The amount of fertilizer needed per acre depends on the nutrient content of the fertilizer and the nutrient requirements of the crop or turf.
General Calculation Method
To calculate how much fertilizer to apply per acre, you can use this formula:
Fertilizer needed (lb/acre)=Desired nutrient rate (lb/acre)Decimal percentage of nutrient in fertilizer\text{Fertilizer needed (lb/acre)}=\frac{\text{Desired nutrient rate (lb/acre)}}{\text{Decimal percentage of nutrient in fertilizer}}Fertilizer needed (lb/acre)=Decimal percentage of nutrient in fertilizerDesired nutrient rate (lb/acre)
For example, if you want to apply 50 lb of nitrogen (N) per acre using a fertilizer that contains 46% nitrogen (such as urea 46-0-0), you calculate:
50÷0.46=109 lb of fertilizer per acre50\div 0.46=109\text{ lb of fertilizer per acre}50÷0.46=109 lb of fertilizer per acre
Similarly, for phosphate or potash, divide the desired nutrient rate by the decimal percentage of that nutrient in the fertilizer
Example for Turf Fertilizer
If a recommendation calls for 0.75 lb nitrogen per 1000 sq ft using a 16-8-8 fertilizer (16% N), the calculation per 1000 sq ft is:
0.75÷0.16=4.7 lb fertilizer per 1000 sq ft0.75\div 0.16=4.7\text{ lb fertilizer per 1000 sq ft}0.75÷0.16=4.7 lb fertilizer per 1000 sq ft
Since 1 acre = 43,560 sq ft, multiply by 43.56 (because 43,560/1000 = 43.56):
4.7×43.56=205 lb fertilizer per acre4.7\times 43.56=205\text{ lb fertilizer per acre}4.7×43.56=205 lb fertilizer per acre
So, you would apply 205 lb of 16-8-8 fertilizer per acre to supply 0.75 lb N per 1000 sq ft
Typical Fertilizer Rates
- For grass or turf, nitrogen rates often range from about 50 to 125 lb N per acre depending on the growth stage and purpose
- Organic fertilizer recommendations might be around 50 lb N per acre, but this varies widely depending on the source and nutrient content
Summary
- Determine the nutrient requirement per acre (e.g., nitrogen lb/acre).
- Identify the nutrient percentage in your fertilizer (convert % to decimal).
- Divide the nutrient requirement by the decimal nutrient percentage to get fertilizer amount per acre.
- Adjust based on specific crop needs and soil test recommendations.
This method ensures you apply the correct amount of fertilizer to meet crop nutrient needs without over- or under-application
