Effects of Compound Biochar Substrate Coupled with Water and Nitrogen on the Growth of Cucumber Plug Seedlings

Since plug seedlings play a key role in automatic transplanting, this work aimed to explore the interaction between the biochar rate, water content, and N–fertilization in the substrate on the cultivation of cucumber seedlings before and after transplanting. The research showed that most of the factors obtained significant individual and interaction effects by measuring and analyzing the growth parameters of seedlings before transplanting. Most growth parameters significantly decreased with the increase in biochar rate except Water Use Efficiency which obtained the highest value of 2.06 g/L when the biochar rate was 10%. Furthermore, some growth parameters increased significantly with the increase in water content, while the Total Dry Matter and Water Use Efficiency reached their highest values, 0.778 g and 1.94 g/L, respectively, when the water content was 65%. All growth parameters reached their highest values when the N–fertilization was 50%; too high or too low of N–fertilization was not conducive to the growth of seedlings. The growth parameters and photosynthesis indices of seedlings cultivated after transplanting indicated that the seedlings with superior growth before transplanting performed better than other treatments in regard to growth and photosynthesis after transplanting. The interactions were in general optimal when the biochar rate was 5%, water content was 80%, and N–fertilization was 50% in the substrate, and seedlings cultivated under this treatment could not only meet the requirements of automatic transplanting, but also ensure rapid growth after transplanting. This study thus provides some guidance for the effective cultivation of vegetable plug seedlings.