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This experiment was conducted to find out the water holding properties and optimal particle size of decomposed rice hull as the substrate for raising vegetable seedlings. Decomposed rice hull was screened to four sizes, under 0.85, 0.18∼1.00, 1.00∼1.41, and over 1.41 ㎜. Hot pepper, tomato, cucumber, and leaf lettuce were sown and raised on 128, 72, 72, and 200-cell plug trays, respectively, filled with the decomposed rice hull substrate of different particle sizes. The mixture of 70% sphagnum peat moss and 30% perlite (v/v) was used as the control substrate. Nutrient solution composed of N-P-K-Ca-Mg = 8.0-2.4-2.4-4.8-1.6 me·L^(-1) was applied every 1∼3 days according to crops and growth stages. Water content of decomposed expanded rice hull was 1015´% higher than that of fresh expanded rice hull under 160 ㎪ moisture tension. When the particle size of decomposed expanded rice hull was less than 0.85 ㎜, water content was more than that of sphagnum peat moss in over 10 ㎪ moisture tension, respectively. The growth of hot pepper, tomato, cucumber, and lettuce seedlings was the greatest in the substrate of particle size smaller than 0.85 ㎜. Substrate pH was more stable and EC was higher in the substrate with smaller particle sizes than that with larger particle sizes.
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