# PACE Climate Appraisal form



## corneliani (Apr 2, 2019)

I'm pulling out this spreadsheet again, trying to better understand the concept behind it (in conjunction with MLSN levels). I'm running the numbers on my fescue lawn in Atlanta and my confusion lies with the Growth Potential and subsequent Nitrogen requirement, especially in the hot summer months. What exactly does this number denote? We all know to stop applying nitrogen in the summer, yet this seems to imply that the turf requires 1.5 to 2#N throughout the June-Aug/Sept timeframe.

How is this form helpful? I was introduced to it initially by thegrassfactor a couple years back but just never understood it.

NOTE: I have not inserted my soil test ppm values so the MLSN values are arbitrary. The avg temps & rainfall were input from weatherbase.com



https://www.paceturf.org/journal/climate


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## bernstem (Jan 16, 2018)

The Pace GPP model predicts grass growth based on average temperatures. Growth rate is then used to calculate fertilizer needs. This model is calculating that your grass will grow the same amount in May, June, and August so will need the same Nitrogen amounts. The growth model works well in my experience, but the temp data is critical. If the temperatures are higher or lower than predicted growth and Nitrogen needs will change. That means you will need to adjust based on actual temperatures.

This model does change the way we think about Nitrogen and meshes well with other research looking at disease in Fescue. The disease data suggests you want to aim for ~1 inch of growth per week to minimize disease pressure. They are both a change in thinking compared to "conventional wisdom", but they also require the turf manager to monitor more variables and adjust inputs based on weather and environmental conditions.

To implement the models, you will need flexibility in Nitrogen application. If weather is forecasted to have low growth, you would decrease Nitrogen inputs. If you find that actual growth is too high, then you would adjust inputs down. This works best with a fast release Nitrogen source (e.g. Urea), applied every 2 weeks so you can rapidly adjust Nitrogen levels.

MLSN is based off soil testing and is different from the PACE model data. The numbers for P, K, etc. on the spreadsheet are calculating nutrient use by grass. You should target MLSN numbers on the soil test to get soil nutrient levels adequate. Once you have reached adequacy with supplemental fertilizer based on the soil test, the PACE numbers from the spreadsheet will estimate what you need to add to maintain soil nutrient levels.

Keep in mind, for cool season turf, growth potential is highest at ~68F. Above and below that the growth potential falls off. 
From PACE turf. Blue is cool season turf. Red is warm season turf:


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## corneliani (Apr 2, 2019)

I appreciate the input @bernstem. When you say that my turf will grow the same amount in May, June, and (I assume you meant)September - you were looking at the "% growth potential" column I assume (those value being 99, 82, and 94%)? If so that makes sense, those are the big growth months... but what's perplexing is July & Aug needing almost 1/2#N each! I can't wrap my mind around that much nitrogen during these months, and then Oct & Nov - the big feeding/recovery months, get less than that! Some of this data just doesn't translate into real world experience. I feel like i'm missing something about this model.


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## bernstem (Jan 16, 2018)

Yes, I meant May, June, and September. That was a typo.

I'm going to tag @g-man as he has more experience with this model than I do. I think you need to view this as a tool that will help predict top growth and not a bible to predict fertilizer. It is very valuable for predicting potential for recovery from damage or stress. It is useful for timing of aeration, dethatching, and other management practices that require recovery. It can be very useful if you are overseeding PRG into Bermuda.

While it can be a guide to what nutrients the grass may need any particular month, it was not, as near as I can tell, developed primarily as a guide for Nitrogen applications. Other factors are going to contribute to nitrogen inputs. Soil temperature can impact growth and when the grass will come out of and into dormancy. Overall goals and concerns about disease can also affect fertilizer inputs.

Bottom line, use this as just one tool to help determine inputs, but grass is complicated and good management is holistic. There is no single metric that you can use to plan your lawn care. I still apply most of my Nitrogen in the winter.


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## bernstem (Jan 16, 2018)

FYI, video on growth potential model: https://www.youtube.com/watch?v=oZgXv3ZaHkQ

The first 20 minutes or so were on cool vs warm season. At ~27 minutes it starts to discuss fertilizer requirement.


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## g-man (Jun 15, 2017)

The gp form is using your historical average. I run the chart using actuals and forecast. It just gives you an expectation of what the turf should do. With the aim of 1in/week of grow, in July you should expect only 0.6in/week.

Nitrogen values are just a guide and don't assume it is applied nitrogen (from fertilizer). During the summer, OM breakdown will provide nitrogen. Sometimes too much nitrogen. Also slow release sources can still be feeding.

In general the current best practice is to monitor your clip rate. Is it growing more than 1in/week, then reduce nitrogen. Not growing enough and it is not July/August, then feed it more.


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## bernstem (Jan 16, 2018)

Another option would be to monitor soluble nitrogen in the soil: https://thelawnforum.com/viewtopic.php?f=24&t=33475
Too much Nitrogen can be as bad as not enough.


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