Corn Response to Stand Reduction at Different Vegetative Growth Stages.

Hail storms can reduce corn (Zea mays L.) grain yield in part through stand reduction. However, the crop stage when stand reduction occurs and the pattern of stand reduction in the field may affect the ability of the remaining plants to compensate, and thus the overall yield loss. From 2006 to 2009, field experiments were conducted over 12 site-years in Illinois, Iowa, and Ohio to determine the effect of uniform and random patterns of stand reduction at different vegetative growth stages. Initial corn stands of 88,900 plants ha^-1 were established by overplanting and hand thinning. Stands were then reduced to 44,500, 59,300, and 74,100 plants ha^-1 in both uniform and random patterns at the five, eight, eleven, and fifteen leaf-collar (V5, V8, V11, and V15, respectively) stages. Corn grain yield was affected by the interaction between the crop stage at stand reduction and final plant density, but not by the pattern of stand reduction. When compared to the non-reduced stand of 88,900 plants ha^-1 which yielded 13.7 Mg ha^-1, yield was reduced as the severity of stand reduction increased and as the time of stand reduction was delayed. The rate of yield loss was greatest when stand reduction occurred at the V11 or V15 corn stages, and averaged 8% for every 10,000 plants ha^-1 lost. In comparison, corn grain yield was reduced by 5 and 6% for every 10,000 plants ha^-1 lost at the V5 and V8 stages, respectively. When 50% stand reduction occurred at the V5 and V15 stages, per-plant grain yield of the remaining plants increased by 66 and 37%, respectively. These results indicate that corn plants can partially compensate for loss of their neighbors between the V5 and V15 stages, although their ability to do so is significantly reduced at the later growth stages.