Roundup Ready Alfalfa Calculator

Mark Renz, Extension Weed Scientist

At the 2006 Pest Management Update meetings held throughout Wisconsin there was quite a bit of interest about the cost of using Roundup Ready Alfalfa.  While the technology fee is very clear ($125/bag) it becomes much more difficult to calculate the real cost as the seeding rate, potential yield loss from traditional herbicides, and cost of the herbicide need to be considered.  To help producers understand the potential costs and benefits of this new technology Dan Undersander has created a calculator that can help you estimate the differences in costs between RR alfalfa and standard alfalfa varieties.  It is currently available at the following URL:

http://www.uwex.edu/ces/forage/pubs/economics_RR_alfalfa.xls

This calculator can be downloaded to your computer as it is an excel spreadsheet.  When you first open up the spreadsheet, values will be pre-entered into the cells.  These values are what we feel are accurate estimates of the costs, use patterns, and yield throughout Wisconsin.  The beauty of this calculator is that it allows the user to change any of the data in table 1.  This will allow the user to enter specific information for a field or farm and provide a more accurate analysis of the costs.

TABLE 1.  Inputs for the calculator.  The user can change all of these values to better represent their field/farm.

Once the data is entered into the spreadsheet several variables are calculated including the total seed and herbicide cost per ton of hay, total cost per ton of hay in the seeding year (assuming $250 fixed and harvesting costs), and the profit/A in the seeding year (see table 2). 

TABLE 2.  Results from calculator.

*Note: spreadsheet prorates seed cost over life of stand but figures full technology fee against seeding year.

For those who truly love crunching numbers, Dan has also added a sensitivity analysis which can be accessed by clicking on that tab at the lower left-hand corner of the spreadsheet.  This tool compares how changing seeding rate, yield, or seed cost will affect the return per acre.  This analysis is helpful in demonstrating which variables, if increased, will result in the greatest increase in return (while the other variables remain constant). As you can see from the graph (using default values), management that maximizes yield was by far the best variable to improve. Seeding rate (lbs/A) and seed cost ($/bag) did not have a large influence on the return per acre (figure 1).  Several studies in other states are evaluating reduced seeding rates of Roundup Ready alfalfa to offset the technology fee.  Results from Michigan found no differences in yield between 4, 8 and 16 lbs/A seeding rates in 2005, but reduced yield between the 4 and 16 lbs/A seeding rates in 2006.  Both sites were treated with glyphosate during establishment and harvest data was only from establishment year.  Additional work needs to be conducted to see how productive these stands are over-time.

Figure 1. Sensitivity analysis.

Probably the biggest difficulty is predicting what the yield loss will be from traditional herbicides.  Studies have been conducted worldwide and have shown variable results from site to site and from year to year.  In Wisconsin, yield loss in the first cutting has been observed to be between 0 to >1 ton/A.  Environmental conditions that stress establishing alfalfa plants are the main cause for this yield loss.  While RR alfalfa varieties have not shown to be susceptible to this injury, the decision on whether to plant these varieties will remain a decision that will be need to be considered field by field.