Monthly Turfgrass Roundup (May 2013)
Getting around the golf course on a sulky

Turfgrass Mystery: why is there a ring of green grass around the collar?

green grass in June near Tokyo

This turfgrass mystery is illustrative of a couple of interesting points. These will be explained once the answer is given. This photo was taken in early June, 2001, at a golf course in Japan, near Tokyo. At right is the collar of the green, mown at 12 mm (1/2 inch). In the center is a band or ring of particularly green grass, and at left the grass is more yellow. At the right side of the photo, the grass condition is basically uniform, but at left there is the green grass and the yellow grass.

Can you identify what has caused this green band of grass, and why the grass at the left is yellow?

This was solved without too much trouble.

It was correctly pointed out that this must have something to do with fertilizer, with the green ring of grass responding to fertilizer that had also been applied to the green. But that is not all there is to it. 

The overlap of fertilizer didn't stop right where the grass turns from green to yellow. The yellow and shorter grass at left is japanese lawngrass (Zoysia japonica), and the grass at right is primarily perennial ryegrass (Lolium perenne). The fertilizer overlap extended into the zoysia. Because of the temperatures during this season, the ryegrass could use the nitrogen, and did, while the temperatures were too cool for the zoysia to make much use of the extra nitrogen.

At this interface between warm-season (Zoysia japonica) and cool-season grass (Lolium perenne), one grass was able to use the applied nitrogen, and the other could not. For the three weeks leading up to the date of the photo, I have calculated the daily growth potential, based on the actual temperature in 2001. This plot shows just how good the weather was for the ryegrass, and how relatively poor the weather was for the zoysia.

In fact, the average cool-season (C3) growth potential in this span was 0.96. For the warm-season (C4) grass, the growth potential never got above 0.5, not even for 1 day, and the average growth potential was 0.29. For more information, see Explaining the Turfgrass Growth Potential.


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