Chemigation & Fertigation Fertigation — The Next Frontier By Charles M. Burt, PE, PhD, D.WRE, CAIS, CID


The irrigation industry has experienced major changes over the past 20 years. So, what is new on the horizon? Now that we understand the concepts of maximizing irrigation efficiency, how can we not only maintain but also increase crop yields with less water and less acreage? The answer lies in improved nutrient management combined with proper irrigation water distribution and management.


Just as irrigation dealers specify pressure relief valves and air vents on all pipelined irrigation systems, irrigation designs now incorporate fertigation (i.e., fertilization through the irrigation system) hardware.


Benefits The benefits of good fertigation are very real and increasingly important. The manufacture of nitrogen fertilizers is very energy intensive. The Cal Poly Irrigation Training and Research Center, on behalf of the California Energy Commission, documented the energy associated with various irrigation practices. The energy required to manufacture the fertilizer can equal the combination of all other energy inputs (e.g., pumping, tractors, pipe manufacture) in vegetable fields. Good fertigation practices can reduce fertilizer applications. In general, the ITRC has found that with subsurface drip irrigation (i.e., buried drip on vegetables) under good management:


• The fertilizer application is reduced about 25 percent.


• The yields increase.


The net result is that the yield per unit of fertilizer (or water) is increased. This is a true measure of improved efficiency.


One can quickly understand that the lower fertilizer applications, coupled with


20 Irrigation TODAY | April 2017


increased yields (i.e., increased intake of fertilizer by the plants), also results in less groundwater contamination with nitrates. This is a major consideration for long-term, sustainable irrigated agriculture.


Irrigation Systems Although fertigation is used with virtually all types of irrigation systems, its advantages are most pronounced when it is combined with fairly high frequency irrigation management. This includes solid-set sprinkler systems, linear moves and center pivots, and all types of drip-microirrigation. Such systems allow managers to finely tune and spoon-feed both water and nutrients. Just as water schedules can be adjusted daily or weekly to match weather demands, fertilizer dosages and types can be adjusted as frequently to match plant demands.


Good fertigation management requires that managers look beyond the supply of nutrients in the soil. They must also look at the availability of those nutrients to the plant. If an irrigation system only provides water once per week or two weeks, the top foot or so of the root zone is quite dry immediately before an irrigation. Many of the important plant nutrients (e.g., phosphorus) are predominately in this top layer, and they cannot move into the plant roots if the moisture content is reduced. High frequency irrigation allows the manager to make certain that if the nutrients are in the soil, they are also available to the plant.


Irrigation System


Distribution Uniformity As long as the fertilizer is completely dissolved and applied in moderately low dosages, the fertilizer will be distributed as


evenly as the water. High irrigation system distribution uniformities (i.e., greater than 0.85) are very important for finely tuned fertigation practices.


Legalities & Safety Certain hardware items are required by the U.S. Environmental Protection Agency for all pesticide injection systems if there is a possibility of pesticide backflow into a well or drinking water supply. Local agencies (e.g., counties, water districts, states) may apply these hardware requirements for fertigation systems also.


In many areas of the United States, enforcement of chemigation regulations is minimal or nonexistent. As fertigation becomes more common and sophisticated, and as it is accompanied by more chemigation of insecticides, fungicides and nematicides, the enforcement will become standard.


Certain hardware should be installed even in cases where there is no hazard of contaminating groundwater or drinking water supplies. Equipment should be installed to prevent fertilizer tanks from overflowing, exploding or draining and to prevent the buildup of high pressures that could cause hoses to burst. Systems should also be installed with a means of limiting the amount of fertilizer that can be injected, preventing overapplication of chemicals.


In other words, an irrigation dealer should not just sell a chemical injector. An irrigation dealer should sell a chemical injection system that includes all the essential safety devices, as well as being simple to adjust and operate. Figure 1 illustrates a configuration with essential hardware.


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