written by: Jayant R Row
• edited by: Lamar Stonecypher
• updated: 12/27/2013
Agricultural hydrogels can change the physical properties of soils by
Increasing their capacity to hold water
The high cost of these hydrogels has been an inhibiting factor that has drastically affected their universal use. Unless costs are brought down, its use will get limited to government and other well funded organizations, leaving out the private farmers and agriculturists who can benefit from its use.
Hydrogel polymers are made from petroleum based products, but recent research has enable their manufacture using soy oil. These hydrogels are more biodegradable and therefore kinder to the environment.
Agricultural hydrogels are referred to as water retention granules because they swell to many times their original size when they come in contact with water. Two broad classes of hydrogels are soluble and insoluble. The soluble variety is used to reduce irrigation erosion in fields. The insoluble variety is used in gardens, nurseries and landscapes to reduce frequency of watering.
Hydrogels are polymers that are physically or chemically cross linked and can absorb large amounts of water while retaining their shape. They also do not dissolve with the ingress of water and the large swelling due to the water does not affect the mechanical properties of the hydrogel. Hydrogels can hold an amount of water that is many times its own weight .This characteristic helps it to store water which can include nutrients. This water is then released slowly negating the evaporation process. This is especially useful in arid lands.
Hydrogels commonly used in agriculture can absorb between 400 and 1500 grams of water for every gram of hydrogel. So using these hydrogels in places where post plantation irrigation has its limitations, the hydrogels can store large quantities of water and make it available to the plantation so that it has time to establish itself.
Hydrogels can be natural polymers, semi synthetic or synthetic polymers. The polymers used for agricultural purposes are the synthetic variety which consists of polyvinylalcohols and polyacrrylamides. The one disadvantage with synthetic polymers is that they may take up to six hours to complete hydration which is three times the time taken by natural polymers. The advantage of synthetic polymers is that they are less biodegradable and would last for a longer time.
Using hydrogels requires some elementary precautions like masks to prevent eye and skin irritation. A lot of care has to be takin in storing hydrogel, as their huge capacity to absorb water can cause an increase in weight.
Soils sometimes form semi hydrophobic crusts which allow the water to run off instead of being absorbed in the soil. The addition of hydrogels in the soil allows the water to percolate instead of running off and this retained moisture is then passed back to the soil over a period of time.
The use of agricultural hydrogels also allows damaged or unusable agricultural land to be reclaimed. When hydrogels are added to the surface of the soil the water holding capacity is increased and rainfall percolates the soil quite easily. Hydrogels also reduce nutrient loss from soils as runoff is prevented. In saline soils however hydrogels seem less effective.
If hydrogels are allowed to dry out they become less effective, so good irrigation practice is important to the longevity of the hydrogels. Hydrogels have been used for turf management for golf courses and athletic fields. It is also useful for fruit and vegetable production. It can be very easily be used to ensure forestry activities especially in remote areas where irrigation cannot be assured.
Hydrogels can be applied by either mixing with the soil or by spraying. While using the spray technique, hydrogels can be mixed with micronutrients and pesticides.