Soil organic carbon dynamics under long-term fertilization in a black soil of China: Evidence from stable C isotopes.

Xiaolin Dou,Ping He,Wei Zhou,Ping Zhu

doi:10.1038/srep21488

Abstract

Effects of different fertilizers on organic carbon (C) storage and turnover of soil fractions remains unclear. We combined soil fractionation with isotope analyses to examine soil organic carbon (SOC) dynamics after 25 years of fertilization. Five types of soil samples including the initial level (CK) and four fertilization treatments (inorganic nitrogen fertilizer, N; balanced inorganic fertilizer, NPK; inorganic fertilizer plus farmyard manure, MNPK; inorganic fertilizer plus corn straw residue, SNPK) were separated into four aggregate sizes (>2000 μm, 2000–250 μm, 250–53 μm, and <53 μm), and three density fractions: free light fraction (LF), intra-aggregate particulate organic matter (iPOM), and mineral-associated organic matter (mSOM). Physical fractionation showed the iPOM fraction of aggregates dominated C storage, averaging 76.87% of SOC storage. Overall, application of N and NPK fertilizers cannot significantly increase the SOC storage but enhanced C in mSOM of aggregates, whereas MNPK fertilizer resulted in the greatest amount of SOC storage (about 5221.5 g C m2) because of the enhanced SOC in LF, iPOM and mSOM of each aggregate. The SNPK fertilizer increased SOC storage in >250 μm aggregates but reduced SOC storage in <250 μm aggregates due to SOC changes in LF and iPOM.

Highlights

Agro-ecosystem represents around 40% of all land on earth[1], which is critical for maintaining agricultural sustainability, environmental stability, and long-term terrestrial carbon (C) sequestration[2,3]
We found that the greatest soil organic carbon (SOC) storage was found in MNPK-treated soils, followed by SNPK and by inorganic fertilizers across all the aggregates (Table 2), which fully supported our previous study and others[9,28,29]
The aggregate distribution was dominated by macroaggregates (2000–250 μ m; 48.31–64.10%); the intra-aggregate particulate organic matter (iPOM) accounted for the largest C fraction (76.87% on average) of the total SOC pool across all the treatments (Table 2)

Summary

Introduction

Agro-ecosystem represents around 40% of all land on earth[1], which is critical for maintaining agricultural sustainability, environmental stability, and long-term terrestrial carbon (C) sequestration[2,3]. Fertilization as an agricultural management strategy, is being used to promote soil C storage[5,6], which could directly or indirectly increase the SOC inputs and thereby change the availability of nutrients and soil turnover[1]. Understanding the changes in new soil C inputs and the decay rate of old C will be essential to revealing soil C dynamics under long-term fertilization. The SOM physical fractionation technique together with natural abundance in stable C isotopic composition, has been considered to be an effective approach for quantifying SOM dynamics under long-term fertilization in agro-ecosystems[1,6,11]. We hypothesized 25 years of fertilization would significantly change organic C storage of soil fractions and turnover rate of soil C (the proportion of soil new vs old C). The objectives of this study were to examine the following issues: (1) how long-term fertilization has potentially impacted the organic C storage in the SOM fractions; and (2) how long-term fertilization affects the new C inputs and decay rates of old C in the native SOM fractions

Objectives

Methods

Results

Conclusion