Prospects of Hydrogels in Agriculture for Enhancing Crop and Water Productivity under Water Deficit Condition

Abstract

In arid and semiarid regions and under rainfed conditions, water availability is one of the principal ecological constraints that hinder agriculture’s sustainability. The super absorbent polymer (agricultural) is water-absorbing and is cross-linked to absorb aqueous solutions through bonding with water molecules. It is a new approach to water management under water-stressed conditions to conserve soil moisture in the active rooting zone of crops by reducing the evaporation, deep percolation, and runoff losses. Agricultural hydrogels are water retention granules which swell their original size to numerous intervals when they come in contact with water. It can absorb and retain a huge amount of moisture under plentiful rainfall and irrigation events and release it back to the soil for mitigating crop water demand when the rhizosphere zone dries up under drought conditions. It plays multifarious roles in agriculture including soil-water retainer, nutrient and pesticide carriers, seed coating, soil erosion reducer, and food additives. It has the extraordinary ability in improving different physicochemical, hydrophysical, and biological properties of soil, simultaneously decreasing irrigation frequency, enhancing the water and nutrient use efficiencies, and increasing the yield and quality of the field, plantation, ornamental, and vegetable crops. These biodegradable materials are nontoxic to the soil, crop, and environment. Hence, the addition of the hydrogel polymer will be a promising and feasible technological tool for augmenting crop productivity under moisture stressed conditions.

Sodium Alginate-g-acrylamide/acrylic Acid Hydrogels Obtained by Electron Beam Irradiation for Soil Conditioning

“…They can absorb a huge amount of water in conditions of abundant precipitation or during irrigation that can be gradually released when the soil area around the roots of the plants dries out in drought conditions. In additional to the water stress reduction, they may have the ability to improve the physicochemical, hydrophysical and biological properties of the soil, increase the efficiency of the use of water and nutrients and increase the yield and quality of crops [5].…”

“…Based on the source materials, hydrogels for agricultural use are classified into three types: natural, synthetic and semi-synthetic [5,6]. Synthetic hydrogels are based on monomers derived from petroleum that are attractive for the synthesis of polymeric hydrogels, due to their very controllable physical and chemical properties compared to natural polymers [7,8].…”

“…Stable covalent cross-links may be introduced into alginate hydrogels using bifunctional cross-linkers, allowing for greater control over the mechanical and swelling properties of the gels [13]. To be used in agriculture, hydrogels must have certain characteristics, such as high water absorption capability, a rate of absorption and desorption capacity according to plant requirements, low soluble content and residual monomer, high durability and stability during swelling and storage, biodegradability or rewetting capability for a long time [5]. While hydrogels based on synthetic monomers (acrylic acid, polyacrylamide) are difficult to degrade in soil, hydrogels based on biopolymers are biodegradable but weak from a mechanical point of view, so they have a short lifespan, requiring frequent replacement [8].…”

“…Nutrient deficiency in poor or depleted soils may be due to the geographical conditions, environmental disasters or simply to the cultivation of the same agricultural crop several seasons in row. The three main nutrients needed for plant growth are nitrogen, phosphorus and potassium, but traces of oligoelements as calcium, magnesium, sulfur, iron, manganese, zinc, copper, boron and molybdenum are also needed [5,[16][17][18]. For these soil conditions, hydrogels as source of water and nutrients represent a viable solution.…”

“…For these soil conditions, hydrogels as source of water and nutrients represent a viable solution. Because the combining of the best properties of natural and synthetic polymers in order to obtain a material with hybrid properties for agriculture is topical [5,8], the first goal of the paper was the obtaining by electron beam irradiation and characterization of some Sodium Alginate-g-acrylamide/acrylic Acid hydrogels. The grafting of the synthetic monomers acrylamide and acrylic acid on the chain of the natural sodium alginate polymer was carried out with the aim of increasing the mechanical resistance of the obtained hydrogel, which allows its multiple reuse and at the same time gives it a biodegradability potential.…”