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Transplanted maize (Zea mays) for grain production in southern England. II. Effects of planting date, transplant age at planting and cultivar on growth, development and harvest index

Maize seedlings (cultivars Bastion, Ace, Anko and Mirna) were raised for 15, 30 or 45 days in a glasshouse and planted in the field between early May and mid-June in 1989 and 1990, at 10 plants/m2. Samples of transplants and direct-seeded crops of the same cultivars were taken at regular intervals throughout the growing season for growth analyses. In both years, the 15-day-old transplants established more rapidly in the field than older transplants, and the patterns of leaf production of these young transplants were similar to those of direct-seeded maize. Transplants flowered earlier than direct-seeded maize from the same planting date. At most harvests, transplants showed significantly higher dry weights than their direct-seeded counterparts, and May-planted maize had significantly higher dry weights than June-planted crops, while cultivar effects were small. Final biomass yields were consistently higher in 1989 (17 t/ha) than in 1990 (11 t/ha). In both seasons, particularly in 1990, there was a trend for a lower harvest index in direct-seeded maize which reflected its immaturity at final harvest. The lowest harvest index (0·07) in 1990 was recorded for direct-seeded maize of the late cultivar, Mirna (June planting), the highest harvest index (0·65) for 30-day-old Mirna transplants (May-planted). A comparison of the experienced effective temperature sums during the vegetative, reproductive and grain-filling phases suggested that the transplant nursery period provides an advancement in thermal time which can affect grain-filling and crop maturity. Year to year variation in climate seems to be of primary importance for yield advantages of transplanted over direct-seeded maize.