Superabsorbent polymer (SAP) materials are hydrophilic networks that can absorb and retain huge amounts of water or aqueous solutions. They can uptake water as high as 100,000%. Common SAPs are generally white sugar-like hygroscopic materials, which are mainly used in disposable diapers and other applications including agricultural use. This article reviews the SAP literature, background, types and chemical structures, physical and chemical properties, testing methods, uses, and applied research works. Due to variability of the possible monomers and macromolecular structure, many SAP types can be made. SAPs are originally divided into two main classes; i.e., synthetic (petrochemical-based) and natural (e.g., polysaccharide- and polypeptide-based). Most of the current superabsorbents, however, are frequently produced from acrylic acid (AA), its salts, and acrylamide (AM) via solution or inverse-suspension polymerization techniques. The main synthetic (internal) and environmental (external) factors affecting the acrylic anionic SAP characteristics are described briefly. The methods for quantifying the SAP practical features, i.e., absorption capacity (both load-free and under load), swelling rate, swollen gel strength, wicking capacity, sol fraction, residual monomer, and ionic sensitivity were discussed. The SAP applications and the related research works, particularly the hygienic and agricultural areas are reviewed. Meanwhile, the research findings on the effects of SAP in soil and agricultural achievements in Iran, as an arid country are treated as well. Finally, the safety and environmental issues concerning SAP practical applications are discussed as well.

In recent years, hydrogels have been considered as one of the mos t promising materials due to their unique properties. Hydrogels are cross-linked hydrophilic polymer s tructures that are able to absorb and holding water or biological fluid. Thus, the hydrogel networks can extensively swell in water media without dissolution. In the las t few decades, hydrogels have been used in various indus tries such as food, packaging, pharmaceutical and drug delivery sys tems, agriculture, biomedical and bioengineering applications, manufacturing of technical and electronic devices, and as adsorbent for the removal of pollutants in environmental applications. Superabsorbent polymer (SAP) hydrogels are a type of hydrogel that, due to the hydrophilic nature of polymer chains can absorb and retain extraordinary large amounts of water or aqueous solution up to hundreds of times their weight. In recent years, new superabsorbent hydrogels have been developed for different applications. High demand for these subs tances, especially in personal hygiene, has led to an increase in their production (now over three million tons per year). Because the main components of commercial and widely used SAPs in indus try are based on raw materials derived from fossil resources (oil, gas and coal), the widespread use of SAPs and their increasing production, on the one hand, have contributed to environmental concerns by contributing to water, soil and air pollution, and, on the other hand, have threatened global price fluctuations and the degradability of fossil resources. Therefore, the replacement of at leas t some components of SAPs with natural, biobased or renewable raw materials (such as lactic acid, succinic acid and itaconic acid) and the production of SAPs with hybrid s tructures have been considered. The purpose of this paper is to review the hybrid SAPs based on some biobased compounds that are used in three s tructural parts of the polymer network including crosslinker, surface modifier and monomer.

The superabsorbent polymers absorb and retain large quantities of water when applied into the soil. This capability is due to its physical and chemical properties. The objectives of this study were to investigate the effects of soil salts on polymer and manure water uptake ability under repeated wetting and drying cycles. The results showed that 1.0 g polyacrylamide made of Iran, had ability to uptake 184.4g distilled water for the first time absorption. It was much less than the same material that had reported in foreign publications. The ability of water retaining for the same polymers was dramatically decreased to 31, 79 and 83 percent than control treatment (distilled water) for waters with 160, 1000 and 2000 mg/l salt concentration, respectively. By 9 times repeated wetting and drying cycles, the ability of polymer had decreased to 22 percent of the first times absorption. As consequently, the amounts of water uptake had also decrease to 72, 81 and 88 percent of distilled water in the same salts after 9 times repeated wetting and drying cycles. At the hottest times of the summer, drying of poly acryl amide super absorbent had take 6 and 2.3 days for distilled and salty water, respectively. The results showed that the negative effects of Na+ were less than those for Ca2+ and Mg2+ on polymer water absorption. For completely decayed animal manure, the retaining of distilled water was 2.3g for 1g dry manure. For water having 4000 mg/l salts concentrations, the uptake ability of manure was not significantly different than distilled water. The drying period of manure had taken the 17 and 18 days for distilled and salty water, respectively.

