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ARS Home » Research » Publications at this Location » Publication #262708
Title: Variable environment and market affects optimal nitrogen management in wheat and cattle production systems

Author
item Zhang, Xunchang
item Mackown, Charles
item Garbrecht, Jurgen
item ZHANG, HAILIN - Oklahoma State University
item EDWARDS, JEFF - Oklahoma State University

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2011
Publication Date: 6/1/2012
Citation: Zhang, X.J., Mackown, C.T., Zhang, H., Edwards, J.T., Garbrecht, J.D. 2012. Variable environment and market affects optimal nitrogen management in wheat and cattle production systems. Agronomy Journal. 104(4):1136-1148.

Interpretive Summary: On average, about 33% of applied fertilizer nitrogen (N) is used by plant for grain production worldwide, and a 1% increase in N use (say from 33% to 34%) could annually save producers 200-400 million dollars worldwide. The N use efficiency can be improved by using computer simulation models to optimize N management. We used a computer simulation model to develop economically optimal N management for wheat (Triticum aestivum L.) and cattle (Bos taurus L.) production for selected climate, soil moisture, and market conditions for the north-central region of Oklahoma. For grain-only wheat, simulation results showed there was a 55% chance that optimal fertilizer N was < 40 kg ha-1 when precipitation during August-February is < 0.3 m, while there was a 90% chance that optimal fertilizer was between 90 and 120 kg ha-1 when precipitation is > 0.4 m. This result strongly supports a split N application strategy with < 45 kg ha-1 applied pre-plant and additional N top dressed in February according to precipitation and grain yield potential. For dual purpose wheat with wet soil at planting, about 20, 60, 80, and 90 kg ha-1 of pre-plant N were needed to maximize live weight gain for stocking densities of 1, 2, 2.5, and 3 heads ha-1, respectively. Net economic returns from wheat and cattle production were maximized at an N rate of 120 kg ha-1. These findings should be useful to farmers to make better decision on N rates based on soil moisture at planting, rainfall amount before February, planned stocking rate, and anticipated seasonal climate.

Technical Abstract: The average efficiency of fertilizer nitrogen (N) in grain production of cereals is about 33% worldwide, and a 1% increase in fertilizer N use efficiency (NUE) could annually save US producers 200-400 million US dollars. Process-based crop simulation models provide a unique opportunity to improve fertilizer NUE by optimizing N and synchronizing N supply with crop demand. We used a computer simulation approach to develop economically optimal N management for wheat (Triticum aestivum L.) and cattle (Bos taurus L.) production for wet, average, and dry years, two initial soil water reserves, and three market conditions. A wheat grazing model was used to optimize fertilizer N for each scenario using optimal planting dates, grazing initiation dates, and stocking densities for the north-central region of Oklahoma, USA. Based on simulated optimal N fertilizer distributions for grain-only wheat, there was a 55% chance that optimal fertilizer N was < 40 kg ha-1 when precipitation during August-February is < 30 cm, while there was a 90% chance that optimal fertilizer was between 90 and 120 kg ha-1 when precipitation is > 40 cm. This result strongly supports a split N application strategy with < 45 kg ha-1 applied pre-plant and additional N top dressed in February according to precipitation and grain yield potential. For dual-purpose wheat (forage + grain) production and an initially wet soil profile, about 20, 60, 80, and 90 kg ha-1 of pre-plant N were needed to maximize live weight gain for stocking densities of 1, 2, 2.5, and 3 heads ha-1, respectively, and about 120 kg N ha-1 to maximize total net economic returns. The yield response to N supply (fertilizer N plus soil residual inorganic N) was adequately simulated in the range of 0-170 kg N ha-1 for grain-only wheat and 0-210 kg N ha-1 for dual-purpose wheat. Overall, the wheat grazing simulation model effectively optimized fertilizer N management for wheat-based enterprises within the aforementioned scenarios for regions with similar physiography and climate as north-central Oklahoma, USA.