Optimum plant population of bt and non-bt corn in Wisconsin

Bt (Bacillus thuringiensis) corn (Zea mays L.) hybrids resist European corn borer [Ostrinia nubilalis (Hubner)] damage and lodge less' creating interest among growers, agronomists, and seed companies in their yield response to increasing plant population. Corn hybrids with Ill and non-Bt traits were evaluated from 2002 to 2004 across 10 locations in Wisconsin in 76-cm rows at target populations from 61750 to 123 500 plants ha(-1) to (i) determine the agronomic and economic optimum plant population for corn and (ii) identify agronomic and economic optimum plant populations for Bt and non-Bt hybrids. The quadratic model for both grain yield and grower return response to plant population was significant. The maximum yield plant population (MYPP) for Bt and non-Bt corn was 104 500 and 98 800 plants ha(-1), respectively. The overall MYPP for corn was 102 400 plants ha which is 28 300 plants ha more than the current Wisconsin recommendation of 74 100 plants ha Planting corn to the MYPP increased grain yield by 4.2% over the current population recommendation. However, the economically optimum plant population (EOPP) for both Bt and non-Bt corn was 83 800 plants ha(-1). It was concluded that Bt corn hybrids require higher plant populations for maximizing yield potential; however the higher harvest costs related to those greater yields and the higher seed costs associated with attaining those populations resulted in no difference in the EOPP between Bt and non-Bt corn. Plant population recommendations for corn should be near 83 800 plants ha(-1), the point where the EOPP was achieved. Since this recommendation is affected by rising seed and management costs and variable market prices, a periodic evaluation of plant population response for newly released hybrids should be done.