AbstractTwelve corn (Zea mays L.) hybrids and selections were planted three times on the same site in the same year at Isabela, Puerto Rico, according to the following schedule: Nov. 5, 1975 (crop 1); April 21, 1976 (crop 2); and Aug. 13, 1976 (crop 3). Average time to midsilk for the 12 entries was similar in crops 1 and 3 (621 and 6 1.6 days, respectively) but was shorter in crop 2 (59.1 days). Average height to the base of the lowest ear for the 12 entries was 87.1, 106.3, and 99.0 cm for crops 1, 2, and 3, respectively. Average test weight was highest (81.2 kg/hl) in crop 1, decreasing to 72.4 and 55.0 kg/hl in crops 2 and 3, respectively. Average severity of leaf blight, caused by Bipolaris maydis (Nisikado) Shoemaker, was similar in crops 1 and 2. Tne best grain yielder in all three crops was hybrid Pioneer 304 C, with yields of 5,975, 4,103, and 3,729 kg /ha in crops 1, 2, and 3, respectively. The average yield for the 12 entries was 4,598, 3,180, and 2,523 kg/ha in crops 1, 2, and 3, respectively. Nematodes in plots were counted and identified after crop 3 was harvested. The nematode most commonly found in the rhizosphere was Pratytenchus zeae. Plots with Pioneer 304 C, the top yielder, had the second lowest nematode count, 480 per 250 cm3 of soil. Plots with PR-3 and the F1 hybrid PRMo2 x PR-3 had the highest nematode counts, 1040 and 1232 per 250 cm3 of soil,
respectively. Although soil disinfestation might have resulted in higher yields, this study showed that three corn crops grown on the same site during the same year can produce grain yields of more than 13,000 kg/ha (205 bu/acre).
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