This research was conducted to develop the fertilization program in root media containing coir-dust used in plant factory. Based on previous studies, coir-dust (CD) was mixed with expanded rice hull (ERH) to the ratio of 8:2 (v/v; CD+ERH), carbonized rice hull (CRH) to 6:4 (v/v; CD+CRH), and ground and aged pine bark (GAPB) to 8:2 (v/v, CD+GAPB).
To achieve the research purpose, various rates of dolomitic lime stone and fused superphosphate were incorporated during the formulation of root media and the influence on growth of red lettuce and changes of chemical properties in soil solution of root media were analysed. The influence of compositions and concentrations of post-planting fertilizer solution on growth of red lraf lettuce and changes in chemical properties in soil solution of root mediawere also analysed .
In the experiment of pre-planting fertilization, red leaf lettuces were transplanted into 300mL pot filled with root media containing various levels of dolomitic lime or fused superphosphate. Then their effects on growth of crops and changes of chemical properties in soil solution of root media were analysed. The proper fertilization levels (g?L-1) of dolomitic lime in CD+ERH, CD+CRH and CD+GAPB media were 7.5, 4.5, and 7.5 and those of fused superphosphate were 6.0, 4.5, and 6.0. The crops grew well in these treatments. The concentration of Ca and SO42- in CD+CRH medium were maintained lower and higher levels than those in other two root media. This is considered to improper for cultivating of red leaf lettuce. Because dolomitic lime and fused superphosphate contain a lot of Ca and Mg, the incorporation rates of the two fertilizers were adjusted to optimum level, such as 75% (4.5g?L-1/5.63g?L-1) and 50% (3.38g?L-1/3.0g?L-1) of the highest growth treatment in CD+ERH and CD+GAPB, respectively.
The experiment of post-planting fertilization was also conducted to investigate the influence of three kinds of fertilizer solution such as acidic (AF), neutral (NF), and alkaline fertilizer (BF) on growth of red leaf lettuce. The fertilizer solutions were controlled to 100 or 200mg?L-1 based on nitrogen concentration and applied once a week to the root media which contained pre-planting fertilizers. The growth investigation was conducted 7 weeks after transplant and soil solution analysis conducted in every two weeks. Nutrients concentrations and ECs in soil solution were higher in the treatments of 200mg?L-1 than those of 100mg?L-1. The soil solution pHs in the treatments of BF200 and AF200 were the highest and the lowest among treatments tested. The pH in the treatment of BF200 in CD+ERH medium was slightly higher than optimum range (of 5.6 to 6.2), but the concentrations of nutrients in soil solution of root medium were in the optimum ranges for cultivation of red leaf lettuce. The chemical properties in the soil soultion of CD+GAPB medium were in the optimum ranger and growth measurements showed the highest among treatments tested when crops were fertigated with AF200.