How To Get the Most Out of Fertigation

Grady L. Miller and Eric A. Brown

Fertigation is a tool to help maintenance managers accomplish goals of agronomic and aesthetic splendor with relative ease. It allows grounds managers to efficiently meet the nutritional needs of turf and ornamentals. Irrigation and fertigation systems are becoming more advanced and easier to use because of new technology. Light frequent applications of nutrients is an effective nutrition management strategy, but may not be practical for large areas using granular material. Fertigation allows many frequent fertilizer applications at low rates. It stabilizes the fertilization program by keeping nutrients in the root zone. This gives grounds managers environmental and economic benefits and allows them more time to concentrate on other priorities.

Getting the most out of your fertigation system is easy. A manager that is exposed to the ease of fertigation and the positive results which can be achieved will wonder why he has not been using it all along. Like any other form of technology there are aspects about fertigation that requires a manager to learn a few principles so that he uses it effectively, without experiencing significant problems. Knowing a little about the potential problems before using fertigation prevents a lot of frustration later.

Fertilizer Materials

Most of the problems encountered in the use of fertigation relate to the quality of the fertilizers being used. A large part of the problems in fertigation revolve around phosphorus fertilizers and their solubility. Depending on formulation, phosphorus fertilizer solubility may range from 30% to almost 100%. Most potassium and inorganic nitrogen fertilizers are almost 100% soluble. Blending fertilizer materials can induce another set of problems. A poorly blended fertilizer material may not stay in solution. It can precipitate, settling to the bottom of the tank to form a messy sludge. This can result in a fouled system and incorrect fertilization rates. The best way to prevent this occurrence is to ensure that the fertilizer is high quality and soluble. The best way to ensure this is to buy from a reputable supplier that stands behind his product.

Even high quality fertilizers designed for fertigation systems can salt-out under certain conditions. Temperature variations may cause solution fertilizers to salt-out and must be considered before storing fertilizers over extended periods. For this reason, check with your local supplier to ensure that your fertilizer is formulated with the time of year and temperatures that will be expected. In the event that salt-out problems do occur, dilute the concentration in the tank with water until the problem dissipates. In extreme cases, solid material at the bottom of the tank will need to be removed by suction pump or manually.

Not all liquid fertilizer materials are compatible. It is important to rinse the tank before new materials are introduced into the tank. For example, phosphorus can be a particularly difficult nutrient to use in fertigation systems when other nutrients are present. Phosphorus will react with magnesium sulfate and calcium sulfate to form insoluble precipitates. When a precipitate forms your system may clog-up and stop working properly. There are a couple of ways to prevent this from becoming a problem. One solution would be to have separate tanks for reactive materials such as phosphorus. A second, less costly solution, is to carefully rinse out the tank before and after using different materials. This is especially effective and less costly since some materials may only be applied a few times a year.

There are many materials that can be added to the fertilizer holding tank without negative results. Micronutrients are often added through fertigation systems. Due to solubility problems, micronutrients are often chelated to help them stay in solution. Surfactants, which may aid in water utilization and therefore nutrient efficiency, are often added directly to the fertilizer mixture. Before adding anything to the tank, test the compatibility of materials using the jar test. To do this, take some fertilizer solution from the holding tank and put into a jar. Then add the material in question at a recommended rate to the fertilizer solution. Observe for any change in composition for a least a few days. If no change occurs, it is most likely safe to add the material to the fertilizer holding tank at a similar concentration.

Materials added to the holding tank that will be applied through fertigation, should have a neutral pH (6.5 - 7.0). If the pH is too low, then the material is very corrosive on equipment. When the pH is high, the micronutrients as well as other additives, may be insoluble. Most suppliers will adjust the pH to prevent problems, especially if they are mixing and providing a prescription fertilizer analysis for you.

