Conversion from Upland to Paddy Field Intensifies Human Impacts on Element Behavior through Regolith

• Published in: Vadose zone journal Vol. 18; no. 1
• Main Authors: Wu, Huayong, Song, Xiaodong, Zhao, Xiaorui, Zhang, Gan‐Lin
• Format: Journal Article
• Language: English
• Published: Madison John Wiley & Sons, Inc 2019
• Subjects: Aluminum; Bedrock; Calcium; Conversion; Drilling; Fertilizers; Fields; Flooding; Groundwater; Human influences; Iron; Magnesium; Manganese; Observatories; Pelagic clay; Quaternary; Regolith; Rice fields; Sandstone; Sedimentary rocks; Soil; Soil profiles; Soil properties; Soils; Topography; China
• ISSN: 1539-1663; 1539-1663
• DOI: 10.2136/vzj2019.06.0062

Core Ideas Conversion of upland to paddy caused significant loss of Fe within about 20 yr. The conversion impacted nearly the whole regolith far deeper than 1‐m soil profile. The magnitude of influence varied among elements. Despite many studies regarding the influence of the conversion from various types of land uses to paddy cultivation on soil change, little is known about how deep this influence may reach and what difference among elements may exist. To investigate the influence of the conversion from uplands to paddy fields on element behavior, we used mass‐balance equations to quantify element loss and gain throughout the regoliths from surface to bedrock at the Red Soil Critical Zone Observatory in subtropical China. The studied regoliths, with a thickness of 7 to 8 m, are acidic and highly weathered and developed from Quaternary red clay underlain by sandstone bedrock. The conversion increased the loss of Fe by 44%, whereas it decreased the loss of Mn by 14% in the top 3 m within a short timescale (about 20 yr). Slight influences of the conversion were observed for Al, K, and Mg, but no noticeable influences were found for Ca, Na, Si, and P. The observable influence of the conversion reached depths of 3 m for Fe, Mn, and Al and 1 m for Mg and K. Below the 4‐m depth, the influence was difficult to separate from the impacts of groundwater fluctuations. The lack of a noticeable influence on Ca and Na was mainly due to almost all of these elements having been depleted at the regolith–bedrock interface. Artificial flooding–drainage cycles and increases in fertilizer inputs in the paddy fields intensified the influence on element behavior via shifting the processes and sources of many elements in the regolith.