Corn Response to Manganese Rates.

Manganese(Mn) application to soybeans is promoted by some agronomists to increase yield. However, little research has been reported on the effects of additional Mn to corn.  In the spring of 2010 a field in Nebraska received an application of 8.3 kg Mn ha^-1 in the form of manganese sulfate. Corn planted that year was severely stunted and chlorotic, and yield was significantly reduced compared to long-term field averages. In response to this observation, studies were conducted in 2012 in Nebraska and in Illinois to evaluate the effect of increasing Mn dose on corn growth and yield.  In Nebraska, Mn was applied at 0, 3.6, 5.4, 9.0 and 12.6 kg Mn ha^-1.  In Illinois, Mn was applied at 0, 0.4, 1.1, 3.4, 6.7, and 10 kg Mn ha^-1.  Each study was replicated four times.  In Illinois, SPAD readings were collected throughout the growing season, and plants were rated for stunting. In both locations, plots were harvested for yield.  In Nebraska, yield was dramatically reduced by the application of Mn.  In the 0 kg treatment yields were 14689 kg ha^-1, compared to 8707 when 3.6 kg Mn was applied.   Increasing Mn rate above 3.6 kg Mn did not reduce yield further.  In contrast, in Illinois Mn rate did not affect leaf greenness as measured by SPAD meters, nor did it result in stunting.  In addition, yield was equal across all Mn rates.  A likely explanation for the different response between the two locations lies in soil characteristics.  The Illinois site had a higher pH and higher CEC which allowed the soil to adsorb more of the Mn and minimize plant uptake.