Rice yield and nitrogen and phosphorus changes in soil profile under different fertilization strategies in Erhai Lake Basin, Yunnan

  Objectives  This study investigated rice yield and N and P leaching in 0–100 cm soil depth under different fertilization regimes. We aim to support nutrient management that meets the requirement of safe surface water quality with empirical data.

  Methods  A two-years localized experiment was conducted at the National Agricultural Environment, Dali Observation and Experiment Station, where the cropping system is rice-garlic-rice-faba bean. Eight fertilization regimes was set up during the rice season: no fertilization (CK), chemical N and P fertilization at the conventional rate (CF), chemical N and P fertilization at 20% less conventional rate (T1), organic fertilizer application in equal N rate with T1 (T2), organic fertilizer application in equal P rate with T1 (T3), organic fertilizer application at N and P available rate in T1 considering 25% mineralization (T4, T5), and controlled release fertilizer at the N rate in T1 (T6). Rice yields were investigated in 2019 and 2020. The total and available N and P contents in 0–100 cm soil depth at 20 cm intervals were measured in 2020.

  Results  T2, T3, T4 reduced rice grain and straw yields compared with CF. Soil total N was mainly accumulated at 0–40 cm depth. In comparison with CF, T4 and T5 increased the total N in 0–20 cm topsoil. The highest soil NH₄⁺-N content was recorded in the 0–20 cm layer, with a successive decrease across the soil depth. Except for CK, all the fertilization treatments had (P < 0.05) lower NH₄⁺-N content than CF. Soil NO₃^–-N was mainly accumulated at 0–40 cm layer, with the highest contents observed in 20–40 cm depth. All the fertilization treatments had lower NO₃^–-N contents than CF in the topsoil. T4 and T5 had higher NO₃^–-N content at 20–40 cm soil layer. The soil total P content decreased slowly with soil depth. T4, T5, and T6 increased the total P content in the topsoil. Soil available P decreased with soil depth and was accumulated at 0–40 cm layer. T4 and T5 increased soil available P at 0–40 cm layer in comparison with CF.

  Conclusions  Under the experimental condition, the total and available N and P were mainly accumulated in the 0–40 cm soil layer, although there were variations among fertilization patterns. Reducing 20% chemical N and P input could ensure rice yield and reduce soil N and P residue, and using controlled-release fertilizer is more effective than common fertilizers. Replacing chemical P with an equal amount of organic P without considering the mineralization rate of organic fertilizers would decrease rice yield but not N and P residue in the topsoil. Replacing chemical N with organic N considering its mineralization would increase soil N and P content and increase the risk of soil leaching. Therefore, we conclude that the large-scale application of organic fertilizers over the long term may cause the downward shift of N and P.