Comparison of the individual salinity and water deficit stress using water use, yield, and plant parameters in maize.

Though water deficit and salinity effects on plants have similarities, they are physiologically different. This motivated us to separately explore the effects of salinity and water deficit on water consumption, yield, and some plant parameters for maize (Zea mays L., var. SC704). Greenhouse experiments were conducted during two seasons. In one experiment, maize was cultivated in wet soil (matric potential of - 10 kPa), and the irrigation water salinity was varied between treatments (osmotic potentials up to - 336 kPa). In a parallel experiment, five water deficit levels were maintained by irrigating with water to accomplish the same daily water uptake as in the salinity treatments. The experiments were conducted in pots with a randomized design and four replicates. Salinity and water deficit stress significantly affected yield and other plant parameters. However, root dry matter in autumn was not significant. We observed a profound effect of evaporative demand on most of the plant parameters and water use, such as water use efficiency (WUE). For same water use rate, the values of osmotic and matric potential were different. In spring season, the ratios of matric to osmotic potential were 0.25, 0.46, 0.44, and 0.43 in corresponding D1, D2, D3, and D4 water deficit and S1, S2, S3, and S4 salinity treatments. For autumn season, these ratios were 0.26, 0.36, 0.34, and 0.36. We concluded crop models that lump water deficit and salinity (additively or multiplicatively) to predict yields can result in inappropriate predictions.

The effect of biochar on severity of soil water repellency of crude oil-contaminated soil.

Crude oil contamination adversely affects soil water repellency. In this study the effect of biochar on this soil characteristic has been investigated in the laboratory. Soil sample was collected from a field located near Pars Oil Company, at the top depth of 0-15 cm below surface. After air-drying and passing through a 2-mm sieve, the soil was artificially contaminated with four levels of crude oil (1:0, 1:25, 1:16.6, and 1:12.5 ratios). Biochars used in this research were generated from beechwood and maize residues at three different pyrolysis temperatures (350 °C, 550 °C, and 750 °C). Chemical functionality of all biochar samples was determined using Fourier-transform infrared spectrometry. Sufficient amounts of beechwood and maize biochars, passed through a 0.053-mm and 2-mm sieves, were mixed into crude oil-contaminated soil at the rate of 0, 0.5, 1, and 2% of total dry soil weight. The mixed samples were then laboratory incubated for 90 days at 24 °C and 10% soil moisture. Water repellency was measured using water drop penetration time (WDPT). The experimental results showed that functional groups on the biochars' surfaces produced at the studied temperatures were distinct. Beechwood and fine size of biochar showed more ability in reducing the hydrophobicity. The produced biochars, at higher temperature, had more potential to alleviate water repellency due to the strong interactions between functional groups of biochars and crude oil. The highest amount of biochar used (2%) significantly alleviated water repellency.

Root-induced changes of Zn and Pb dynamics in the rhizosphere of sunflower with different plant growth promoting treatments in a heavily contaminated soil.

Root induced changes are deemed to have an important role in the success of remediation techniques in contaminated soils. Here, the effects of two nano-particles [SiO2 and zeolite] with an application rate of 200mgkg-1, and two bacteria [Bacillus safensis FO-036b(T) and Pseudomonas fluorescens p.f.169] in the rhizosphere of sunflower on Zn and Pb dynamics were studied in greenhouse conditions. The treatments reduced the exchangeable Zn (from 13.68% to 30.82%) and Pb (from 10.34% to 25.92%) in the rhizosphere compared to the control. The EC and microbial respiration/population of the rhizosphere and bulk soil had an opposite trend with the exchangeable fraction of Zn and Pb, but dissolved organic carbon followed a similar trend with the more bioavailable fractions. As a result, the accumulation of Pb and Zn in the plant tissues was significantly (p < 0.05) reduced by the application of amendments, which might be due to the shift of the metals to immobile forms induced by the nature of the treatments and changes in the rhizosphere process. The empirical conditions of this research produced the intensification of the rhizosphere process because the findings highlight those changes in the rhizosphere EC, pH and dissolved organic carbon can affect the efficiency of zeolite/SiO2 NPs and bacteria to immobilize Pb and Zn in the soil, depending on the chemical character of the metals and the treatments. Generally, the affinity of the biotic treatment for Pb was more than the abiotic and conversely, the abiotic treatment showed a higher ability to immobilize Zn than the biotic treatment.

Geochemical fractions and phytoavailability of Zinc in a contaminated calcareous soil affected by biotic and abiotic amendments.

Many studies have conducted to determine the best management practice to reduce the mobility and phytoavailability of the trace metals in contaminated soils. In this study, geochemical speciation and phytoavailability of Zn for sunflower were studied after application of nanoparticles (SiO2 and zeolite, with an application rate of 200 mg kg-1) and bacteria [Bacillus safensis FO-036b(T) and Pseudomonas fluorescens p.f.169] to a calcareous heavily contaminated soil. Results showed that the biotic and abiotic treatments significantly reduced the Zn concentration in the aboveground to non-toxicity levels compared to the control treatment, and the nanoparticle treatments were more effective than the bacteria and control treatments. The concentration of CaCl2-extractable Zn in the treated soils was significantly lower than those of the control treatment. The results of sequential extraction showed that the maximum portion of total Zn belonged to the fraction associated with iron and manganese oxides. On the contrary, the minimum percent belonged to the exchangeable and water-soluble Zn (F1). From the environmental point of view, the fraction associated with iron and manganese oxides is less bioavailable than the F1 and carbonated fractions. On the basis of plant growth promotion, simultaneous application of the biotic and abiotic treatments significantly increased the aboveground dry biomass yield and also significantly reduced the CaCl2-extractable form, uptake by aboveground and translocation factor of Zn compared to the control treatment. Therefore, it might be suggested as an efficient strategy to promote the plant growth and reduce the mobile and available forms of toxic metals in calcareous heavily contaminated soils.