Proper timing of nitrogen is critical to achieving your yield goal in corn. Generally speaking, the V4-V6 stage are the critical growth stages to having enough nitrogen on corn to ensure that it isn’t a limiting factor in the early ear development phase. The amount of nitrogen topdressed during this time depends on your management plans and what the environment has been since you planted. If you have less than 50 to 75 lbs N per acre available going into the transition phase (between vegetative and reproductive), I suggest starting your topdressing by V4 and no later than V5. Having a greater amount of N available earlier allows you a little more time to apply your topdressing but not much. It is important to be finished by V6-V7 if you cannot inject nitrogen through your pivot and have to finish all of your N applications by ground equipment.
If you have irrigation, injecting N through the pivot is the most efficient and effective method of applying nitrogen in corn. Dribbling nitrogen (both liquid or dry) by the row is the next preferred method as it keeps the majority of N closet to the root system early in the growth phase and ear development phase. Broadcasting N is an efficient application but may not be the most effective as some N will be captured in the whorls of leaves causing some burning of tissue. It will require rainfall or irrigation to get that which does fall into to whorls dissolved in solution and ultimately in soil solution by washing off the plant and onto the soil. In addition, nitrogen in the middle of the row is far enough away that it takes time for roots to reach the area where the nitrogen is available and can negatively impact the yield potential if you don’t have enough nitrogen closer to the row.
The general nitrogen recommendation ranges from 1.0 to 1.2 lbs of nitrogen for every bushel in your yield goal depending on your soil type. For example, if you believe your farm and management style has the capacity to produce 250 bushels per acre then it would take 300+ lbs of N per acre. Yes, corn is and can be more efficient and produce a bushel for every 1.0 pound of nitrogen per acre however in sandier, coarse soils with low CEC, it is better to error on the high side. If you have the capability to apply N though your pivot, divide your total N supply into increments and apply every 10 to 14 days, finishing up at tassel.
In a year with less than stellar pricing, the challenge is to be most effective with every input and make every dollar count. Getting behind in corn does cost yield and reduces your returns on your investment. Think through your choices carefully. Take extra time to know exactly what stage of growth the crop is in as you plan your inputs so as not to get behind.