How I used nitrogen then vs. now
With charts!
I introduced this series of nitrogen1 posts with the title Nitrogen and why I find it fascinating. I find it fascinating, because it is the crux of everything we do in turf management. I once told a mechanic, who was new to golf: “when you get called to the course, bring gas, or fuel because 90% of the time, the problem will be an empty tank.” After a year of experience, he told me he couldn’t believe it, but I was right. In a similar way, I would guess that nearly 90% of turf problems are related to nitrogen; either too much, or too little. It impacts every single thing we do on the golf course. How much disease, how much and how smooth the ball rolls, the need, or not for aerification and the need, or not for topdressing. With the possible exception of irrigation, there is no turf management input I think about more than nitrogen. It wasn’t always this way for me.
In my first years as a superintendent, the only thing I really knew about nitrogen was that plants needed it. I bought it in liquid and granular form and applied it as someone else told me I should. As time went by, I desired to learn more, so I asked, listened and read, eventually coming to have my own approach to how I applied N, and the timing and types I used.
The approach I developed in those early years can be visualized in chart 1. It was a slam it and forget it approach; the chart shows what this approach would have looked like over the course of a season. The blue dots represent individual applications of N, the red line is the accumulated total of N applied, while the yellow line represents accumulation of N, predicted by growth potential (GP)2, the plant is likely to have used.
This slam it and forget it approach was aimed at starving annual bluegrass to the point of weakness, then providing a large amount of N to still healthy bentgrass, allowing it to take over the weakened annual bluegrass. On soil based greens at Northland Country Club, this approach worked pretty well. It was likely the native soil could hold on to some of the large N apps, allowing the deep bentgrass roots access until the next N app, while the shallow rooted annual bluegrass had less access to N. At least in theory, this is how I thought of the approach. On sand-based greens at Hazeltine, the approach didn’t work as well. I suspect much of the N applied was simply flushed right out the bottom of the rootzone. This approach didn’t allow the bentgrass plants to support the desired mowing and rowing, nor the typical golfer traffic.
I quickly moved to a more traditional spoon-feeding approach, but kept the late-season nitrogen apps. You can see how this may have looked in chart 2. At some point while using this approach, I got into a conversation, probably on Twitter, about late-season nitrogen and Micah Woods weighed in with something I recall being very much like this quote from his October 3rd blog post.
Many turf managers get great results with late fall nitrogen applications. But that is not the way I would fertilize turf. I don’t expect what I write here to change anyone’s mind, or way of fertilizing – at least this year – but I hope that when early and mid- and late-fall N applications are made, you might remember this, and observe the turf next spring, and see if what I’m writing about might be right.
A late-season nitrogen approach probably does make the turf look better in the spring. But it almost certainly also wastes a great deal of the nitrogen being applied. At that time of the year, the weather is too cold for the grass to use the nitrogen. This can be seen in the yellow line of any of the charts. By about October 10, the grass is done growing and done using nitrogen.
Fast-forward to the present day; and my approach is much more in line with points 1 & 2 in the guideposts from the Six Seasons…article I’ve referenced in the past and have posted above. Today, I’m applying only enough N to allow the grass to recover from foot traffic, mowing and rolling. And I’m only applying N during periods when the plant is actually using it.
Chart 3 shows our N apps on putting surfaces in 2023.
My approach today still holds back on N applications in the spring; until the plants are actively growing, it makes little sense to apply any N. Once the weather starts to warm, I like to match N applied to N use predicted by GP; at least early in the season. As the summer goes on, I have found that continuing to match applied N and predicted N leads to more growth than desired. The delta increases slightly throughout the summer until fall, when the delta expands. I’ve used this approach on our sand-based putting greens for the past three seasons and the results have been excellent.
For clarity purposes; throughout this post, I will sometimes use N to represent nitrogen. Sometimes one fits, sometimes the other, so I use both.