|
| There are two opposing philosophies about variable rate N and I don't know if either works.
I know from my 2007 experiments in going short on N that the yield was more dependent on corn variety, than on soil type, though it didn't get harvested with a working yield monitor on the combine. My main number was from Crow's selected to thrive on short nitrogen. The second number was an Ottlie left over from 2005 on my farm and the third was a Dynagro I got less than half a sack to finish the field when the Crows ran out before I had planned, and then the Ottlie ran out. Riding the combine the Crows had nice ears as did the Ottlie. The Dynagro had tipped back half the ear, making popcan ears or shorter. They were fat but short. I fed the three numbers (planted about 35K population, planned for 34 but the planter dropped an extra seed on the average about every 15 feet) 111 pounds of N, split with 10 pounds spread from MAP before planting, 60 pounds as 32% with the planter, and 40 pounds as 32% dribbled on just before a rain with the corn about 4 feet tall. And there was a couple pounds of AMS from two passes of glyphosate. The dry yield was 173.2 bushels. The late season stalk test was low, 237 ppm which hints there could have been a yield response to more N. That was after 36 bushel beans in 2006. With the late side dressing the lower leaves on that corn didn't fire until several weeks after the neighboring fields all with much more applied N had fired, but it did come to a point where the stalks were beginning to fail. Fortunately that was about 15.5% moisture and I was able to get my custom combiner in it quick.
The variable rate philosophies are: 1. Short the poor places, since they won't produce with any great amount of N, and feed the good places since they may produce more if given more N. 2. Short the good places, because they will do good enough without all that N, and feed the poor places to bump up their yield, presuming the poor is from lack of nutrition.
I don't know if either scheme really works every year. I rented the place out in 2009 and it took to 2011 for my strip tilling corn on corn tenant to beat my 2007 yield. And he didn't short it on nutrients any year and concentrated them in the strips so the roots didn't have to hunt. The wet ground that I had left out of production still didn't produce until 2012 and the more normal ground produced until 2012 when the dry shut it down.
I'm sure that split application can maintain yield with some less purchased N. I'm sure that variable rates can save on the cost of N, but I'm not sure that either variable rate scheme will maintain yield year in and year out. I'm pretty sure that variable rate based on 2009 to 2011 yield maps on my place would have resulted in very little crop in the dry year, where with uniform N, P, and K, the wet spots peaked at 248 and the field average was 153 while some of my tenant's other fields produced 0, 30, and 60 bushel corn fed the same way. Its a gamble every year, and I remain unconvinced shorting a corn that "responds to nitrogen" (which I read to mean, it demands nitrogen or it won't produce) because its in unusually good soil or unusually poor soil is a way to maximize profit. A corn like the Crows I planted rated to thrive on marginal nitrogen will treat the whole place better, than the corn that "responds to nitrogen" in my opinion but that corn number is hidden from commerce as far as I can tell.
Most corn farmers use way more nitrogen that I did in 2007 so that lowering the rate of the whole field will come closer to maintaining yield than either scheme 1 or 2, I think.
At the FPS show in 2006, I asked most seed vendors about corn good for not needing as much N and only Crows had that one number for my latitude, most of the rest claimed to be working on breeding for that and promised it to be out about 2012. I've not noticed any advertising claims to that effect yet.
Gerald J. | |
|
Variable Rate Nitrogen (sidedress) discussion