Background and Objectives: The need for water storage is steadily growing because of increasing water demands by growing population in arid and semiarid areas such as Iran where droughts occur frequently. Super absorbent polymers are conditioner’ s group which can absorb precipitation or irrigation water and prevent water loss. Soil amendments have more effects on soil water storage when there are more droughts in soil with the intermittent rain fall, retaining the limited humidity and decreasing evaporation losses and increasing plant available water for crop growth. Applied polymer increased soil moisture, reduced mechanical resistance and increased dry-land wheat root growth. Materials and Methods: In this investigation, the effects of superabsorbent polymer on soil humidity absorption were assessed. The study used a split-plot design format. Main plots were potassium sulfate fertilizer at 2 levels (200 Kg per hectare and no potassium sulfate) and sub plots were superabsorbent at 4 levels (0, 500, 1000, 2000 kg/ha) with4 repetitions. The research was carried out in Gorgan University of Agriculture Sciences and Natural Resources Research Farm located at SeyedMiran during 2014-2015 growing season. Row spacing was 20 cm, used 268. 5 kg ha-1 (seeds were drilled manually). Fertilizer rates were based on soil test results and which were added to soil surface before planting and incorporated. Soil mechanical resistance at 6 stages during wheat growing season using a cone penetrometer (0-5 cm soil depth) and so soil moisture at 0-8 and 8-16 soil depths were Measured. Data analysis include the analysis of variance and mean comparisons using LSD and correlation which carried out using SAS software. Results: Results show that potassium fertilizer did not affect soil moisture at 0-8 and 8-16 cm depths polymer consumption had a significant impact on soil moisture, however. 1000 and 2000 kg per hectare polymer increased soil moisture at 0-8 and 8-16 cm depths. 500 kg per hectare polymer had no impact on soil moisture. Soil moisture improvement at 0-8 cm depth, where polymer was already incorporated was comparable with the underlying 8-16 cm depth. Polymer reduced possibly evaporation from lower 8-16 cm depth as much as it enhanced soil moisture in the incorporated depth. Increased soil moisture content within 0-16 cm depth lowered soil mechanical resistance and enhanced root growth. Conclusion: Hysteresis does not affect polymers water because they are almost always saturated during swelling and shrinkage, except when they are nearly desiccated. Due to hysteresis however, desorbing soil which surrounds polymers remains wetter than absorbing soils further away. This explains why super-absorbents are generally wetter than the surrounding soil and are non point water resources for plant use.

A pot trial was conducted to investigate the effect of a superabsorbent polymer on the growth of Panicum antidotale and nitrogen leaching in three soil textures (heavy, medium and light-textured soils) and three irrigation regimes (4, 8, and 12-day intervals). Results showed that the greatest amount of plant growth and dry biomass was obtained at moderate-textured soil and 14-day irrigation interval. According to the obtained results, the effects of polymer, irrigation regime and soil texture on dry matter production, plant height, and nitrogen leaching were significant. Furthermore, the interaction effects of irrigation regimes and soil texture on dry matter production and nitrogen leaching were significant. The highest dry matter production (7.2 g) was obtained at medium-textured soil with polymer at a four-day irrigation interval. In treatments without polymer at a light-textured soil and a 12-day irrigation interval, plants were lost before harvesting. Our results clearly showed that the studied treatments caused to the increased height of Panicum antidotale. Statistically, the effects of a four-day irrigation interval and a heavy-textured soil were the most significant. In addition, the effects of polymer, irrigation regimes, and soil texture treatments on nitrogen leaching were significant. The interaction effects of irrigation and soil treatments showed that the amount of nitrogen leaching decreased by increasing irrigation intervals. The application of polymer obviously decreased nitrogen leaching from 880 mg N/l in control treatment to 550 mg N/l in soils containing polymer material.

The use of superabsorbent polymers is one of the effective solutions to increase water use efficiency and optimal use of rainfall in arid and semi-arid areas. In this study the effect of different levels of superabsorbent STOCKOSORB is investigated on wheat yield and yield components under rainfed and irrigated conditions. For this aim, an experiment was conducted in the Research Field of Agriculture Faculty, Tabriz University, in the growing season of 2015-2016, in which the superabsorbent STOCKOSORB was applied at three levels of 0, 50, and 100 kg/ha. Based on obtained results, application of superabsorbent at 100 kg/ha increased the seed yield and water use efficiency of both rainfed and irrigated wheat farming significantly. The application of 50 kg/ha increased rainfed wheat yield but not irrigated wheat yield, significantly. Results showed that the effect of superabsorbent on yield and water use efficiency in irrigated wheat was larger than rainfed wheat. Also, the effects of superabsorbent application were significant in rainfed conditions at treatment of S1 (increase of water use efficiency equal 25. 9 percent) and in irrigated wheat at treatment of S2 (increase of water use efficiency equal 19. 2 percent). Due to ratio of the increasing benefit as a result of yield increase to cost, application of superabsorbent is not recommended in wheat farming.

Water deficiency or drought is among the most important factors in reducing crop production (Heidari, et al., 2013). Water deficiency or water stress occurs when transpiration is more than water absorption (Alizadeh, 2008). One of the methods that researchers have been studying to increase water use efficiency and performance over the last decade is the use of superabsorbent polymers and deficit irrigation (Khyrabadi, et al., 2014). The superabsorbent polymer is a kind of hydrocarbon, which absorbs water several times as much as its own weight. Due to the drying of the root environment, the water inside these polymers is gradually evacuated and placed at the disposal of the plan, thus the soil will remain moist for a long time without the need for re-irrigation (Abedi Kupai, And Sohrsb, 2005). Considering that the most important advantage of superabsorbent application is reducing the effect of drought stress, this study investigated the effect of deficit irrigation and different levels of superabsorbent on yield, yield components and water use efficiency of lettuce.