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Predictive Equations for Maize Inbred Emergence¹

Accurate estimates of maize (Zea mays L.) inbred seedling emergence are currently unavailable. Inbred planting rates, therefore, are adjusted by using criteria normally applied to hybrid seed.

In this study, temperature-dependent predictive equations that would assist the seedsman in estimating planting rates, to obtain acceptable stands during the planting season, were developed for 15 maize inbreds. The equations were developed on the basis of the multiple linear regression of field emergence on standard germination and days to 50% emergence for all dates of planting. The slopes of the regressions differed among inbreds.

The equations are applied by calculating the days to 50% emergence on the basis of the known number of growing-degree units that a particular inbred would require to reach 50% emergence. Past meteorological data would be used to estimate the probable number of days required to accumulate the growing-degree units for any planting date.

It was assumed initially that growing-degree units to 50% emergence would remain constant while days to 50% emergence could vary for each inbred line and would vary for different field plantings. However, growing-degree units to 50% emergence for lots within inbred lines, field plantings, and the field plantings by inbred line interactions were all significant at the 0.01 probability level.

Although the variability in growing-degree units to 50% emergence indicates that we have not yet arrived at a final answer, the predictive equations show considerable promise in reducing the subjectivity presently involved in determining planting rates. The refinement and ultimate application of these equations, as superior predictors of field emergence, will require testing under actual production conditions and a more complete understanding of temperature effects, not accounted for in the formula used to compute growing-degree units.

Key Words: Cold test • Growing-degree units • Stand establishment • Zea mays L.

² Graduate research assistant and professor, Seed Science Center, Iowa State Univ., Ames, IA 50011.

Received for publication May 16, 1979.

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