Rolla, ND | ksufan - 10/13/2008 23:02
Not wanting to make fertility equal want to fertlize high yielding areas as to what they are making and the lower yielding areas at to what they are making. If spots make 280 fertilize them for 280 not 240 and if spots make 180 fertilize them for that not 240 and hopefully cut back on fertilizer across the field and also raise average yield at the same time is what i am thinking correct me if i am wrong.
I'm not familiar enough with your situation to really speak directly to it. One thing you have to do when going variable rate is to pay attention to what the field tells you. Now you might think higher yielding means more nitrogen but that's not the case here. Often the highly fertile areas will produce more crop and still have more residual nitrogen. You are still thinking more bushels means you need to add more nitrogen but notice the general trend in nitrogen recommendations is actually away from a bushel of grain needs a certain amount of N and more to you need a certain amount of N without regard to yield goal.
I haven't talked about anything other than nitrogen. Maybe I should do that for a bit. Phosphorus and Potassium are pretty straight forward. Use your yield and replace them. That's going to be a lot closer than any sampling program. Do some soil tests, particularly on high or low yielding areas. You will likely find the highest yielding areas are the lowest testing because the crop has removed a lot more there and the field has had uniform applications.
I would think where you are that lime isn't used.
Now back to the nitrogen. If your soil types are pretty uniform across the field then things are going to split out really nice. The variability you would have would be largely organic material. More organic material will give you more nitrogen so the testing that will split that organic material difference out very well is conductivity.
So if it was an ideal world. I'd run a conductivity meter on that field. And I'd do it in fairly close passes, say about half the width of your nitrogen applicator.
Now instead of doing that and then making all sorts of changes up front. I'd really like to see one year of what you've been doing. That is do the conductivity tests, and then do a bunch of directed soil testing to see where the levels of nitrogen going in are. Then do some stalk testing at the end of the season to see how the conductivity lines up with whether the plants are sufficient or deficient. Be nice to pull some soil samples then too.
If you find stalks that test too low in nitrates, that will tell you you need to increase nitrogen in those areas, if you find only sufficient there is likely areas you can decrease and you might be lucky and have areas that you both increase and decrease.
That would be if you are a guy that really wants to do it right. Most don't because it's a lot of work. Here's whats would be more typical. Make some guesses, go with it. Maybe use some tissue tests or a spad meter to check for deficiencies. Get a seat of the pants feel for it, look at the yield map, and do it again.
Anyway, that's kind of an overview. For phosphorus and potassium you use crop removal as your foundation. For nitrogen and sulfer you use organic material.
Marv |
What information are people using for variable rate application of fertilizer?
