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April 2015

The choice is economic, not agronomic

This question came by e-mail:

Are you a fan of controlled release or straight release fertilizers for spoon feeding N and K, little and often?
What about Potassium?
I know that on very sand rootzones you need to apply little and often of N and K and cheaper forms can be used at much less cost. But, I can also see the potential of controlled release Pottasium in very sandy systems with high Ksat, low CEC or in areas with lot of rainfall.
But, with controlled release, you are beholden to some phased release where availability is dictated by temperature, warmth or the thickness of the coating. I think that with straight release, you in control and can apply when the turf need it i.e. heave wear, recovery, weather etc.

If I were spoon feeding N and K, little and often, then I would use fast-release (soluble) forms of those elements. I would be controlling the release through the low rates and frequent applications.

Controlled release products have a benefit when one is not spoon feeding. That is, they save labor cost.

One can choose what will work best for a particular site based on an evaluation of fertilizer cost, labor cost, equipment availability, and personal choice. The grass is going to respond the same whether the nutrient supply is controlled by spoon feeding of soluble materials or controlled release of insoluble ones. The choice between controlled release and fast release is economic, not agronomic.

Soil test phosphorus in turf soils: 2 datasets

Selection_090Landschoot et al. wrote about a large dataset of Mehlich 3 phosphorus data in Summary of Mehlich-3 P Data from Home-Lawn Soil Tests in Pennsylvania.

How are the data distributed? The median of the Pennsylvania data is 57 ppm, and 40% of the samples are less than or equal to 45 ppm, which is the cutoff level for P fertilizer recommendations to home lawns by the Penn State Agricultural Analytical Services Laboratory (AASL). Home lawn samples greater than or equal to 45 ppm P will not receive a fertilizer recommendation from AASL. For golf course putting greens the recommendation is different; P fertilizer is recommended by the AASL for putting greens when the soil test P is less than 90 ppm.

I looked at the Global Soil Survey (GSS) Mehlich 3 P data through August 2014. For these GSS data, the median value is 76 ppm, compared to 57 ppm for the Pennsylvania data, and only 35% of the GSS samples are less than or equal to 45 ppm, compared to 40% falling below that value in Pennsylvania lawns. Here is a histogram of the GSS data collected through August 2014:

Histogram_gss_m3pIn the GSS data, 11% of the samples were below the MLSN guideline of 21 ppm for P. The average expected P use by grass on putting greens is about 22 ppm, based on the average nitrogen application rate to putting greens in the US. Using the MLSN interpretation of the GSS data, and assuming P use at an average level, 33% of the GSS samples would receive a P fertilizer recommendation, compared to 40% of the Pennsylvania samples.

2 similar approaches to fertilization, with 1 notable difference

At first appearance, the demand-driven fertilization of STERF seems almost the same as the growth potential (GP) and MLSN approach. If you are not familiar with this approach from STERF, you can download their Precision Fertilisation -- from theory to practice, written by Tom Ericsson, Karin Blombäck and Agnar Kvalbein.

And I recommend you do download it. It is a great explanation of turfgrass nutrient use and requirements in only 20 pages.

Selection_089First, the similarities. These quotations will sound familiar, but they are not from me. These are quotes from the Precision Fertilisation handbook -- text in [ ] brackets is mine:

"fertilisation can be adapted based on the nitrogen requirement of the grass"

"light and heat control the growth potential of grass"

"warm summer days lower the nutrient requirement" [of cool season grasses adapted to a Nordic climate]

"when photosynthesis is slower, there is a decrease in the growth capacity of grass and thus also in its nutrient requirement"

"nitrogen is the nutrient that grass plants require most"

"By controlling the nitrogen concentration in the leaves through fertilisation, the growth rate is also controlled. A growth rate corresponding to 60% of maximum growth is often sufficient to produce a surface with good playing qualities. However, if the turf needs to repair some form of damage, the growth rate needs to lie around the maximum capacity for a period and therefore the nitrogen concentration also needs to be higher.

An experienced greenkeeper can judge from the colour of the grass whether the fertilisation level is right or wrong. The amount of clippings produced also sends a clear signal about the nitrogen of the grass."

"Since the potential growth of grass is controlled by the availability of light, heat, and water, the fertilisation level must be adapted to the growing conditions."

[When the growth capacity is reduced:] "The same argument applies when the cutting height of the turf is lowered before competitions. When the leaf area is reduced, the capacity of the grass to capture solar energy is also reduced. This decreases the growth capacity and the nutrient requirement. In order to avoid changes in the growth pattern of the grass above and below the ground and to maintain leaf structure and carbohydrate levels in the tissues, the fertilisation intensity must be decreased." [see also this on the lower nutrient requirement of stressed turf]

"Adding extra potassium in late summer/autumn to turf which already contains a surplus of this compound therefore has no additional effect on the ability of the grass to survive low temperatures. Addition of extra phosphorus in the spring when the soil temperature is low is also superfluous when a well-balanced fertiliser is supplied in small, frequent doses. As discussed, a moderate lack of nitrogen poses no serious problems for the health of turfgrass and in fact actually increases the quality of the turf."

So what is the difference between demand-driven fertilization of STERF and the MLSN approach I use? It is accounting for nutrient supply from the soil.

I say, follow the approach exactly as described by Ericsson et al. in their Precision Fertilisation, but if the soil is above the MLSN guideline for a particular element, then that element does not need to be applied as fertilizer, because the soil can supply enough to meet the grass requirements.

