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Dynamics of maize straw residue 13C incorporation into aggregates of a Mollisol as affected by long-term fertilization

Li, Ming, Wang, Yang, Ding, Fan, Xu, Yingde, Zhu, Ping, Ding, Xueli, Wang, Jingkuan
Journal of soils and sediments 2019 v.19 no.3 pp. 1151-1160
Mollisols, Phaeozems, corn, corn straw, cow manure, field experimentation, isotope labeling, microaggregates, mineral fertilizers, sieving, soil organic carbon, soil sampling, stable isotopes, China
PURPOSE: Soil aggregates play a crucial role in the sequestration of soil organic carbon (SOC). Returning crop residues to soil is known to strongly influence soil C stocks, but the specific contribution of crop residues to soil aggregates influenced by long-term fertilization remains largely unknown. This study investigated the effects of long-term fertilization on the distribution of ¹³C-labeled maize straw residue in different aggregate size fractions and their retention in soils over a 1-year incubation. MATERIALS AND METHODS: The dynamic variation and the distribution of maize straw-derived ¹³C in soil aggregates were monitored using a ¹³C stable isotope mass-balance approach. The following three fertilization treatments were selected: (1) without fertilization (CK), (2) mineral fertilizer (NPK), and (3) cow manure with mineral fertilizer (NPKM). Soil samples were collected from the surface layer (0–20 cm) of a long-term field experiment of Mollisols (Luvic Phaeozem) in 2015 at Gongzhuling, Jilin Province, China, which was established in 1980. Soils were incubated for 360 days at 25 °C, with or without ¹³C-labeled maize straw and destructively collected on the days of 45, 90, 135, 180, and 360. Soil aggregates were separated into two fractions (macroaggregates, > 250 μm; microaggregate, < 250 μm) by wet sieving. RESULTS AND DISCUSSION: The NPK treatment retained the most of maize straw ¹³C in macroaggregates (28.49%), but more maize straw ¹³C was incorporated in microaggregates for NPKM soil (4.02%) than NPK and CK on day 45. The highest amount of maize straw ¹³C was incorporated in macroaggregate on the days of 90, 135, and 180, and in microaggregate on the days of 135, 45, and 135 for CK, NPK, and NPKM, respectively. Organic manure-amended soil tended to sequester more maize straw ¹³C in the microaggregate fractions as compared with the NPK and CK treatments throughout the incubation. The maize straw ¹³C remaining in both of macro- and microaggregates followed the order of NPKM > NPK > CK for all soil aggregates after the 360-day incubation. CONCLUSIONS: Our results illustrated that long-term application of manure with mineral fertilizer helps to stabilize or increase the retention of exogenous C in the soil aggregates.