replicationss nested within dates) became the appropriate error term to

evaluate the effects of planting date on yield components. However, the

whole-block error term did not have sufficient degrees of freedom (<6)

to constitute a valid F test (Gomez and Gomez, 1984; Montgomery, 1984).

Therefore, the whole-block error term was pooled with either the three-

way interaction term, or the subplot pooled-error term, on the condition

that the newly added error term was not different from the whole-block

error term at the 75% level of probability.

 Differences in environmental conditions during the two time

periods when the crops were in the field are impossible to assess. One

of the more obvious differences was in the quantity and distribution of

rainfall (Fig. 5-1). Seedlings in the first-planting period experienced

considerable wilting due to the slow-starting rainy season. Seedlings

of the second-planting had frequent early rainfall and showed no

wilting. Both plantings experienced frequent mid- and late-season

rains; however, the second planting received more total water because

the rainy season peaked in August and September, after the first

planting had been harvested.

 The differential effects of climatic factors on grain and stover

yields may be attributed to the seasonal partitioning of plant

photosynthetic and mineral resources into different yield components.

Corn plants continue to increase in total dry-matter accumulation

throughout the season, until near harvest. However, once past silking,

most of the increase is due to grain filling. The dry-matter content of

other plant components remains relatively constant during this period

(Fig. 5-2)(Hanway, 1962). Tropical maize, in general, including the