Production Blog
Dan Davidson DTN Agronomist

Tuesday 02/09/10
VRN - Not Yet Popular

There has been alot of talk about variable rate nitrogen (N) the last decade since Precision Ag and its tooks came on the market. But adoption is slow becaue the value, relative to the cost just isn't there.

One of the things that intrigues me about variable rate N application is do you put on more or less N on the best producing areas. There are arguments for each approach. Some say you should put more N on the best producing areas and less on the poorer producing areas. But there is also evidence that the opposite works, i,e. that the poorest producing areas need more N than the best producing areas. I don’t yet have an opinion on this.

So I asked the Poll Question “If you variably apply nitrogen (N) on corn, how do you treat the highest-yielding area compared to the lowest-yielding areas?"

About 22% said then apply more N to high yielding areas.

Only 4% said they apply less N to high yield areas (I thought this number would be higher).

About 10% said that sometimes they use more N and sometimes less N, dependomg on the field.

2% said they didn't know and let their agronomist decide the approach.

And a whooping 60% said they don't variable rate N at all (which I guess isn't a surprise.

Cost relative to value is a big concern and has been since the technology and tools came availble to us. And one grower reminded us of this.

One grower said in an email "Are the results of the poll reflective of the cost of variable rate application equipment and the respective soil testing, variable application of chemicals, variable application of irrigation, yield-on-the-go harvesting/mapping, computer/software, education, etc. for decision making?"

"It has long been my belief that each "supplier" of the respective components, needed to complete the overall system, price their pieces of the puzzle as if they were the only component needed. Some of these components are priced according to what they "do" not what they "are". Therefore, the farmer cannot justify the total investment vs. the net bottom line return."

"Unless/until businesses are willing to price their products reasonably enough and accept their respective contribution to the synergy of a "system", to allow the farmer to make a fair profit, not a risky maybe profit, we will continue to waste dollars on inputs."

In another email a grower wrote "We use the application map for DAP and apply more N where less P is applied or less N where more P is applied." In the end this farmer variable rates N to make sure each acre gets roughly the same amount. I used to variable rate MAP according to P soil tests so that meant a variable rate application of P. We then compensated with variable rate application of N at the same time to even out the N application. This made sense to me how I am not sure what strategy to follow to decide how to variable rate N based on soil or yield productivity classes. But the cost of the technology prohibits me from doing it at the moment.
Posted at 11:04AM CST 02/09/10 by Dan Davidson
Comments (9)
Dan, We are also uncertain whether to put more or less N on the best producing ground. We do similar to your other grower and take off half of the N that the 11-52-0 contributes. We already had the equipment for the row shutoffs which quickly paid for itself. We just don't know how to write a prescription to vary the N rate. The extention doesn't really know either.
Posted by Steve McGrew at 8:21AM CST 02/10/10
Dan I think GPS and flow control devices such a Cold flow and other systems pay better dividends so we have better control on our rate applied
Posted by Steven Brummel at 10:39PM CST 02/10/10
If you do variable rate nitrogen on anything other than a soil based system you will not be successful. The majority of N that get into the corn plant is from the soil, applied fertilizer only is a supplement to the soil. How do we know how much to successfully supply if we don't know what is coming from the soil. Only soil tests, sensors and rate plots can give you that information. If you are doing anything else you have been sold something that has little chance of working.
Posted by Tim Smith at 7:36AM CST 02/11/10
I agree with Tim, I am 3yrs into zone soil testing and variable rate fert. apllication. From 10 yrs of yeild maps and the last 3 of variable rate application of N-P-K-S and lime, there is a 10-15bu. increase on corn and 3-5 on beans.
Posted by ROGER HULS at 9:40AM CST 02/11/10
Tim - I agree that one approach is to use soil productivity to tell us how much N to apply. But an even better way is to let the plant tell us how much N to apply because it not only integrates in the productivity of the soil but the environmental conditions and management practices for that season as well. I have felt that the best way to know how much N to apply is to let the plant tell us how hungry it is. And there are technologies like GreenSeeker, Crop Circle and OptRx can do that successfully. This technology does work.
Posted by Daniel Davidson at 8:08AM CST 02/12/10
Dan, I agree that sensor technology does work. It has some major limitations that will limit it's general use. It tells us the status of the plant at the stage of growth which is being sensed but does not tell how much N is needed. The soil determines how much N will be supplied, the plant can only tell us if it has sufficient or deficient N at that time. Also at the stage of growth needed to sense good information from the plant timing becomes so critical that being able to apply N on great number of acres becomes a problem. Sensors do have a place but will never reach a high percentage of acres.
Posted by Tim Smith at 8:16AM CST 02/12/10
Tim - I don't agree. While the sensors only tells N status relative to a N rich plant, it is the algorithm that computes a rate. I actually used that method last summer along with a few other method (but not the sugar amino test) and found it cut my over all N rate but not yield. That is the thing about sensors vs soil approaches - you either believe in one or the other but usually not both. I still believe letting the plant integrate its environment and then tell us how hungry it is is the best approach. It is like bellying up to the dinner table when you let your stomach decide how much you eat and not let the site of all that good food tempt you.
Posted by Daniel Davidson at 5:31AM CST 02/13/10
" Algorithm computes rate." based on ? I think only current conditions not conditions that will be around when peak N demand occurs. N management is a marathon not a sprint.
Posted by Tim Smith at 8:21AM CST 02/15/10
We have experimented with using a digital camera by air and with software (SMS) that does similar to a Greenseeker. We used test plots and didn't actually apply the N. You can get a percent yield of the nitrogen rich plot verses the yield of your target. You can assume the difference is due to nitrogen and can even adjust it compared to previous years. This needs to be done on larger corn (9 leaf ?). It works better on large amounts of nitrogen needed instead of predicting 10 or 20 pounds. There is a lot to know and you can learn by Googling about it.
Posted by Steve McGrew at 10:06PM CST 02/16/10
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