Plants & Human Affairs - Introduction
 Plants & Human Affairs (BIOL106)  -  Stephen G. Saupe, Ph.D.; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321; ssaupe@csbsju.edu; http://www.employees.csbsju.edu/ssaupe

Comparing Cost of Fertilizers based on Nitrogen

Nitrogen is the most important element � because it is required in the greatest amount (1-4%)  Since it is a major consideration, calculate cost.  To calculate the cost, use the formula:

Nitrogen cost (\$/kg) = cost of fertilizer (\$) x 1/ %N  x  1/pack mass (kg fertilizer)

The first one is done for you.  Complete the remainder of the table.

 Fertilizer Costs Brand Type N-P-K Pkg Price (\$) Pkg Wt (kg) Nitrogen cost (\$/kg) RaPid Gro S 23-29-17 1.99 0.227 38.10 Peter's Houseplant S 15-13-7 1.19 0.071 Jobe's Spikes C 10-10-4 1.49 0.015 Miracle-Gro S 15-30-15 2.19 0.227 Osmocote C 14-14-14 4.95 0.553 Schultz Instant Liquid L 10-15-10 4.99 0.397

S= soluble, L = liquid O = organic C = controlled

This exercise is adapted from Hershey, D (1990) Sleuthing the nutrients that make your houseplants grow.  Science Activities 27: 17 � 20.

Last updated:  01/11/2005 / � Copyright  by SG Saupe / URL:http://www.employees.csbsju.edu/ssaupe/index.html