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This article in AJ

  1. Vol. 71 No. 4, p. 577-580
    Received: Sept 5, 1978

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Harvest Index of Corn Affected by Population Density, Maturity Rating, and Environment1

  1. Richard L. DeLougherty and
  2. R. Kent Crookston2



Harvest index (HI) is one of the indices currently used to evaluate a crop's partitioning efficiency. The objective of this study was to determine how the HI of fieldgrown corn (Zea mays L.) was affected by changes in population density and relative maturity (RM) of hybrids. Plots were established at three locations. Ten hybrids (two from each of five RM groups) were grown at five population densities at each location. The Minnesota maturity groups represented were 75, 90, 105, 120, and 135 RM. Populations were 12.5, 25, 50, 100, and 200 thousand plants/ha. Substantially different environments (drought vs. normal) developed among the locations during the study. This provided an opportunity to also observe the effect of environment on HI.

The adapted hybrids (105 RM) planted at a normal production density (50,000 plants/ha) had an average HI of 0.39 (range = 0.32 to 0.47) over all environments. At each location, the maximum HI value was 0.50. As plants encountered increasing stress, they partitioned less and less dry matter into grain, eventually producing only stover.

Increasing population density resulted in significant decreases in HI at all locations. Differences in RM did not consistently affect HI, although the latest maturing hybrids did have decreased indices. The HI of corn appeared to be affected more by environment than by either population density or relative maturity. Harvest index and grain yield exhibited high positive correlations in the stress environment (r = 0.96), but were weakly correlated in the nonstress environment (r = 0.28). Also, harvest indices obtained in one environment had no predictable relationship to grain yields in a different environment. We thus conclude that population density, and especially environment, must be taken into consideration when evaluating HI information.

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