2008 Joint Annual Meeting (5-9 Oct. 2008): Economics of Nitrogen Rate and Application Timing Effects on Wheat.

The proper rate of spring fertilizer nitrogen (N) application to wheat has taken on a new meaning with the high cost of N fertilizer and the high current price of wheat. Recent N rate and timing of application studies across Illinois have allowed us to determine the optimum economic N rate to apply in the spring to wheat. The spring recommended N rate is based on N price, wheat price and percent soil organic matter (OM). In general, N rates decrease as soil organic matter increases.  This is due primarily to the N released from OM, along with a lower probability of N losses from the higher OM soils. Within an OM level, N rates change as the ratio of N price to wheat price changes. So at the same wheat price, N rates decrease as the price of N increases.  And, at the same N price, N rates move in the same direction as the wheat price. Farmers on low-OM soils who wait to apply their N until later in the spring or split apply their N in the spring with the majority of the N applied just before jointing, are able to gain some N efficiency and should be able to reduce their N rates.  We did not see this same effect on our high-OM sites.