Migration of Nitrogen and Phosphorus in Paddy Soil as Affected by Irrigation and Fertilization

Abstract

【Objective】 Fertilizer applications in paddy soils are prone to leaching and improving irrigation and fertilization to improve water and fertilizer use efficiency is critical to sustaining rice production. Taking nitrogen (N) and phosphorous (P) as an example, this paper investigated how changes in irrigation and fertilization alert N and P migration in soils. 【Method】 The experiment was conducted from June to September 2019 in the lysimeters at the Zhanghe Irrigation District, Hubei Province. We compared continuous flooding irrigation (CF) and alternating wet and dry irrigation (AWD). For each irrigation there were two fertilizations: conventional fertilization (N1) and fertilization using slow-release fertilizers (N2). In each treatment, we measured the changes in nitrogen (N) and phosphorus (P) at different soil depths. 【Result】 The concentration of total nitrogen (TN), nitrate-nitrogen (NO3--N) and ammonium nitrogen (NH+ 4-N) in the top 0~25 cm of soil was higher under N1 than under N2. W1+N2 increased TN and NH+ 4-N concentrations significantly (P<0.05) compared to other treatments. The average concentrations of TN, NO3--N, NH+ 4-N, and total P (TP) in the subsoil below the depth of 25 cm did not show noticeable difference between the treatments. The variation of TN and NO3--N along the soil profile can be characterized as follows: competition zone between root uptake and leaching in the 25~40 cm, fast leaching zone in the 40~55 cm layer, buffer leaching zone in the 55~125 cm, steady leaching zone in the 125~245 cm. W1+N2 increased the average concentrations of NO3--N and NH+ 4-N to 2.37 mg/L and 0.75 mg/L, respectively. Slow-release fertilization increased the average concentration of NH+ 4-N and NO3--N by 29.0%~193.8% and 3.7%~3.9%, respectively, compared to the conventional fertilizer. AWD reduced the average NO3--N concentration by 12.5%~12.7% while increased the TP concentration by 29.2%~49.2%, compared to CF. 【Conclusion】 Among all treatments we compared, W1+N2 was optimal by maintaining nitrogen in the 0~25 cm of soil and but less effective than W2+N2 in maintaining phosphorus; it reduced N leaching at the expense of potential increase in phosphorus leaching.

Keywords

• paddy fields
• irrigation mode
• fertilization methods
• soil nitrogen and phosphorus leachate
• leaching risk