Determining an Optimum Seeding Rate for Spring Wheat in Northwest Minnesota

In wheat (Triticum aestivum L. emend. Thell.), the seeding rate to maximize grain yield can be derived from the parabolic response curve of grain yield versus number of plants per unit area. Since cultivars genetically differ for yield components, individual cultivars need to be tested at a wide range of seeding rates to determine their optimum seeding rate. Seven Hard Red Spring Wheat (HRSW) cultivars were planted from 1996 to 1998 at two planting dates and six seeding rates. The planting dates were 13 May and 30 May in 1996, 10 May and 28 May in 1997 and 1 May and 22 May in 1998. The seeding rates ranged from 5.8 to 63.1 live seeds per ft2. The optimum seeding rate across all cultivars was 45.0 live seeds per ft2 for the first planting date, which corresponded with an initial plant population of 34.5 plants per ft2. For the second planting date, the optimum seeding rate was 49.1 live seeds per ft2, which corresponded with an initial plant population of 35.9 plants per ft2. A significant interaction between cultivars, seeding rate, and planting date was detected for grain yield in 1996 and 1997, but not in 1998. Producers in northwest Minnesota need to adjust their seeding rates upward from the current practices because the initial plant population to maximize grain yield is 10 to 15% higher for the cultivars included in this study when compared to the standard recommendations. More importantly, based on these results, producers should assume when calculating a seeding rate a stand loss of 20 to 25% rather than the 10 to 15% previously assumed. In addition, individual cultivars differ for the optimum seeding rate and variety-specific recommendations can be made.