After reading Lesson 1, there are probably a flurry of “what if” scenarios going through your mind and perhaps a question like “Why is the profitable N rate range from 135 lb/ac to 190 lb/ac (55 lb span) for a 0.05 price ratio but only 90 to 120 lb/ac (30 lb span) for a 0.20 ratio?”  Okay, you probably didn’t ask this question but it made for a nice lead-in sentence.   Let’s take a visual look at the new program as presented in the graph below.

        Note that under favorable economic conditions (the top line with 0.05 price ratio), the penalty for missing the MRTN (indicated by the star) is relatively small.  The curve is much flatter than under unfavorable economic conditions as can be seen by looking at the bottom line (0.20 price ratio).  This occurs because the high price of N relative to the low corn price eats into profits in a hurry. 

What about manure?

        How does N applied as manure fit into this program?  The pure economist might say that nothing changes and manure should be valued at the same high price as commercial N.  This might be true if you’re buying it from a neighbor at that price, but for the producer applying manure on his/her own fields, I would use the more favorable price category of 0.05.  If all N is being applied as manure on a certain field, use the high end of the range to determine rates (180 to 190 lb/ac for corn following corn and 150 to 160 lb/ac for corn after soybeans).  If a mix of manure and commercial N is applied, using the 0.15 price ratio rates seems reasonable. 

        As stated many times before, but bears repeating, manure in today’s fertilizer price environment is a valuable bi-product of raising livestock.  Plan to use it accordingly.   

Determining and Analyzing Price Ratios

        It’s a bit difficult to quickly determine the impact of corn and N prices on the price ratio.  The following table will help in that regard. 

Table 1.  Impact of corn price and N price on price ratio (N price per lb divided by corn price per bu)

At this point in time, it’s difficult to know what the price of N will be at planting time, but certainly the days of $0.30/lb N are in the rear view mirror.   

Working within the Range

        The range of N rates for each price ratio is offered for several reasons.  First, it gives producers and consultants some flexibility.  Further, it allows for adjustment under various conditions and management systems.  UW Soil Scientists recommend the following: 

• If > 50% residue cover at planting, use the upper end of the range.  This is done because soil temperatures will be cooler.
• When corn follows small grains, use the mid to higher end of the range on the corn following soybean chart.
• For non-sandy soils: 1) if organic matter is < 2.0 %, use the upper end of the range; 2) if organic matter is > 10% use the lower end of the range.
• If you think there may be carryover (residual) N from last year: 1) Use the lower end of the range; or 2) Use the upper end of the range and take preplant nitrate test (PPNT) credits.
• When corn follows a forage legume, green manure, or leguminous vegetable, use the table for corn following corn and take the appropriate N credits.  The N credits for alfalfa have not changed.  Generally figure at least 120 lb N per acre.
• Remember, starter N counts towards total N applied.

For those who sidedress N, the pre sidedress soil N test is still appropriate and often well worth the time and expense in situations where manure was previously applied.