ISSUE 6   June 17, 2010


During the past week, soybeans have reached the first true leaf stage (first trifoliate) and in soils susceptible to iron deficiency chlorosis (IDC) they have started to express the symptoms of interveinal chlorosis on the newest leaves. To make soybeans susceptible to IDC a soil must first have free carbonates. A soil test is available that can provide a calcium carbonate equivalence (CCE) that will help explain why some areas are affected and some are not. In addition, wetter calcareous soils are more susceptible to IDC than dry soils. Wet soil conditions solubilize carbonates to form the ion bicarbonate, which is the culprit in causing IDC. Additional environmental and cultural conditions increase the incidence and severity of IDC. These are listed below with their counterpart to the right that decreases the risk and severity of IDC:

  • cool soil and air temperatures, compared to warm temperatures. 50's are bad, low 80's are good.
  • high soil nitrate, compared with low soil nitrate
  • high soluble salts, compared to salt levels below 0.5 mmohs
  • wet soils, compared to dry soils
  • poor North Dakota IDC tolerant varieties compared to Grade A varieties
  • solid-seeded, compared to 20 inch and wider row spacings

    Last week and the weekend were not good for IDC tolerance. The rain was cold and so was the air temperatures. The combination of rain and cold has contributed to the present symptoms on problem soils. Iron foliar amendments have not resulted in consistent yield benefits in our region.



    The cool, wet weather has resulted in emerging corn leaves that are yellow in color. These symptoms are almost all due to the coolness, and not to any nutrient deficiency. In my corn plots observed June 14, the symptoms were seen regardless of N rate. Wait for some 80 degree temperatures for a couple days in a row before deciding if a sulfur/zinc application is warranted. If symptoms persist and the corn most affected is located in sandier, lower organic matter areas, sulfur may be a problem and may need to be amended by dribbling ammonium sulfate or ammonium thiosulfate between the rows. If the problem is zinc, persistent striping and a tissue test AND soil test indicating that zinc is low may be diagnostic. A foliar zinc product of nearly any kind will pull corn out of a zinc problem.



    Canola is not like wheat. By heading, wheat has determined its yield potential. By early flower, canola is still in the decision mode. If N appears short, additional stream-bar N may be applied during bolting and early flower. After early flower it is probably too late to make a difference. The flowering period may be two weeks or longer, so application early in the first week may still make a yield benefit. In determining practicality, figure about 10% yield increase in fields with questionable N levels, but also factor in the canola lost from driving over it to apply the 30 lb N/acre. If the result is a positive number considering the cost of N (about 50 cents/lb N from my state sources), then it would be good to apply. If not, save the money.



    Some slow-release product sales people are promoting addition of their product at a low rate (1-2 gallons/acre; 2.5-5 lb total N) with a fungicide application at flowering. I would not support this application on two levels. First, none of the slow-release products are 100% slow release. Most are 1/3 to urea or 28% N, with the rest slow-release. The urea or 28% would not be healthy for the delicate wheat flowers and may reduce the efficiency of pollination. Secondly, the amount of benefit for the buck with these products is very low. Please recall that the recommended recipe post-anthesis N application is 10 gallon 28% with equal water. This amounts to 30 lb N/acre, which often results in 0.5-1% higher protein with no yield decrease at harvest. According to Carrington research in 2009, 30 lb slow-release N gives equivalent protein increase. Therefore 2.5-3 lb N/acre as a slow-release product would only give 0.05-0.1% protein (1/10 as much) increase for probably a similar cost as 15-20 lb N as 28%. Please do not use or promote the application of slow-release N at flowering.

    Dave Franzen
    NDSU Extension Soil Specialist

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