Effect of Plant Density on Yield of Inbred Lines and Single Crosses of Maize (Zea Mays L.)1

Grain yields of seven single crosses and their component inbred lines were examined at populations of 37,000, 62,000, and 86,000 plants/ha. Inbreds as a group were more population‐responsive than hybrids. Thus, increasing the population from 37,000 to 86,000 plants/ha raised mean inbred yields 48% and mean hybrids yields 37% in one experiment, and 54 and 43%, respectively, in a second experiment. At 86,000 plants/ha one inbred in the first experiment yielded as much as the 37,000 rate of the single cross in which it appeared. The highest individual inbred yield observed in these studies was 62.2 q/ha at 62,000 plants/ha. The first population increment increased yields considerably more than did the second increment. Grain yield heterosis was observed when hybrids and inbreds were compared at equivalent leaf area indexes at silking time. Large differences in grain‐producing efficiency per unit of leaf area were observed among the inbreds, but not even the highest.yielding inbreds were as efficient as any of the hybrids.