*2.2. Experimental Design*

The long- and short-term biochar experiments commencement in May 2009 and May 2016, respectively, within a continuous rice rotation. The long- and short-term plots were adjacent to one another in the field, using the same experimental design for both experiments; within the text below, the short and long-term experiments are designated as "S" and "L". Individual 4 × 5 m plots were laid out in a randomized complete block design with three replicates per treatment.

Biochar was created from wheat straw via pyrolysis at ~450 ◦C at the Sanli New Energy Company, Henan Province, China. Treatments included four biochar application rates of 0(C0), 10 (C1), 20 (C2) and 40 (C3) t ha<sup>−</sup>1, which were surface-applied, raked to relative uniformity, and then fully incorporated into the soil to approximately a 15 cm depth by plowing. Biochar and background soil were collected, returned to the lab, ground to pass a 2-mm sieve, with basic biochar and soil properties determined using methods outlined by Lu [25]; data are presented in Table S1.
