Effects of wetting agent application on substrate water absorption and Chinese cabbage plug seedlings

Plug seedling has been the primary way to raise the vegetable seedlings on a large scale in China. The hydrophobicity and surface tension of the seedling substrate surface can be used to prevent the water from the rapid and uniform wetting of the substrate. A direct impact can also be obtained on the growth of vegetable plug seedlings during production. Taking the Chinese cabbage plug seedlings as the research objects, this experiment was carried out to clarify the effect of wetting agents on the substrate water absorption, together with the plant growth and development. Specifically, the experiment was conducted in a glass greenhouse from October 2021 to March 2022. Three wetting agents were selected, including the SP, GY-S903, and KT. Four additions were set as 0, 0.15, 0.30, and 0.60 mL/L in a total of 10 treatments. A gravity sensor was used to record the weight change of the plug trays in real time, which was adopted to represent the water content of the substrate. Finally, the change curve was plotted for the substrate moisture after measurement. The seedlings were sown in the 50-hole plug trays. The morphological indexes of Chinese cabbage seedlings were then measured after 30 days of growth. The test results show that the water absorption of the substrate increased by 23.90%-74.70%, the water absorption height increased by 46.03%-94.28%, and the water absorption rate increased by 60.57%-116.26%, compared with the substrate without the wetting agents. The best effect was found in the GY-S903 among the three wetting agents. Specifically, the higher the amount of wetting agent was added, the more the water absorption capacity of the substrate increased. The water absorption rate of 0.60 mL/L wetting agent GY-S903 was 12.33 and 24.56 g/min higher than that of 0.30 and 0.15 mL/L, respectively. Moreover, the addition of wetting agents failed to slow down the rate of water evaporation from the seedling substrate, whereas, there was an improved water retention of the substrate to maintain a high-water content. Meanwhile, the addition of a wetting agent was enhanced the uniformity of water absorption in the substrate between plug trays in the ebb-flow irrigation seedbeds, where the coefficient of variation in the water absorption was only 0.68%. Further determination was then obtained on the growth and development parameters of Chinese cabbage plug seedlings after wetting agent addition. It was found that there was no adverse effect of the appropriate addition of wetting agent on the growth of Chinese cabbage plug seedlings, but the excessive addition of wetting agent was limited the root development of seedlings. Except for the KT at 0.6 mL//L additive amount, other wetting agents and additive amounts, compared with the control Chinese cabbage seedling emergence rate, the total leaf area of plug seedling, stem and root dry matter accumulation, and root to shoot ratio all failed to reach a significant difference level. In summary, firstly, the wetting agent can represent an essential means to improve the water inhomogeneity of the substrate, in order to significantly improve the water absorption and absorption rate of the substrate, with the amount of wetting agent exerting a significant influence on the improvement of the water absorption capacity of the substrate. Secondly, the addition of a wetting agent can make no change in the rate of water evaporation from the substrate, but an improvement can be found in the water retention of the substrate and the relative water content of the substrate after evaporation. Thirdly, an adequate addition of wetting agent presented no adverse effect on the growth of Chinese cabbage plug seedlings. This finding can provide a theoretical basis and reference for the performance improvement of plug seedling substrate under ebb-flow irrigation.