Ericsson et al. write that "greens built according to USGA norms have a low capacity to bind and supply nutrients to the grass. On this type of green, it is very important that the fertiliser compound used contains all essential nutrients." I would say that the fertilizer does not need to contain all essential nutrients, if the soil can supply them. And if the soil has nutrient levels above the MLSN guideline, then I am confident the soil can supply them. If the soil will drop below the MLSN guideline, then I agree, it is important that the fertilizer compound used contain that element.

Seminar questions: availability (again), and foliar applications in the context of soil guidelines

When I spoke about estimating turfgrass nutrient use in Ontario, there were a couple questions that I answered quickly during the seminar. I take the opportunity to elaborate on my answers here.

1. When looking at soil test results, how to consider the availability of nutrients?

A soil test already is measuring the availability of nutrients. The interpretation of the test result is the way the availability is assessed. For example, the MLSN guidelines have a value of 21 ppm for phosphorus (P). If the soil test result using the Mehlich 3 extractant is more than 21 ppm, then we can be confident that enough P is available to the grass. If the soil test result is less than 21 ppm, then there may not be enough available P, and P fertilizer will be recommended to increase P availability.

Soil tests by definition measure the availability. For more information on the availability topic, see concerning the availability of nutrients in soil.

Liquid2. If fertilizer applications are being made to the leaves, as a liquid, how can one use the MLSN guidelines which are for the soil?

I don't think it matters what type of fertilizer one is applying, liquid or granular, in terms of using the MLSN guidelines. Turf grows in the soil, and turf that is growing in soil that has nutrient levels above the MLSN guidelines is almost certainly going to have access to enough of those nutrients. So when making fertilizer applications, I would choose the fertilizer product and application method based on what I want to apply, and how I want to apply it. And for the rate of application, I would make sure I was applying enough to keep the soil above the MLSN guideline. No matter the type of fertilizer used, I don't want to grow grass in soil with nutrient levels lower than the MLSN guideline.

Visits to this site: desktop, mobile phone, and tablet

You may have noticed a few changes in the layout of this site. I made the changes this week to improve the content display across all devices. When I started this blog in 2009, more than 99% of the visits were made from a computer with a browser, coded as "Desktop" in this chart.

Viridescent blog audience devices

That has changed a lot over the past six years, and in the 12 months ending today, less than 50% of the visits are made from a computer. And Google searches from mobile devices are now using mobile-friendliness as a ranking signal.

It was well past time for this site to be updated. I hope you like it.

Is the annual N rate a useful measure?

The annual N rate is useful for comparison of the same site from year to year, and I use it for that purpose, but when it comes to making decisions about N addition, I'll use a monthly, weekly, or daily assessment. The annual N is the sum of those additions, and it is whatever it comes out to be.

Selection_088I like the temperature-based growth potential (GP) of PACE Turf as a way to estimate the N use of a particular species at a particular site on a daily, weekly, or monthly scale.

My interest in this topic is related to seeing the same grass grown in quite different conditions. I've recently seen Miniverde bermudagrass in Thailand, Tennessee, and New Delhi. Comparing annual N rates for Miniverde in those locations is nothing more than a curiosity. To get a reasonable estimate of what might work, one needs to consider the "growing season" at each location, and the GP does just that.

I looked up the climatological normal temperatures for Bangkok, New Delhi, and Knoxville, and then calculated the monthly GP and plotted for each location.


Those three locations are quite different, but one can grow the same grass in each of them. How does the annual N estimate work out for these three cities? Using a monthly maximum N of 4 g m-2 (see this guide for more details on how this is done), I get an annual N use estimate of 10 g N m-2 in Knoxville, 31 in Delhi, and 43 in Bangkok. That's about 2 lbs N/1000 ft2 in Knoxville, 6.2 in Delhi, and 8.6 in Bangkok.

Similar differences occur with cool-season grasses too. Imagine the annual N use of creeping bentgrass in London, Minneapolis, and Sydney.

C3citiesGPUsing a monthly maximum N of 3 g m-2 for creeping bentgrass, these annual totals come to 10 g m-2 in London, 13 in Minneapolis, and 29 in Sydney. That's 2, 2.6, and 5.8 lbs N 1000 ft-2, respectively.

Annual N rate, comparing the same location year to year? I like it. Annual N rate, comparing different locations, or different species, or both, as a curiosity, or to point out how different they are? I like it. But for making a plan of how much N to use at a particular site? I like to break it down to a monthly scale, or weekly, and don't worry about annual N except as the sum of those fine scale applications.

What happened on January 16, or how to increase interest on what you tweet by more than 75%

@TurfDiseases is one of my favorite Twitter accounts. Tonight I downloaded the last 1000 tweets from that account (using this script), then filtered them to remove the retweets, and looked at the interaction that has happened on each tweet by adding the number of favorites and retweets that happened on each of the @TurfDiseases tweets.

I was glad to see that since noon on January 16, the favorites per tweet are up by 120%, the retweets per tweet are up by 50%, and the overall interaction with each tweet (favorites + retweets) are up by 75.8%. This density plot shows how the interactions per tweet are distributed, before and after January 16.

TurfdiseasesSo what changed with the @TurfDiseases account on January 16?



Do you know how much salt is in your irrigation water?

Selection_084My column in the March-April issue of GCM China is about salt. The salt in water is invisible, so one needs to test the water to find out how much salt is in it.

As I wrote in the article, water with total dissolved solids (TDS) of 800 ppm would add 56 g salt/m2 (11.2 pounds salt/1000 ft2) in a 2 week period if irrigation is applied at 5 mm/day. Being aware of how much salt is in the irrigation water is the first step in determining if leaching will be required.