Responses of Wheat Production, Quality, and Soil Profile Properties to Biochar Applied at Different Seasons in a Rice-Wheat Rotation

In the rice-wheat rotation system, biochar (BC) can be applied at the initiation of the rice or wheat season. Here, we compared the effects of BC that were applied at two different crop seasons on wheat production, quality, and soil profile properties in a rice-wheat rotation system with nitrogen (N) fertilizer applied at 280 kg/ha rate. Results showed that both wheat grain production and N recovery use efficiency were influenced by BC applied at two crop seasons. Biochar application did not affect the total non-essential amino-acid, but when applied during wheat season, BC significantly (p < 0.05) increased total essential amino acid in grain by 12.3%, particularly for the valine (+48.2%), methionine (+43.8%), and isoleucine (+ 10.3%). We found that BC significantly (p < 0.05) decreased the pH of soil at 0-6 cm and 20-30 cm by 0.14-0.18 and 0.05-0.08 units, respectively. The NH4+-N content of the whole observed soil profile were reduced by BC application, however, the effect of BC on NO3--N content varied with the application season and profile depth. Interestingly, BC applied at wheat and rice season significantly (p < 0.05) improved topsoil N contents by 48.4% and 19.7%, respectively. In addition, data suggested that BC applied during wheat season performed better in enhancing soil available phosphorus, potassium, and organic matter contents. In conclusion, we suggest that the optimum application time of BC for enhancing crop production and quality (take amino-acid content for example) and improving soil fertility is at the initiation of the wheat season.