This post was originally made by Dr. Lenny Wells in 2024. We are re-posting with a few updates since many growers are utilizing this method. Calibrating your nitrogen per acre is the purpose of this post.
We are in the middle of fertilization season again and many are choosing to inject their N through the irrigation system. This is a great way to fertilize pecan trees with N. It’s cheaper and allows you to spoon feed them a little at the time through the season. The trees respond well to this method of fertilization and you don’t lose as much N when applied this way. In reference to my point about being cheaper—its cheaper and more efficient only if you are applying your N based on the treated area. When you inject through a microsprinkler system you are covering only a small fraction of the orchard.
As an example, if you have a 100-acre orchard spaced 40 X 40 (27 trees per acre) that’s 2,700 trees total. If you have a 360-degree microsprinkler tip that sprays a circle 19′ in diameter, you figure the area of that circle and multiply by the 2,700 trees in the orchard:
A=3.14(r2)—–(I can’t find the symbol for pi on the keyboard through the program in which I’m writing this)
r = 19/2 = 9.5
9.52 = 90.25
A = 3.14 (90.25) = 283 square feet
283 X 2700 = 765,139.5 square feet total
765,138.5/43,560 = 17.5 acres
So, in our example, if you are injecting 25 units of N/acre at the time on 17.5 acres, that’s 437.5 units of N X $0.79/unit = $345.63 total per injection.
Let’s say you do a total per year of 125 units/acre, so at 5 injections over the course of the year, that’s a total of $1728.15 spent on N fertilizer.
A lot of people figure the entire orchard area when they are injecting and thus over-estimate and over-apply what they actually need. Your fertilizer dealer will like this, but it’s not helping your pocketbook or your production. If you compare our example above with injecting based on total orchard area, you are looking at 25 units N/acre X 100 acres per injection, 2500 units total X $0.79 per unit = $1975 per injection X 5 injections = $9875 spent on N fertilizer. That’s a big difference and the results on the tree will be the same as if you figured on 17.5 acres.
The exact numbers for drip may vary and depend on the spreading pattern in various soils as well as the number and volumes of emitters per tree but the formula above for microsprinkler could serve as a rough estimate.
If you are applying dry urea at $0.55/unit to the entire 100 acres, that’s $0.55X 125 units = $68.75 X 100 = $6875 spent on N fertilizer. If you only apply that to your herbicide strip, which covers about 30% of the orchard floor, that’s $2062.50 spent on N fertilizer. Again, a big difference with the same results on tree N and yield.
