SOWING DATE AND MAIZE PRODUCTIVITY .1. CROP GROWTH AND DRY-MATTER PARTITIONING

Changes in the environment that are associated with different sowing dates can be expected to alter maize (Zea mays L.) growth and development in temperate regions. The objective of this work was to study the effect of sowing date on growth and dry matter partitioning of maize crops grown without water and nutrients limitations. A commercial hybrid (DK636) was grown in the field at four sowing dates (mid-September through mid-December) for 3 yr. Delays in sowing date hastened development between seedling emergence and silking, decreasing cumulative incident radiation on the crop during the vegetative period. However, late sowings increased crop growth rate during the vegetative period because of high radiation use efficiency and higher percent radiation interception. Conversely, late sowings decreased crop growth rate during grain filling because of low radiation use efficiency and low incident radiation. Late sowings affected grain yield by decreasing kernel weight and kernel number per unit area. Moreover, maize subject to these treatments accumulated more dry matter before silking than from silking to physiological maturity, while the inverse was true for early sowings. Thus, delaying the sowing date strongly decreased dry matter partitioning to grain.