Methods
These budgets are a summary of the major nutrient inputs (manure and fertilizer, and in some instances biosolids) and outputs (harvested crops) for cropland.
The nutrient balance of either nitrogen (N) or phosphorus (P) for a state, county, region or watershed is calculated as follows:
Nutrient balance = Manure nutrient + Fertilizer nutrient - Crop nutrient removed
Manure Nutrients:
For each type of animal, the annual manure phosphorus production is calculated as follows:
| Annual manure nutrient | = | inventory (or animals sold) | * | nutrient excreted (per animal per production period) | * | recoverable manure fraction |
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The total manure nutrients produced in a state, county, region or watershed is the sum of the manure nutrients produced by each type of animal.
Additional information:
Manure assumptions
Manure coefficients
Fertilizer Nutrients:
Several types of data are used for fertilizer phosphorus, including:
- Tons of phosphate or nitrogen fertilizer by county
- Tons of total fertilizer by county
- Tons of phosphate or nitrogen fertilizer by state
- Acres of cropland by county and state
Fertilizer sold in each county was used directly in the budgets if available. Otherwise, we estimated fertilizer nutrient use by counties. For these estimates, the fertilizer sold in a state was allocated its counties according to their percentage of the state's total fertilizer tonnage.
Fertilizer phosphate is converted to fertilizer phosphorus as follows:
Annual fertilizer P (lbs) = Fertilizer phosphate (lbs) * (0.437)
Additional information:
Fertilizer assumptions
Fertilizer data sources
Crop Nutrients:
For each type of crop, the annual phosphorus harvested is calculated as follows:
| Annual crop removal of nutrient | = | Quantity of crop harvested | * | Nutrient removed per yield unit |
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The total nutrients harvested in crops for a state, county, region or watershed is the sum of the nutrients in each type of crop harvested.
Additional information:
