The injection equipment at Los Altos G&CC, including a large-capacity metering injection pump, was supplied by Robert Evans of Burlingame Engineers in Burlingame, Calif.

2001 Leo Feser award candidate

Fertigation is the use of an irrigation system to deliver fertilizer to the soil. Only a small group of golf course superintendents practice fertigation. Foliar feeding produces a rapid response (usually within 24 hours). Foliar feeding through irrigation systems is useful under various scenarios during the growth season.

What if you could have an immediate desired turf plant response by using your existing automatic irrigation system to apply foliar-absorbed nutrients any time, day or night?

When I became superintendent at a 1920s-vintage 18-hole golf course, Los Altos (Calif.) Golf & Country Club, I discovered that our 40-year-old native-soil greens would thin during the summer, and a white, hard impermeable layer would form on the surface. Walking on the crust with cleats produced a crunching sound. The crust was a composite of magnesium and calcium carbonate, and tests showed that our well water contained calcium and magnesium, as well as 400 parts per million (ppm) bicarbonate.

We believed we could alter and manage the magnesium and calcium carbonate to improve our water quality. The goals were to "gas-off" the bicarbonate by injecting sulfuric acid into our irrigation system and to convert magnesium and calcium carbonates to magnesium and calcium sulfates. Given that magnesium sulfate is 650 times more soluble than magnesium carbonate, and calcium sulfate is 140 times more soluble than calcium carbonate, basic chemistry dictates that this proposed acid reaction should reduce soil crusting and improve water movement on our entire golf course.

Before commercial sulfur burners were available, concentrated sulfuric acid was, without question, the cheapest source of acid, although it required special handling. We found a buffered sulfuric acid that was specially manufactured for turf.

After a few months of acid injection, we'd gained only marginal reduction of visual carbonate salts and well-water bicarbonates. Not satisfied with 15 percent improvement, we decided to go after 60 percent of our bicarbonates. However, our efforts were merely an exchange of one problem for another: carbonate salts for sulfate salts.

Sulfates can be reduced in an anaerobic environment by a number of anaerobic active bacteria in two genera, Desulfovibro (five species) and Desulfotomaculum (three species). The organisms use the combined oxygen in sulfate to oxidize organic materials. When iron is present, it is most likely to be found in the ferrous form, and the reaction could produce black layer. Sulfate naturally occurs in our well water at a rate of 84 ppm. Overwatering our greens between late spring and early fall produced black iron sulfide (black layer).

Increasing the amount of injected sulfuric acid in our irrigation water raised the sulfate level to 300 ppm, and soil sulfates tripled from just the previous year. Granted, these increased levels of sulfate salts are not considered excessive, but given the level of free oxygen in our soils, many of our drained greens that had rarely had problems showed signs of black layer. It became apparent that high levels of these particular salts, though damaging, were a symptom, and the primary problem was the inability of our soils to exchange gases and move water through the soil profile.

With help from Larry Stowell of P.A.C.E. Consulting in San Diego, who has performed our lab testing, we now weekly monitor and manage not only individual salts but also our entire salt load.

The sulfuric acid we used to solve our problem had a urea (nitrogen) component. This small amount of urea (approximately 11/2 to 21/2 pounds of nitrogen a year) was enough to maintain consistent growth and color on fairways and roughs with only minimal clipping residue. With an 80-year-old hodgepodge irrigation system, 80 pounds of pressure loss and 25-year-old control components, we supplemented our irrigation by hand watering many areas that had received poor coverage. Because all the irrigation water, even the hand watering from a hose, has proportionally injected fertilizer, we have been able to maintain turf growth and color throughout the course. Fertilizer injection has been our sole source of turf plant fertility for fairways and roughs for the last 10 years. We currently use an 8-1-8 blend. The formula has often changed, as we better understand the relationships among soil, water and turf plants.

Los Altos assistant superintendent Jason Green, a seven-year GCSAA member, applies 10 gallons of the solution to a putting green.

Fertigation, defined as the use of an irrigation system to deliver fertilizer to the soil solution, is still only practiced by a small group of superintendents.

Why change when your current method of fertilizing works? Well don't, but if you haven't had great success, and you are interested in additional control of nutrient release, fertigation might be worth evaluating. In our situation, we became comfortable with fertigation as we learned to reduce well-water bicarbonates.

Foliar feeding
Another method of fertilizing that is widely accepted by superintendents is foliar feeding: liquid or soluble fertilizers distributed evenly over the turf surface. The plants absorb the majority of the nutrients through their leaves. With fertigation, you can inject less than 50 ppm daily in the irrigation water, whereas with foliar feeding, you can expect more than 1,000 ppm weekly to monthly.

Foliar feeding produces a rapid response (usually within 24 hours). Because many superintendents already have foliar pesticide spray programs established for greens and tees, it's simple to incorporate soluble fertilizer in the tank as a supplement, or in some cases a replacement, to the dry fertilizer program.

