Productivity and Nitrogen Use Efficiency of Continuous Corn with Stover Removal.

In the Upper Midwest, there has been limited adoption of conservation tillage systems for continuous corn (Zea mays L.) due to concern about grain yield reductions resulting from large amounts of crop residue and cool, poorly-drained soils. However, stover removal may enhance the competitiveness of conservation tillage systems for continuous corn and may affect optimum N fertilizer rates and N use efficiency (NUE). In the fall of 2008, field experiments were established at two locations in southern Minnesota on clay loam Mollisols to assess the effects of stover removal, tillage system (disk-rip, strip-, and no-tillage), and N fertilization (0, 45, 90, 134, 179, and 224 kg N ha^-1) on continuous corn yield and N use efficiency. Removal of corn stover increased grain yield by 15%, regardless of tillage system, and did not affect the response of grain yield to N fertilization. Stover removal also increased agronomic NUE, especially at ≤ 90 kg N ha^-1, but did not affect physiological NUE. Grain yield increased as tillage intensity increased, but tillage system did not influence agronomic or physiological NUE, or residual soil nitrate after harvest. Stover removal increased fall residual soil nitrate in the 0- to 1.2-m depth by 36 and 42% at the 179 and 224 kg N ha^-1 rates, respectively. These results demonstrate that stover removal in continuous corn can increase grain yield and agronomic NUE, but can lead to higher residual soil nitrate levels when N fertilizer is applied at rates near or above those which are economically optimal for grain yield.