Friday, 24 November 2017

The evolution of precision fertilizer application.


I recently returned from an amazing trip to Ireland and Iceland. There's nothing that teaches me more about greenkeeping than going to see other greenkeepers and learn how they grow grass. This trip was no exception and in my discussions with other seriously deep thinking greenkeepers it got me thinking about how the way I fertilize my grass has changed over the years and helped me understand that basically what I have been doing is trying to reduce the amount of guesswork and luck and resources required to grow good grass.

For the most part my experience with fertilizing grass has gone like this;
  1. Guess at how much fertilizer to apply based on generalized guidelines,
  2. Adjust rates based on observations
  3. Guess again....
For the most part we are guessing because fertilizing grass is extremely difficult compared to other crops. Unlike agriculture, we do not want maximum yield. We want optimum yield which means growing the grass just enough to keep up with wear and tear and not too much to reduce mowing requirements. This is something that first became clear to me when I read Micah Wood's incredible book A Short Grammar of Greenkeeping

The following picture shows general recommendations for different turf areas from my college fertilizer class. 


1st Method: Generalized monthly/annual rates

The rates roughly follow the classic growth characteristic of cool season turf. You know the one. Growth spikes in the Spring and Fall with dips in growth in the Summer and Winter. I would set annual rates based off of research that would show various annual nitrogen rates and how they impacted diseases such as fusarium.

I didn't know it at the time, but this method of generalized fertilization caused all sorts of issues. Excess disease, thatch production, fuel consumption, mowing requirements, clipping management, labor needs the list goes on and on. But without really looking inward at what I was doing and why I was doing it this method of fertilizing grass seemed like a good way to go. After all, everyone core aerates right?

It's kind of funny looking back but one of the most important qualities of mower selection for me used to be clipping dispersal. We used to have huge issues with excessive clippings when we fertilized this way.

Fertilizing this way wasn't all bad. For the most part I was still able to maintain good quality playing surfaces. The grass was green and there were few bare spots.

I think this is also the way most turf managers still fertilize their grass. It isn't bad and I would bet that some of the best managers out there can fertilize with way with extreme precision for their respective courses. I'm not that good though so I need more help.

As I get older and learn more about what I'm actually trying to do as a turfgrass manager I have found that most of our issues at turf managers come from generalizations. We grow grass outdoors and our plants are influenced significantly by the environment that they grow in so any broad recommendation has no place in our industry in my opinion. The trouble is is that making recommendations for each individual climate would be cost prohibitive so we are stuck with generalizations to help us make our decisions.

2nd Method: Growth Potential and MLSN

This method of determining fertilizer rates was a game changer to me. It showed nitrogen rates that were specific to my climate and this made sense to me. We didn't get super hot weather that limited the growth of our poa (at the time) greens in the summer and for the most part the grass grew very little if at all in the winter.

The MLSN also helped me only apply what was needed and helped me use up the nutrients that were already in my soils. I often wondered about the impacts of excessive nutrients and MLSN offered me a way to try and minimize any excessive nutrients in my soils.
Growth Potential was a game changer for me

This growth predicting formula helped me more accurately time my nitrogen applications and made a big impact on my operation.

Aside from allowing me to cut my nitrogen rates in half without compromising turf quality, I have seen reductions in turf diseases, thatch, required mowing, fuel use and labor. It might seem obvious but the rate at which your grass grows has a huge impacts on how expensive it is to maintain. I also started to noticed more bentgrass on my greens and I wonder if  improved nitrogen timing removed the advantage from the poa. I was reminded of the differing nitrogen requirements between poa and bentgrass during a presentation in Ireland by Agnar Kvalbein from STERF about precision fertilisation. Poa likes more nitrogen than bentgrass so applying more nitrogen will result in more growth of the poa than bentgrass thus giving poa the advantage. Applying significant amounts of nitrogen in the Spring and Fall like I used to with the 1st method described in this post definitely gave the advantage to poa.
Accumulative nitrogen rates on greens over the years.
Data compiled and animated by Micah Woods

The trouble with this though, is that it is still essentially a generalization and doesn't take into account the actual growth conditions that are occurring because again, there are so many variables that go into grass growth.

3rd Method: Growth Potential Adjusted Observations

I then started adjusting rates based on observations. If I noticed that the weather coming up was conducive to producing a growth surge I would hold off on the recommended nitrogen rates. This offered some improvement but for the most part it was still relying too much on my judgement and honestly there's no way I can guess how much nitrogen is needed without making measurements of some kind.

I was measuring clipping yield at the time but it wasn't in a meaningful enough way. Sure I could adjust my fertilizer rates to try and keep growth controlled but it just wasn't accurate enough for my needs.

How accurate are my needs? I want to maximize the conditions of my course and maximize the profit. To do this I need to identify areas where we are guessing or where we can improve the precision of our actions. With a booming economy we can afford to guess. When things get tight, we need to stop guessing. When the economy for golf improves, those how guess less, will make more money. I don't need to tell you that if you don't make money, you won't be growing grass for very long....

