The beginning of silage harvest is a good time to evaluate your nitrogen program, say Pennsylvania State University soil specialist Doug Beegle and Franklin County Extension educator Jonathan Rotz.
Some silage harvesters will notice brown leaves, which may signify nitrogen loss resulting from a wet spring and summer. Nitrogen (N) deficiency not only reduces yield, but also results in lower protein content and higher fiber levels in the silage.
However, brown leaves do not necessarily indicate yield loss, say Beegle and Rotz. Research in central and southeastern Pennsylvania has shown that, when four or five green leaves are present at and below the corn ear leaf, 95% of the time there was no yield deficiency. When there were less than four green leaves, only half the plants were nitrogen-deficient.
So, while brown leaves can be a good rough indicator of N deficiency, they are not a perfect predictor. Furthermore, if a plant is green all the way to the ground, it may indicate that too much nitrogen was applied.
The best way to evaluate the effectiveness of your nitrogen program is by taking a late-season stalk nitrate test. To really refine your program, combine the late-season stalk test with a pre-sidedress nitrate test and use of a chlorophyll meter.
To read more, go to http://fcn.agronomy.psu.edu/2009/fcn0922.cfm#d, and scroll down to "
Assessing Nitrogen Losses in Corn.” To view a fact sheet about the late-season stalk nitrate test, visit http://cmeg.psu.edu/pdf/agfact70.pdf. You can view a video about the test at http://cmeg.psu.edu/video/stalk_test/stalk_test.cfm.