With foliar feeding on the rise, nitrogen use declines

While the principle of fertilization has remained the same – supplying nutrients to the plant for optimal health – technology has changed the amount used, application techniques and sources of nutrients.

Analyzing greens fertilization today, we see two very big changes. First, the total amount of nitrogen used per 1,000 square feet has dropped dramatically over the past 25 years. James B. Beard’s 1973 textbook “Turfgrass Science and Culture” (widely regarded as the Bible of turfgrass management) stated that the nitrogen requirement for bentgrass should be 0.8-1.4 #N/M per growing month. Looking back, even Beard himself acknowledges that was too high. Today, we have some greens being managed with as low as 1-2 #N/M per year. Disregarding a grow-in situation, the nitrogen amounts have dropped from Beard’s first recommendations to the current 0.25 – 0.50 #N/M range per growing month.

The second change is the incredible popularity of foliar feeding. This may be the one practice that has led to the use of less nitrogen. Spraying low amounts of nitrogen, with the use of a solubles/liquids, has become one of the most popular methods of fertilization over the past 10 years. This method, or “spoon-feeding” as it’s been called, is not strictly limited to greens. Many courses have used this approach on tee surfaces and, of late, fairways. The ability to spray these materials at a greater frequency, while using extremely low rates, has shown great benefits to turfgrass health. This type of approach can’t be accomplished with traditional granular fertilizers.

When it comes to greens fertilizer programs, there is no true standard in today’s industry. It is certainly a matter of experience and preference of the individual superintendent. The general program that seems to be emerging in popularity is one or two granular applications, usually in the spring and/or fall, and a spoon-feeding approach for the remaining months. For example, to calculate the total nitrogen of this type of program, it might be a spring and fall application at 0.5 #N/M of a granular material, and applications of soluble/liquids at a rate of 0.1 #N/M every 10 days throughout the season. In an approximate seven-month growing season, this nitrogen total is in the 2.5 #N/M range.

However, along with the amazing popularity of spoon-feeding, questions are being raised regarding the efficacy of foliar feeding. What are the maximum amounts of nutrients that the plant can absorb through the leaf tissue? Does the type of nitrogen matter? How much is lost to volatilization?

There has been very little research done on foliar feeding of turfgrass. In the agriculture industry, foliar research has been conducted for many years. The initial work that has been done indicates that a maximum of 0.1-0.125 of #N/M may be absorbed through the foliage. Research has shown that about 50 percent of the material is absorbed during the first hour after spraying, then 25 percent will be absorbed during the next 24 to 48 hours, and the remaining will most likely be lost. This will also vary depending on mowing and irrigation schedules. Research has also shown that water pH of the spray mix and type of nitrogen used will greatly influence how much is absorbed by the plant. A tank mix with high water pH has the potential to convert the nitrogen to the ammonium form and have a high volitization potential. Nitrogen compounds that are positively charged can also be absorbed electrically by the plant cells, whereas negatively charged nitrogen compounds cannot.

So what does all this mean for the industry? Even though foliar feeding has become the rage of greens fertilization programs, there are still many questions that remain to be answered from a scientific basis. Research needs to be conducted to answer the questions that are being asked. Only time will tell if foliar feeding will become the standard method of fertilization.