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Nitrogen Rates and Timing Comparison

With all my talk about nitrogen lately I thought it would be cool to compare how different methods of nitrogen fertilization would look. As nitrogen is one of the few things that if we add more the plant will use more the differences in application rates can have a varied affect on plant health and response. The following chart illustrates the same amount of nitrogen applied per season but at different rates at different times of the growing season.


Now we know that the blue line is what the plant actually needs so if the lines from the other application methods are above the blue line you are essentially over applying nitrogen and if the lines are below the blue line you are under applying. Over applying and under applying both have their purpose in turfgrass management but they also carry consequences.

I read somewhere that a visual turf response can be seen at nitrogen rates as high as 6Kg N/100m2 per season! Currently my rates are about 1.4Kg N/100m2 per season. So essentially I can see a difference if I applied 4.3X as much nitrogen as the GP model suggests for my climate. I can then use this data to compare the difference between the different fertilization strategies to see exactly how my turf is able to use the nitrogen I am applying. The following chart compares the different nitrogen use rates between the GP method and the constant rate method and also shows the difference in multiples of the required amount of N.

rates are in Kg N/100m2
So essentially I could expect to see a difference in growth response if I applied up to 4.3x as much N as was actually required by the plant. Looking at the column to the far right it shows that the constant method would be applying as much as 9.6X as much fertilizer as was required by the turf in March. It isn't until June that this method stops over applying nitrogen and in July and August I am applying half as much nitrogen as is required by the turf. No wonder I was getting hammered with disease!

What are the consequences of these practices? Applying more nitrogen than is required is wasteful and can't be good for the environment either. Under applying in the summer can only make your challenges more difficult.

This brings up another problem that I see with nitrogen fertility in the industry right now. With all of the different slow release nitrogen formulations how can you be assured that you are getting the release that is required. Each different product releases differently under different temperatures, soil moisture and particle sizes. Changes in the weather can really make a big difference in what you apply and what is made available to the plant, especially in the long term. For this reason I use soluble nitrogen sources exclusively on my putting surfaces. On my fairways I have a little more room for error as I do not use pesticides on them anyway. By using Urea and Ammonium Sulphate I am able to have a better idea of what is actually available to my plant and eliminate a lot of guesswork when it comes to how much nitrogen my plant has. When it comes to the importance of nitrogen fertility on plant health I cannot afford to guess!

Having the power and the knowledge to use nitrogen to our advantage is a great tool! We have the ability to apply a bit extra when needed to increase growth a bit or to recover from damage. We also have the power to reduce rates to slow the growth down which requires less mowing, less diesel and makes for faster firmer playing surfaces. What we need to know is how far off from what is required our nitrogen applications are and what the potential consequences may be. Is filling in those holes a few days quicker really worth the cost associated with an extra fungicide application? Financially and environmentally? Is that half pound N application really going to be usable by your turfgrass with the current temperatures?

I encourage everyone to compare their methods of nitrogen fertility to the growth potential model to see how far off of the plant's actual needs you are. Applying half as much nitrogen as is required surely has to have it's consequences. It's nice to be able to adjust the rates but it is important to keep the adjustments reasonable to avoid any negative consequences  It is the responsible thing to do for your bottom line and the environment.






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