This question came some months ago:
"I'm just pondering something about MLSN levels for Bent vs Poa and so hopefully you can clear it up.
Having seen a bit of research coming out about k levels affecting disease pressure differently for poa and Bent does that not mean there should be two different MLSN's for the two species?
Sorry if this is a rubbish question, I might have missed something somewhere."
That is not a rubbish question. There are three general points I'd like to make about this.
MLSN is a method for interpreting soil tests to prevent deficiency. That is, MLSN is designed to be conservative. The MLSN guideline serves as a quantity of K in the soil that the grass will never touch. The amount of K recommended as fertilizer using the MLSN approach differs based on three things: grass type, growth of the grass, and the quantity of K in the soil. The fertilizer recommendation for K changes for every situation, but the MLSN guideline remains the same.
This article by Doug Soldat has more about varying K fertilizer amounts and bentgrass and Poa annua diseases. If one wants to adjust the K fertilizer in an attempt to incite or suppress anthracnose or snow mold, or winter kill, then one might err on the side of a little bit more K for Poa in summer, and a bit less K for bentgrass, especially in autumn.
MLSN is meant to be simple, and is meant to answer two questions. Is this element required as fertilizer? If the answer to the first question is yes, then the second question it answers is "how much of the element is required?" It is meant to err on the side of recommending too much, rather than too little. One can use those recommendations as a reference, and then if one wants to try to reduce the intensity of snow mold, then cut the K.
After Paul Robertson asked if anyone is using a Pelzmeter, a long discussion followed, and the notifications on my Twitter account blew up. I think the conversation is still happening.
My only contribution to that conversation was to share a link to an article by Richards et al. that shows the Pelzmeter and the Stimpmeter give the same results with "no differences in measurement repeatability."
The conversation kept going, eventually touching on the quantity of clippings mown from the turf, which is some indication of how much the grass is growing, and the green speed. I was reminded of a question from a correspondent a few months ago. He wrote with this question:
"Have you correlated yield to speed? I have to assume that as yield changes speed changes also."
I replied:
"In the big picture view, yes the clipping volume will be negatively correlated with speed. When clipping volume goes up, the speed has to go down.
I don't really need to show any data for this to be certain. Take, for example, warm-season greens. Are they faster when growing in August (clipping volume is a positive number), or when dormant in February (clipping volume is 0)? They are lightning in February and of whatever speed they are in August.
I attach a chart with clipping volume in L/100 m2 (same as quarts per 1000 ft2) on the x axis and green speed on the y axis. That's from a couple years of tournament week measurements in Japan. Speed is affected by other things but the clipping volume is sure to have some effect and I don't think it will ever be in the direction of more growth = faster speeds.
This is the chart I attached.
Today I looked up the data from 2016 and added it to the chart, and this includes a couple measurements from July 2016 a month before the tournament week.
Here it is without the July measurements.
And here are the data broken down by year.
Bill Kreuser showed data on bentgrass where the quantity of clippings was not related to the previous day's stimpmeter measurement. Those data are surely correct. But if one thinks about the big picture view, of the range of growth rates one can have over the course of the year, and the range of green speeds, I think it makes sense to think of green speed as being affected by how much the grass is growing.
And this leads me to something else that I can't help but mention. Bill can show data that demonstrate an interesting point; clipping yield was unrelated to green speed under the conditions of his experiment. I can show data that demonstrate an interesting point; clipping volume in the situation I describe is obviously associated with green speed. These experiments are not that hard to do; one could generate some kind of data about green speed and could make it show whatever one wanted to, if one planned it right, because there are a lot of factors that influence green speed! So why is it so difficult to find data about Si and green speed? I still think it is ridiculous that a stiffer leaf would make for a faster green speed.
I received this question about leaching salts from the rootzone:
"I remember talking to you once before regarding flushing excess salts from the root zone and the application of gypsum or other calcium products before the flush and you telling me it was not necessary. I have since discovered that same conclusion for myself. I remember you sent me an article or a link to one of your blogs but I can't seem to find the email or article. Could you please send it to me again?"
I wrote back:
I don't recall that I've written anything specifically about that. I have written about Ca not being required in sand rootzones for the purposes of dealing with sodicity issues, because no matter how much sodium one puts into a sand rootzone, the soil structure cannot be affected, so gypsum won't be required. Relevant blog post:
Is sodium an imaginary problem?
