Is that Fertilizer a Good Deal, or Not?

It looks like we are heading into a year of volatility in the fertilizer markets, which will mean growers are looking for pricing opportunities. It is easy to do price comparisons when you are comparing the same product from different suppliers, but comparing two different products is not as straightforward.

The solution is to convert the price per tonne (or per litre) into a price per unit of nutrient.

The math is pretty simple with a hand calculator as long as you know the price per unit weight of the material, and the fertilizer grade. For example, you know that the local price for urea is $920/tonne, and you find a supply of ammonium sulphate (21-0-0) for $500/tonne. The price per tonne is attractive, but should you buy?

Price per tonne of material / Fertilizer grade x 10 = Nutrient Cost ($/kg of nutrient)

By this calculation, the nitrogen from urea will cost ($920/460) = $2.00/kg. Using the same calculation, the ammonium sulphate will cost $2.38/kg, so urea is still a better buy. If you are more comfortable dealing with imperial units, simply divide the prices per kilogram by 2.2 to get the price per pound.

Liquid fertilizers, particularly starters, are a bit more complicated, since they are often priced by volume so the specific gravity (density) of the material needs to be considered. To determine the price per kilogram of nutrient in a liquid, divide the price per litre by the liquid density multiplied by the percent nutrient in the material.

Price per litre of material / (Density (kg/I)x Fertilizer Grade/100 = Nutrient Cost ($/kg of nutrient)

A 6-24-6 liquid fertilizer is priced at, for example, $1.50/litre. We know that the density of this fertilizer is 1.329 kg/litre, so the price of the phosphate in this fertilizer is $4.70/kg. Using the calculations above for granular fertilizer, the phosphate from MAP at $1500/tonne is 2.88/kg. The MAP is obviously the more economical nutrient source in this example.

It is a good idea to run through these calculations when approached by someone making you an offer you cannot refuse. Some simple math can reveal that in the end you are not getting that good of a deal for what you are buying.
(modified from an article by David Henry and Robert Mullen that originally appeared in the C.O.R.N. Newsletter)