Abstract
Reports regarding the effects of long-term organic and inorganic fertilization on the quantity and quality of soil organic carbon (SOC), particularly in Vertisols, are scarce. In this study, we combined SOC physical fractionation with 13C NMR spectroscopy technology to investigate the effect of 34 years of continuous fertilization on the SOC physical fractions and its chemical composition of 0–20 cm soil layer in a Vertisol. This study consisted of six treatments: no fertilization (control), chemical nitrogen, phosphorus and potassium fertilizers (NPK), low and high amounts of straw with chemical fertilizers (NPKLS and NPKHS), and pig or cattle manure with chemical fertilizers (NPKPM and NPKCM). Over 34 years of continuous fertilization, the SOC sequestration rate was from 0.08 Mg C ha−1 yr−1 in the control treatment to 0.66 Mg C ha−1 yr−1 in the NPKCM treatment, which was linearly related with the C input (P < 0.01). Of the five SOC physical fractions, two silt plus clay fractions (S + C_M, S + C_mM) dominated 74–92% of SOC, while three POM fractions (cPOM fPOM and iPOM) were only 8–26%. The two manure application treatments significantly increased all the SOC physical fractions except for the silt plus clay fraction within macroaggregates (S + C_M) compared with NPK treatment (P < 0.05), which was dependent on the larger amount of C input. Also, the two manure application treatments increased the levels of alkyl C and aromatic C but decreased O-alkyl C (P < 0.05), whereas the straw application (NPKLS and NPKHS) had no impact on the C functional groups (P > 0.05). Overall, the combination of animal manure with inorganic fertilization could enhance the SOC sequestration and alter its quantity and quality in Vertisols.
Highlights
The enhancement of soil organic carbon (SOC) sequestration through judicious agricultural management practices is a promising strategy for improving soil fertility and crop yields[1,2]
Ultisol amended with pig manure (42 000 kg ha−1 yr−1) demonstrated more aromatic C, O-alkyl C and carbonyl C than Ultisol amended with straw[15]
Predict, and potentially manage SOC sequestration, the total SOC can be generally separated into five fractions by the physical fractionation technique: coarse particulate organic matter, fine inter-microaggregate particulate organic matter, intra-microaggregate particulate organic matter within macroaggregates, silt plus clay fraction within macroaggregate (S + C_M), and silt plus clay fraction within microaggregates occluded within macroaggregates (S + C_mM)[18]
Summary
The enhancement of SOC sequestration through judicious agricultural management practices is a promising strategy for improving soil fertility and crop yields[1,2]. Www.nature.com/scientificreports contrast, Yan et al.[4] reported that 31 years of continuous application of pig manure (15 000 kg ha−1 yr−1) had a minimal effect on the chemical composition of SOC in an Anthrosol (paddy soil) in Jinxian, China. These previous reports indicate that, the chemical composition of SOC may be controlled to some extent by the quantity and quality of the organic amendments. The objectives of this study were to (1) evaluate the long-term effects of fertilization with straw and manure on crop yields and SOC sequestration rates, (2) determine the effect of long-term fertilization on the chemical composition of SOC with 13C NMR spectroscopy technology, and (3) determine the response of SOC fractions to different fertilization practices with the SOC physical fractionation technique
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