Influence of pre-planting application of dolomite at various rates in coir-dust containing root media on the growth of red-leaf lettuce

This research was conducted to evaluate various levels of dolomitic lime incorporated as pre-planting fertilizers on the growth of red-leaf lettuce. To achieve this, three root media were formulated by mixing coir dust with expanded rice hull (CD+ERH, 8:2, v/v), carbonized rice hull (CD+CRH, 6:4, v/v), and ground pine bark (CD+GRPB, 6:4, v/v). During formulation, equal amounts of essential nutrients, except dolomitic lime, were incorporated into all root media and the levels of dolomitic lime were varied from 0 to 7.5 g L -1 at 1.5 g increments. Seedlings of red-leaf lettuces at the 3rd leaf stage were transplanted into each medium treatment. Crop growths were measured 5 weeks after transplant and soil solutions were collected every week and analyzed for pH, EC, and nutrient concentrations. The treatments showing the heaviest fresh and dry weights in CD+ERH, CD+CRH, and CD+GRPB were 4.5 g, 4.5 g, and 7.5 g L -1 of dolomite, respectively. The pHs of three root media yielding the highest crop growths were in the ranges of 6.4 to 7.1. These ECs in CD+CRH medium were around 1.0 dS m -1 higher than those of CD+ERH and CD+GRPB when application rates of dolomitic lime were equal. K⁺ concentrations were higher than Ca +2 and Mg +2 concentrations until week 2 in three root media. But Ca +2 and Mg +2 concentrations were higher than K⁺ concentrations after week 3 in all root media. The concentrations of PO₄-3 in all root media got abruptly lower until week 2. These results indicate that appropriate levels of dolomitic lime, as pre-planting nutrient charge fertilizers in CD+ERH and CD+GRPB media, are 4.5 and 7.5 g L -1 , respectively.