The 20th century saw a tremendous growth in fertilizer consumption throughout the world. By the close of the century, developing countries had increased their consumption to over 60% of the world's fertilizer use. These countries also now account for 55% of worldwide nitrogen fertilizer production.

Application Methods

Basically, there are three methods to apply fertilizer: broadcasting, foliar and fertigation. Broadcast fertilizing spreads a recommended rate of granular or liquid fertilizer evenly over the growing area utilizing a hand held, push or trailer type broadcast spreader. The fertilizer then slowly filters into the soil or is incorporated into the soil with a rototiller, spade or with irrigation water. Broadcasting is ideal for fertilizing large areas and is the method most often used by landscape maintenance crews today.

Fertigation, or liquid fertilization, uses very soluble nutrients which are dissolved in water, and injected into the irrigation system. Nutrients can be applied through drip or spray systems, and can vary in concentration and composition. Fertigation provides uniform and relative ease of distribution of nutrients and can be finely tuned to the nutritional requirements of a particular site.

Slow Continual Release Of Nutrients

Water for the irrigation system moves through white pvc pipe to the small tank where the fertilizer mixture is injected into the system. The water then circulates back out into the irrigation system feeding shrubs, trees, ornamental and turf areas.

Usually slow release fertilizers are applied with a broadcast spreader and contain a group of nutrients that release immediately and another group that releases in a few weeks. The initial dose, which will be used up fairly quickly, provides a massive dosing of fertilizer followed by a sudden and excessive leaf growth spurt with little root development. Once the initial dose of nitrogen, potassium and other nutrients are used up, which occurs in a matter of days, the plant material begins to starve, creating significant stress on the plant. Depending upon the conditions at the site (ie: temperature, amount of water, soil type), the slow release portion of the feeding may or may not begin to take affect within a few weeks. Unfortunately, many times the slow release chemical has been washed away with rain or normal irrigation cycles before it is released and can provide nutrients to the plant material.

TruGreen LandCare San Diego maintains an estate in Rancho Santa Fe, CA, which utilizes this fertigation system. The system, adapted from an agriculture system, includes a 750 gallon tank of fertilizer which feeds the entire landscape and turf areas for over a month.

An alternative to slow release fertilizers that is gaining some notice is fertigation. This process provides continuous, uniform feedings that eliminate the growth spurts and subsequent stress caused by slow release fertilizers. Since only small amounts of fertilizer are applied at each feeding, plants are able to take up the majority of the nutrients, eliminating chemical runoff and build up of fertilizer salts in the soil.

The Growth of Fertigation

The amount of fertilizer injected into the system is controlled by these valves.

• On the end of relatively inexpensive and simple, Olson Irrigation Systems in Santee, CA, developed the EH-12 emitter system (www.olsonirrigation.com). This convenient drip irrigation head has all components of the drip system in one head including 12 outlets for distribution tubing, a filter, and a receptacle for a slow release fertilizer pellet which releases nutrients as the system irrigates.

The EH-12 head includes 12 outlets for drip irrigation distribution tubing, a filter and a small receptacle for a fertilizer pellet which slowly releases nutrients during the irrigation cycle.

• Dosatron International (www.dosatron.com), a French company, developed fertilizer injectors powered by water pressure for use with existing irrigation systems. Additionally, the Easy Gro System, designed for residential use, automatically feeds lawns, trees, shrubs and gardens through the irrigation system.

A small fertilizer pellet fits into the Olson Irrigation Systems' EH-12 emitter head providing a complete feeding to plants during the irrigation cycle.

What Is Fertigation?

Fertigation is the process of supplying fertilizer (ferti-) simultaneously with water through an irrigation system (-gation). This type of feeding is generally more accurate, creates less buildup of salts and solids, is easier to apply evenly and less labor intensive than traditional methods of fertilizer application. Fertigation can also supply the optimal amounts of all necessary nutrients through a fertilizer mix created specifically for the soil conditions of the site.

The EH-12 emitter head, designed by Olson Irrigation Systems in Santee, CA, provides a simple yet effective form of fertigation.

In general, an irrigation system consists of a main line, sub-main lines (or headers), feeder tubes, and drip tubes. In addition to these components, the fertigation system includes a fertilizer tank and injector, a filter, a pressure gauge, check valves, and a pressure regulator. Key in keeping the system operational is a good filter. The fertilizer solution should be injected into the line in front of this filter so that any undissolved solids are removed before they enter the rest of the irrigation system.

Determining The Fertilizer Mix

A successful fertigation system can add an immeasurable amount of beauty to any commercial landscape.

1. Soil Sampling

Soil testing is a must for responsible and effective fertilizer application. These tests allow the horticulturist to prescribe a fertilizer plan that will make up for nutrient deficiencies in the soil, while being environmentally responsible. Proper collection and handling of soil samples is extremely important in the accuracy and repeatability of the soil test.

California regulations require personnel applying chemicals to be fully outfitted with protective clothing including gloves, respirator, boots and goggles.

