Virginia Cotton: Considerations for Fertilizer Side-Dressing

Fertilizer application in cotton. ©Debra L Ferguson Stock Photography

The cotton during the first week of planting is all at about the 7 leaf stage and the 8th leaf is clearly visible in the bud.  This has brought us to the window to apply the layby nitrogen, and none too soon.

  • We have had various amounts of rain over the last two weeks with some areas approaching 5 inches while some spots have only had around 2. The average has definitely been over 3.
  • Our lightest land that has not had any fertilizer since before planting is showing nitrogen deficiency symptoms with red cotyledons at the bottom. Some saturated land also shows these symptoms because the root system is hurt and cannot access the nutrients close by.
  • For both of these situations, a little bit of Ammonium sulfate broadcast will be the best and fastest cure. It only takes 100 to 150 pounds.
  • If you are planning on dribbling nitrogen in the middles, this light land or cotton with damaged roots will not pick up that dribble quick enough and I still recommend some dry material broadcast.
  • If you make this as an additional trip that you were not planning to do, be sure to account for this nitrogen as we do not need to apply extra nitrogen on this later than average crop.
  • We have not really had leaching, and I believe the nitrogen we have applied up til now is still there just too deep for small plants to pick it up, but it will find it later.
  •  Applying a half pound of boron at sidedress will eliminate the need for foliar applications, or you could apply a quarter pound to the soil and the remainder in one foliar trip.
  • Basically the recommendation is for a half pound “in season” which can be made to the soil or foliar although the foliar trip can only have a quarter pound at one time.
  • Sulfur is readily available if you have organic matter in soil or clay within 12 inches of the surface.  Our main concerns are on deep light soils.
  • Similar to nitrogen, sulfur can leach, however, only about 20 pounds is needed at sidedress time.  If you have 35 pounds of sulfur on light soil or 20 already on loamier soil, you are probably in good shape; otherwise use some sulfur in your side dress to meet these goals.
  • Potassium should not have leached. If you had planned on adding potassium with your sidedress application to meet the soil sample recommendation, just continue as planned.
  • I like splitting potassium on the white sand that typically has the light land syndrome and this year it is showing up just like almost every year. You cannot put out enough at planting to last on these spots.
  • Splitting is not necessary on our typical sandy loam, productive soils where leaching only comes from monsoons like we had May of 2016.
  • The Layby rig or Injection rig is considered to be the best way to apply sidedress nitrogen but is also slower.
  • One big advantage is that it stabilizes nitrogen against environmental loss so you do not need to add stabilizing products that reduce leaching or volatilization. This in part likely explains its efficiency rating of 120%.  In other words there is a 20% gain over broadcasting or dribbling.
  • We don’t recommend cutting nitrogen when using it although you could. Rather there is some evidence that it puts that efficiency towards added yield potential if the rain pattern favors higher yield.
  • Another advantage is that it puts nitrogen closer to the plant than dribbling and it does not need rain to activate it. Being closer to the plant can help some of these current symptoms we are seeing on white sand and from damaged roots, although broadcast is still a better cure for this problem.
  • Using urea in blends or by itself is has some pluses and minuses. Ammonium sulfate is stable and provides a lot of sulfur, but creates so much acidity plus is the most expensive way to add nitrogen.
  • Some are looking for other options, and for dry broadcast, urea meets some goals.
  • Urea is fairly unstable and melts from humidity plus if you put it on top of wet soil, it will turn to gas and you can lose a lot of it. For this reason, we recommend coating it with a urease inhibitor product. 1.5 pounds of NBPT/ton of urea provides the best happy medium between cost and effectiveness.
  • If you have already met the sulfur requirement then using pure urea is simple and economical. If you blend it with some Ammonium sulfate to meet the sulfur requirement, treat the urea first before making the blend, because only the urea needs treating. Apply it the day it was blended as the AMS breaks down the coating.
  • ESN is urea with a physical coating for slow release. It may require as long as 6 weeks to completely release so it needs to be applied early.



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