Fertigation offers ease and efficiency

Fertigation-applying fertilizer through an irrigation system-is a tool that can help you accomplish goals of agronomic and aesthetic splendor with relative ease. It allows you to efficiently meet the nutritional needs of both turf and ornamentals.

Irrigation and fertigation systems are becoming more advanced and easier to use because of new technology. Combined with the knowledge that light, frequent applications of nutrients are an effective nutrition-management strategy, the technique is becoming more popular in the turf and landscape industry. Fertigation stabilizes your fertilization program by keeping nutrients in the root zone. Doing so gives you both environmental and economic benefits and allows you to concentrate on other priorities. Getting the most out of your fertigation system is easy. In fact, once you are exposed to the ease of fertigation and the positive results you can achieve with it, you'll wonder why you haven't been using it all along.

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Like any other form of technology, some aspects of fertigation require you to learn a few principles so you'll use it most effectively and without experiencing significant problems. Knowing a little about the potential problems before using fertigation prevents a lot of frustration later.

Differences in fertilizer materials Most of the problems encountered in the use of fertigation relate to the quality of the fertilizers you use. A large part of the problems revolves around phosphorus fertilizers and their solubility. Depending on formulation, phosphorus-fertilizer solubility may range from 30 percent to almost 100 percent. Most potassium and inorganic nitrogen (N) fertilizers are almost 100 percent 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 do this is to buy from reputablesuppliers that stand behind their products.

However, even high-quality fertilizers designed for fertigation systems can precipitate or salt-out under certain conditions. Temperature variations can cause this occurrence, and you should consider the potential for this problem before storing fertilizers for extended periods. Check with your supplier to ensure that the fertilizer you've chosen is formulated for the time of year you'll be using it and the expected temperatures in your area.

In the event that salt-out problems occur, dilute the concentration in the tank with water until the problem dissipates. In extreme cases, you'll need to remove solid material at the bottom of the tank either manually or by suction pump.

Compatibility can be a problem Keep in mind that not all liquid-fertilizer materials are compatible. It is important to rinse the tank before you introduce new materials into it. 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.

You can prevent this from becoming a problem by taking a couple of different steps. One solution is 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 because you may only apply some materials a few times a year.

You can add many materials to the fertilizer holding tank without negative results. For example, many grounds managers add micronutrients through fertigation systems. Due to solubility problems, micronutrients are often chelated to help them stay in solution. You'll also often see surfactants 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 it into a jar. Then add the material in question at the recommended rate. Shake the jar thoroughly and, over the next several days, watch for any change in composition. If no change occurs, it is most likely safe to add the material to the fertilizer holding tank at a similar concentration.

Check the pH of any materials you add to the holding tank. They should have a neutral pH (6.5 to 7.0). If the pH is too low, then the material could be corrosive to your 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.

Know your irrigation system You shouldn't install a fertigation system without first consulting an industry specialist. 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 you may need to address before attaching fertigation components to an older irrigation system.

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. In addition, microemitters require contaminant-free fertilizer solutions. Therefore, perform an irrigation audit to evaluate your entire system before adding a fertigation system. With a little work, you'll likely be able to fit your irrigation system with fertigation components to give you a working system.

Also keep in mind that because 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 can cause algae to grow on the sand in green-side golf-course bunkers. Also, ornamental plants typically do not require as much fertilization as turf areas, so you should adjust a fertigation system to meet the end-use demands.

Calibrating your fertigation system When using a fertigation system, the pumping rate per unit time or irrigation cycle is of major importance. Once you calibrate the system, you can apply exact quantities of nutrients with confidence. To properly calibrate a fertigation system, you don't need to understand advanced mathematics or the hydrology of the irrigation system. You simply need basic math skills, an understanding of proper irrigation frequency and a reasonable estimate of the irrigated area.

For example, you can apply 1 pound of N per 1,000 square feet per month by fertigating 16 times (about every other day) at a rate of 0.06 pound of N per 1,000 square feet each cycle. Using an estimation of the area being irrigated and the analysis of the fertilizer, you can determine the amount of N to apply by measuring the decrease of fertilizer in the tank.

For example, let's say the area you're irrigating is about 10 acres. To apply 1 pound of N per 1,000 square feet requires roughly 435 pounds of N. If your fertilizer is 11 percent N, it takes 3,960 pounds of fertilizer. You want 0.06 pound of N each time you irrigate, so divide 3,960 by 16. The result: you'll use about 250 pounds of 11 percent fertilizer during each irrigation.

The weight of 11 percent N fertilizer is about 10 pounds per gallon, so 25 gallons (250 pounds) is equal to 0.06 pound of N per 1,000 square feet for 10 acres.

With this information, you can set the fertigation system's injection proportioners 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, you can adjust the proportioners until you reach the desired application rate.

Several scenarios could take place that might require you to re-calibrate your system. These include a change in the concentration of the fertilizer added to the tank, altering irrigation frequency or irrigation-system design changes. As the nutrient content of the fertilizer increases, you need less fertilizer. To achieve the same fertilizer application rate when you increase the irrigation frequency, you should inject a correspondingly lower rate of fertilizer 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, you can control the fertilizer application without weighing fertilizers and driving over the area multiple times during the year. Fertigation also allows you to spoon-feed the turf with inexpensive soluble liquid fertilizers instead of using costly controlled-release fertilizers. You also don't have to depend on moisture, timing, microbes or temperature, which slow-release fertilizers require. In addition, you minimize the leaching of nutrients because of the low application rate. You store the "extra" fertilizer in a tank near the irrigation pump house, not in the soil where it may leach out.

You can use fertigation as a primary source of fertility or to supplement a dry fertilizer program. One popular use of fertigation is to give the entire turf area a quick green-up just before a tournament or special event. With everyone getting ready for the big event, you may not have the manpower to spare to apply dry fertilizer over the entire turf area. The fertigation system allows you to best use your resources as well as provide optimum conditions. Only after you become familiar with your system will you realize the full benefits of fertigation.

Dr. Grady L. Miller is an assistant professor and Eric A. Brown is a graduate research assistant at the University of Florida's Institute of Food and Agricultural Sciences (Gainesville, Fla.).

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