Lack of response to a fertilizer application
These pots of variegated tropical carpetgrass (Axonopus compressus) received an application of granular 16-16-16 fertilizer twelve days before this photo was taken. The grass on the right responded with a lot more growth than did the grass at left.
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The fertilizer was applied at the same rate to both pots. Here’s a top view.
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What’s happening here is a phosphorus (P) deficiency. These two pots were maintained with different levels of P fertilizer. For the past year or so. I deliberately withheld P from one of these pots.
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Tropical carpetgrass is the best grass I’ve seen for showing phosphorus (P) deficiency—especially in this organic soil. These pots are filled with coconut coir that tests for Mehlich-3 P less than 20 ppm and a Bray-2 P less than 5 ppm.
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The same symptoms are seen in a nearby park with acid soil and no fertilizer: carpetgrass has this same response, with new leaves green and old leaves purple.
Having some fun with P deficiency, that’s what I am doing here. But for managed turfgrass, this is an avoidable disaster. I recommend using the MLSN method of soil test interpretation to ensure the grass is supplied with enough P. If you were to look only at the top two images, I think you might fail to recognize that this is a P deficiency. And in these pots the deficiency doesn’t matter, and I’ve caused it on purpose. But on professionally managed turf that gets traffic? There’s no reason to mess around.