and soil pH. Increasing applied Zn to soil decreased the plant biomass yield and increased adsorption of Zn by DGT. Calcium (Ca) to Zn ratios for all treatments except controls were <26 for shoots and <13 for roots. The CaCl2‐extractable Zn and effective concentration (CE) correlated well with plant Zn concentration. A critical shoot Zn concentration for 90% of the control yield was chosen as an indicator of Zn toxicity. The performance of DGT, CaCl2 extraction, Ca/Zn ratio and plant Zn concentrations were similar for assessing Zn phytoavailability.