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Efficient Fertilizer Use — Fertigation: by Dr. Bill Segars

SECTION CONTENTS: • Introduction • Soil Chemistry • Water Quality Concerns • Fertilizers for Injection Into Irrigation • Use Fertigation Properly and According to Regulations • Irrigation Scheduling & Fertigation • Other Important Factors to Consider When Fertigating

Fertigation is defined as the application of nutrients using an irrigation system by introducing the nutrients into the water flowing through the system. The first reported application of commercial fertilizer through a sprinkler irrigation system was in 1958. Today, we routinely inject fertilizer solutions and suspensions into irrigation systems via calibrated injection pumps that insure precision over both space and time.

Fertigation has increased dramatically in the past 15 years, particularly for sprinkler and drip systems. For drip systems, the expansion is mostly in horticultural and high value crops. In agricultural areas with declining water supplies, drip systems have also increased. With increased irrigation, a corresponding increase in fertigation has taken place. It will continue to grow since such Figure 10.1 Overhead sprinkler irrigation system. systems result in less water usage and better uniformity and lend themselves to the technique much more readily than the less water-efficient and non-uniform furrow and flood systems being replaced. Effective fertigation requires knowledge of certain plant characteristics such as optimum daily nutrient consumption rate and root distribution in the soil. Nutrient characteristics such as solubility and mobility are important and irrigation water quality factors such as pH, mineral content, salinity and nutrient solubility must be considered. The need for irrigation is the main factor in fertigation because the irrigation system is primarily installed to provide water. The opportunity to fertigate is an added benefit. This chapter will address issues that must be considered to achieve maximum benefits when fertigating.


Efficient Fertilizer Use — Fertigation: by Dr. Bill Segars

Figure 10.2

Growers often plant vegetables under plastic mulch and fertigate using drip/trickle irrigation.

Soil Chemistry
Cropping and fertilization history as well as basic soil chemical properties also need to be considered prior to fertigation. Soil testing by the method recommended in a specific area is the best way to assess current fertility needs. Particular attention should be given to soil pH and its adjustment to an appropriate range for the crop to be grown. Proper pH can have a great effect on the availability of residual nutrients in soil as well as those added via fertigation. Any required soil pH adjustments should be made using conventional incorporation techniques. Fertigation is not utilized to alter soil pH’s. Cation exchange capacity (discussed in The Soil Defined) is an important consideration in determining the quantity of cations that will be retained during fertigation. In order to maintain an acceptable concentration of cations in solution, a soil with a low CEC must have its cations replaced via fertigation more often than one with a relatively high CEC, which can hold a greater quantity of ions. Since nutrients are easily added with fertigation, it is most practical on sandy, droughty soils with low CEC. These soils need frequent irrigation and nutrient replenishment. Previous chapters in this book have explained soil movement of nutrient elements when applied by conventional fertilization methods. Since fertigation does not negate classical soil chemistry, fertigated nutrients behave similarly to conventionally applied soluble nutrients followed by rainfall or irrigation. A reminder - only small quantities of nutrients applied by an overhead sprinkler system are absorbed by the foliage. There is some concern that since nitrate nitrogen (NO3-N) is highly mobile, it may leach past the root system and reach groundwater....
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