Abstract:

【Objective】 The objectives of this study were to investigate the effects of biochar feedstocks, pyrolyzing temperatures and biochar components on plant growth and to uncover the mechanism that how biochar increased crop yields. 【Method】 Six biochars were made from sawdust and maize stalk at pyrolyzing temperature of 350, 450, and 550℃. Each biochar was then separated into two parts through hot water extraction method, including the water soluble biochar extract and the washed biochar residue. A pot trial was conducted to investigate the effects of untreated biochar (BC), biochar extract (BE) and washed biochar residue (WB) application on the growth of non-heading Chinese cabbage (Brassica campestris ssp. chinesis). 【Result】 The aboveground biomass of Chinese cabbage under the addition of maize stalk biochars and their components was 16.1 g/pot on average, which was significantly higher than the values under sawdust biochars and their components (13.0 g/pot) amendment and the control (13.5 g/pot). Similarly, the root morphology index of root length, surface area, root volume and number of root tips under the addition of maize stalk biochars and their components improved greatly compared with sawdust biochar and the control. The aboveground biomass under the addition of washed biochar residues was 16.5 g/pot on average, which were 26.9% and 17.9% higher than the values under the addition of untreated biochar and the biochar extracts, respectively. The root length, surface area, root volume and number of root tips under washed biochar residues addition increased by 64.1%, 51.1%, 38.3% and 80.0%, respectively compared with biochar extracts addition. The biochars under different pyrolyzing temperature had no significant effect on the aboveground biomass and root growth of Chinese cabbage. Compared with the untreated biochar, the washed biochar residue addition increased the concentration of nitrogen (N) in aboveground biomass by 25.9%, while the concentration of phosphorus (P) and potassium (K) decreased by 39.7% and 14.1%, respectively. Soil pH, the concentration of soil organic carbon, total N, available P and K under the addition of maize stalk biochar and their components increased by 0.1 unit, 20.3%, 19.1%, 29.1% and 189.2% respectively compared with wood biochar addition. Compared with the untreated biochar, the washed biochar residue addition decreased soil organic carbon, total N, available P and K by 14.6%, 6.6%, 41.3% and 55.1%, respectively, while soil pH increased by 0.13 unit. Soil organic carbon, total N and available P under the addition of biochar extracts decreased by 49.8%, 18.9% and 24.2%, respectively, while soil pH and available K content was not affect. Correlation analysis showed that the aboveground biomass was positively related to root length, surface area, root volume, the number of root tips and soil pH value; while it was negatively correlated to the P concentration in the aboveground of Chinese cabbage. 【Conclusion】The feedstock and biochar component were the two main factors that regulating the response of plant growth to biochar amendment. The biochar from maize stalk was more suitable for soil amendment compared with wood biochar in terms of crop yield increase, and more crop yield could be obtained when maize stalk biochar was amended after hot water extracting. The water-soluble components presented in biochar played a key role in crop yield increase via promoting root growth. The promotion effect was closely related to biochar feedstock, pyrolyzing temperature and the chemical composition in biochar extracts.

Key words: biochar water extract, non-heading Chinese cabbage, crop yield, root morphology, the mechanism that regulating crop yield increase