Nitrogen (N) fertility management is important when producing any grain crop. While the N requirements of common grain crops like corn and wheat have been studied extensively, the N required to produce a high-yielding KernzaTM crop is unknown. Furthermore, maintenance of soil N over the life of a perennial stand will likely be important for maintaining yields throughout the life of the stand. However, as Kernza will be used and viewed as a sustainable crop with positive environmental impacts, it is important to not overapply N fertilizer to Kernza stands. The N rate that optimizes yields without excessive N loss from the system must be identified.
To identify the agronomically optimum N rate (AONR), Kernza grain yields across N fertilization rates ranging from 0 to 180 lb/acre, applied in the form of urea, were measured at five sites throughout the state of Minnesota. Results indicate that Kernza yields were greatest (858 lb/acre) in the first production year following fertilization, at AONRs of 55 to 85 lb N/acre. Nitrogen rates above 85 lb/acre generally resulted in lodging, which decreased Kernza grain yields and made harvest more difficult. Kernza grain yields tend to decline with the life of the stand, and declined by about 40% following the second year of production.
These ranges are notably lower than N requirements for wheat and corn, and Kernza is a crop with high N uptake efficiency potential. However, N fertilizer applications must be made with the goal of optimizing grain yields without resulting in harmful nitrate leaching from the system. Research is being conducted to further refine perennial grain N requirements in later years of the stand.