2018 ASHS Annual Conference

This study was conducted to investigate influences of the aging of coir dust used as a root substrate for growing tomato and hot pepper seedlings in plug trays. The raw coir dust was placed in the greenhouse and moistened with ground water and turned over once in every two weeks. At each time of moistening and mixing, the aging coir dust was characterized for its physical and chemical properties while being used as root substrate for seedling culture. The percentage of substrate particles in 0.355 mm to 1.4 mm sizes increased as they become aged in comparison to the raw coir dust. The total porosity and air-filled porosity of aging coir dust decreased until week 12 and then increased until week 24 of aging, showing a quadratic response curve. However, container capacity of the root substrate increased until week 12 and then remained unchanged. The pH of the root substrate changed from 5.04 at week 0 to 6.0 at week 4 and remained in the range of 5.6 to 6.0. The electrical conductance (EC) changed from 9.19 dS·m^-1 for non-aged coir dust to 1.8 dS·m^-1 for aged coir dust after 4 weeks. The root substrate concentrations of major cations (K⁺, Ca²⁺, Mg²⁺) and anions (Cl^-, PO₄^-3, SO₄^2-) decreased until week 4 of coir dust aging treatment. Although ammonium form of nitrogen (NH₄⁺-N) and nitrate form of nitrogen (NO₃^--N) decreased during the early stages of coir dust aging, NH₄⁺-N concentrations stayed in the range of 30 to 60 mgL^-1 after week 4, while NO₃^--N started to increase after week 8. When grown for 4 weeks, the fresh weight of tomato seedlings increased linearly as the aging time for coir dust used in the root substrate increased. The relationship between the fresh weight of hot pepper seedlings and the coir dust aging period showed a quadratic response when determined for 5 weeks of culture.