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Sunday, October 21, 2012

Variable Rate Fertilizer

Variable Fertilizer is on my mind tonight because that is what I am working on.  We still have many customers who do not use variable rate prescriptions as such, but we  have been making site specific recommendations for many years.  Since our sample zones are often visible on the landscape, some of our customers have been using our "poor man's" variable rate system for years.  As a result, many of the fields we sample are fairly even in fertility.  On uniform soils, this might be expected.

On variable soils, I am expecting that in the  long term some of the fields we sample will develop variability in fertility because of variability in yields.  This will be a long term issue, but in the short term we may still be doing blanket applications.  I have mentioned that we find variability in pH because the soils with higher clay content need more lime in order to move the pH and calcium balance in the right direction.   pH controls availability of all nutrients, so it is important to keep the whole field in the ideal range.  Too high is just as bad as too low. 

The other advantage to variable rate applications is the saving in material.  If you don't need it, don't spend the money on fertilizer.  The nominal fee for variable rate spreading is well worth the cost if you have a few zero areas in the field.   I also think there is money to be made if some areas of the field are extremely low. 

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