Side-dressing nitrogen application window
“What is the application window for side-dressing nitrogen (N)?” I hear this question a lot from corn growers thinking about using crop sensors for variable rate N application. Imagine how much better we could answer that question if we knew the weather! Unfortunately we don't have that luxury.
For those who may not be familiar, the application window for corn is quite simply growth stage V5-V12. V5 growth stage is close to filling a 30″ row or about 1.5-2.0' tall. V12 is approximately 5.5-6.0' tall.
Since I first started working with crop sensors in 2007, I've had many conversations with growers about the application window. When the grower says, “I can't get over all my acres in that time frame”, that's a clue to me their applicator is a tractor pulling a N toolbar. My response is that toolbars typically can get through corn taller than V5, but some are still concerned about covering their acres before the corn gets too tall.
So how can the application window be extended? Answer: High clearance applicator. That's not to say there isn't more than one way to skin a cat, but turning a high clearance sprayer into a N side-dress machine is an option, a very good option in fact. Installing drop hoses on the boom between each corn row turns a sprayer into a N side-dress machine. Another option is high clearance sprayers made to accept a high clearance toolbar with arms that go between the rows to inject liquid N into the soil.
But what if you don't have your own high clearance applicator? Your local custom applicator probably has a machine that will do the job. In fact crop sensors (Ag Leader's is called OptRx) are a good way for a custom applicator to set themselves apart from their competitors. I can't speak for other products, but field testing results showed OptRx routinely outdoes growers' flat N rate by $15-30/acre. That's a pretty nice new service for a custom applicator.
In conclusion, crop sensors have many applicator options; some have longer application windows than others. Always consider the goal at hand – how can you get the most return on your investment?