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Southeast WI | To answer the OP - doubtful it's more than a few %.
To those that variable rate N:
(1) what do you base the variation on?
(2) how big of a range do you vary? 100 units to 250 units, etc?
(3) and the big kicker here - how do you measure how close you are to being correct? I don't mean how do you think you are correct, how ARE you measuring your correctness?
There was a panel discussion on variable rate N at the Discovery Farms winter conf in Dec and several WI farmers were trying this. Not one was measuring anything to prove they were close to selecting correct rates. This is really running blind.
The reason I ask #3 especially is I worked with the UW doing 10 years of on-farm N response trials. Not just on my farm but on anywhere from 3-6 sites that I controlled each year. Heavy black ground to light sandy loam soils and in between. Over 10 years we saw very similar N response curves each individual year. In other words, the best N rate on black ground in year X was the best N rate on the lightest soil in year X, too. Obviously yields were different but it took the same amount of N to get to the EONR. Soil N mineralization each year tops any applied N. | |
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POLL! What % of corn belt N goes on as variable rate?
