Fertigation: Using Your Irrigation System to Correct the Feast

T he application of fertilizers through an irrigation system has been used effectively in agriculture for decades. More recently, golf course superintendents have embraced this technology that offers increased control of nutrients in the rootzone, as well as labor and equipment savings. Fertigation technology exists to deliver golf course quality to all types of landscapes.

For landscape irrigation contractors, fertigation has been refined to offer a simple solution to consistently balancing nutrients in the soil profile. Steadily injecting small amounts of elements through the irrigation system can efficiently maintain an optimal supply of specific plant nutrients, particularly in sandy soils that have little native fertility.

Fertigation is best used in regions where irrigation is required at least weekly. Fertigation principles lose their impact if managers irrigate solely for the purpose of distributing nutrients.

Through modern landscape fertigation systems, fertilizer can be metered out in frequent, light doses, simulating the action of controlled release fertilizers, except that the landscape manager dictates the release rate. The idea is to apply nutrients in a steady, modest rate to eliminate the feast or famine effect of quick-release, granular fertilizers. Consistent growth and maintenance characteristics, better root structures and more pest and disease tolerance are added benefits of fertigating landscape turf and ornamentals.

Many soils serve as a bank for nutrients like calcium, magnesium, and phosphorous. However, nitrogen, potassium, sulfur, iron and other micronutrients are poorly retained in some soils. Fertigation can be used to deliver such nutrients at appropriate levels for plant availability. Spoon feeding nutrients also can reduce nitrogen leaching by eliminating application rates that exceed the turfgrasses capacity to absorb nitrogen.

Properly used, fertigation defeats the excessive growth that follows heavy fertilizations and the slow growth at the end of conventional fertilization cycles. This greater efficiency can lead to less overall fertilizer use. Costs can be lower when water-soluble sources replace slow-release nitrogen sources.

Equipment Options

First and foremost, all types of injection systems require the installation of a backflow preventer between the injector and the water source. Usually, the injector is mounted at a lower elevation than the backflow device and at a higher elevation than the irrigation main.

Fertigation equipment can range from the simple to the complex. Generally, an injector system that delivers nutrients proportionally is the most effective, requiring less management. In a venturi system, suction is used to draw the liquid fertilizer from a container, much like a hand-held proportioner. The faster the flow of irrigation water in the pipe, the more fertilizer solution is fed into the system.

This proportional blending is based on the flow rate of the irrigation system. Therefore, a constant ratio of irrigation water to fertilizer solution can be maintained. This is necessary for almost any irrigation system because differences in flow are necessary for various irrigation zones.

A small proportioner pump can also be used to inject fertilizer solution into the main irrigation line. The rate at which the fertilizer is injected can be adjusted according to season or specific need, such as plant type in the active irrigation zone or seasonal growing habits. For example, turf during grow-in needs higher nutrient levels, but these levels need to be brought down prior to winter overseeding. By factoring the amount of fertilizer needed per week or month (in pounds per thousand square feet or per acre) with the concentration of the fertilizer in the tank, the right amount of fertilizer can be set for each specific zone during the selected time period. If the planned irrigation frequency has to be altered, then so can the injection rate. A sight gauge on the fertilizer tank tells you whether the fertilization schedule is being followed.

Injectors that Fit

Injectors come in a range of sizes, based on flow rate. All irrigation zones should fall within the specified range of the injector system. Zones with flow rates far removed from the specified range should be separated and provided with the proper size injector. Holding tanks for the fertilizer solution should be sized according to dilution rate and total flow of the full irrigation schedule. An injection system with a dilution rate of 300 gallons of water to 1 gallon of fertilizer would consume that gallon of fertilizer in 50 minutes, at a flow rate of 6 GPM.

Before you select the materials to inject, test the soil and water. Then customize nutrition according to proper levels of acid or other specific elements. Correcting soil and water problems is a bonus to the controlled application of fertilizers. A good fertilizer dealer can custom blend almost any desired solution.

Virtually any irrigation system that delivers water relatively uniformly is suitable for fertigation if fertilizer is applied frequently at low application rates. Corrosion of irrigation valves, sprinkler heads and other components is of little consequence because they encounter only highly diluted fertilizer solutions. There is little risk of fertilizer burn on turfgrass or other plant material and no need to flush irrigation lines at the end of each fertigation cycle.

Daily fertigation provides more uniform turfgrass appearance and growth. It decreases nitrogen and potassium leaching beyond the root zone while maintaining a more stable levels in the root zone.

Good nutrition for plant material is similar to that for your body. A strict, consistent regimen of properly balanced nutrients fortifies your body with the strength to resist disease. Fertigation precludes succulent growth and the associated weak cell structure and root growth of plant material as well as the maintenance hardships flush growth creates.

Equally important is the strength of the plant material that consistent, light doses of nutrients provide. It can be used as a supplement to conventional fertilizer applications. Strengthen your services, reduce your labor and brighten your landscape with fertigation.