The price of nitrogen (N) continues to climb, a theme that has been ominously recurring since 2001.   Since that time, local N prices have more than doubled.  Current prices put urea at $0.50 per unit of N and 28% liquid forms pushing $0.60 per unit N.  The N price to corn price ratio ranges from 0.13 to 0.16 depending on where you want to put a corn price ($3.20 to $3.80 per bushel).  Total cost of applied N will depend on method of application, who makes the application, and N source. 

Should N rates be lowered given the higher prices? 

        The first question that comes to most producers' minds is "Will it pay to cut nitrogen rates in 2008?”  In essence, we’re sitting at about the same place we were at this time in 2005, but with both lower corn and N fertilizer prices.  The table at the bottom of the page is extracted from the Nitrogen $ Rate of Return calculator, a computer spreadsheet that can be obtained off the internet at:  http://www.uwex.edu/ces/crops/NComparison.htm .   It determines the rate of return on increasing units of applied N for various rates and corn prices.  Given the current price of N ($0.51 per unit) and based on yield response data from University of Wisconsin N-rate studies, the optimum N rate for corn following a non-legume falls to 120 pounds per acre when corn is $3.20 per bushel or less.  The optimum N rate increases to 130 pounds per acre when corn price is $3.60 to $4.00 per bushel.  Keep in mind that applying more N will result in slightly higher yields, but no longer does the increase in yield more than compensate for the added cost of the N.  Nitrogen rates can be reduced when corn follows a legume like soybean (105 to 110 lbs. N per acre should get it done according to the calculator). 

        Higher N prices put an increased importance on the retention of N that is applied in the form of fertilizer or manure.  Remember that N from dry urea will volatilize and be lost if fertilizer granules are left on a dry soil surface for an extended period.  Either light soil incorporation or applying just before rain will insure that the N is not lost.  For an additional cost, urease inhibitors can be added to the fertilizer to guard against potential N loss under dry conditions.  Similarly, but to a somewhat lesser degree, N may also volatilize where liquid 28% N is applied over the dry surface without incorporation. 

        Leaching and denitrification losses are also an important consideration.  All forms of applied N are eventually converted to the nitrate (NO₃) form in the soil.  Nitrate is subject to both leaching and denitrification under wet conditions.  Again, for additional cost, nitrification inhibitors can be added to the fertilizer material to help delay the conversion from ammonium to nitrate.  With the higher risk of NO₃ losses occurring early in the growing season, there is also the option of sidedressing all or a portion of applied N to the reduce the risk of N loss. 

        Higher N prices will mean that not taking proper nutrient credits from manure and legume sources will be more costly…..a lot more costly.  Although most producers are aware of the first-year credits following manure applications or a forage legume stand, there are also legitimate second-year credits.  For example, a second year corn field in 2008 (alfalfa terminated in fall, 2006) can be credited 50 pounds of N per acre.  The second-year N credit for manure is 1 pound for each ton of solid dairy manure applied per acre in the fall or winter of 2005 and 2 pounds of N for each 1000 gallons of liquid dairy manure applied.