Optimal nitrogen fertilizer, which determines straw properties, and pyrolysis temperatures produce desired-biochars that can be used as a soil amendment

This study investigated the straw harvested after nitrogen (N) fertilizer application levels (0, 75, 150 and 225 kg N hm-2). The N fertilizer increased straw yield by 115.4-190.6%. In addition to N fertility, the pyrolysis temperatures (300, 500 and 700 °C) induced significant changes of the straw-derived biochar samples. The yield reduced from 41.4 wt% to 23.2 wt%, the residence time increased from 272 yr to 2194 yr, and the residual coefficient of organic C (Fperm) increased from 0.65 to 0.93 for the biochar samples as the temperature rising. The parameters of C sequestration were mainly affected by pyrolysis temperature. The N + P2O5+K2O content (5.6-8.8%) of the biochar samples was more in the 500 °C treatment. The characteristics of nutrient supply were affected by both the N fertility and pyrolysis temperature. The N fertilizer rate of 150 kg N hm-2 in the soil for wheat straw, together with the 500 °C treatment induces the best nutrient donor and C sequestration after biochar incorporation into the soil.