Long-term fertilization alters chemically-separated soil organic carbon pools: Based on stable C isotope analyses.

Xiaolin Dou,Wei Zhou,Xiaoli Cheng,Ping He

doi:10.1038/srep19061

Abstract

Quantification of dynamics of soil organic carbon (SOC) pools under the influence of long-term fertilization is essential for predicting carbon (C) sequestration. We combined soil chemical fractionation with stable C isotope analyses to investigate the C dynamics of the various SOC pools after 25 years of fertilization. Five types of soil samples (0–20, 20–40 cm) including the initial level (CK) and four fertilization treatments (inorganic nitrogen fertilizer, IN; balanced inorganic fertilizer, NPK; inorganic fertilizer plus farmyard manure, MNPK; inorganic fertilizer plus corn straw residue, SNPK) were separated into recalcitrant and labile fractions, and the fractions were analysed for C content, C:N ratios, δ13C values, soil C and N recalcitrance indexes (RIC and RIN). Chemical fractionation showed long-term MNPK fertilization strongly increased the SOC storage in both soil layers (0–20 cm = 1492.4 gC m2 and 20–40 cm = 1770.6 gC m2) because of enhanced recalcitrant C (RC) and labile C (LC). The 25 years of inorganic fertilizer treatment did not increase the SOC storage mainly because of the offsetting effects of enhanced RC and decreased LC, whereas no clear SOC increases under the SNPK fertilization resulted from the fast decay rates of soil C.

Highlights

Soil organic carbon (SOC) plays a positive role in soil fertility, soil sustainability and crop yield in agricultural ecosystems[1,2]
Both total C and N contents were greater in MNPK- and SNPK-treated soils and lower in IN- and NPK-treated soils compared with CK (Table 1)
The δ 13C values of the leaf and roots varied from − 13.36 ‰ to − 16.23‰ and from − 12.67 ‰ to − 14.35‰, respectively, in the corn-planted field, which were typical of C4 plants (Table 2)

Summary

Introduction

Soil organic carbon (SOC) plays a positive role in soil fertility, soil sustainability and crop yield in agricultural ecosystems[1,2]. The relative contribution of new SOC vs old SOC can be estimated based on the mass balance of C isotope contents, and it becomes possible to estimate SOM turnover rate in situ[20,21] This technology has increasingly been applied to important issues such as land-use change and reforestation with no shift in photosynthetic strategy in www.nature.com/scientificreports/. We hypothesise that 25 years of fertilization would significantly change SOC storage and C turnover rate in a black soil of northeast China. To test this hypothesis, we measured the δ 13C, C and N content in the soil organic pools (labile and recalcitrant pools) and plant samples from the top 40 cm of different fertilizer-treated soils

Methods

Results

Conclusion