Comparison of Nitrogen Management Zone Delineation Methods for Corn Grain Yield

It is important for today's farmer to manage his fields efficiently to maximize economic return and minimize environmental impacts. Managing agricultural inputs based on spatial variability in a field may help to achieve these goals. The objective of this study was to develop and compare different N management zone delineation methods and investigate the effect that variable N fertilization directed by these zones had on corn (Zea mays L.) grain yield over 4 yr. The zone delineation methods were based on: (i) supervised classification of bare soil color; (ii) cluster analysis of soil N, apparent electrical conductivity (EC a ), and 1 yr of yield data; or (iii) a summation of standardized EC a , elevation, and 5 yr of yield data. The different delineation methods resulted in relatively similar zone patterns. Applied N rates were mostly affected by varying yield goals due to low variability of soil test N between zones. The effect of zone method on yield was inconsistent over the study period, with the soil color zone yields corresponding best to hypothesized productivity potential. The uniform treatment yields were not significantly different than yields from most of the N management zones. Increases in applied N for management zone treatments resulted in small yet not statistically significant yield increases in most years, with economic benefits over the uniform treatment observed in 2 yr. Yield was affected by adverse weather conditions in 2 yr, resulting in significant increases in subsurface soil N and reduced economic benefits of zone management versus conventional management.