So, why couldn't we use our irrigation system not only to fertigate but also to foliar-feed 100 acres? The question naturally follows: Why would we want to?

The following examples suggest a few possibilities when considering foliar feeding of nutrients during the growth season and the reduced-growth season.

Fertilizer solution with 1,500 ppm of nitrogen and potassium contained and infiltrating.

Foliar feeding through irrigation systems is useful under various scenarios during the growth season.

In the early spring, to jump-start feeding before soil microbes are actively converting nitrogen into a useable form of plant food. The idea is to bypass the soil solution and use foliar intake.
If your three-month, dry-release material has lasted one and a half months, and it's not possible to reapply dry fertilizer and achieve needed results in time for an upcoming event.
If you would rather not have to buy a complete nutrient package to correct a specific minor nutrient deficiency, or if you want to intensify color without stimulating growth.
If it's too wet to have fertilizer or chemical equipment on your course without making tire ruts, but additional fertility is needed.

Turf results at Los Altos CC one week after soil and turf drenching.

Of course, we could use our boom-type sprayer to foliar-feed the golf course. However, it is not the most efficient use of labor nor always convenient for golfers. In this case, the effort would outweigh the benefit. What if you could use your existing irrigation system with the addition of a large-capacity metering injection pump to deliver up to 1/2 pound nitrogen, phosphorus or potassium or any substance that you can dissolve or suspend in water? In this case, it might be worth the effort

If we used this proposed method for fertilizer injection, what would we kill when our antiquated irrigation system failed?

To evaluate how turf plants would respond to a 1,500-ppm solution of nitrogen and potassium, we encapsulated 1 square foot of green and infiltrated approximately 14 inches of solution through the soil/root profile. Our conclusion was the turf plant would survive an irrigation system failure. There was slight root and tip burn, but the turf plants recovered. As long as the flow meter sends a signal to the metering pump, a consistent dilution factor will prevent salt accumulation. If the flow meter does not produce a signal, the metering pump will not operate.

Our irrigation piping holds approximately 20,000 gallons of water. How do we pre-load fertilizer (or any chemical) proportionally into the irrigation system, especially when our pump station is not centrally located but at one end of the golf course? We have 1,150 heads with an output of 20 gallons a minute. In one minute, the combined sprinkler usage is approximately 23,000 gallons. It will take a one-minute run-time (cycle) from each sprinkler to load fertilizer into our piping system. If our goal is to complete one sprinkler revolution with fertilizer, we will need three additional minutes from each sprinkler. If we started fertilizer injection at the beginning of the first minute through the third minute, the fourth minute we would remove the fertilizer from the pipes and thus complete one sprinkler revolution with injected fertilizer.

To determine the amount of fertilizer injected in irrigation water, samples were drawn after each cycle from various locations on the course. This location, near the pump house, showed the closet resemblance to the original prediction of fertilizer, salt levels and loading timetable.

With a pump station located on one end of the property, our approach to attain proportional distribution was to have four one-minute cycles from each sprinkler equally distributed throughout the golf course. The theory was that this proportional demand would balance the fertilizer load process and still complete one fertilized revolution. In order to determine the amount of fertilizer injected in the irrigation water, a sample was drawn after each cycle at the noted locations. The lab results are indicated in parts per million of total nitrogen and potassium salts. The lab results, of area No. 1, near the pump house, showed the closest resemblance to our original prediction of fertilizer, salt levels and loading timetable. Only minimal fertilizer salts were detected in the first cycle. The fertilizer salts were fairly balanced and were delivered in the approximate time necessary to complete one sprinkler revolution in the second through fourth cycles. Somewhere between the fourth and fifth cycles, the fertilizer salts were removed from the irrigation pipes. The lab results of areas No. 2 and No. 3 (opposite end of the course and the end of non-looped mainline) were not as accurate. However, unlike the less-than-perfect lab results, the turf results were impressive throughout the golf course. Visual results were obvious in less than 48 hours.

Even if these results are an accurate depiction of our piping hydraulics and not a lab or sampling error, it would be an easy task to use a computerized central control to balance any piping hydraulic issues. For instance, the first cycle run times would vary depending on your piping hydraulics. Therefore, at the start of the second cycle, all sprinklers on the golf course would have the same desired fertilizer salt load. Once the pre-load cycle was balanced, the three remaining one-minute cycles would follow to foliar-feed any time, day or night.

The possibilities are endless. With a computer and a simple understanding of your piping hydraulics, it is possible to deliver not only fertilizer salts to a specific site, but with the right labeling, any chemical that can be dissolved or suspended in water. This method is not for everyone, but for those interested, this protocol does work. Even the best superintendent misses the fertility window sometimes, and if nothing else, you have one more tool to answer Mother Nature when she is misbehaving.

Michael Simpson is CGCS at Los Altos (Calif.) Golf & Country Club and a 15-year GCSAA member.