Hydrogel Agriculture Technology – A Beginners Guide

Hydrogel Agriculture Technology:

Today, let us get into discussion of Hydrogel Agriculture Technology or Hydrogel In Farming.

What is Hydrogel?

Hydrogel are also known as Super Absorbent Polymers, SAP, absorbent polymers, absorbent gels, super soakers, super slurpers, water gel is a new type of macro molecular synthetic water absorbing polymer material. Hydrogels are cross-linked polymers with a hydrophilic, they   have the capacity to  absorb  large quantities of  water  without  dissolving  in  water.  Water absorption capacity of the soil arises from the hydrophilic functional groups  attached  to  the  polymer  backbone  while  their  resistance to  dissolution  arises  from  cross-links  between  network chains.

How do Hydrogel Works?

• The hydrophilic groups (viz. acrylamide, acrylic acid, acrylate, carboxylic acid, etc.)  of the polymer chain is responsible for the water absorption mechanism of Hydrogel.
• When the polymers are put in water, the water enters into the Hydrogel system by osmosis (movement of water through in a solvent) and hydrogen atoms react and come out as positive ions.
• This process leaves negative ions along the length of the polymer chain. Then the Hydrogel will have several negative charges down its length, these negative charges repel each other, and forced the polymer chain to unwind and open up. They also attract water molecules and bind them with hydrogen bonding.
• Hydrogel can absorb more than 400 times its weight of water in this process.
• And When its surroundings begin to dry out, the Hydrogel gradually dispenses up to 95% of its stored water.
• When exposed to water again, it will start to rehydrate and repeat the process of storing water. This Hydrogel works for 2–5 years, and it is a biodegradable Hydrogel that decomposes in the soil.

Hydrogels for Agriculture:

SAPs are white sugar-like hygroscopic materials that swell in water to form a clear gel made of separate individual particles and which can retain moisture even under pressure without risk of conflagration or rupturing/blasting.

Super Absorbent Polymers used in agriculture are made from acrylic acids and a cross-linking agent like potassium by solution or suspension polymerization. The polymer produced is called a polyacrylate.

The swelling capacity and gel modulus depend greatly on the quantity and type of cross-linker used. Polyacrylates polymers are non-toxic, non-irritating and non-corrosive in nature and tested to be biodegradable with a degradation rate of 10%-15% per year. These polymers show high water absorbent  potential and can freely release 95% water of the same under suction pressure by plant roots.

Read: Frequently Asked Questions About Irrigation.

Hydrogel for Agriculture:

Hydrogels are extensively used in agriculture for improving the mechanization of farming and growing crops, to enhance the cultivation of plants under adverse weather conditions, and for effecting more favorable conditions for plant development. They are used in agricultural plantations in steadily increasing amounts to obtain higher yields of harvests and for improving the quality of plants in a shorter time and using less space at lower costs. Polymers are used in such agricultural applications as soil conditioners, planting and transplanting gels, seed coatings for controlled germination, soil aerators, and in soil sterilization.

Polymers can benefit plants in the various stages of development: germination, growth, evapotranspiration, flowering, and fruit formation. Their successful application in agricultural plantations includes more rational plant spacing and improved economization, especially regarding plant containers, films for soil sterilization, and as coverings and sheeting’s for protective structures.

Application and Benefits of Hydrogel in Farming Lands:

There are three most common soil conditions that slows down the growth of the plants and the crop yield are low water retention capability, high water loss and soil moisture leaching. Not only these conditions, there are many factors like sudden drought conditions, degradation & salination, overuse of synthetic fertilizers and pesticides and improper irrigation practices will affect the soil and plants, often results in damage of soil biota.  Hydrogel technology in agriculture can improve soil quality, preserve water and resist drought stress, and it can improve the seed sprouting and seedling development leads to better crop yields. Considering the environmental aspects, Hydrogel technique is  non-polluting and biodegradable, it helps in reducing irrigation frequency & water consumption and creates a simple cyclic process to provide water directly to the roots and prevent soil compaction.

