AbstractAn experiment was conducted during the summer of 1975 (June 5 to September 24) on a clayey Oxisol in northwestern Puerto Rico to test the performance of 7 cultivars of corn at 2 different levels of N (67 and 134 kg/ha) at 3 different times of application (all at planting, 1/4 at planting + 3/4 one month after planting, and all one month after planting). There were no significant differences in yields between the 2 levels of N, but there was a significant 5% increase in yield with all N applied postplant in comparison with all preplant. There were also significant differences between grain yield of cultivars. The best grain yields were obtained with Pioneer X- 3068 with more than 8,000 kg/ha at both N levels and times of application. An almost neglected local cultivar, Diente de Caballo, had a high mean yield of 7,387 kg/ha, which was significantly higher than those of the other 5 cultivars. Funk's G-795W and Opaque-2 type Sp 622 were the lowest yielders with about 5,400 and 4,800 kg/ha, respectively. Standard local cultivars (Mayorbela, and two other Opaque-2-Tuxpeño x La Posta and Composite K, hard endosperm) were intermediate in yield with over 6,000 kg/ha. Pioneer X-3068, Diente de Caballo, Tuxpeño X la Posta and Composite K, hard endosperm, produced over 6,000 kg/ha of stover, while Sp 622 produced only about 3,900 kg/ha. Plants of Pioneer X-3068 and Diente de Caballo were the tallest, while those of Sp 622 were the lowest. Plants of Funk's G- 795W had the smallest mean stem diameter. Mean leaf Nat silking was higher for all cultivars in the high N level (134 kg/ha) than in the low N level (67 kg/ha), except in Mayorbela. There were no significant interactions between cultivars, N levels and time of N applications.
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