4.6 Article

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

Journal

PEDOSPHERE
Volume 32, Issue 4, Pages 629-636

Publisher

SCIENCE PRESS
DOI: 10.1016/S1002-0160(21)60091-7

Keywords

aggregating agents; aggregate stability; long-term nitrogen fertilization; soil structure; straw incorporation

Categories

Funding

  1. National Natural Sci-ence Foundation of China [41725004, 42007007, 41930753]
  2. Natural Science Foundation of Jiangsu Province, China [BK20201104]

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Long-term N fertilization can degrade soil aggregation due to increases in monovalent ions and decreases in microbial biomass carbon during soil acidification. However, straw incorporation treatment can improve soil aggregation.
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.

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