Effect of Plant Spacing on Phenological Development of Early and Midseason Corn Hybrids in a Semiarid Region 1

Within recent years, early maturing hybrids ( Zea mays L.) (less than 70 days from seeding to silking) have become commercially available. This study at Mandan, N. Dak. was conducted to evaluate phenological differences between early and midseason maturing hybrids under semiarid conditions. Hybrids with 68 and 85‐day relative maturity were grown at plant populations of 20, 30, 40, 60, and 74 thousand plants/ha in 50 and 100‐cm spaced rows for 3 years. The 20, 40, and 74 thousand‐plant populations were sampled at intervals of 2 weeks in 1968 and 1969 and 3 weeks in 1970 to measure phenological development of leaf area and weights of stalks, leaves, and ears. Leaf area index during midseason was generally highest for the highest population and for the later maturing hybrids. Likewise dry weights of leaves and stalks, but not necessarily of ears, were usually highest for the 85‐day hybrid and for the higher populations. Particularly in drier years the 68‐day hybrid silked I to 2 weeks earlier than the 85‐day hybrid, providing more time before late summer drought or frost for grain filling. Treatments that resulted in less than about a 7‐week growing period after silking generally produced immature grain. Correlations between leaf area duration and total plant and grain yields were positive when water stress was not severe, but negative when water stress was severe. Higher populations fixed the greatest percentage of solar energy, as indicated by dry matter production. Row spacing generally had little or no effect upon the development and yield of the plant parts measured for either hybrid. Results indicate that early maturing hybrids are generally adapted to semiarid agriculture.