Effects of biochar on soil nutrients, yield and quality of vegetables

Objectives China is the largest producer of greenhouse vegetables in the world. However, with the continuation of planting years, problems such as soil secondary salinization, decreased vegetable quality and reduced yields, are becoming increasingly prominent. In this study, biochar was used in greenhouse vegetable cultivation as soil amendment to investigate its effect on growth of vegetables and soil nutrient supply, to explore a green and sustainable method for agricultural production in greenhouse and seek a basis for the rational application of biochar in greenhouse vegetable cultivation.

Methods Field experiments were conducted in a greenhouse, celery and eggplant were planted successively as the tested crops. The treatments were comprised of five biochar addition levels: 0 (B0), 20 (B20), 40 (B40), 80 (B80), and 160 t/hm² (B160) biochar. The effects of biochar on vegetable yields, nitrate content of celery, vitamin C content and catalase activity of eggplant, and soil nutrients were studied.

Results Compared with B0, B20 and B160 treatments increased celery yield by 31.6% and 30.3%, respectively, whereas B40 and B80 treatments had no significant effect on celery yield. B20 treatment had no significant effect on celery nitrate content, but B40, B80 and B160 treatments significantly reduced the celery nitrate content by 37.0%, 37.2% and 49.1%, respectively, the difference among treatments was not significant. On eggplant, the application of biochar had no significant effect on the yields, V_C content and catalase activity. When the amount of biochar increased to 160 t/hm² (B160), the nitrogen and phosphorus accumulation of eggplant fruit was inhibited. Compared with B0, B80 and B160 treatments significantly increased soil available potassium content by 95.8% and 196.2% after harvesting celery, respectively, while B160 treatment increased soil available potassium content by 165.5% after harvesting eggplant. For soil available phosphorus content, the addition of biochar had no significant effect in two cultivation seasons. In contrast, the effect of biochar on soil alkali-hydrolysable nitrogen was complicated, that was, it had no significant effect on soil alkali-hydrolysable nitrogen content after harvesting celery, but B40, B80 and B160 treatments decreased alkali-hydrolysable nitrogen content by 11.7%, 10.0% and 20.3% after harvesting eggplant, respectively. In addition, economic analysis showed that the B20 treatment had the highest benefit among all treatments. Compared with B0, B20 treatment improved net income by 9.4%. With increase of biochar addition, the input cost increased and the benefit of B160 treatment was the lowest among all treatments.

Conclusions At the biochar dose of 20 t/hm², celery yield was the highest and the benefit of greenhouse was the highest among all treatments, but it had no significant effect on vegetable qualities. However, when the amount of biochar was increased to 40 t/hm², the nitrate content of celery was significantly decreased. Therefore, it is necessary to continue to study the optimum amount of biochar between 20 and 40 t/hm² to achieve the goal of improving yields and qualities of vegetables.