21st century has witnessed a steady decline of irrigation water potential conjugated with the ever growing global population & enhanced economic activities among countries specially located in arid and semi arid regions of the world. As these regions are ever facing water crisis due to uncertain and inadequate natural precipitation, the problem with water scarcity may possibly aggravate further. Global survey shows, the worst affected areas would be the semi arid regions of Asia (India), the Middle-East and Sub-Saharan Africa, all of which already face issues with heavy population growth and majority of them below the poverty line.
It is estimated by 2025 water scarcity will be a major issue in India requiring immediate redressal. As per the Central Water Commission, the demand for water is growing at a steady rate but the availability of clean water in future is declining even faster. In the Indian scenario, Agricultural irrigation practices seem to be responsible for consumption of 80% of the available potable water. There is an increasing trend to this with the further intensification of agro based industries. Due to the large geographical dimensions of the sub-continent and varied soil and farming practices, modern irrigation practices can still only cater to 40% of the grown crops. The remaining areas are far more susceptible to improper practices thus greatly lowering the effective and judicious use of available water for crops.
The predominant irrigation practice is surface draining i.e. direct application of water to crops from surface. It’s a problematic and flawed system as the crops can utilize only 50% of the provided water while the remaining is lost in conveyance, as runoff and by evaporation. Modern methods like drip irrigation and use of sprinklers can effectively reduce the wastage of irrigation water but high initial costs, inadequate government subsidy and cooperation, lack of technical input and after sales service, faulty equipment, damage due to pests and high costs of spares prohibits the farmers from opting these techniques.
It is worth mentioning that 98 million of the total 120 million farm holdings are small and marginal farmers; thus net income from small farms makes farmers reluctant to adopt such water management practices in agriculture. Spatial diversification in soil characteristics, shortage of large land holdings and underprivileged conditions discourage farmers from adopting advantageous and economical application of water conserving irrigation techniques, even in arid zones with distinct scarcity of water. The stress on sustainable development practices even in the agricultural sector has laid emphasis on further judicious, economic and optimum utilization of land, water and plant resources with the major goal to maximize land and water productivity without threatening the environment and available natural resources.
Extensive research all over the world, particularly Iran, China, Europe and USA has led to the development of a particular class of Super Absorbent Polymers that can increase water use efficiency and enhance crop yield. Soil conditioning with SAP is an interesting and innovative facet in the field of modern agriculture as well as rain-fed agriculture. It was shown that SAP materials are hydrophilic networks that can absorb and retain large amounts of water or aqueous solutions. Their uptake can be as high as 100,000% and even more. SAPs are in general, small sugar like hygroscopic crystals that can be directly added to cultivation soils. They are predominantly used for improving irrigation efficiency; smart delivery materials that can help combat plant pathogens even with lower pesticide dosage, reducing the quantity of soluble NPK fertilizers per crop cycle thus greatly contributing to water and environmental conservancy practices.
Hydrogel agriculture technology involves gel forming polymers that are insoluble water absorbing polymers designed exclusively for agricultural use by the late 1980’s. They were developed to improve physical properties of soil to:
Hydrogels as they are commonly called are cross-linked three-dimensional networked water absorbent polymers. Three main types of Hydrogels have so far been found appropriate for agricultural use:
Potassium Polyacrylate is the principle material used in SAP industry and marketed as hydrogel for agricultural use because of its longer retention and high efficiency in soil with nil toxicity issues. They are prepared by polymerizing Acrylic acid with a cross linker. Cross-linked polymers can hold water 400 times their own weight and release 95% of that to growing plants. Use of Hydrogel leads to increased water use efficiency by preventing leaching and increasing frequency for irrigation. During summer months particularly in semi arid regions, lack of soil moisture can cause plant stress. Moisture released by hydrogel close to root area helps reduce stress and increase growth and plant performance. Hydrogels can reduce fertilizer leaching and reduce application of pesticides.
