Effect of Physical Properties of Medium and Its Water Distribution on Uniform Emergence of Tomato Plug Seedlings

Abstract

To improve the uniformity of emergence, the effect of the physical properties of a medium on the emergence of tomato was investigated. In experiment 1, tomato ‘CF momotaro york’ was sown in plug trays with 4 different medium conditions: bulk densities of a commercial medium made from mainly peat moss of 0.12 (PM/L) and 0.15 (PM/H), and bulk densities of granular rockwool of 0.14 (RW/L) and 0.28 (RW/H). When the plug trays were irrigated with different amounts of water, pF showed emergence rates at 4 days after sowing as follows: PM/L, 1.53; PM/H, 1.48; RW/L, 1.37; and RW/H, 1.58. In experiment 2, the seeds were sown in petri dishes at a depth of 5 mm in the same media as in experiment 1. The range of pF exceeding 90% of the germination rate at 72 h after sowing was: PM/L, 1.23~3.06; PM/H, 1.17~3.20; RW/L, 0.85~1.46; and RW/H, 1.40~1.87. In experiment 3, the water distribution in cells of plug trays with the 4 different medium conditions and different irrigation amounts was investigated. Under all conditions, pF of the top layer (depth of 0~1 cm) did not change between 1 and 48 h after irrigation. pF of the top layer in PM/L and RW/L stayed in a range with a germination rate exceeding 90% in experiment 2 regardless of the irrigation amount. The range of pF in cells 48 h after irrigation in experiment 3, corresponding to the maximum emergence rate in experiment 1, was: PM/L, 1.47~1.65; PM/H, 1.32~1.64; RW/L, 1.07~1.35. Water distribution in the medium was, therefore, necessary for improving the emergence rate at 4 days after sowing. pF in cells should be kept within the range of 1.4~1.6 to achieve a high germination rate.