CHAPTER 1: GENERAL INTRODUCTION Starter fertilizer (SF) often increases early-season growth and reduces time to maturity for corn (Zea mays L.) (Bermudez and Mallarino, 2002; Bullock et al., 1993). Effects of starter fertilizer on corn grain yield have varied with some researchers finding that hybrids responded differently to starter fertilizer application (Gordon et al., 1997), while others have found that hybrids responded similarly (Buah et al., 1999). Agronomists that found differences in hybrids response to starter fertilizer also found that the root systems of hybrids that responded to SF were generally smaller than those that did not respond to SF (Gordon and Pierzynski, 2006; Rhoads and Wright, 1998). Many farmers in central Iowa abandoned SF applications due to the cost and weight of placement units, costs associated with handling the fertilizer, and lack of grain yield responses in their fields. Plant-to-plant variability in corn growth and grain yield is often associated with reduced grain yield (Muldoon and Daynard, 1981). Increased variability in growth is often associated with plant spacing standard deviation, however, grain yield responses to plant spacing uniformity are variable. While some researchers have found that reduced plant spacing standard deviation increases yield (Nielson, 2001), others have found that plant spacing is not important in grain yield (Liu et al., 2004b). Variability in emergence is important in final yield and agronomists have developed recommendations for replanting based on variation in emergence within a field (Liu et al., 2004a; Nafziger et al., 1991). Uniformity in seeding depth and soil factors such as moisture, temperature, residue cover, and crusting often affect uniformity in plant emergence (Alessi and Power, 1971; Nafziger et al., 1991).