Nutrient levels in soil vary not only over an area, but also with soil depth. A proper soil sample includes a uniform volume from the top of the sample to the bottom. Supplying a wedge shaped sample, or a handful of soil from the surface and another at depth, will not provide accurate, consistent results. For best results, samples should be taken with a soil probe.

2. Water Analysis

Occasionally, spot treatments are necessary and can be made utilizing the hose and sprayer at the rear of the boom sprayer.

During a water analysis, watch for concentrations of calcium, magnesium, carbonates, sulfates, sodium bicarbonate, sodium chloride, iron and boron. As a general rule, irrigation water should not contain more than: 100 ppm calcium, 50 ppm sodium, 25 ppm magnesium, 0.75 ppm boron, 60 ppm carbonates, 250 ppm sulfate, 70 ppm chloride. If large amounts of calcium, magnesium or sulfates are detected, these elements should be subtracted from the recommended percentage of the fertilizer mixture to be applied. High levels of bicarbonates, on the other hand, may cause iron deficiencies in plants. A horticulturist should be able to provide guidance on rectifying problems caused by other contaminants.

3. Equipment

A traditional method of applying chemicals to large turf areas is the boom sprayer. This option allows chemicals to be evenly distributed over a large area in a relatively short time.

4. Choosing The Right Fertilizer

When using a fertigation system, all fertilizer sources must be highly soluble. Labor cost savings can be quickly negated if an irrigation system becomes clogged with insoluble fertilizers, algae, or sand. Good soluble sources of nitrogen include calcium nitrate, ammonium nitrate, and potassium nitrate. Potassium sources include potassium nitrate or potassium chloride.

Solubility Limits

Water temperature is also an important factor when determining solubility. Therefore, the time of year may be a consideration when determining how much fertilizer will dissolve. In cooler weather, such as very early spring or late fall, less fertilizer will stay in solution than during warmer months.

Solubility limits can be increased by continuous agitation of the materials by mechanical paddle or recirculating pump, or by elevating the temperature of the water.

When fertilizer is being injected into a drip irrigation system, certain precautions should be taken: (Source: Mississippi State University Extension Service.)

Traditionally granular fertilizers have been applied to large turf areas using a broadcast spreader such as the Lely granular spreader.

•Select fertilizer solutions that will help adjust water pH if necessary.

•The suctionline in the fertilizer tank should not rest on the bottom of the tank.

•A fine screen should be put on the end of the suctionline. This will help filter out solid particles or undissolved fertilizer.

•Do not inject fertilizer in combination with pesticides or chlorine.

•Be sure the injection point is upstream of the filtering system so the filter will remove any undissolved fertilizer or precipitants.

•Before beginning fertilizer injection, or fertigation, bring the drip irrigation system up to operating pressure.

•After all of the fertilizer is injected, irrigate with plain water so the lines are flushed out and fertilizer is washed into the plant beds.

•Be sure the time needed to distribute the fertilizer is less than the required length of the irrigation cycle.

•Avoid overwatering as this will leach some of thefertilizer out of the root zone.

Fertilizer Injectors

There are many types of injector pumps available today including positive displacement pumps and proportioner injectors, and the venturi bypass.

When using a boom sprayer, fertilizer concentrate is added to the boom sprayer tank and diluted with water.

Proportioner injectors sense the rate of flow and adjust the injection rate as the flow rate changes. These pumps do not require an outside power source, but require some pressure to operate. Pressure changes in the system can alter the rate of injection, which may or may not be proportional to the desired rate.

Regardless of the device chosen, the size of the injection pump should accommodate the maximum amount of fertilizer to be injected at any time during the season. Also, consider that on any given cycle, the fertigation process should be completed in less time than is necessary to meet the irrigation needs of the plant material. The system should flush itself with clean water at least once after distributing the fertilizer solution.

Backflow Prevention

Keeping weeds in check is key to a successful landscape maintenance plan. At top, a hand held sprayer is used. A boom sprayer can also be converted to a hand held sprayer for spot treatments. Accurately measuring and mixing chemical fertilizers is key to the success of a fertigation program.

A low pressure drain and vacuum breaker should be installed between the injection line and the water source to prevent seepage into the water source when the system is not running.

Injection Point Location

Benefits Of Fertigation

Fertigation eliminates many of the problems of traditional feedings. Because nutrients are "spoon fed" to plants, that is, small doses are applied continually, feedings are more accurate, lighter and more frequent, eliminating the feast and famine cycles usually found with granular applications and the build up of salts in the soil. The release of liquid fertilizer is also more constant than that of granular keeping plants healthier and more able to resist pests and disease. Because dry fertilizers are dependent upon outside factors such as temperature and rainfall, which cannot be adequately predicted, granular applications are not always consistent. Fertigation eliminates this problem since food and water are provided simultaneously. In addition, there is no danger of burn to the landscape because the fertilizer is diluted as it is applied. Fertigation is also more environmentally friendly than granular applications. The smaller amounts of nutrients applied are almost completely absorbed by the plant material, so fewer chemicals are leaching into ground water or running off into environmentally sensitive areas.