• In agriculture, the Hydrogels act as micro water reservoirs at the roots of the plant. They absorb the both the natural and supplied water 400-500 times their own weight and release it slowly on account of the root capillary suction mechanism which prevents water loss in soil by leaching and evaporation.
• Hydrogels can create a consistent cyclic process of absorption and release of water; the water so released through Hydrogel technique can provide optimum moisture for quick germination and seedling maturation. Thus reduce the seedling mortality by several folds in nurseries.
• In cold regions, death during germination and maturation of seedling is common due to moisture freezing in & around plant root tissue. Using the Hydrogels in these regions, absorbed moisture in Hydrogels does not freeze and makes easy accessibility to the plants. This technique also regulates seedling growth temperature, preventing death by freezing.
• Hydrogels will reduce the irrigation frequency, which helps to save water and labor costs, and help face the drought condition. They act as soil conditioners, prevent leaching in sandy soils, runoffs in mountainous and sloping fields, improve virescence efficiency in plants and also restores soil biota.
• Hydrogels can reduce overuse of fertilizers and pesticides in farming. The chemicals so absorbed along with water are slowly released when required, by extending the operational life and the uptake efficacy by root systems.
• Hydrogels act as soil matter flocculants. They help in closely binding the loose soil and forming loams that can help better root latching. And the repeated absorb-release mechanism prevents over compaction of soil minerals and improves the aeration in the soil and develops of soil edaphon.
• Hydrogels are widely used in agriculture, forestry, industrial planting, municipal gardening, drought management, water conservation, they help to reduce soil erosion by surface runoff, prevents fertilizer and pesticide runoffs into ground water, and reduces the cost of water and irrigation and success rate of growth and high yields of crops.

Read: Drone Farming.

Key Characteristics of Hydrogels in Agriculture:

• Hydrogels are less affected by the presence of salts in the soil.
• They improve the physical properties of soils and restores its biota.
• They promote the seed germination rate and the rate of seedling emergence
• They can improve root growth and plant density.
• They relieve the plants from moisture stress and make them to withstand prolonged moisture stress.
• They reduce nursery establishment period.
• They reduce the irrigation frequencies and fertilization requirements of crops with improved input use efficiency.

Types of Hydrogels:

Hydrogels are also known as cross-linked three-dimensional networked water absorbent polymers. There are mainly three types of Hydrogels for agricultural use:

• Starch-graft copolymers
• Cross-linked Polyacrylates
• Cross-linked Polyacrylamides & Acrylamide-acrylate copolymers

Potassium Polyacrylate is the major element used in Hydrogel technology and marketed as Hydrogel for agricultural. This is mainly used for its capability for longer periods of water retention and high efficiency in soil with absolutely no toxicity issues.

Hydrogels are prepared by polymerizing Acrylic acid with a cross linker. Cross-linked polymers can hold water 400 times to 500 times than their own weight and release 95% water of that to growing plants.

Use of Hydrogel helps to increase the water usage efficiency by preventing leaching and increasing frequency for irrigation. In semiarid regions, during summer, lack of soil moisture can cause plant stress. Moisture released by Hydrogel close to root area will reduce stress and increase growth and plant performance. Hydrogels can reduce usage of fertilizer leaching and reduce the application of pesticides.

Hydrogel application methods:

There are two methods for applying Hydrogels, as soil conditioners to stabilize the surface of soils to inhibit crust formation and improve water-holding capacity or to improve the poor structure at greater depths by aggregation and to enhance plant growth.

1. Dry method to subsoil: Dry polymer such as PAAm or PVA is applied to the subsoil by mixing with the sandy soil into depths of about 15–25 cm and then subjecting to wetting for swelling prior to cultivation. After the polymer has swollen the soil structure is improved and the water penetration and retention capacity increases, decreasing water runoff and erosion. This method is applied for long-term intentions as the polymer must absorb water prior to becoming beneficial, it is not recommended for immediate sowing.
2. Wet method to topsoil: The polymer solution is sprayed onto initially wetted topsoil, followed by drying to create a water-stable aggregates that resist erosion. This method is particularly well adapted to sowing immediately afterwards and can also be adopted to reduce water consumption in irrigation systems where water losses occur due to the soil’s poor ability to retain moisture. These wet polymer methods can also decrease soil erosion by being applied to topsoil or to driveways of irrigation. Surfactants have positive effects on aggregate stability, hydraulic conductivity and the distribution of conditioners.

