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Step 7. Total Cropland Required

Using two different approaches, this worksheet estimates the total cropland required for manure application.

Example Information:

Method #1 - This is the preferred method, when a soil test has been performed and P is below 25 ppm.

1. Total nutrients produced per year from solids: amount of nutrient/year (step 1) x amount of plant available nutrient in manure (step 4) =

Nitrogen: 1174.5 T/yr x 8.53 lbs N = 10,018.5 lbs N/yr
Phosphorus: 1174.5 T/yr x 18 lbs P2O5 = 21,141 lbs P2O5/yr
Potassium:1174.5 T/yr x 26 lbs K2O = 30,537 lbs K2O /yr

 

2. Total nutrients produced per year from solids and sludge: amount of from solid + amount from sludge (step 5) = total amount produced

N = 10,018.5 lb + 328 lb = 10,347 lbs N/yr
P2O5 = 21,141 lb + 842 lb = 21,983 lbs P2O5/yr
K2O = 30,537 lb + 362 lb = 30,899 lbs K2O/yr

 

3. Total crop acres based on soil fertility needed for 100 bushel barley crop: Total nutrients produced divided by nutrient required/ac (step 3)

Nitrogen: 10,347 lbs N/yr divided by 160 lbs/ac = 65 ac for N
Phosphorus: 21,983 lbs P2O5/yr divided by 50 lbs/ac = 440 ac for P2O5
Potassium: 30,899 lbs K2O /yr divided by 75 lbs/ac = 412 ac for K2O

 

Method #2 - This is the preferred method, when a soil test has NOT been performed.

4. Total crop acres based on nutrients used by 100 bushel barley crop 
(See page 24. Fertilizer Guidelines for Montana Crops, EB 161, 2003)

One bushel of Barley grain use:
0.87 lbs N
0.36 lbs P2O5
0.25 lbs K2O

One ton of Barley straw uses:
14 lbs N
4.1 lbs P2O5
30 lbs K2O

Barley Grain to Straw Ratio is 1 to 1.3
(48 lb/bu x 100 bu) x 1.3 divided by 2000 = 3.12

Grain:
N = 0.87/bu x 100 bu/ac = 87 lbs/ac
P2O5 = 0.36/bu x 100 bu/ac = 36 lbs/ac
K2O = 0.25/bu x 100 bu/ac = 25 lbs/ac

Straw:
N = 14 lbs/T x 3.12 T/ac = 44 lbs/ac
P2O5 = 4.1 lbs/T x 3.12 T/ac = 13 lbs/ac
K2O = 30 lbs/T x 3.12 T/ac = 94 lbs/ac

Total Nutrients used by 100 bushel barley crop
N = 87 + 44 = 131 lbs N/ac
P2O5 = 36 + 13 = 49 lbs P2O5/ac
K2O = 25 + 94 = 119 lbs K2O/ac

Acreage needed based on nutrients produced per year from manure 
N = 10,347 lbs divided by 131 lbs/ac = 79 ac for N
P2O5 = 21,983 lbs divided by 49 lbs/ac = 449 ac for P2O5
K2O = 30,899 lbs divided by 119 lbs/ac = 260 ac for K2O