Also, this: water and soil handout.
I have made a note to write a blog post [and here it is] about leaching salt from sand rootzones and Ca not being required. I'll do that sometime.
Real quick, water problems are divided into 3 main categories, and each has a different solution.
Salinity -- this is the total salt. The solution to salinity problems is to add extra water to leach the salts below the rootzone. No Ca is required for this. The water does the leaching.
Sodicity -- this is a soil structural problem that occurs in soils when the sodium gets too high. It is defined as exchangeable sodium percentage > 15%. This is irrelevant in sand rootzones because the sodium does not cause any structural problems in sand. This is a problem in clay soils. The solution to this problem is to add gypsum. The Ca in the gypsum then replaces some of the sodium and restores the soil structure.
Saline-Sodic -- in this case, the sodicity occurs and is combined with high total salts. Also irrelevant in sand rootzones because of reason mentioned above. The solution to this problem is to add gypsum, to restore soil structure, and then to add extra water to leach the salts.
I saw a video today with the question "what is your favorite fertility practice?" That segment starts at the 2:00 mark.
Then on Twitter I saw some comments about how funny the answers to that question were. I had a laugh because the answers are correct, but it is the question that misuses the word.
I don't expect the turf industry will change its jargon on this. But if one misuses the word fertility in conversations with the general public, it should not be a surprise if the responses are about fertility.
Jon Scott wrote to me about my recent post on a poor way to fertilise.
"While this superintendent has solved his problem of nitrogen input by monitoring salinity level that has worked for him, this is probably a very unique situation. It may be relevant to other golf courses where similar salt levels exist, but there are too many variables to draw general conclusions. Thus, I would focus on salt levels as related to this situation and not extrapolate. What he has said may be relevant to similar situations, but it all depends on the salt levels."
I agree, and I meant to make that clear in the original post. Let me try now to explain in clear terms.
If there is a salinity problem at a site, then one will always want to minimize the salinity in the soil. If one is always trying to minimize salinity in the soil, then it is impossible to use any measure of salinity as a criterion for fertilizer application.
In a case where there is not a salinity problem at a site, it might sound reasonable to try to use salinity as an index of nutrient content in the soil. However, there are three big problems with this, and these I did describe in the original post. First, most turf managers don't want fluctuating nutrient supply; second, salinity says nothing about which nutrients are there; and third, the salinity measurements from soil moisture meters, whether EC or a salinity index, are so affected by the water content of the soil that using the salinity of non-saline soils to make decisions about fertilizer is like chasing a target that moves randomly.
I like using soil moisture meters to measure the water content in the soil. I think it is useful to assess the salinity of the soil with the meter too, if that function is available. But I don't think it is a good idea to make fertilizer decisions based on soil salinity.
I replied to Jon that "I think it is ridiculous but tried to be as polite as possible."
He wrote back:
"You, trying to be polite? Don’t lose your edge ... I think you need to clarify how unique this situation is so that others don’t try to jump on his bandwagon. His premise is flawed when applied outside of his operation."
A few years ago I wrote about how everyone knows zoysia grows slower than bermuda, except when it doesn't. In particular, I was discussing the growth of the nuwan noi variety of manilagrass (Zoysia matrella) in tropical Southeast Asia.
One of the examples I used in that post was the expansion rate for patches of nuwan noi in the bermudagrass fairways at the Santiburi Samui Country Club. I was back at Samui this week, and I went to the 18th hole to check the nuwan noi.
Just around the dogleg, and down the hill near the landing area, there is a large patch of nuwan noi that has overgrown the bermuda.
I paced it off, and the diameter of that particular patch is now 17 meters. If that started as a single plant in January 2007, and has now grown 8.5 meters in every direction, then the expansion is 850 cm in 125 months, or 6.8 cm per month.
This approximate rate keeps coming up in a number of measurements I've made. I have estimated the expansion at 7 to 8 cm per month. And in pot experiments, I get a similar rate too. For example, planting nuwan noi stolons at a rate of 1,500 nodes per square meter gives 1,500 nodes in 10,000 cm2. If each node occupies 1 cm2 at the start of the month, and then the coverage goes from 1,500 to 10,000 cm2 by the end of the month, that's an expansion rate of 6.7 cm2 for each plant in a month.
Why does this matter? Because I've hypothesized that the most sustainable grass for a given location is the one that has the most growth per unit of N and per unit of H2O applied.