Read: Watercress Farming.

Hydrogel Applications and Uses for Soil:

The application of polymeric soil conditioners as additives to soils to improve their aggregate conditions can be extended into other areas: to reduce soil erosion and to prevent crust formation and general stabilization.

• Hydrogel for Soil fixation: It treats of poorly structured soils are to improve stabilization and solidification of soils by varying the physical and chemical features of soils for construction and other structural applications where soil movement must be reduced or eliminated. The process generally requires the use of more than one additive. Hydrogel can be used to fix soil particles into aggregates by incorporating a cross linking agent with them in the soil. They can be incorporated to improve water retention in the soil and provide a better growth medium. This technique is designed to allow crop cultivation without irrigation in areas where natural rainfall is inadequate due to drainage and evaporation losses or long dry seasons. Hydrogel can enable the existing water supply to be used more efficiently.
• Hydrogel for Soil conditioning: Hydrogel aids for increasing the available water content of soils, for improving plant growth, and reducing irrigation requirements due to reduction of water loss and evaporation, thus, allowing the intervals between irrigations to be increased. The improved water retention in the soil will protect the plants against hydric stress. This is particularly suitable in arid areas where agriculture is marginal due to infrequent rainfall. Polymers can be incorporated into the soil to improve soil structure and water retention by reducing leaching and increasing water supply to the roots.
• Hydrogel for Soil erosion control:  Soil erosion and runoff are serious land degradation problems in arid and semiarid regions caused either by rain or wind. It is a significant environmental problem for agricultural lands that results in destruction and eventual abandonment of the land and the loss of civilization itself. Sediment in runoff from agricultural landfills in reservoirs and rivers endangers aquatic life and reduces soil productivity. Hydrogels can be applied to aggregate the soil by surface treatment and hence to provide surface stabilization during the early phase of crop growth. Thus, Hydrogels act to reduce erosion from water and wind by stabilizing the surface layers, reducing runoff and soil losses, decreasing the infiltration rates of water into the soil, and promotes the hydrophilic nature of the soil surface which fastens the germination.
• Hydrogel for Seepage control: Seepage control can be achieved by certain polymeric Hydrogels which form a water-impermeable layers or membranes in the soil and can be efficiently used to control the movement of water and dissolve salts through their interactions with charged sites on the surface of the soil particles. Thus, Hydrogels are used for seepage control by the formation of membranes in the soil that restrict the movement of water thereby protecting crops from salt damage. This technique can be used to save irrigation water, to control salt damage to crops caused by irrigation in arid soils and finally to prevent the seepage of such water into rivers and reservoirs.

Disadvantages of Hydrogel in Agriculture:

These water absorbent polymers or Hydrogels have been around for a couple decades and are not as useful in plant agriculture as they might appear to be.

• The amount of water Hydrogels absorb decreases greatly if there are any ions in the water. The data for Hydrogel water absorption are usually in distilled water. In the real world, soils contain ions from fertilizers and irrigation water, that substantially reduce the water absorption by the Hydrogels.
• Most soils can hold reasonable amounts of water for plant growth. If there is insufficient rainfall, the soil water is depleted. Hydrogels will not solve that problem.
• Hydrogels are very costly, which limits their use to high value crops such as potted ornamental plants, landscape trees and for home garden uses. One study found that adding peat moss costing the same as the recommended rate of Hydrogel increased the water-holding capacity of a potting soil by the same amount as the Hydrogel.

Possibly the most common commercial use of Hydrogel in plant agriculture is as a slurry to coat bare-rooted transplants. This supposedly prevents the roots from drying out.

Read: Tilapia Fish Farming.