Objectives The objective of this research is to explore the evolutionary characteristics of soil organic matter (SOM) and its components during the cultivation history of paddy soil in northern China, and to provide theoretical basis and data support for the improvement of SOM quality, rational utilization of paddy soil and improving its production potential, and establishment of high and stable-yielding paddy fields.
Methods The submerged paddy soils developed from brown soils and meadow soils in different planting years in Liaoning Province were chosen as the research objects. Combining investigation, field fixed-site test and indoor analysis, the effects of rice cultivation history on the content and fractions of SOM and humus characteristics of paddy soil were elucidated.
Results There was no significant correlation between the total SOM content and the age of rice cultivation (P > 0.05), and the total SOM content was maintained at 18.60–26.3 g/kg. With the increment of rice cultivation years, the proportion of easily oxidized organic matter (ROM) in SOM was reduced by 18%–20%, even though its content was above 50% at the beginning, and the organic matter oxidation stability coefficient (Kos) was below 1.2, with an increase of 52%–57%. The ratio of humic acid to fulvic acid (HA/FA) and the relative color (RF) of HA were increased, the activation degree of humic acids (AD) and the looseness/tightness of soil humus decreased significantly, with the increment of the rice cultivation years, respectively.
Conclusions With the extension of the planting years of rice, the soil organic matter become stable in property and less active, which leads to weakened ability of paddy soil in supplying and storing nutrients, and is unfavorable for exerting the production potential of the paddy fields. Appropriate tillage and nutrient managements should be considered to slow down and prevent the decline of soil fertility eventually.
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