So many of our cultural practices are required to manage the result of the guesswork that for the most part, we are forced to live with but I wonder if we can reduce the guesswork to the lowest level possible, if we can reduce the need for remedial cultural practices?
Can we reliably eliminate the need for pulling a core?
As of today I am still required to do remedial practices such as aerification and topdressing to dilute and remove excessive organic matter. Why is there excessive organic matter? If we guess at fertilizing we get excessive organic matter if we want to produce grass that grows fast enough to tolerate the wear and tear of golfer traffic and maintenance. If we don't apply enough fertilizer, we get very little if any organic matter production in the soil but the turf quality also suffers. So in theory, we should be able to find the spot where we are neither producing excessive organic matter or not producing enough organic matter. So how can we reduce the need for guessing on how much nitrogen to apply?

4th Method: Matching Nitrogen Applied to Nitrogen Removed

It took me embarrassingly long to finally be persuaded to measure clipping yield on individual putting greens using a unit of measurement that had meaning. All of a sudden I had a way to calculate how much nitrogen I was removing from my greens thanks to the teachings of Micah Woods. When I compared this to how much nitrogen I applied I could see if there was any difference.

To me this is so new that I have no clue how it will all work out or be worthwhile but I have heard anecdotal evidence that getting away with no core aerification is possible I just hadn't figured out how to do it for myself yet. I do think that what I am about to describe might be the closest yet that I have got to reducing the guesswork of fertilizing my grass.

So how does this all work?

If you multiply the total Liters of clippings/100m^2 by 0.63 for bentgrass you get the approximate dry mass of the clippings in g/m^2. From this we can calculate the approximate amount of nitrogen removed from the system because 4% of the mass of dried turf clippings is nitrogen.

So I compared how much nitrogen I had removed through clipping harvest to how much nitrogen I applied to each green.



If you look at the numbers in blue you will notice that for the most part they are pretty consistent. This is the amount of nitrogen removed per square meter from my greens since Jun 16 when I started measuring clipping volume from each specific green.

If you then look at the row directly beneath that you will notice that the amount of fertilizer applied varies greatly. This row is the amount of fertilizer applied. As soon as I was aware of the differences in growth rates on my greens I wanted to take action and I did by applying different fertilizer rates to each specific green. How I did that is a topic for a blog post on it's own but it really isn't that difficult. Essentially I am comparing the theoretical growth potential N requirements to actual harvest and splitting the difference as long as it results in desirable growth rates for my disease and playability management needs. Simple eh? haha.

A look at my highly experimental way of determining how my N to apply. It takes actual yield, optimal yield, and differences between each green into account to give fertilizer rate recommendations for each individual green. So far it seems to be working.
The reason I had such variable growth rates this summer was that I was pushing growth of my 5 winter damaged greens until the beginning of June when recovery was complete.
Once recovery was complete I had greens that were growing much faster than the greens that weren't damaged but it was hard to tell without measuring.
The bottom row of the table shows the difference between nitrogen applied vs nitrogen removed on each green. A negative number means that I am using nitrogen already contained in the soil and a positive number means that I am adding additional nitrogen to the soil that isn't being harvested through clippings.

You might also notice that greens 2,3,4,5, and 7 all received very little nitrogen during this time but also had some of the highest growth rates. This is because of the excess nitrogen applied during the spring. It might also be because of the excess mineralization of nitrogen from organic matter from all the poa that died the previous winter. Either way, I was aware of the excess growth and was able to adapt my practices to achieve consistent playing conditions and maybe use up some of that excess soil N no matter where it came from.

What I find especially interesting is that on greens that weren't damage, the amount of nitrogen harvested is almost exactly the same as the amount of nitrogen applied.

With the exception of my 8th and upper practice green the undamaged greens all had a difference less than +/- 0.15g/m^2.

As for the 8th and upper practice greens I think there is something else going on as I couldn't get them to grow as fast as I would like. They are both the newest greens on the course and could suffer from too low organic matter. They are also both almost purely bentgrass where my other greens all have some poa still left on them.

My lower practice green had high growth despite low N inputs. Maybe high soil OM from unrelated reasons as it wasn't damaged last winter. It is my shadiest green and they do say that shady grass needs less nitrogen so who knows?

Being aware of huge jumps in growth caused my n release from soil (spikes in blue line) OM might help us reduce excessive fertilizer applications.
Back to precision fertilizer.

The very similar numbers that I got from nitrogen applied vs nitrogen harvested on my undamaged greens tells me that it's possible to find a balance that might be able to allow me to eliminate the need for organic matter management. Of course I will need to confirm this with OM tests next spring.

The similar growth rates on greens that had excess spring fertilizer and OM also tells me that I can get consistent growth despite no added fertilizer if we are aware of the growth differences and add fertilizer accordingly.

In the past few years I have consistently applied much more fertilizer than I harvested but I also wasn't measuring and applying fertilizer based off of growth with this precisions.

In 2016 I harvested 5.6g N/m^2 but applied 12.3g N/m^2. So either I was seeing a lot of nitrogen losses, had bad measurement (I was only measuring clippings from 2 greens instead of all of them) or was building excess organic matter in the soil because I wasn't taking organic matter mineralization of nitrogen into account like I was this year.

I am excited about trying out some new things next year to see how to best implement the strategy of precision fertilizer application and will share what I learn over the next year or two. Now let's hope with winter is kind to my grass and I can focus on optimizing things instead of recovering things!