[Meta Analysis on Yield Effect of Biochar for Staple Crops in China]

In order to quantitatively evaluate the impact of biochar on the yield of staple crops in China, a total of 866 pairs of data from 116 published studies were collected. Meta analysis was used to quantitatively analyze the impact of biochar on the yield of staple crops in China and its influencing factors. Meanwhile, a structural equation model (SEM) was constructed to further explain the interaction among the factors. The results showed that compared with no biochar application, biochar application could improve the physical and chemical properties of the soil in the main grain fields and increase the yield of the main grain crops, with an average yield increase rate of 8.77%. Among them, when the pH of biochar was 7-8, the average yield increase rate was the highest, reaching 26.49%. When C/N<60, the average yield increase rate was 13.73%, which was significantly higher than that of C/N≥60. Applying biochar to acidic or neutral soil could give full play to its yield-increasing effect. When the amount of carbon applied was 10-20 t·hm^-2, the average yield increase rate of wheat and corn was the highest. The average yield of rice was the highest when the amount of carbon was 15-25 t·hm^-2. However, the yield-increasing rates of rice with different carbon application levels were similar, so it is possible to consider losing part of the yield and give consideration to the economic benefits by appropriate reduction. In addition, the yield-increasing effect of biochar decreased with the increase in application years, and generally the yield-increasing effect was not significant after three years. The SEM showed that the application amount of biochar not only directly affected the yield of staple crops but also indirectly affected the yield of staple crops by improving soil fertility, whereas biochar C/N and pH only affected the yield of staple crops by improving soil fertility. Therefore, in the future application of biochar, priority should be given to applying it to acidic or neutral soil with low fertility, and its C/N and pH should be controlled below 60 and 7-8, respectively. Soil conditions, biochar characteristics, and field management measures should be comprehensively considered to maximize the yield of staple crops. This research can provide scientific basis and theoretical basis for the popularization and rational application of biochar.