Water Absorption with Hydrogel
Hydrogel works as water reservoirs round the root mass zones of the plant. In presence of water, it expands to around 200-800 times the original volume. There is ample possibility to trap irrigation and rainwater that can then be collected, stored and gradually released for crop requirements over prolonged durations. Hydrogel mixed with soil increase soil permeability and improve germination rates. It is compatible with a wide range and type of soils and thus has in general a tendency to increase plant performance and yield. Rainwater retention, soil erosion by storm water run-offs, especially in sloped terrains can be greatly averted. There has been proof of decrease in fruit & vegetable loss due to insect by around 10-30%.
Agriculture specific applications of Hydrogel
Hydrogel application in agriculture in terms of proposed practices and their advantages are summarized herein.
Water stress due to scarcity of moisture around root zones is often associated with premature leaf shedding, decreasing chlorophyll content, reduced seed yield, less fruit and flower yield per plant. Use of hydrogel can help moderate these impacts caused by deficit irrigation. Being a water retaining agent greatly increase irrigation period of cultivation, enhancing irrigation efficiency particularly in arid & semi-arid belts.
Drought stress can lead to production of Oxygen radicals that result in increased lipid perioxidation and oxidative stress in the plants. Visible effects include stunned height, decrease in leaf area and foliar matrix damage etc. Hydrogel can reduce drought impact on plants leading to reduced stress and oxygen radical formation. This in turn provides scope for better growth and yield even in unfavorable climatic conditions.
Irrigation technology has major constraints in the fields of application of fertilizers, herbicides and germicides. Studies suggest the use of synthetic fertilizers can be greatly reduced when hydrogel agriculture is practiced without hindering with crop yield and nutritional value. It would indeed be a more appropriate practice for sustainable agriculture in arid and semi-arid conditions and regions with similar ecological constrains. Moreover, potassium polyacrylate is safe and non-toxic thus prevents pollution of agro ecosystems.
Studies have confirmed that hydrogel is sensitive to the action of UV rays, and degrades into oligomers. The Polyacrylate becomes much more sensitive to aerobic and anaerobic microbiological degradation and can degrade at rates of 10-15% per year into water, carbon dioxide and nitrogen compounds. The hydrogel molecules are too voluminous to be absorbed into plant tissue and have zero bioaccumulation potential.
Considering the efficiency of hydrogel in soil conditioning and moisture retention, it can be understood that an optimum mixing ratio is needed to get maximum efficacy of the method. Since the moisture holding capacity is a function of soil characteristics, dosage of hydrogel is also varied and designed based on the type of soil it is used with. A simple dosage chart has been illustrated herein but the ultimate quantity and application can only be determined after testing specific soils to be conditioned.
Type of Soil
Suggested dosage of Hydrogel
Arid & Semi-arid Regions
For all level of water stress treatment and improved irrigation period
To delay permanent wilting point in sandy soils
0.2-0.4g/kg OR 0.8% of soil whichever is more
To reduce irrigation water by 50% in loamy soil
2-4g/ plant pit
To improve relative water content and leaf water use efficiency
To reduce drought stress
0.2-0.4% of soil
To prohibit drought stress totally
225-300kg/ha of cultivated area
To decrease water stress
3% by weight
ALSTA HYDROGEL : Super Absorbant Polymer for Agriculture
ALSTA HYDROGEL is a potassium polyacrylate based super absorbent polymer manufactured by Chemtex Speciality Ltd. for agricultural sector. The granular polymer has a capacity to absorb water 300-500 times its own weight and release it gradually directly to the plant roots over a period. It is effective at reducing irrigation frequency, maintaining soil texture and permeability while ensuring proper and healthy growth of the plants themselves. It can be used conveniently with de-ionized and de-mineralized water to retain soil moisture as well as reduce use of synthetic NPK fertilizers. It finds large scale applications in Open Field & Protective Cultivation, Terrace Farming, Vertical Farming, Domestic Gardens, Arboriculture, Bare Root Dripping, Hydro Seeding, Hydroponics etc.
Source : Hydrogel Agriculture