Elsevier

Pedosphere

Volume 32, Issue 4, August 2022, Pages 629-636
Pedosphere

Nitrogen fertilization degrades soil aggregation by increasing ammonium ions and decreasing biological binding agents on a Vertisol after 12 years

https://doi.org/10.1016/S1002-0160(21)60091-7Get rights and content

ABSTRACT

Degraded soil aggregation arising from nitrogen (N) fertilization has been reported in many studies; however, the mechanisms have not yet been clarified. Elucidating the impact of N fertilization on soil aggregation would help to improve soil structure and sustain high crop production. The objective of this study was to determine the impact of long-term N fertilization on soil aggregation and its association with binding and dispersing agents. A 12-year (2008–2019) N fertilization field experiment on a Vertisol was performed, covering a wide range of N application rates (0, 360, 450, 540, 630, and 720 kg ha-1 year-1) and including straw management (straw return and straw removal) in a wheat (Triticum aestivum L.)-maize (Zea mays L.) cropping system. Soil samples of 0–20 cm depth were collected from 12 field treatments with 3 replications in 2019. Soil aggregate stability (mean weight diameter (MWD)) and contents of soil organic carbon (SOC), glomalin-related soil protein (GRSP), microbial biomass carbon (MBC), and mineral N (NH4+ and NO3-) were determined. Long-term N fertilization under straw removal conditions reduced soil MWD by 12%–18% at N rates from 0 to 720 kg ha-1 compared to that under straw return (P < 0.05). Soil MWD was positively associated with pH (P < 0.05) and MBC (P < 0.05), but negatively correlated with NH4+ (P < 0.05) and NO3- (P < 0.05). Compared with the straw removal treatment, the straw incorporation treatment significantly improved the contents of aggregating agents (SOC, GRSP, and MBC) (P < 0.001), but did not affect that of the dispersing agent (NH4+) (P > 0.05); consequently, it improved soil aggregation. Overall, our results indicate that long-term N fertilization may degrade soil aggregation because of the increases in monovalent ions (H+ and NH4+) and the decrease in MBC during soil acidification, especially when the applied N dose exceeded 360 kg ha-1 year-1. Our finding can minimize the negative structural impacts on Vertisol.

Section snippets

INTRODUCTION

Nitrogen (N) fertilizers are routinely applied to agricultural soil, and are essential in promoting soil fertility and stimulating crop growth. Therefore, N fertilization can increase crop residues in terms of the above- and belowground biomass of crops (as C input into soil) (Zhao et al., 2018). It is expected that an increase in C input can result in an increase in soil organic carbon (SOC) and further improve soil aggregation (Blanco-Canqui et al., 2014; Mustafa et al., 2020). However,

Site description and experimental design

A long-term field experiment (2008–2019) was conducted at the Agricultural Science and Technology Demonstration Center in Mengcheng County (33°09′ N, 116°33′ E), Anhui Academy of Agricultural Sciences, Anhui Province, China. The Vertisol is derived from fluvio-lacustrine sediment and has a clay loam texture (31.5% sand, 38.0% silt, and 30.5% clay) (Li et al., 2011). Before the experiment was conducted in 2008, the soil (0–20 cm) contained 8.22 g kg-1 organic carbon, 0.99 g kg-1 total N, 0.67 g

Crop yields

The mean annual yields of wheat and maize (2014–2018) were affected differently by the N application rates and straw management (Fig. 1). When the N rates increased from 360 to 630 kg ha-1, the wheat and maize yields under straw removal conditions gradually increased by 9.7%–22.7% and 1.63%–2.9%, respectively. Relative to N fertilization at a rate of 630 kg ha-1 when straw was not added, an N fertilization rate of 720 kg ha-1 slightly reduced wheat and maize yields by 2.13% and 1.9%,

DISCUSSION

Under straw removal conditions, N fertilization substantially reduced the soil aggregate stability (P < 0.05) compared to no-N treatment (Fig. 3). However, the SOC content also considerably increased (P < 0.001) (Table II), which is inconsistent with many reports in the literature, showing that N fertilization not only increased SOC content, but also improved soil aggregation and MWD (Guo et al., 2018, 2019a; Mustafa et al., 2020). This discrepancy may be related to the changes in soil

CONCLUSIONS

Our study provides direct evidence that long-term N fertilization degrades soil aggregation because it creates more monovalent ions (H+ and NH4+) in acidified soil despite the increasing SOC, especially when the applied N rate exceeds 360 kg ha-1 in a wheat-maize cropping system. In contrast with sole N fertilization, straw incorporation remarkably increased the aggregating agents but did not affect the dispersing agents, thus improving soil aggregation. Thus, optimized N input and straw

ACKNOWLEDGEMENT

This study was supported by the National Natural Science Foundation of China (Nos. 41725004, 42007007, and 41930753) and the Natural Science Foundation of Jiangsu Province, China (No. BK20201104).

References (36)

  • X L Xin et al.

    Effects of long-term (23 years) mineral fertilizer and compost application on physical properties of fluvo-aquic soil in the North China Plain

    Soil Till Res

    (2016)
  • X Yan et al.

    Carbon sequestration efficiency in paddy soil and upland soil under long-term fertilization in southern China

    Soil Till Res

    (2013)
  • H J Yin et al.

    Balancing straw returning and chemical fertilizers in China: Role of straw nutrient resources

    Renew Sust Energ Rev

    (2018)
  • H D Zang et al.

    N fertilization decreases soil organic matter decomposition in the rhizosphere

    Appl Soil Ecol

    (2016)
  • X K Zhang et al.

    Organic amendment effects on aggregate-associated organic C, microbial biomass C and glomalin in agricultural soils

    Catena

    (2014)
  • H Blanco-Canqui et al.

    Does inorganic nitrogen fertilization improve soil aggregation? insights from two long-term tillage experiments

    J Environ Qual

    (2014)
  • J Dai et al.

    Arbuscular mycorrhizal fungal diversity, external mycelium length, and glomalin-related soil protein content in response to long-term fertilizer management

    J Soil Sediment

    (2013)
  • Z M Dai et al.

    Long-term nitrogen fertilization decreases bacterial diversity and favors the growth of Actinobacteria and Proteobacteria in agro-ecosystems across the globe

    Glob Chang Biol

    (2018)
  • Cited by (9)

    View all citing articles on Scopus
    View full text