Iron loss of paddy soil in China and its environmental implications

Abstract

Iron (Fe) is an important element for the terrestrial and marine ecosystems through its biogeochemical cycling on the Earth's surface. China has a long rice cultivation history, with extensive rice distribution across many types of paddy soils. Paddy soils are the largest anthropogenic wetlands on earth with critical roles in ecosystem functions. The periodic artificial submergence and drainage during paddy soil evolution result in significant changes in soil moisture regime and redox conditions from the natural soils, which facilitate the increase of Fe solubility and mobilization. However, there is a lack of systematic assessment on the magnitude of the migration and loss amount of Fe from paddy soils. In order to quantify the Fe loss and assess the dynamic evolution of Fe in the soils after rice cultivation, seven paddy soil chronosequences derived from different landscapes (bog, plain, terrace) and parent materials (acidic, neutral, calcareous) with cultivation history from 0 to 2,000 yr were studied. Results showed that the rates and trajectories of Fe evolution showed distinct patterns among the studied seven paddy soil chronosequences. However, net losses of Fe from 1 m soil depth occurred at all studied paddy soil chronosequences regardless of the original landscapes and parent materials. Fe in the paddy soils derived from the calcareous lacustrine sediments in the bog area showed a slight accumulation during the initial stage (50 yr) of paddy cultivation, with a loss rate of 0.026 kg m −2 yr −1 during the 50-to 500-yr time period. For the paddy soils developed on the calcareous marine sediments in the plain area, Fe evolution was dominated by the internal movement in soil profiles through coupled reducing-eluviation reactions in the surface horizons and oxidation-illuviation in the subsurface horizons within 1,000 yr of paddy cultivation, with an averaged net loss rate of 0.029 kg m −2 yr −1 during the 1,000-to 2,000-yr time period of rice cultivation. In contrast, Fe in the paddy soils derived from the acidic and neutral parent materials in the plain and terraced upland areas was rapidly lost during the initial stage of paddy cultivation, with a maximum loss rate of 1.106 kg m −2 yr −1 , while the Fe loss rate decreased gradually with increasing paddy cultivation age. Soil pH, CaCO 3 , and organic matter contents of the original soils, the length of time of paddy cultivation, landscape types and positions, and changes in soil moisture regime and redox condition induced by artificial submergence and drainage were the main factors controlling the rates and trajectories of Fe loss during paddy soils evolution. The amount of Fe loss caused by rice cultivation at the national scale was estimated based on the data collected from this study and the literature. The Fe loss fluxes of paddy soils in China were about 46.4-195.7 Tg yr −1 , and the amounts of Fe losses from paddy fields nationwide were about 5,121.5-9,412.2 Tg. Quantifying Fe loss from paddy fields is important to scientifically assess the impact...

Rice planting acceleration of the activation and loss of soil iron in the red soil region of southern China

“…Soil profile Fe represents a significant reservoir in the global iron cycle; however, estimations of soil profile Fe loss from paddy fields are often overlooked (Chen et al, 2022). In this study, we estimated that the soil profile (0−100 cm) of all woodland converted to paddy fields in the southern subtropical zone of China may experience a loss of 2 872 Tg of Fe t while accumulating 694 Tg of SOC.…”

“…Paddy fields are characterized by frequent redox fluctuations, which may drive C cycling and result in the production and transportation of different Fe forms (Li et al, 2019). Further exploration is needed to understand the long-term loss of Fe under rice cultivation at regional scales and the contribution of different forms of Fe (Chen et al, 2022).…”

Impact of Flooding–Drainage Alternation on Fe Uptake and Transport in Rice: Novel Insights from Iron Isotopes

“…Paddy soils constitute the largest anthropogenic wetlands worldwide . The redox-alternating conditions during rice planting are the main factors controlling soil Fe loss, which is strongly linked to biogeochemical cycling on the Earth’s surface. − The uptake strategies and sources of Fe plaque and soil solutions in paddy rice were identified using Fe isotopes. , Rice undergoes Fe excess and restriction in the soil solution during typical flooding–drainage alternation during rice growth; however, the uptake mechanisms underlying the redox-alternating conditions remain largely unknown. This study indicated that Fe­(III) uptake from Fe plaques predominantly occurs via strategy II during the flooding periods, and its contribution generally increases during the vegetative stages.…”

Cyberbullying and Public Policy in China: A Case Study of Liu Xuezhou’s Family Search

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“…Furthermore, there are discussions over the influence of public opinion. Studies on regulating public opinions have been regarded as essential and forceful regulations on public opinions have proven effective (Chen & Song, 2022). In China, studies on public policy at a macro level can be separated into domains including the government, legislation, platforms, and society.…”