develop a qualitative understanding of field-crop behavior where more

determinate methods (irrigation) are unavailable (Frey, 1981). Overall,

water requirements increase with planting densities. In this field

study, the higher plant densities yielded more grain, stover, N, P, K,

and Ca than the lower plant densities (Tables 5-6 and 5-8). The higher

densities and consequent greater demand on soil moisture did not induce

sufficient stress to affect yield components. However, superior yield

production by all of the fertilized treatments (irrespective of the

density) over the unfertilized control is sufficient evidence to support

the hypotheses that ambient soil fertility and not water availability

limited production of non- or minimally-fertilized plants for this soil.

The larger grain and stover yields of the fertilized treatments versus

those for the non-fertilized controls resulted from much larger plants,

which would have required larger quantities of soil water.

 The historical rainfall-distribution pattern for this area

 suggests that moisture stress would most likely occur early in the

 growing season. Early-season water stress has been shown to be less

 detrimental to eventual grain yields than stress during silking or grain

 filling (Denmead and Shaw, 1960; Claassen and Shaw, 1970; Grant et al.,

 1989). The need to replant part of this experiment was most likely due

 to the infrequent occurrence of rainfall during a 4-wk drought following

 a seemingly normal to slightly-wetter-than-normal start of the rainy

 season. The early-season stress experienced by the plants in the first

 crop-growth period was insufficient to decrease grain yield for the

 higher densities relative to the lower densities.

 The insignificant planting-date by density interaction indicated