Planted acreage reached a high in 1981 with 14.4 million acres planted for all purposes and has hovered near 12.5 million acres since the early 1990s. Table 1 shows the trend in corn acreage, yield, and production since 1900 as reported by the Iowa Agricultural Statistics Office. Total production and average yield per acre records were set during the 1994 season. • Corn yields have trended upward over the past 40 years. Considerable year-to-year variation indicates that the weather has a major influence on corn production. Many factors are responsible for these yield increases, including better hybrids, more efficient use of fertilizers, better pest management (weeds, insects, and diseases), and better management overall. Producer-controlled management factors (row spacing, planting dates, planting depth, plant densities, and replant options) that affect yield will be addressed in this guide.