EMERGENCE AND EARLY GROWTH OF AN EPIGEAL SEEDLING (DAUCUS-CAROTA L) -INFLUENCE OF SOIL-TEMPERATURE, SOWING DEPTH, SOIL CRUSTING AND SEED WEIGHT

This study describes and analyses how seed placement and seed weight i nfluence the response of emergence and early growth of carrot seedling s to changes in seedbed conditions (temperature and surface structure) . The first experiment was carried out in a glasshouse with different sowing conditions (1, 3 and 5 cm sowing depths, 2 and 5 mm wet or dry crusts) and two seed weight ranges. The final emergence percentages (4 0-94%) and times from 50% germination to 50% emergence (55-105 degrees Cd) varied widely. Seed weights had a marked influence only in the mo st extreme conditions. Seedling growth was then analysed in growth cha mbers at two temperatures (10 and 20 degrees C), for the same two seed weight ranges and different times of growth in the dark Hypocotyl elo ngation rates and growth forces decreased when this time increased. He avy seeds had longer final hypocotyl lengths and greater growth forces , which explained their better emergence from deep sowing and with sur face obstacles. Growth after emergence both in the glasshouse and grow th chamber was influenced by seed weight and time from germination to emergence. the seedling weight at emergence depended only on initial s eed weight; the seedling relative growth rate was not influenced by th e initial seed weight, but decreased with increase in time before emer gence. This was due to a decrease in cotyledon photosynthetic efficien cy. Poor seedbed structure and seed placement control affect not only emergence but also early growth, These results provide basic informati on for modelling the emergence and early growth of dicotyledon epigeal seedlings.