Corn stover (stalks, leaves, cobs but not grain) is being used to create ethanol
ID: 114119 • Letter: C
Question
Corn stover (stalks, leaves, cobs but not grain) is being used to create ethanol that meets the “cellulosic biofuel” requirement in the Renewable Fuel Standard.
A typical removal rate is 2.0 tons of stover per acre. Corn stover contains 0.50% nitrogen, 0.15% phosphorus, and 0.80% potassium by weight. When it is removed from the land, the nutrients must be replaced.
A particular corn producer is supplying corn stover to a biorefinery making ethanol. The producer has these fertilizers available:
• anhydrous ammonia nitrogen (82-0-0) @ $509/ton;
• diammonium phosphate or DAP (18-46-0) @ $425/ton; and
• potash or potassium (0-0-60) @ $318/ton.
Fertilizer nutrient content is designated as (N-P-K) where N = % nitrogen, P = % phosphorus and K = % potassium, all on a weight basis. Thus, anhydrous ammonia is 82% nitrogen by weight, 0% phosphorus and 0% potassium.
What is the nutrient replacement cost for this corn producer? Express your result in both $ per acre and $ per ton of stover removed. (Hint: DAP contributes both nitrogen and phosphorus – do that one first.
Explanation / Answer
The corn removal rate = 2 tonnes/acre. = 1815 kg/acre
So, Nitrogen removal rate = 1815*0.005 = 9.075 kg/acre
Phosphorus removal rate = 1815*0.0015 = 2.7225 kg/acre
Potassium removal rate = 1815*0.0080 = 14.52 kg/acre
For Potassiun we need 14.52/0.60 = 24.2 kg of potash which will cost, (24.2*315)/1815 = $4.2
While adding phosphorus we will add nitrogen also.
For phosphorus we need 2.7225/0.46 = 5.919 kg of diammonium phosphate which will cost, (5.919*425)/1815 = $1.39
and the nitrogen we will get will be, 5.919*0.18 = 1.066 kg
The remaining nitrogen will be, 9.075 - 1.066 = 8.009 kg
For that nitrogen we need, 8.009/0.82 = 9.78 kg of anhydrous ammonia nitrogen which will cost, (9.78*509)/1815 = $2.75
So total cost fornutrient replacement for the 2 tonne of corn is = 4.2 + 1.39 + 2.75 = $8.34
So the cost is, 4.17 $/tonne and the 1 acre produces 2 tonnes of corn stoves so it is 8.34$/acre.