How Does Bio-Organic Fertilizer Combined with Biochar Affect Chinese Small Cabbage's Growth and Quality on Newly Reclaimed Land?

The cultivated land area in China is approaching the red line for farmland protection. Newly reclaimed land possesses a large exploratory potential to become a reserved land resource. Identifying a fertilization strategy is vital for improving the poor properties and weak fertility of newly reclaimed land. An experiment was conducted to study the effects of traditional compound fertilizer (Fc) or bio-organic fertilizer (Ft), alone or in combination with biochar addition (6.85 t·ha^-1 and 13.7 t·ha^-1) on the growth, photosynthesis, yield and quality of Chinese small cabbage (CSC) plant. The results showed that compared to single compound fertilizer application, bio-organic fertilizer application promoted the plant's growth, indicated by the plant height, stem diameter and leaf area index (LAI), and significantly enhanced the yield and dry matter accumulation of CSC. In terms of the combination with biochar, the promoting effects were positively related to the biochar addition rate in the compound fertilizer group, while it was better to apply bio-organic fertilizer alone or in combination with biochar at a low rate of 6.85 t·ha^-1. The highest yield was obtained under B2Fc and B1Ft with 29.41 and 37.93 t·ha^-1, respectively, and the yield under B1Ft was significantly higher than that under B2Fc. The water productivity (WP) significantly improved in response to both kinds of fertilizer combined with biochar at 6.85 t·ha^-1. There was a significant difference between the photosynthetic characteristics of plants treated with single-compound fertilizer and those treated with bio-organic fertilizer. The photosynthetic characteristics increased under compound fertilizer combined with biochar, while they regressed under bio-organic fertilizer combined with biochar. The quality of CSC, especially that of soluble sugars and total phenolics, improved under single bio-organic fertilizer application compared with that under single-compound fertilizer. The nitrite content of the plants increased with increasing biochar addition rate in both fertilizer groups. In conclusion, there is a significant promoting effect of applying bio-organic fertilizer to replace chemical fertilizer alone or combining compound fertilizer with low-rate biochar addition on newly reclaimed land. It is a recommended fertilization strategy to substitute or partially substitute chemical fertilizer with bio-organic fertilizer combined with biochar in newly reclaimed land, and it is of great significance to achieve fertilizer reduction.