Emergence and early growth of an epigeal seedling (Daucus carota L.): influence of soil temperature, sowing depth, soil crusting and seed weight

Abstract This study describes and analyses how seed placement and seed weight influence the response of emergence and early growth of carrot seedlings 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 (40–94%) and times from 50% germination to 50% emergence (55–105°Cd) varied widely. Seed weights had a marked influence only in the most extreme conditions. Seedling growth was then analysed in growth chambers at two temperatures (10 and 20°C), for the same two seed weight ranges and different times of growth in the dark. Hypocotyl elongation rates and growth forces decreased when this time increased. Heavy seeds had longer final hypocotyl lengths and greater growth forces, which explained their better emergence from deep sowing and with surface obstacles. Growth after emergence both in the glasshouse and growth chamber was influenced by seed weight and time from germination to emergence: the seedling weight at emergence depended only on initial seed weight; the seedling relative growth rate was not influenced by the initial seed weight, but decreased with increase in time before emergence. This was due to a decrease in cotyledon photosynthetic efficiency. Poor seedbed structure and seed placement control affect not only emergence but also early growth. These results provide basic information for modelling the emergence and early growth of dicotyledon epigeal seedlings.

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