Soybean Response To Nitrogen Fertilizer

 

As the plsc.beutow.kandel.1.chlorotic soybean plantsoybean plants develop the first or second trifoliolate leaves, iron deficiency chlorosis (IDC) is starting to show up in some fields. Interveinal yellowing of the leaves with the leaf veins staying a dark green are IDC symptoms. Chlorosis is caused by the plant not being able to take up enough iron (Fe), even if there is sufficient Fe in the soil.  The form of Fe that plants can take up becomes less soluble at higher soil pH. The stunting of the plant due to IDC can result in a lower soybean yield. There are many factors that contribute to the expression of IDC and it is a problem especially in eastern North Dakota. Excess nitrates in the soil is one of the factors which aggravates the IDC expression in the plant. An experiment was conducted in 2013-2014 to evaluate the effect of N fertilizer application on the level of IDC. In the experiment we observed four varieties, each with different IDC ratings, growth types, and maturity ranges. Different fertilizer treatments were applied to each variety. The treatments were: a check of no additional fertilizer, 25 lbs of N per acre as urea, 50 lbs of N per acre as urea, and 75 lbs of N per acre as urea, all applied at plant emergence. Application of additional N gave significantly higher IDC scores (Table 1), indicating that the plants where more chlorotic.

 

 

 

 

There was no yield increase due to fertilizer application in 2013, but in 2014 N treatments yielded significantly more than the control (no additional fertilizer). Combined across 2013 and 2014 all N treatments yielded significantly higher than the control (P≤0.10). There were no yield differences among the fertilizer treatments themselves.

 

 

 

Although there was a significant increase in yield over the two years (42.8 bushel for the control vs. 45.2 bushel per acre average for the N treatments), there were no significant differences in financial returns after cost of fertilizer was accounted for. In summary: N application in this experiment made the plants more chlorotic and did not result in financial benefits.