Evaluation of nitrogen management strategies and comparison of cool-season perennial forage systems

Chapter I: Nitrogen management plays a crucial role in optimizing winter wheat production in the Southern Great Plains. This study evaluates the economic performance of two nitrogen management systems: the conventional farmer practice (CS) and the nitrogen-rich strip system (NRS). Using the DSSAT-CERES-Wheat model, integrated with a radiative transfer model and a nitrogen fertilization optimization algorithm, the study simulated wheat yields and economic outcomes under each system over multiple growing seasons. The CS system applies nitrogen either pre-plant or in split applications at a fixed rate, while the NRS system dynamically adjusts mid-season nitrogen rates based on real-time crop data. Although CS yields are marginally higher, the NRS reduces nitrogen use by an average of 127 kg/ha, saving $90/ha and enhancing nitrogen efficiency. The NRS also yields higher net returns with an average value of information of $19 ha⁻¹. Chapter II: Nitrogen (N) carryover is an important factor influencing the efficiency and economics of nitrogen management in winter wheat production systems. This study evaluates the economic value of managing nitrogen carryover across three cropping systems in the Southern Great Plains: wheat-fallow, wheat-soybean, and wheat-sorghum. Using the DSSAT crop growth model, the study simulated crop growth, yield, and nitrogen dynamics over 30 years. The analysis incorporates a dynamic programming approach to determine economically optimal nitrogen application rates that maximize the net present value of returns. Managing nitrogen carryover reduced nitrogen application rates by up to 114 lb/ac annually in the WSG system, with savings ranging between $32/ac and $43/ac annually across systems. Chapter III: Winter wheat is an important forage for livestock in the Southern Great Plains. However, rising input costs and changing climate conditions have prompted the search for alternative feed sources. This 5-year grazing and economic study compared winter wheat with two varieties of summer-dormant tall fescue under different management practices, including nitrogen fertilizer application and interseeding with alfalfa. The research, conducted over five years in Oklahoma, found that although winter wheat produced higher livestock weight gains and revenue, the tall fescue systems had significantly lower costs. As a result, the net returns from the perennial systems were similar to those from winter wheat, suggesting that these perennials could be a viable, cost-effective alternative for producers looking to reduce livestock feed expenses while maintaining profitability.