Nutrient concentrations and root substrate formulations influence the performance of seedling grafts of tomato

Abstract

The purpose of this research was to investigate the influence of fertilizer concentration on plant growth, nutrient uptake, and changes in chemical properties of peat containing root substrates during the production of plug-grown seedling grafts of tomato. Two different substrate formulations containing sphagnum peat moss (PM) plus perlite (PL) (5:5, v/v, PM+PL) and PM plus vermiculite (VM) (7:3, v/v, PM+VM) were used. Five variations (0, 0.1, 1, 2, 4× conc.) of a standard fertilizer (SF) consisted of (mg L1 substrate) 190 N, 54.5 P 2 O 5, 149 K 2 O, 542 CaO, 24.3 MgO and 19.5 S, and micronutrients in pre-plant fertilizers were used for seedling growth before grafting. The rootstock (‘J3B Strong’) and scion (‘Sunmyung’) were grown in 50 cell (volume 33 cc) and 105 cell (volume 18 cc) trays, respectively. Those were fertilized once a week with the N concentration of 50, 120 and 200 mg L1 nutrient solution (using 14-00-14 and 20-10-20 commercial analysis fertilizers alternately) in stages 2, 3, and 4, respectively. At 31 d after sowing, seedlings of both the rootstock and scion were excised from the plug trays and used for grafting. The cut seedling grafts (‘Sunmyung’ scion/ʻJ3B Strong’ rootstock) were then planted into 50-cell plug trays (cell volume 33 cc) containing the two different substrate formulations. The graft union and new adventitious roots were induced under a shaded plastic tunnel inside a greenhouse for 7 d. The rooted grafted plants were gradually acclimatized for 6 d with lower humidity and then fertilized once a week with the solution containing 4 different N concentrations (0, 50, 100, 200 mg L1). When determined after 31 d from seed sowing, the highest fresh weights of the root-stock seedlings were obtained with 4× SF in PM+PL mix (7.1 g seedling -1) and 1× SF in PM+VM mix (7.3 g seedling -1). The electrical conductance (EC) of the PM+PL mix with 4× SF and the PM+VM mix with 1× SF was 0.79 and 1.35 dS m -1, respectively. The root substrate ECs of these two treatments were 0.58 and 1.33 dS m -1, respectively. During the formation of graft union and rooting, fresh weights of the seedling grafts grown for 13 d with the same plug fertilizer concentration were greater when they were grown in the PM+VM mix than in the PM+PL mix. As the fertilizer increased to 4× in the PM+VM mix, fresh weights of the grafted plants increased. Root substrate EC of the PM+VM mix with 4× SF treatment was 3.23 dS m -1. Fresh weights of the grafted plants grown for 31 d were greatly influenced by fertilizer concentrations with the largest plants being obtained at 200 mg L -1 N treatment in the PM+PL mix and 100 mg L -1 N treatment in the PM+VM mix. The substrate ECs in these two treatments were 0.89 and 1.41 dS m -1 indicating that the desirable range of soluble salts in soil extracts is higher in the PM+VM mix than the PM+PL mix. Results of this study suggest that fertilizer strengths need to be adjusted differently for each root substrate formulation to produce high quality seedling grafts of tomato.