Increasing Seeding Rates and Nitrogen Rates for Irrigated Corn - Practical Considerations.

The popular press has been inundated with stories of record corn yields across the country in small “garden” blocks with producers asking how they can accomplish this on their farm and in their growing conditions. Research in producer fields in the 2000’s in the Mississippi Delta found significantly higher grain yields as seeding rates increased from 25,000 to 40,000 plants/acre (25K to 40K) on 38-in bedded rows in a twin-row (TR) system. On-farm research evaluated both nitrogen (N) rates and seeding rates with large-scale plots. No yield plateau was established with increased seeding rates up to 40 K/acre. In 2017, a multi-year study was initiated at Stoneville, MS to evaluate higher seeding rates (25K, 35K,45K, 55K and 65K/acre in both single-row (SR) and TR planting systems. Three N rates were selected (240, 280, and 320 lb N/acre) for evaluation with 120 lb N/acre applied near at planting and the remainder as sidedressed applications (SDN) or at tasseling. All treatment in the 2x5x3 modified factorial were replicated six times. Cultural practices were held constant throughout the growing season with irrigation applied as needed depending upon the growing season. The center two rows of each 4-row plot was harvested with a commercial combine modified for plot harvest with a grad sample collected to determine harvest moisture, bushel test weight and Seed Index (100-seed weight). Corn grain yields were significantly affected by increased seeding rates but not by increased N rates. In most years, 35K and 45K seeding rates produced the best yields when averaged across N rates and planting patterns. There were significant differences, depending on the year, between planting patterns. In 2017 and 2019, SR grain yields were 5-8 bu/acre higher than TR. However, in 2018, TR grain yields were 25 bu/acre higher than SR.