Purpose

Understanding the underlying mechanism of soil carbon (C) and nitrogen (N) accumulation is of great significance for soil C sequestration and climate change mitigation, as well as soil fertility improvement. The objective of this study was to evaluate the response of C and N accumulation in aggregates and fine soil particles to long-term mineral fertilizer and manure application.

Materials and methods

Five treatments from a long-term experiment with double maize cropping were examined in this study, i.e., (1) no fertilizer (control); (2) mineral nitrogen, phosphorus, and potassium application (NPK); (3) doubled application rate of the NPK (2NPK); (4) pig manure alone (M); and (5) mineral NPK fertilizers and manure combination (NPKM). By using physical particle-sized fractionation, we analyzed soil organic carbon (OC) and total nitrogen (N), and δ¹³C of OC in bulk soil and aggregates (53–2000 μm) and, coarse silt-sized fraction (5–53 μm), fine silt-sized fraction (2–5 μm), and clay-sized fraction (< 2 μm) under those five treatments.

Results and discussion

Fertilizer application for 24 years, particularly M and NPKM treatments, significantly increased the concentration and proportion of OC and total N associated with aggregates and clay-sized fraction as compared with control. Manure application significantly increased the proportion of OC by 6.6–7.8 points in aggregates, whereas it was by 22.6–25.0 points in clay-sized fraction. Clay-sized fraction-associated C and N showed a non-linear response to C and N accumulation in bulk soil, contributing approximately 47% and 69% to soil OC and total N, respectively. Moreover, the mass proportion of aggregates and the mass ratio of aggregates to fine soil particles increased significantly with C accumulation in fine silt-sized and clay-sized fraction.

Conclusions

Organic carbon and total nitrogen accumulation in soil clay-sized particles play important role in soil C and N sequestration in red soil. Our results also suggested that C accumulation in fine soil particles might benefit soil aggregation in intensive cropping system of South China.

中文翻译：

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长期施肥和集约种植可以提高华南红壤土大小的颗粒中碳和氮的积累

目的

理解土壤碳（C）和氮（N）积累的潜在机制对于固碳和减缓气候变化以及提高土壤肥力具有重要意义。这项研究的目的是评估骨料和细土壤颗粒中碳和氮积累对长期施用矿物肥料和肥料的响应。

材料和方法

在这项研究中，研究了长期种植双季玉米的五种处理方法，即：（1）不施肥（对照）；（2）矿物氮，磷和钾的施用（NPK）；（3）将NPK（2NPK）的施用率提高一倍；（4）单独的猪粪（M）；（5）氮磷钾矿物肥料和肥料组合（NPKM）。通过使用物理颗粒尺寸的分级，分析土壤的有机碳（OC）和总氮（N），δ ¹³ OC的下在土体和聚集体（53-2000微米），并且粗粉粒尺寸的级分（5-在这五种处理下，粉尘大小的碎屑（2–5μm）和黏土大小的碎屑（<2μm）为53μm。

结果与讨论

与对照相比，施肥24年，特别是M和NPKM处理，显着提高了与骨料和粘土级分有关的OC和总氮的浓度和比例。施用肥料显着提高了骨料中OC的比例，增加了6.6-7.8点，而粘土大小部分则增加了22.6-25.0点。粘土大小的分数相关碳和氮表现出对散装土壤中碳和氮累积的非线性响应，分别占土壤OC和总氮的47％和69％。此外，团聚体的质量比例和团聚体与细土颗粒的质量比随着C在细粉土和粘土尺寸级分中的积累而显着增加。

结论

土壤黏土大小颗粒中的有机碳和总氮积累在红壤中的碳和氮固存中起重要作用。我们的研究结果还表明，在华南集约化耕作系统中，土壤细颗粒中的碳积累可能有利于土壤聚集。