Combined effect of rock dust and vermicompost on dahlia (Dahlia pinnata) plant growth and development

A mixture of rock dust (RD) and vermicompost (VC) provides a nutrient-rich and microbiologically-active natural growing medium for plants. However, their complementary effect is understudied. A greenhouse experiment was performed to determine the combined effect of RD and VC on dahlia (Dahlia pinnata ‘Cobequid Celestial Star’) plant growth, flower production and tuberous root yield. The experimental treatments were: Promix BX™ alone (control), 20 g RD + 22.5 g VC, 20 g RD + 45 g VC, 40 g RD + 22.5 g VC, 20 g RD alone and 45 g VC alone. The 20 g RD + 45 g VC and the 45 g VC alone significantly (P<0.01) increased anthocyanin contents of the dahlia plants relative to the control. Chlorophyll content and plant height did not vary statistically (P>0.05), but were slightly higher in the 20 g RD+45 g VC treated plants. However, photosynthetic activities were significantly (P<0.05) highest in the 45 g VC alone treated plants. Tuberous root diameter was significantly (P<0.01) highest in the 20 g RD alone and the 45 g VC alone treatments, and the least in the 20 g RD+45 g VC treatment. Indices of photosynthetic efficiency were consistently and significantly (P<0.05) highest in the 45 g VC alone but were significantly (P<0.05) reduced by the control and the 40 g RD + 22.5 g VC. Flower production and flower bud opening were significantly (P<0.05) reduced by the control and the 20 g RD + 22.5 g VC but were significantly (P<0.05) increased by treatments 20 g RD + 45 g VC and the 45 g VC alone. Thus, the present study suggested that application of vermicompost with (20 g RD + 45 g VC) or without (45 g VC alone) rock dust improved plant growth and flower production. The effectiveness of vermicompost can be boosted by rock dust. Future studies should consider effects of moisture content and mycorrhizal activities.