Developmental Morphology of Dent Corn and Popcorn with Respect to Growth Staging and Crop Growth Models

Crop growth staging and developmental modeling (using regression analysis) requires a series of easily understood and documented field descriptives plus a continuous numerical analogue capable of generating data which conform with the underlying assumptions of regression analysis. One numeric phenological key and two mixed phenological keys combining alphabetic and numeric codes are presently used within the U.S. Corn Belt to describe and model the growth and development of dent corn and sweet corn (Zea mays L.). With respect to developing crop growth regression models, the phenology of popcorn has neither been adequately described nor compared with its assumed analogue, dent corn. The purpose of this research was to (i) document the phenology of popcorn, (ii) evaluate the suitability for popcorn of three commonly used phenological keys developed for dent corn, and (iii) if necessary, develop a universal set of phenological field descriptives and a continuous numeric analogue appropriate to developing corn regression growth models. One locally adapted dent corn cultivar (B73 × Mo17) and three differently maturing popcorn cultivars (P410, P609, and Iopop 12) were evaluated for three seasons (1982–1984) across three planting dates at one location in eastern Nebraska at the University of Nebraska Field Laboratory near Mead in Saunders County. None of the phenological keys tested were completely suitable for describing or modeling (using regression analysis), or both, the phenologies of dent corn and popcorn materials, which displayed contrasting morphological characteristics associated with leaf development, leaf number, grain type, and grain development. The universal phenological key and numeric analogue described in this article was therefore developed for modeling the phenology of genetically diverse cultivars grown across a range of environments.