Knowing Your Irrigation System

A fertigation system should not be installed without first consulting with an industry specialists. In computer terms, the plug-and-play concept does not apply to hooking up a new fertigation system. Irrigation efficiency and system design are two areas that may need to be addressed before fertigation components are attached to older irrigation systems. Some fertigation system designs require a higher pressure to operate effectively than the standard irrigation system. If an irrigation system does not uniformly apply water, it will not uniformly apply fertilizers. Micro-emitters require pure fertilizer solutions. An irrigation audit should be done to evaluate your entire system. With a little work, most all irrigation systems can be fitted with fertigation components to give you a working system.

Grounds managers should also keep in mind that since a fertigation system distributes fertilizers, it is important to only irrigate areas that require nutrients. Over time, fertigation can cause problems such as algae growth on sidewalks or other surfaces. In some instances nutrient rich water may cause algae to grow on sand found in green-side sand bunkers on golf courses. Ornamental plants typically do not require as much fertilization as turf areas, thus a fertigation system should be adjusted to meet the end-use demands.

Calibration of the Fertigation System

When using a fertigation system, the pumping rate per unit time or irrigation cycle is of major importance. Once the system is calibrated, exact quantities of nutrients can be applied with confidence. In order to properly calibrate a fertigation system, a turf manager does not have to know advanced mathematics or the hydrology of the irrigation system. Basic math skills, irrigation frequency, and a reasonable estimate of the area that is irrigated is all that is required. For example, a manager can apply one pound of nitrogen per month by fertigating 16 times (about every other day) at a rate of 1/16 pound of nitrogen each cycle. Using an estimation of the area that is irrigated and the analysis of the fertilizer, a manager can determine the amount of nitrogen applied by measuring the decrease of fertilizer in the tank.

For example, lets say the area to be fertilized is approximately 10 acres. To apply 1 pound of nitrogen per 1000 square feet would require roughly 435 pounds of nitrogen. If our fertilizer was 11% nitrogen, it would take 3960 pounds of fertilizer. We want 1/16 of a pound of nitrogen each time we irrigate so by dividing 3960 by 16 we determine that we will use about 250 pounds of 11% fertilizer during each irrigation. The weight of 11% nitrogen fertilizer is about 10 pounds per gallon, so 25 gallons is equal to 1/16 pound of nitrogen for 10 acres. With this information, the injection proportioners can be set for the necessary flow rate. Double check the system by visually monitoring the amount of material pumped out of the tank during an irrigation cycle. Through experience, the proportioners can be adjusted until the desired application rate is reached.

There are several scenarios that will require you to re-calibrate your system. These include a change in the concentration of the fertilizer added to the tank, altering irrigation frequency, and irrigation system design changes. As the nutrient content of the fertilizer increases, less fertilizer is needed. To achieve the same fertilizer application rate when the irrigation frequency is increased, there should be a correspondingly lower rate of fertilizer injected into the irrigation system. The calibration procedure is the same for any size area from golf courses to home lawns. The control over nutrient application is as easy as a few simple calculations and turning a dial.

Using a properly calibrated fertigation system, one can control the fertilizer application without weighing fertilizers and driving over the area multiple times during the year. Fertigation also allows a turf manager to spoon feed the turf with inexpensive soluble liquid fertilizers instead of using costly controlled release fertilizers. There is no need to depend on moisture, time, microbes or temperature that slow release fertilizers require. Leaching of nutrients is also minimized because of the low application rate. The extra fertilizer is stored in a tank near the irrigation pump house, not in the soil where it may leach out.

Fertigation may be used as a primary source of fertility or may be used to supplement a dry fertilizer program. One popular use of fertigation is to give the entire turf area a quick green-up just prior to a tournament or special event. With everyone getting ready for the big event, a manger may not have the manpower to spare for dry fertilizer application over the entire turf area. The fertigation system allows one to best utilize his resources as well as providing optimum conditions. After a manager becomes familiar with their system, the confidence achieved will allow them to realize the full benefits of fertigation.