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Potential risk of leaf injury from topdressing N this week (too hot and windy!)

Amanda de Oliveira Silva, Small Grains Extension Specialist and Brian Arnall, Precision Nutrient Management Specialist

The forecast indicates hot (~75 F) and windy (~20-30 mph) conditions this week in Oklahoma (Mesonet). If you plan to topdress N to wheat, be aware that there is a high risk of causing leaf burn due to the predicted weather.

When comparing application methods, a stream bar is better than a flat fan for topdressing N in general. A flat fan would burn and even kill the wheat if used this week. However, using a stream bar under 20-30 mph wind is also problematic, as the wind will spread out the stream over the wheat, making it splash over larger areas result in more foliar burn.

Streamer nozzles provide uniform application of UAN in a wide variety of environmental conditions.

What rate can I apply without causing leaf burn from N this week?

There is a high risk of causing leaf burn by applying any rate (20 to 200lbs/ac) of N in the next 2-3 days (March 8-11, 2021). If using streamer nozzles the total amount of leaf damage could be small resulting in no yield loss. In this case, applying N this week may result in streaked fields later, but the wheat should grow out of it if conditions are appropriate. However, as you start to increase coverage (i.e. the amount of leaf burn) there is a threshold at which yield is lost. In cases with flat fan the high N rate will potentially kill the majority above ground biomass and negatively impact yield.

Other options to reduce the potential risk of injury. Wait to topdress N when the weather cools down (if you believe you will be able to get into the field before jointing) or split the N rate between now and sometime before jointing. If you want to apply and are very worried about tissue damage, one option is to dilute the UAN with water. Usually a 50/50 (UAN/H2O) ratio does a good job of reduction impact of the salt in UAN. 

If you have questions, please feel free to reach out to us!

Brain Arnall at b.arnall@okstate.edu

Amanda de Oliveira Silva at silvaa@okstate.edu

Time to topdress, but be realistic

Normally, I would be sounding the wheat topdress alarm in early January. When you have 5.5 million acres to cover, it is important to start early. However, this year we have mostly kept the topdress rigs in neutral with a wait and see approach due to the drought. The recent rain brought life to portions of the Oklahoma wheat belt and it is time to make a decision regarding topdress nitrogen. I have posted three slide presentations with audio regarding topdressing wheat at my YouTube channel available by clicking here or by searching YouTube for OSU Small Grains. I have listed some additional facts and items to consider below.

  • In order to have full benefit, nitrogen must be in the rooting zone by the time wheat is jointing. Jointing occurs around the first of March in southern OK and around the second week of March in northern OK.

  • On average it takes about 2 lbs/ac of N for every bushel of wheat yield. In addition, dual-purpose wheat requires 30 lbs/ac of N for every 100 lbs/ac of beef removed. You can subtract your soil test NO3-N from these total requirements.

  • It is okay to adjust topdress N plans based on your current yield potential. When you submitted your soil test, you might have stated a 50 bu/ac yield goal which would require 100 lbs/ac of nitrogen; however, it is important to take a hard look and determine if this yield goal is still realistic based on your current crop status. I am not suggesting to adjust based on what you think the weather might do, but it is okay to take inventory and adjust your topdress N up or down based on current field conditions.

  • Don’t have an N-rich strip? It would be a lot cooler if you did. An N-rich strip would take the guess work out of adjusting your topdress N up or down based on your current crop conditions. Your county extension educator can provide more information on N-rich strips and you can find more information on the web at www.npk.okstate.edu