Stability of soil organic matter accumulated under long‐term use as a rice paddy

Abstract

To understand the mechanism responsible for the enhanced accumulation of soil organic matter (SOM) under long-term use as a rice paddy, soil samples from the plow layer from 16 fields that have been used for irrigated rice production from 5 to 2000 years in the Hangzhou Bay, China, were analyzed. The humin in silt/clay particles was isolated as a representative relatively stable SOM pool, and isotopic signatures (δ 13 C, δ 15 N, and 14 C concentration), 13 C nuclear magnetic resonance (NMR) spectra, and biodegradability in an incubation were examined. The amounts of C and N in the bulk soil, silt/clay, and silt/clay-humin increased with increasing period of use as a rice paddy within the east and west zones, respectively. The degree of humification determined for humic acids indicated that the progression of humification did not contribute to the accumulation of C beyond 100 years. The δ 15 N of silt/clay-humin suggested an increase in organic N derived from chemical fertilizer or recent biological fixation with increasing amount of this fraction. The 14 C concentration showed a negative correlation with the amount of silt/clay-humin C. The structural property with regard to 13 C NMR spectra and biodegradability of the silt/clay-humin remained constant with the length of use as a rice paddy or 14 C concentration. These results suggest that the larger C or N accumulation in the soils with a longer rice paddy history can be attributed to an enhancement in the accumulation of recently generated SOM rather than the stable accumulation of humus over the years.

Fe‐modified biochar improved the stability of soil aggregates and organic carbon: Evidence from enzymatic activity and microbial composition

“…complexes (Nakahara et al, 2016). There is evidence that the iron (Fe) cycle is also closely related to SOC dynamics (Wiesmeier et al, 2019).…”

“…Chen, Zhang, Liu, Liu, et al (2022) demonstrated that macroaggregates could increase the stability of SOC and reduce the loss of soil C mineralization. Soil C stability is not only related to aggregates structure but also to metallic mineral complexes (Nakahara et al, 2016). There is evidence that the iron (Fe) cycle is also closely related to SOC dynamics (Wiesmeier et al, 2019).…”

Phytolith assemblage analysis for the identification of rice paddy

“…Currently, the methods for studying ancient and present-day rice paddies mainly focus on the physical and chemical properties of paddy soil 7 , 8 , such as micromorphological features 9 , organic matter 10 – 12 (including organic carbon 13 – 18 and nitrogen 19 , 20 , fatty acids and polycyclic aromatic hydrocarbons 21 – 26 ), forms of iron 27 , 28 , mineral characteristics 29 , bacterial communities 30 – 34 , soil fertility 35 , pollen features 36 , and phytolith accumulation 37 . Although these methods are effective for analysing the characteristics of paddy fields, they can only be applied to known paddy fields.…”