What is the cost of nutrients to produce a single 150 g (5+ oz) head of hydroponic lettuce,
assuming a simple mixture of ingredients to produce hydroponic nutrient solution (half-strength
Hoaglands solution.)?
Data:
Assume: Lettuce contains 0.29 g N/ head = 0.010 oz N/head
Nutrients added for 1000 gallons of "standard" nutrient solution
130 oz Peters Hydrosol 5-11-26
130 oz calcium nitrate (CaNO3•c3H2O)
20 oz epsom salts (MgSO4•7H2O)
Nitrogen contained in nutrients
Hydrosol: 130 oz at 5% N = 6.5 oz N (yields 50 ppm)
Calcium nitrate: 130 oz at (14/(40+14+48+3*2+3*16)) = 8.97% N = 11.7 oz N
Together = 18.2 oz N (provides approximately 140 ppm)
Enough for 18.2/0.010 = 1820 heads of lettuce
Example prices in early 2011
Crop King $30 for 50 lb bag of Hydrosol 5-11-26 = $0.0375/oz
Griffin $42 for 25 lb bag of calcium nitrate = $0.1050/oz
CVS $5 for a 6 lb bag of epsom salts = $0.0521/oz
Total cost for the 1000 gallons = 130(0.0375) + 130(0.1050) + 20(0.0521) = $19.57
Which suffices for 1820 heads, or $19.57/1820 = $0.011/head or 1.1 ¢/head if no quantity discounts are sought.
Conclude?
The cost of inorganic nutrients in a head of hydroponic lettuce is likely to be less than a penny per head. Calcium nitrate is the major cost in the proposed analysis.
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