Denitrification, Leaching, and Turf Manager Expectations

Nitro-30 SRN™ (30-0-0), Nitro-22 (22-0-0), The Classic (18-3-6)
October 2015

Like everyone else, turf managers have expectations that are not always met -or expectations, in certain circumstances, which need a little extra work to achieve!

For example, this summer some turf managers expected their regular fertilizer application would last the same 6 to 8 weeks as it did last year. But when an area gets 7" of rain over a period of two weeks, or when pools of water cover a patch of turf for days in a row, a turf manager needs to reassess their expectations and take action.

Consider All the Factors

In any situation, turf managers should ask what factors -environmental or otherwise -are in play that might require a little extra work, investigation, or schedule-tweaking.

What is one of the first factors to consider? Water! Whether it is too much or too little, water matters a lot. Too much water can cause leaching and/or denitrification:

• Leaching occurs when too much rain moves nitrates and other water-soluble nutrients out of a plant's root zone. Sandy soils are most prone to leaching, and while adding organic matter to sandy soils helps reduce leaching, in times of excessive rain some leaching is inevitable. Because of environmental concerns about groundwater contamination, most of us are fairly aware of the dangers of leaching.

• Denitrification occurs when soil nitrates are converted to nitrous gases that are then lost into the atmosphere. As Dr. Karl Danneberger explains in his textbook Turfgrass Ecology & Management, water-logged anaerobic soils are highly prone to denitrification, and this becomes particularly problematic for turf managers when temperatures are high. Danneberger states that turf under these conditions will appear chlorotic and most likely will need a nitrogen application.

Waterlogging impacts plant stands and nitrogen status of the soil.

Denitrification is carried out by denitrifying bacteria. These bacteria utilize the nitrate as an oxygen source.

If leaching or denitrification occurs, visual clues will abound. In addition to the yellowing of leaves, turf will develop diseases such as dollar spot, brown patch, red thread and rust, and overall turf decline and thinning will shortly follow

Testing and Tweaking

As soon as a turf manager suspects that soil might be anaerobic tests should be conducted. Regular soil tests are not very accurate during times of excessive rain, so I recommend tissue analysis or soil respiration testing. Tissue analysis pinpoints the level of N in the turf, while a Solvita® soil respiration test identifies the potential for biological activity in the soil which, in turn, is directly related to the amount of oxygen in a soil. Water-logged soils have little oxygen, consequently impairing nutrient availability.

Using the test results, turf managers can determine if they should tweak their routine by providing supplemental nitrogen. Growth Products' slow-release liquid fertilizers are always a good bet. My top choices include:

Nitro-30 SRN™ (30-0-0) contains 85% slow-release nitrogen in a form that sticks to the leaf cuticle after a spray application. The nitrogen then slowly breaks down and is absorbed through leaf openings.
Nitro-22 (22-0-0) contains 40% slow-release nitrogen and 4% water soluble sulfur. Because of its sulfur content, Nitro-22 is especially beneficial for areas with alkaline soil, as the residual sulfur will help reduce soil pH.
The Classic (18-3-6) has 50% slow release and 50% quick-release nitrogen, 3% phosphorus, 6% potash, plus immediately available micronutrients (copper, iron, manganese,and zinc) which are a boon to damaged turf.

Take-Away Lessons

A turf grass manager is at their best when they are constantly observing turf, using their knowledge, and adapting to current situations. A good manager realizes that the timing of fertilizer applications cannot be guided solely by the calendar, but may need to change under extreme conditions. They are also aware that nitrogen can "disappear" from the soil (quite literally in the case of denitrification!), and that even short periods of one or two weeks without sufficient nitrogen can cause turf damage.

By letting go of an unrealistic expectation that a fertilizer application will always last the same number of weeks, regardless of weather conditions, a turf manager can achieve success with a higher expectation of maintaining healthy, attractive turf year after year.

As you move into fall and think about your expectations and goals for the remainder of the year, feel free to give us a call. We're here to answer your questions and lend our expertise. Our goal is to make your goals and expectations come true.