Corn Yield Responses to Plant Height Variability Resulting from Tillage and Crop Rotation Systems in a Long-term Experiment

Tillage and crop rotation system effects on corn (Zea mays L.) growth and development have been studied extensively over the past 30 years, but most studies have principally focused on the effects of tillage and crop rotation on mean corn response parameters such as plant height, grain moisture content, and grain yield. As a result, many agronomists and growers have concluded that instances of lower corn yields in no-till versus conventional tillage systems are due to reduced mean plant heights at critical developmental stages in the growing season. However, mean plant heights may not be accurate morphometric indicators of decreased yields in no-till corn. This study, involving portions of a 30 year long-term tillage and rotation experiment, attempted to determine the effects of early-season plant height variability (expressed as coefficient of variation (CV)) versus mean plant heights on yields of a single corn hybrid planted over a 14 year period. The experiment was conducted from 1981-1994 in north-central Indiana on a Chalmers silty clay loam (i.e., a dark prairie soil). The effects of no-till and moldboard plow tillage systems on mean plant height 8 weeks after planting, plant height variability 8 weeks after planting, and grain yield were examined in both continuous corn and corn-soybean rotations. For 10 of the 14 years, the continuous corn, no-till treatment resulted in significantly lower yields relative to the other 3 treatments. The continuous corn, no-till treatment had lower mean plant heights for 11 out of the 12 years when height data at the 8 week stage were available. Plant height variability was numerically greatest for the continuous corn, no-till treatment in 7 out of 12 years of the study; but only significantly higher than one or all other treatments in 5 of those years. Annual yield decreased approximately 122 kg ha for each 1% increase in height variability for the no-till plus plow treatment combination in continuous corn. Examination of cumulative precipitation effects revealed that height CV in no-till continuous corn was independent of rainfall quantity accumulated 4 weeks preto 4 weeks postplanting, but decreased by 0.30% for each 1 cm increase in rainfall for all other treatments. Weather and other non-treatment factors may also have influenced the degree to which final yields were affected by height CV relative to mean height earlier in the growing season. Nevertheless, our results suggest that increased plant height variability is at least as plausible a factor as lower mean plant heights in being associated with grain yield declines that are common in continuous corn and no-till production systems.