Effects of biochar and arbuscular mycorrhizal fungi on the growth of continuous cropping pepper and soil nutrient status

In this study, a pot experiment was conducted to investigate the synergistic effects of biochar and arbuscular mycorrhizal (AM) fungi on the alleviation of the continuous cropping obstacles of pepper, improve soil nutrient status, and further provide theoretical foundations for continuous cropping soil improvement and new fertilizer development. A total of eight treatments were set as growth conditions of pepper consisting of four biochar addition levels (0, 1%, 2%, and 3%) with or without AM fungal inoculations (+AM and -AM), each treatment was replicated four times. Peppers were harvested after 60 days, and the physiological index, soil enzyme activity, and soil nutrient content were analyzed. Results showed that the biochar+AM treatments significantly promoted the growth of successive cropping pepper and increased the net photosynthetic rate (P_n), transpiration rate (T_r), stomata conductance (G_s), and chlorophyll content in pepper leaves. The treatments of only AM fungi inoculation also showed an increase in the growth and yield of peppers; however, biochar+AM had the best combined treatment effect. The effect of only AM fungal inoculation on P absorption in pepper plants and fruits showed a better result compared with that of only biochar, while the effect was opposite on K absorption. Moreover, the contents of N, P, and K in the root of pepper treated with 3% biochar+AM fungi increased by 74.04%, 106.42%, and 78.82%, compared with 0 biochar without AM fungi (control), respectively. The mycorrhizal infection rate under the treatment of 3% biochar+AM was 58.96%, which was 41.59% higher than that of the control. Soil pH and activities of urease and sucrase increased with an increase in biochar application; although, there was no significant difference in pH. AM inoculation showed not significant effects on soil enzyme activity. In addition, the available contents of K, P, and organic matter in the soil also increased with an increase in biochar application. The most significant improvement was achieved under the 3% biochar+AM treatment, while the treatment of only AM fungal inoculation showed no marked effect on these indexes. In conclusion, biochar, especially the treatment of 3% biochar+AM, had a significant synergistic effect on the growth and soil nutrient improvement of the continuous cropping pepper.