Abstract: With the extension of plants growth, the ion content in root zone showed a trend of increasing gradually in substrate culture. Tomatoes growth and development would be influenced by the changes of the ion concentration and its composition. In order to relieve the damage to the tomato plants caused by the nutrient enrichment in the substrate cultivation, taking "Yingfen 8" tomatoes as the experimental materials, a rock-wool potted experiment was conducted in the climatic chamber of National Agricultural Intelligent Equipment Engineering Technology Research Center from August 2019 to January 2020. The experiment included three treatments as leaching once a day (C1), leaching once a week (C2) and no leaching (CK), leaching liquor was 1/2 concentration nutrient solution. The environmental conditions of the artificial climate chamber were: daytime (9:00−17:00) temperature of 25℃, night (19:00−7:00 the next day) temperature of 15℃, sooner or later every 2h temperature transition; the average photosynthetic active radiation (PAR) of canopy was 300−400 μmol·m−2·s−1; the average CO2 concentration was 400−500mmol·mol−1; and the relative humidity was 65%/85% (day/night). From the 5th day after planting, 50mL of root zone solution and 50mL of backflow solution were collected at the end of leaching/irrigation drainage every day, and 105 times of samples were collected until the end of the experiment to determine their electrical conductivity (EC). Filtered irrigation fluid, root zone solution and reflux liquid were stored in a refrigerator at 4℃ every 7 days for nutrient ion determination, 16 times total. The role and effect of leaching with low-concentration were analyzed by testing the EC, ion concentrations, plant growth （height and stem thick）, yield and other indexes. The results showed that the nutrients in the rhizosphere were enriched to different levels and the EC of the rhizosphere increased by 31.26%−69.06% compared with the irrigation liquid. Low concentration nutrient solution leaching could effectively reduce the EC, ion concentrations of root zone and reflux solution. Compared with treatment CK, the EC of root zone solution treated with C1 during the whole growth period reduced by 22.36%, the concentrations of , Ca2+, K+ and Mg2+ were decreased by 48.51%, 27.25%, 25.54% and 39.58%, respectively. The change trend of the reflux solution treated with C1 was consistent with that of root zone solution. In addition, compared with treatment CK, treatment C1 could promote the plant height growth and the yield of tomato. The yield per plant of C1 increased by 6.26%, among them, the single fruit weight of the 4th panicle and 5th panicle increased by 17.02% and 14.51%, respectively, also the yield per panicle increased by 13.42% and 33.86%, respectively. The EC and ionic concentrations of the root zone solution and reflux liquid treated with C2 were significantly lower than those of CK, but higher than those treated with C1. The EC of root zone solution of C2 was decreased by 9.64%. However, single fruit weight on average and yield of C2 treatment were not significantly different from those treated with CK. Therefore, leaching with low-concentration nutrient solution once a day (C1) can more effectively alleviate nutrient enrichment in the root zone in the middle and later stage of tomato growth in soilless cultivation, which could provide theoretical basis for nutrient management in the root zone of substrate cultivation.

Key words: Tomato, Ion concentration, Rock wool, Nutrient enrichment, Leaching