Department of Horticultural Sciences, Chungnam National University1
Department of Biosystems Engineering, Chungbuk National University2
This research was conducted to investigate the influence of various levels of fused superphosphate as pre-planting fertilizer on the growth of red-leaf lettuce and changes in the chemical properties of the soil solution in three root media, namely coir-dust plus expanded rice hull (8:2, v/v; CD+ERH), carbonized rice hull (6:4; CD+CRH), or ground and aged pine bark (8:2; CD+GAPB). The amounts of fused superphosphate (FSP) incorporated into the three root media during formulation were controlled from 0 to 6.0 g･L-1 in 1.5 g･L-1 increments. The root media containing fertilizers were packed into 300 mL plastic pots and seedlings of red-leaf lettuce at the 3rd leaf stage were transplanted. After transplanting, the crops were fed with a solution of neutral fertilizer (100 mg･L-1). The growth of red-leaf lettuce was investigated 5 weeks after transplanting and soil solutions were extracted and analyzed every week for pH, EC, and concentrations of macro-nutrients. The elevation of application rates of FSP in the three root media resulted in better growth, and the crops grown in CD+ERH and CD+GRPB had greater fresh and dry weights than those in CD+CRH when compared among the treatments of equal amounts of FSP. The pH and PO43- concentrations in the soil solution of CD+CRH at 3 weeks after transplant were in the ranges of 4.0 to 4.8 and 20 to 100 mg･L-1, respectively. These were lower pH and higher PO43- concentrations than those in CD+ERH and CD+GAPB. The K+ concentrations were higher in CD+CRH than those in the other two root media, and the elevation of FSP application rates resulted in higher Ca+2, Mg+2 and SO4-2 concentrations in soil solution of the three root media. The NO3-N concentrations in soil solution rose continuously during crop cultivation, implying that the leaching percentage was elevated. The soil solution EC varied, showing the same tendencies as the NO3-N concentrations. The above results indicated that the CD+ERH and CD+GRPB media performed better than CD+CRH, and optimum application rates of FSP in the three root media were 4.5 to 6.0 g･L-1 for pot cultivation of red-leaf lettuce.
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