July 7 , 2008
 
University of Arkansas, Division of Agriculture, Cooperative Extension Service

Turfgrass Science Program (http://turf.uark.edu/) – Turf Tips

Nitrogen Arithmetic: Reducing Fertilizer Costs with Math and Management

It’s not new news that fertilizer costs are rising. Urea costs have increased 16% from May 2007 to May 2008 and it is likely that costs will continue to rise more in the near future. A 50 lb bag of urea will likely cost you about $18.50 this month (July 2008) and could be even more by the end of the summer.

Why are fertilizer costs rising? Most are aware that fertilizers costs are directly tied with fuel costs since natural gas is one of the first ingredients used to make urea. Fertilizer costs are also increasing because there is increasing demand from the agriculture market which has increased grain production in response to higher commodity prices.
 
Because costs are rising, purchasing decisions become are more and more important. A review of how to get the most nitrogen (N) for your money is below.

Cost of application in price per pound of N

General formula

Cost

1 lb fertilizer

Amount

Analysis

Example 1. What is the cost per pound of N for a 50 pound bag of urea (46-0-0) that costs $18.50?

$18.50

1 lb fertilizer

50 lb fertilizer

0.46 lb N

This should be computed as $18.50 × 1 lb fertilizer ÷ 50 lb fertilizer ÷ 0.46 lb N = ________

Answer = $0.80 per pound of nitrogen

Example 2. Two fertilizers are available from your local salesperson. Assume both contain the desired nutrients and nitrogen release characteristics. Calculate which fertilizer is the best buy according to its price per pound of nitrogen.

Fertilizer 1: Slow-release N using PCSCU (50 pound bag of 27-0-8), 70% WIN. Cost is $28.99.

$28.99

1 lb fertilizer

50 lbs fertilizer

0.27 lbs N

This should be computed as $28.99 × 1 lb fertilizer ÷ 50 lb fertilizer ÷ 0.27 lb N = ________

Answer = $2.15 per pound of nitrogen

Fertilizer 2: Slow-release N using MU (50 pound bag of 35-0-8), 55% WIN. Cost is $35.99.

$35.99

1 lb fertilizer

50 lbs fertilizer

0.35 lbs N

This should be computed as $35.99 × 1 lb fertilizer ÷ 50 lb fertilizer ÷ 0.35 lb N = ________

Answer = $2.06 per pound of nitrogen

The second fertilizer is the best buy per pound of nitrogen. Even though the second fertilizer costs more per bag, less will be needed because it contains more nitrogen.

Using spreadsheets to calculate costs

In addition to calculating fertilizer math problems by hand, computer spreadsheets can also be a useful tool for calculating your fertilizer needs. Using spreadsheet software programs such as Microsoft Excel allows managers to more rapidly calculate various problems.

It is possible to compare a couple of products or hundreds of products using spreadsheets. Spreadsheets can be customized in order to calculate specific fertilizer problems relevant to your company’s needs. When creating these spreadsheets, always check your spreadsheet answers with hand calculated answers.

Reducing costs

Although fertilizer costs are increasing, where possible we need to make sure not to reduce turf fertilization. We are all aware of the benefits of turfgrass fertilization such as improved root growth, recovery, turf quality, color, etc.  Areas managed with traffic, clipping removal, sandy soils, and damage (divoting, drought, etc.) all need additional nitrogen to encourage recovery and maintain turf health and it is imperative that N fertilization continue in these areas. 

There are some ways that you can cut your fertilizer costs by implementing site-specific management. Reduce nitrogen rates 25% on older well established turf areas with high organic matter. Reduce nitrogen rates by 25-50% in shaded areas since these areas do not require as much N fertilization as full-sun locations. Reduce nitrogen fertilization in areas with disease such as large patch, take-all root rot, brown patch, or Pythium.  Monitor plant growth by assessing clipping production and fertilize turf when clipping levels indicate a need. Simply by fertilizing specific areas on an as needed basis rather than on a schedule basis will help many mangers cut-back there fertilizer inputs and help offset the rising costs of N fertilizers.

Most will use N sources with more quick release N (urea, ammonium sulfate, etc.) to reduce fertilizer costs.  Another approach is to use more slow-release N sources at higher application rates in order to reduce labor by reducing the number of fertilizer applications. Individuals will have to evaluate their options to determine the best strategy for their location.

Aaron Patton, Turfgrass Extension Specialist
University of Arkansas, Division of Agriculture, Cooperative Extension Service