Salt removal by puddling to reduce concentrations of chloride and sodium ions and of exchangeable cations in sandy paddy field soil that was flooded by tsunami

Abstract

We investigated the effects of salt removal by soil puddling on the concentrations of Cl^-, Na⁺, and soil nutrients in three sandy paddy fields (A, B, and C) on the Kujukuri coast of Chiba prefecture, Japan, which was flooded by the tsunami caused by the Great East Japan earthquake on 11 March 2011. All three fields had high concentrations of Cl^- (108.5–240.1 mmol kg^-1), soluble Na⁺ (64.7–137.0 mmol kg^-1), and exchangeable Na⁺ (15.2–48.8 mmol kg^-1), particularly in the plow layer. Salt removal decreased ion concentrations by 49%–99% (to 1.3–16.7 mmol kg^-1) for Cl^-), 2.2–23.1 mmol kg^-1 for soluble Na⁺, and 1.8–12.0 mmol kg^-1 for exchangeable Na⁺). It also decreased the percentage of exchangeable sodium from 17%–67% to 2%–18%. In field A, the concentrations of both Cl^- and total Na⁺ (soluble + exchangeable) were <4.4 mmol kg^-1 at a depth of 0–75 cm. In fields B and C, they were 1.0–23.6 mmol kg^-1 (both Cl^- and Na⁺) at a depth of 0–30 cm, and 2.4–29.6 mmol kg^-1 (Cl^-) and 6.1–31.4 mmol kg^-1 (Na⁺) at 30–90 cm. The concentrations of exchangeable Ca²⁺, Mg²⁺, and K⁺ increased after the tsunami by 1%–52% and decreased after salt removal by 3%–37%. Paddy rice was transplanted after salt removal without midsummer drainage. The yield of brown rice per unit area was lower by 19% in field A and by 28% in field B than the average annual yield.