Adoption of variable seeding rates has increased dramatically in recent years due to ability and feasibility of determining soil and topographic variability within fields. This research explores soil and topographic attribute interactions with seeding rate and the effect they have on corn yield, yield components, and grain composition. Experimental treatments included five seeding rates (61,750; 74,100; 86,450; 98,800; and 111,150 seeds ha-1) in a randomized complete block design in three central Iowa fields from 2012 to 2014. Soil samples were analyzed for available P, exchangeable K, pH, soil organic matter, cation exchange capacity, and texture. Topographic data was determined with Light Detection and Ranging included elevation, slope, aspect, and curvature.

Seeding rate optimization resulted in seeding rate by attribute interactions: four site-years had a single seeding rate interaction (pH, in-field elevation, or curvature) and one site-year had three seeding rate interactions (pH, CEC, and SOM). When seeding rate optimization was performed, three site-years resulted in seeding rate responses warranting variable rate seeding.

When seeding rates increased, kernel rows ear-1, kernel number ear-1, and kernel weight decreased. Kernel number ear-1 was influenced by available P and pH, whereas kernel weight was influenced by available P, pH, slope, and in-field elevation. Zipper ears and plant barrenness were more prevalent as seeding rates increased and when rainfall was limiting. While seeding rate and individual soil and topographic attributes influenced yield components, interactions with seeding rate rarely influenced yield components.

Grain composition was not affected by seeding rate. Seeding rate interactions with soil and topographic attributes infrequently influenced grain composition. Grain yield always explained more of the variation in grain composition than the selected soil and topographic attributes. Available P, exchangeable K, and in-field elevation did influence individual grain composition parameters.

Corn seeding rate is an important determining factor for grain yield and yield components, however, it did not influence grain composition. Seeding rate along with its interactions with soil and topographic attributes may be used for explaining yield components on a field by field and year to year basis.