Nutrient Management Research Database

Results  from  the  first  two  years  of  this study  support  the  concept  of  variable  rate  N application  in  potato  production,especially  when  based  on  Imagery  zonal  management.    This method showed significant increases in total yield, as well as U.S. No. 1 tubers.  The recognized increase  in  yield  and  quality  more  than  compensated  for  the  increased  cost  of  this  method  of variable rate N fertilization.  Using EC added another layer of information but did not further improve yield  and  net  returns,  but  more  research  regarding  interpretation  of this data  in  Idaho  soils  is needed  before  conclusions  are  drawn.    Grid  sampling  alone  does  not  seem to  be  an  effective method  for  variable  rate  N  fertilizer  application,  most  likely  due to  the  fact that  spatial differences  in  yield  potential  are  not  being  considered  with  this method.    It  is  reasonable  to assume that the results for the grid method would improve if a variable yield goal and/or added layers of information (such as imagery) were added.  The cost of making yield goal adjustments is  minimal  and,  as  such,  is  a  recommended  addition  for  this method.    This  was  not  included  in this trial  because  an  evaluation of  grid  mapping  as  it  is  currently  practiced  in  industry was desired for comparison with the other methods.  Adding imagery to the already high cost of grid sampling  may  be  cost  prohibitive,but  the  added  layer  of  information  would  be  expected  to improve the results.  These combinations were not evaluated in this study and, therefore, are only surmised.  Further evaluation of these methods for variable rate N application is planned

This study investigated the potential benefits of variable rate pre-season fertilization.

Four methods of fertilization were applied:

1. Traditional (i.e. non-variable rate)
2. Grid Mapping
3. Bare Soil Imagery
4. Bare Soil Imagery + EC mapping

Traditional rate was determined based on a single yield goal with a single composite test for soil nitrate.

Grid mapping determined N application rates based on testing from a 1.25 acre grid map.

Bare soil imagery is used to identify areas of potential difference and sampling each of those areas to determine applciation rates.

Bare soil + EC mapping used the bare soil approach along with a map of electrical conductivity.

Potato yield and quality were assessed.

In the first year, all three variable rates approaches increased yields, though no differences were determined between the three. The average yield increase was 17 cwt per acre.

In the second year, an average increase of 20 cwt per acre was found when using the variable rate techniques.

In the third year,  only the bare soil imagery approach increased yields at a rate of 28 cwt per acre.