Wednesday, March 23, 2011

Did the heavy rains reduce nitrogen in wheat?

The following are some comments from Lloyd Murdock, Extension Soil Scientist, University of Kentucky

There a number of the low lying spots where the wheat is turning yellow due to water standing for extended periods of time.  In some cases, these yellow areas are wheat streak mosaic virus, but in other cases the yellow color was probably due to the lack of oxygen for extended periods of time.  All of the yellow leaves were mainly the older ones and the newer leaves where healthy and well colored (i.e. green). In these cases, wheat in lowest parts of the low spots has more yellow leaves and is more stunted.  Assuming no more extended monsoons, I would expect that most of the plants to continue development and do well.  The most stunted plants may be a little restricted on yield.   If there are areas where the plants are entirely yellow then these plants would not be expected to recover or would recover and be severely limited in yield.

The amount of nitrogen lost in these fields is probably not that much.  Since it was cool during these waterlogged conditions, denitrification was probably not very active during this time. The primary source of nitrogen loss would be leaching but not much leaching occurs in our silt loam soils.  A safe guess for nitrogen loss from our silt loams soils would be a maximum of about 25% of N applied and less than that in most cases. So if 50 pounds N/acre was applied before the rainy spell then one would only expect about 12 pounds N/acre to have been lost, at the most.

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