Effect of ridging and fertilization on soil redox in cold waterlogged paddy fields

Soil redox was one of the most important chemical process in cool waterlogged paddy fields that occurred in the entire process of soil development. It importantly influenced the migration and transformation of soil materials and determined biological effectiveness of soil nutrients and contaminants. Soil redox research was still largely lacking in cold waterlogged paddy fields. The effects of ridging and fertilization on the state of soil redox in cold waterlogged paddy fields were analyzed in this study to lay relevant references for improving cold waterlogged paddy soils. An experiment of four ridge treatments control (CK), ridge height of 10 cm (LG₁₀), 15 cm (LG₁₅), and 20 cm (LG₂₀) and eight fertilization treatments CK (without fertilization), NPK (N 180 kg?hm^-2, P₂O₅ 90 kg?hm^-2 and K₂O 120 kg?hm^-2), NP₁K (N 180 kg?hm^-2, P₂O₅ 72 kg?hm^-2 and K₂O 120 kg?hm^-2), NP₂K (N 180 kg?hm^-2, P₂O₅ 108 kg?hm^-2 and K₂O 120 kg?hm^-2), NPK+Zn (N 180 kg?hm^-2, P₂O₅ 90 kg?hm^-2, K₂O 120 kg?hm ^-2 and Zn 0.75 kg?hm^-2), NPK₁ (N 180 kg?hm^-2, P₂O₅ 90 kg?hm^-2 and K₂O 96 kg?hm^-2), NPK₂ (N 180 kg?hm^-2, P₂O₅ 72 kg?hm^-2 and K₂O 144 kg?hm^-2), NPK+Si (N 180 kg?hm^-2, P₂O₅ 90 kg?hm^-2, K₂O 120 kg?hm^-2 and SiO₂ 0.75 kg?hm^-2) was conducted to study soil redox in cold waterlogged paddy fields. Results showed that soil redox potential was 48.5~ 198.0 mV in cold waterlogged paddy fields, which was far lower than that (450~700 mV) in normal paddy fields. Ridging increased soil redox potential in the top (0~5 cm) soil layer while suppressing it in the lower (5~20 cm) soil layer. Total reductions in cold waterlogged paddy soils were 5.7~15.6 cmol?kg 1 under ridge treatments and 7.7~16.0 cmol?kg 1 under fertilizer treatments. Ridging increased total reduction over the short-term. While applications of potassic, zinc- and silicon fertilizer retarded total reduction, application of phosphate had no effects on total reduction. Average soil Fe²⁺ content was 3 388.92 mg?kg 1 in the 0~25 cm soil layer and 3 356.39 mg?kg^-1 in the 25~50 cm soil layer. About 60 days after ridging, soil Fe²⁺ content decreased with increasing ridge height. NPK₂, NPK+Si and NPK+Zn treatments sharply decreased soil Fe²⁺ content compared with CK and NPK. Ridging and fertilization initially decreased soil Mn²⁺ content and then increased it in cold waterlogged paddy fields.