Economic feasibility of site-specific optical sensing for managing nitrogen fertilizer for growing wheat

A site-specific nitrogen fertilizer application system that uses optical reflectance measurements of growing wheat plants to estimate N requirements has been developed. The machine enables unique applications of liquid N fertilizer at a grid level of 0.37 m2. To achieve widespread adoption, the precision application system must be efficient enough to overcome the cost advantage of pre-plant applications of anhydrous ammonia (NH3) relative to top-dress applications of either dry or liquid N sources on growing wheat. The objective of this research is to determine if the system is more profitable than conventional methods. Data from on-farm N fertilizer experiments were collected across three years and nine locations in the Southern Plains of the U.S.A. Net returns were calculated for each of eight treatments. The site-specific precision system was competitive economically, but it was not unambiguously superior to the conventional alternatives because it could not overcome the cost advantage of NH3 pre-plant N sources relative to the cost of applying urea-ammonium nitrate (UAN) during the growing season. The value of the precision system is sensitive to the price of UAN relative to the price of NH3.