Performance of seedling grafts of tomato as influenced by root substrate formulations, fertigation leaching fractions, and N concentrations in fertilizer solution

Abstract

Influence of root substrate formulations, leaching fractions (LF) of fertigation during seedling growth before grafting and fertilizer N concentrations after grafting on growth of tomato grafted seedlings and changes in root substrate chemical properties were investigated. Sphagnum peatmoss + perlite (7:3, v/v, PP) and coir + perlite (7:3, CP) containing pre-plant fertilizers were used as substrates. LF (volume leached/applied) was set as 0, 0.25, 0.50, 0.75 and 0.9 during seedling cultivation. Seedlings of rootstock (J3B Strong) and scion (Sunmyung) were grown in 50- and 105-cell trays, respectively. Plants were fed with 50, 100, or 200 mg·L−1 N using 14-0-14 and 20-10-20 commercial fertilizers alternatingly for seedling stages 2, 3, and 4, respectively. Grafted tomato seedlings planted in 50-cell trays containing PP or CP were callused and rooted inside a humid greenhouse plastic tunnel for 7 days. When grafted tomato seedlings were rooted after acclimation under lower humidity condition, N fertilizers with 4 different concentrations (0, 50, 100, 200 mg·L−1) were applied. During 31 days of culture, highest fresh weight of rootstocks was obtained with 0.75x LF in CP, while PP showing no influence on seedling growth by LF. Electrical conductance (EC) of CP with 0.75x LF was 2.88 dS·m−1. Growth of scion seedlings was largest with 0.25x LF in PP, and EC of this treatment was 0.855 dS·m−1. For 13 days post-grafting, plant growth was better as LF increased for both substrates. When seedlings were grown with 0.90x LF, EC for PP and CP was 0.833 and 2.923 dS·m−1, respectively. Fresh weight of grafted plants grown for 31 days after grafting was the highest with 50 mg·L−1 N for PP and 0 mg·L−1 N for CP. Substrate EC in these treatments were 0.66 and 1.42 dS·m−1, respectively. This study suggests that LF and fertilizer N concentration must be optimized according to substrate formulations for growing high-quality grafted seedlings.