1. Determine your average yield for the last 5 years that corn
was grown on a particular field:
Yield last 5 years (bu/acre)
Sum
across
years
Divide
number
of years
Average
Year
1
Year
2
Year
3
Year
4
Year
5
2. Multiply average yield by 1.05 to get “Target Yield” (The increase of .05 accounts for increased yield potential due to improved hybrids and cultural practices.)
Average Yield x 1.05 = Target Yield
3. Multiply “Target Yield” by 1.20 lb N/bu to get N needed per acre
Target Yield x 1.20 = N needed (enter in #5 below)
4. Reduce N needed by subtracting all N credits (adjust for all of the following which apply)
a) Previous crop of soybean (40 lb N/acre) ______
b) Previous crop of alfalfa/clover (>5 plants/ft.2) ______
c) Application of ammoniated phosphate (multiply lb material times percent N).
Ex: 200 lb 18-46-0=200 x 0.18=36 lb N/acre ______
d) Manure application [total lb N in manure divided by 2] ______
e) Herbicide carrier N solution (multiply gallons per acre times 3 for 28% N or times 3.5 for 32% N solutions) ______
f) Starter (multiply rate (lb per acre) times percent N) ______
g) N in irrigation water (inches irrigation water x ppm NO3-N x 0.23) ______
Total N credits (total a through g) ______
5. N to apply = (N needed) – (Total N Credits) = (N to be applied)
