Five comments about the ATC Office Hours on OM246
Correspondence work in southern Thailand.A colleague from Canada wrote to me with five comments after finishing this ATC Office Hours with Chris Tritabaugh (or listen as a podcast here).
Just listened to your talk with Chris and wish I had the where about to attend it live, as I would have kept the chat room real busy!
I’m sure he would have. I’m glad to have this type of thoughtful feedback, and I take the opportunity to reply to these comments (labeled a) to e) here), as I think they may be of broad interest.
a) I like to monitor the organic matter at the deeper depths as it tells me, that our improved cultural/management practices are producing roots down there where in the past they were concentrated only in that top 2.0 cm. The 440 picks that up!
Could be.
Of course I have the affliction of not being terribly concerned about roots, and the problem with using loss on ignition to measure that is even if the test is sensitive to measuring differences in root mass—and I expect it could be—I wouldn’t know from the test result whether the roots were dead or alive. What I recommend for an 18 hole facility is to test three greens all the way to the 6 cm depth. For me, that’s sufficient to assess what’s happening at that depth. Because there is a lot more variability closer to the surface, I like to spend a bit more sampling effort, and testing cost, on doing more samples right at the surface.
To check roots, I’d like to look at them. I still monitor organic matter at the deeper depths (2 to 4 cm, 4 to 6 cm). It’s just that I like to measure extra samples for OM at the surface. There is a lot of information on the OM246 reports, and a lot that can be gleaned from the data. Chris and I made a decision to focus our conversation on the top 2 cm, for purposes of brevity, and it still went to 2.5 hours!
b) Related, agree that dry ject operations can place sand deeper than required….can the depth of the unit be adjusted?
I don’t know. I presume so. One of the things I find so useful about OM246 test results is the breakdown of how OM is changing over time by depth. The maintenance work can then be adjusted to do work at just the right depth.
c) we are discussing the 5% OM content here [this is referring to the OM percentage in the top 2 cm] but what is the influence of the other 95% on your greens speed, your bobble test, your firmness testing etc. Would have to believe the C.U. value of that other 95% is of influence. Out west, the common source of sand is well rounded uniformed drenched from Fraser River. Major concerns with traffic and surface instability affecting putting quality.
The other 95% must have some effect on those playability factors. The OM246 test is not looking at that, however. The OM246 test is looking at the total organic material by depth, and how it has changed over time. In this way, the integrated effects of organic matter accumulation, decomposition, dilution, and removal can be measured. If there are problems with traffic and surface instability that are related to the sand and not to the organic matter, then those can be addressed. If one really wants to adjust the firmness of the greens, I’d look to do some physical analyses of the sand and would be looking especially at the CU.
d) You continue to down grade the importance of potassium; I can take that but how does a super easily apply sulphur to maintain at least 7.0 ppms (the MLSN value I believe) when 0-0-50, sulphate of potash … is an easy way to apply sulphates as a granular or soluble at low rates through the season … My goal is 15 to 20 ppms to allow for a leaching rain event before the next spray tank application can recharge the system.
Good question. S is a tricky one. And an important one. Let me deal with K first.
Potassium deficiencies are not pretty and are what I have called a very bad thing. I don’t mean to downgrade the importance of K. I do like to be careful about how much K is applied, and when the grass can get enough K from the soil, I try to avoid recommending it as fertilizer.
For sulfur, the MLSN value is 7 ppm at the moment. An analysis of Global Soil Survey data also identified the same 7 ppm value, and the median in the GSS dataset was 14 ppm. Fifteen to 20 ppm certainly seems ample but I don’t know that so much is necessary, if half the GSS samples, which were explicitly from good-performing turf, were at 14 ppm or less.
An aside here about MLSN. We include numbers for S, Ca, and Mg in the MLSN guidelines because, well, there were numbers for those elements in “Table 1. Typical soil test SLAN sufficiency ranges for macronutrients using common extractants” in Carrow et al.’s Clarifying Soil Testing: III. SLAN sufficiency ranges and recommendations. When we developed MLSN, we intended that to be an alternative to the standard guidelines, and thus we calculated MLSN values for all the same elements that were in Table 1. However, I don’t worry too much about how S, Ca, and Mg relate to MLSN when making fertilizer recommendations. Yes, there are minimum values for those elements. But I don’t use them quite the same as I do for P or for K.
Back to S—I do want to make sure there is enough S available to the grass. I worry sometimes that there is not. Especially when the soil is low in organic matter. Turfgrass leaves have about the same amount of S as they do P. I also expect, as you do, that leaching rain events will do just that to sulfate-S in the soil. I figure the grass is using N and S in about an 8:1 to 10:1 ratio. That is, for every eight grams (or pounds) of N the grass uses, expect it to use about one gram (or pound) of S. If the soil test S is 6 or 7 or 8 ppm, close to the MLSN minimum, I often suggest being sure to add some S through the year. That might come from sulphate of potash, or from sulfate of ammonia, or iron sulphate. The way I do it is based on how much the plant can possibly use. And I use the soil test as a trigger for when I ignore S, or when I mention it as something that one should make a point of thinking about.
This is another element that the grass can get a lot of just from irrigation water. This guide from Penn State says normal irrigation water is 10 to 30 ppm S. Let’s say the grass has been fertilized in one year with N at a rate of 15 g/m2 (3 lbs N/1,000 ft2). The maximum expected S use would be $\frac{1}{8}$ of that, or 1.9 g/m2. If the irrigation water contained 20 ppm S, it would only take 95 mm (3.7 inches) of irrigation to supply that entire annual supply of S. In a lot of places, the irrigation water will supply all the S the grass can use.
To summarize how I approach this: S is really important, but the grass uses it in relatively low quantities so I don’t worry much about maintaining S at a certain level in the soil—although I do use soil test values of S close to the MLSN minimum as a trigger for pointing out that S is in the lower 10, 20%, whatever, of good-performing turf soils—and I do keep in mind that I want to make sure the grass gets supplied in those cases with S at about $\frac{1}{8}$ to $\frac{1}{10}$ the N rate. That turns out to be a tiny (but important) amount of S.
e) Brookside has been very co-operative … to develop the 440/360 and now just the 440 test package. I would have hoped that somewhere in your spreadsheets or verbally that you would have acknowledged the source of your information.
Thanks for the opportunity to mention that all the work I’ve done with the OM246 testing, both research related to the test development, and the commercial tests that I offer, are through the excellent Brookside Labs. You can see many occasions when I have mentioned where the tests are done, for example in these:
If I didn’t mention Brookside Labs in that conversation with Chris Tritabaugh, it was because he and I knew, and I guess we expected that many of the listeners would know also, that this is a test that can be done at Brookside Labs and through any of the Amplify Network consultants.