How Much Nitrogen Should I Apply?
DR. AJ FOSTER
BLOOMFIELD, MO.
Nitrogen is the nutrient farmers tend to apply in the largest amount, it is also the most costly, most susceptible to misuse and losses. It is important for a producer to have a good knowledge of how much nitrogen to apply. Not apply the appropriate amount can be costly, as applying too little can result in low yields while applying too much can cause lodging, delay harvest, increase pest and disease pressure and off-site pollution.
But the question still remains how do you know how much? I believe that there is a correct N rate for each field, just like I believe there is a correct seeding rate for each field. I also believe that these rates also vary from year to year based on environmental condition. With seeding rates, once the seeds are in the ground we can't go back and increase or decrease the rate if conditions for the growing season change and favor a lower or higher rate. So, for seeding rate, I will settle for the rate that gives the best result most consistently from year to year. But, regarding N rate we can make adjustment throughout the growing season. So we do have some flexibility here. I would say producers now and in the future will need to adopt methods that increase nitrogen use efficiency and profitability at the field and farm level. Every farmer is aware that grain yields vary from year to year, but most are unaware that the amount of N that environment delivers to the crop for free varies also. The N rich strip (NRS) concept can tell you how much N the environment delivers. In my opinion, this is the best way to figure out your N rate for each field. How is it done? You create a strip with sufficient N applied pre-plant or soon thereafter in each and every field, and use the difference between the NRS and your conventional practice to determine how much N the environment delivers and whether or not you should apply additional fertilizer N. For example, in wheat, if you cannot see the difference between the NRS and your conventional practice (visual interpretation from January to March), you are unlikely to obtain any benefit from mid-season fertilizer N. In other words, what the N rich strip does, is it serves as a guide to how much top dress N should be applied to maximize yields, taking into account how much the environment delivers for free. For more information on the Nitrogen rich strip visit Oklahoma State University NUE website: http://www.nue.okstate.edu/Index_Publications/Nstrip%20brochure.pdf.
If you are interested in utilizing N rich strip in your fields next year feel free to contact AJ foster by phone at 573-568-3344 or email fosteraj@missouri.edu. ∆
DR. AJ FOSTER: Agronomy Specialist, University of Missouri