Impact of maize residues decomposition on aggregate turnover

The decomposition of maize residues has a vital influence on soil aggregate buildup-breakdown (turnover) processes, but the following remain unclear: i) which size aggregates of Mollisols are primarily affected by the decomposition of maize residues and ii) the turnover proportions of these aggregates. In the study, rare earth oxides (REOs) were used to trace and quantify the buildup-breakdown paths of soil aggregate fractions during the whole incubation time. The two treatments were designed as follows: i) REO-labelled soil with maize residues addition (maize residue treatment) and ii) REO-labelled soil without maize residues addition (control, CK). The soil respiration, aggregate size distribution, REO concentrations, SOC and pH were measured during 84 days of incubation. The results showed that on days 0-14, the incorporation of maize residues significantly increased soil respiration and promoted the formation of 2-5 mm and 0.25-2 mm aggregate fractions at the expense of <0.25 mm aggregates. On days 14-84, the addition of maize residues continued to promote the formation proportions of the 2-5 mm aggregate fractions and reduced the breakdown proportions of the 0.25-2 mm aggregate fractions. At the end of incubation, the proportions of 0.25-2 mm, 0.053-0.25 mm, and <0.053 mm aggregates that formed into 2-5 mm aggregates were 5.1 %, 5.7 %, and 6.4 %, respectively, in the maize residue treatment, and the proportions of 0.25-2 mm aggregates that broken into 0.053-0.25 mm and <0.053 mm aggregates decreased by 23.2 % compared to those in the CK treatment. The larger the aggregate size was, the greater the buildup rate in the maize residue treatment. The buildup rate of the 2-5 mm aggregate fractions in the maize residue treatment was the largest and increased with increasing incubation time, reaching 529.3 % at the end of incubation. The 2-5 mm, 0.053-0.25 and <0.053 mm aggregate fractions mainly transferred (buildup or breakdown) to the 0.25-2 mm aggregate fractions. The addition of maize residues significantly increased organic matter contents during the whole incubation time, increased the soil pH on days 0-42. This study provides a reference for the impact of maize residues on Mollisols soil structure.