Don’t lose your shirt to nitrogen deficiency
Watching many fields from ground level is difficult and not very accurate. Getting up in an airplane with a camera is much better. Many local airfields have a pilot who can be hired.
I can predict how much yield will be lost from a straight-down aerial photo of corn that is at least hip-high. If you’re interested in trying this, call me. We can process a limited number of fields this year. Obviously the problem with this is that a limited number of machines are available that can apply N to corn this tall. The corn itself won’t mind at all.
Watching the corn is the most reliable indicator of whether additional N is needed, but requires waiting. Plans to get N applied may require quicker action on at least some fields to accomodate equipment limitations. Watching weather may need to be the basis for at least some decisions. The map above comes from my Nitrogen Watch page, which is based on cumulative precipitation maps and is updated weekly. You can find these maps at: http://plantsci.missouri.edu/nutrientmanagement/nitrogen/Nitrogen%20watch%202013/nitrogen%20watch%202013.htm
This is the most important part. If you need to act and don’t, you will lose a lot of yield and a lot of money.
I think that most producers in the cross-hatched area of the map who applied all their N before planting will profit from applying additional N even if it is not targeted. This is especially true for fields fertilized in the fall.
Fields that received anhydrous ammonia this spring, or that received the bulk of their N after planting, are least likely to need additional N.
Watching fields and targeting additional N to those fields that need it most, or putting higher rates on the fields that need it most, will increase the odds of profitability.
Targeting N within fields would be even better. My research shows the best return on rescue N applications in the areas with the greatest N stress. And my observations show that there is usually a wide range of N stress in fields that have lost N. You can see this in the N loss aerial photo galleries on my website: http://plantsci.missouri.edu/nutrientmanagement/nitrogen/loss.htm
Crop canopy sensors are the most widely available way to target N applications within fields, applying higher rates to more stressed corn and lower rates to less stressed corn. However, not all sensor interpretations follow this logic so look for those that do.