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Read your fertilizer bag!

The experimental rates are constant, but nutrient amounts in fertilizer differ even for the "same" product.

This may mean you have to apply different amounts of fertilizer in different years--the most important thing is that each nutrient is applied at 10 g m-2y-1


Application Rates and timing: N, P, and K are applied at 10 g m-2y-1 by elemental mass, before the growing season of each treatment year. The micronutrient mix is added once, at the first treatment application, into K treatment plots.

To get amount of fertilizer to use: divide 10 by the fraction of that element in the fertilizer. For instance, for a 43-0-0 urea formulation, you should apply (10 / 0.43) = 23.3 g m-2. Be sure to correct for the relative fraction of the appropriate compound given in the Analysis. For instance, if a label analysis states 45% P2O5, this means the fertilizer contains only 19.63% P by atomic mass. The amount of fertilizer would then be (10 / 0.1963) = 50.9 g m-2.

N Fertilizer types: N should be applied as time-release urea, which is polymer-coated to delay absorption and prevent loss due to volatilization. There are many types of timed-release urea. NutNet uses forms that are granular, non-sulfur coated, 60-90 day release urea. Be sure to check with your supplier to confirm these details, and always read the label information.

In areas where time-release urea is not available, ammonium nitrate has been used. However please avoid this if at all possible. If ammonium nitrate is used it should be applied in multiple visits over a few months, although the total N per year should be the same as with the time-release urea.

P Fertilizer types: P should be applied as "triple super phosphate" (TSP) which is a generic compound rather than a brand name. Be sure your P fertilizer is not sulfur-coated and does not contain added sulfur. The amount of sulfur in the TSP analysis should only be 1-3%.

K+ Fertilizer types: K is applied as potassium sulfate (K2SO4), meaning it is also a sulfur addition treatment.

Micronutrient Fertilizer types: The experiment begain in 2007 using Scotts Micromax brand of micronutrient mix (see detailed compound content in chart below). Since then Scotts has changed its name to Everris, and Micromax is not universally available, especially outside of North America and Western Europe. If you are unable to locate a supply of Micromax for initial treatment year application, contact NutNet HQ and we may be able to help.


Example worksheet for fertilizer application

Nutrient Form/Element Analysis mass fertilizer needed for rate (g m-2y-1)
Nitrogen: time-release urea (NH2)2CO or N2H4CO 43.00% N  23.3
  (NH2)2CO or N2H4CO 40.00% N 25
Phosphorus: Triple Super Phosphate P2O5 45%


  P (by atomic mass) 19.63% (10g / 0.1963)
  Ca 16%  
  S 1%  
  Mg 1%  
Potassium Sulfate (K2SO4) K (by atomic mass) 44.9%  22.3
  K   (10g / 0.449)
  S (by atomic mass) 18%  
 Micronutrient mix: "Micromax" only applied in treatment year 1 100
  Ca 6%  
  Mg 3%  
  S 12%  
  B 0.10%  
  Cu 1%  
  Fe 17%  
  Mn 2.50%  
  Mo 0.05%  
  Zn 1%  
Typical Plot Application AMOUNTS      plot=25m2, 15 plots/nutrient treament (5 treatments X 3 reps)
 Fertilizer grams/plot/year pounds/exp/year kg/exp/year
time-release urea (43% N)
Postassium sulfate


Fertilizer Suppliers

Fertilizer type and availability varies widely even within regions. If you cannot find a certain fertilizer be sure to check with other NutNet colleagues from your continent, or with NutNet HQ.

Region Formulation Brand name Retail suppliers
United States time-release urea (N) Agrium "Duration" Crop Protection Services
United States triple-super phosphate Triple Super Phosphate widely available
United States potassium sulfate potassium sulfate widely available
United States micromax Everris Micromax BFG Supply Co.