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Soil organic matter and ammonium affect potassium retention in soil microaggregates under long--term fertilization
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  • Mingjun Chen,
  • Xiaoqin Chen,
  • Shahbaz Muhammad,
  • Tida Ge,
  • Huoyan Wang,
  • Shu Wang,
  • Wenzhao Zhang
Mingjun Chen
Southwest Forestry University

Corresponding Author:[email protected]

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Xiaoqin Chen
Institute of Soil Science Chinese Academy of Sciences
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Shahbaz Muhammad
Centre for Environmental and Climate Science
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Tida Ge
Institude of Subtropical Agriculture, The Chinese Academy of Sciences
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Huoyan Wang
Institute of Soil Science, Chinese Academy of Sciences
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Shu Wang
Southwest Forestry University
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Wenzhao Zhang
Institute of Subtropical Agriculture Chinese Academy of Sciences
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The adsorption and fixation of potassium in agricultural soils are important as they influence K availability for crops. Soil organic matter (SOM) and ammonium (NH4+) exist in soils and play indispensable roles in soil fertility and crop yield; however, the effects of SOM and NH4+ on K retention in soil aggregate remains unclear. This study aimed to evaluate the effects of SOM and NH4+ on K adsorption and fixation in soil microaggregates (<0.25 mm). Soil microaggregates were extracted from three long-term fertilization treatments under rice-wheat rotations: no fertilizer (CK), fertilized with inorganic NPK (NPK), and inorganic NPK fertilizers combined with straw return (NPKS). Long-term fertilization, particularly the application of inorganic NPK combined with straw return, significantly improved the SOM content in microaggregates. Both NPK and NPKS treatments increased K adsorption but decreased K fixation, and SOM oxidation of microaggregates reduced K adsorption but increased K fixation in all treatments, indicating the positive and inhibitory effects of SOM on K adsorption and fixation, respectively. NH4+ significantly inhibited K adsorption and fixation, and this inhibitory effect was more significant in microaggregates with a higher SOM content. Although NH4+ reduced the positive effect of SOM on K adsorption, it enhanced the inhibitory effect of SOM on K fixation. Conclusionally, long-term fertilization increases K adsorption but reduces K fixation by improving SOM content, where NH4+ enhances SOM inhibited K retention in soil microaggregates, which is considered to improve K availability in soils amended with K fertilizers. Keywords: soil organic matter, NH4+, K, adsorption, fixation