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ABSTRACT:The swelling rate and the environmental sensitivity of novel superabsorbent gum arabic-acrylic hydrogel hybrids were investigated. The swelling kinetics of the hydrogel hybrids was studied by means of a Voigt-based viscoelastic model. The effects of concentration of the initiator, crosslinker, and the monomer ratio on the swelling rate were studied. The superswelling properties of the hydrogel hybrids were evaluated in various environmental pH, salinity and solvent-water mixtures. The optimally prepared hydrogel, MR5, showed a reproducible on-off switching behavior when the swelling medium was alternatively changed between distilled water and alkaline solutions. The hydrogel hybrid MR5 was also tested to be swollen and deswollen alternatively in distilled water and sodium chloride solution. The sorption-desorption behavior was found to be quite repeatable. A similar capability was interestingly observed when a calcium chloride solution with the same molar concentration was used. The swelling changes of the hydrogel hybrid were examined in various water-solvent systems including the aqueous solutions of methanol, ethanol, acetone, ethylene glycol, glycerol, and dimethylsulfoxide. One and/or two volume-phase transitions were induced by the nonsolvents. The transitions were explained according to the solubility parameters of the solvents and water-solvent mixtures. The swelling-deswelling capability of the hydrogel in alternatively changed solventwater mixtures was also studied.

Phytohormones, such as auxin and cytokinin, are known to be involved in the regulation of plant responses to salinity stress and counteract the adverse effect of stress conditions. This work investigated the effects of the exogenous spraying of indole-3-acetic acid (IAA) and kinetin (KIN) during the reproductive phase on grain yield by examining the 1000-grain weight and filledgrain percentage as well as the changes in starch, total soluble sugars, sucrose, glucose and fructose concentrations in the grains of two rice cultivars under salt stress. The results indicated that the applied IAA and KIN led to an increased grain yield, 1000-grain weight and filled-grain percentage for both rice cultivars under salt stress. The storage starch content in the grain of the salt-sensitive cultivar was more than that in the salt-tolerant cultivar under IAA application compared with KIN, whereas a decrease in the total soluble sugar content was observed with both IAA and KIN treatments, in comparison to the non-hormone treatment. Interestingly, this study showed that IAA led to a much higher increase in the sucrose content in grain, as compared to the KIN. Furthermore, this experiment suggests that glucose and fructose may play important roles during salt stress because there were clearly higher concentrations of these sugars in the grain of the stressed cultivars under IAA and KIN application: it appears that their accumulation was the earliest response detected during the grain-filling period in rice. Finally, this work indicated that an increase in the rice grain yield, 1000-grain weight and filled-grain percentage are associated with an increase in the contents of starch, sucrose, glucose and fructose in grain caused by the application of IAA and KIN.

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ing N 2 -fixing symbioses with rhizobia. Indeed, Fierro et al. (1997), in a greenhouse experiment, demonstratedThe paper de-inking process produces a waste by-product, dethat growth and nutrition of the N 2 -fixing legumes gainking paper sludge (DPS), which contains paper fibers, clay particles, and inks and has high C and Ca and low N and P concentrations. lega (Galega orientalis Lam.) and sweetclover were not Use of high rates of DPS to increase the soil organic matter thus negatively affected by DPS, provided that sufficient P requires provision of high rates of N for adequate plant growth. Using was supplied. dinitrogen (N 2 )-fixing forage legumes is an alternative to the N fertil-Considerable efforts have been directed to the develization under such circumstances. In a 2-yr field study (1995 and 1996), opment of methods for measuring N 2 fixation (Rennie the effect of different rates of DPS (0, 50, or 100 Mg dry matter ha Ϫ1 ), and Rennie, 1983; Hauck and Weaver, 1986; Shearer applied once in October 1994, were evaluated on symbiotic N 2 fixation and Kohl, 1986; Danso et al., 1993; Chalk and Ladha, of forage legumes established on two soil types in Eastern Quebec, 1999). Selection of a suitable method to estimate N 2 Canada. Symbiotic N 2 fixation was measured in alfalfa (Medicago fixation is of outmost importance. Available methods sativa L.), birdsfoot trefoil (Lotus corniculatus L.), red clover (Trifohave distinct advantages and disadvantages, i.e., experilium pratense L.), and sweetclover (Melilotus officinalis L.); bromegrass (Bromus inermis L.) was used as the reference (non N 2 -fixing) mental conditions, complexity, and cost of analyses. The crop. Dinitrogen fixation was estimated by the 15 N natural abundance methods that are currently the most reliable for demethod. The percentages of N derived from the atmosphere increased termining N 2 fixation imply the use of stable isotopes significantly with DPS in the year of establishment (1995). In the first of N (Unkovich and Pate, 2001). production year (1996), the effects of DPS on N 2 fixation were mainly Nitrogen-15 isotope dilution techniques, including 15 N observed at the first cut. Our results show that DPS used as an natural abundance ( 15 N-NA) and 15 N enrichment ( 15 N-E) organic amendment generally led to similar or greater forage legume methods, to quantify N 2 fixation by legumes, have been productivity and greater N 2 fixation compared with unamended conused extensively. With these methods, N 2 fixation in trols in the first production year and is compatible with sustainable forage legumes can be estimated over long periods of agricultural practices.