Using Low Seeding Rates to Simulate Thin Wheat Stands to Make Replanting Decisions.

Plant stands are one of the major components of grain yield in wheat. Occasionally, farmers find they have less-than-ideal plant stands in their wheat fields to maximize grain yield. Farmers are faced with the decision to either leave the stand, replant, interseed to increase the plant stand, or to destroy the wheat crop and plant a summer crop the following spring. The objective was to find plant stands at which yield could be maintained as close to those using the optimal planting date and seeding rate. The experiment consisted of seeding rates planted at an optimal planting time and a later, interseeded planting date, over eight location-years near Manhattan (2010, 2011, and 2012), Partridge (2011 and 2012), and Belleville (2011, 2012, and 2013). The seeding rates for the optimal planting date were 11.2, 22.4, 33.6, 44.8, and 67.3 kg ha^-1, planted in late September to early October.  The interseeded treatments were 11.2, 22.4, 33.6, 44.8 kg ha^-1, planted at the optimal date, then interseeded 3-4 weeks later with 100.9 kg ha^-1, plus a 100.9 kg ha^-1 treatment as a late-planted control. There were 10 seeding rate-interseeding treatments in a one-way randomized complete block design with four replications. Independent of year or location, an evenly spaced stand at the optimal planting date, equivalent to at least 33.6 kg ha^-1 could achieve yields within 15% of the 67.3 kg ha^-1 rate. However, late planting at 100.9 kg ha^-1 resulted in lower yields. Interseeding when stands are equivalent to less than 33.6 kg ha^-1 could raise yields significantly over the non-interseeded stands. Our results suggest that interseeding is beneficial when plant stands are equivalent to 11.2 and 22.4 kg ha^-1 seeding rates due to less inter-plant competition than at the 33.6 and 44.8 kg ha^-1 rates.