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<p>While several studies have shown that soil nitrogen (N) levels decline by introducing upland crops into paddy rice monoculture, the net effect onto soil N supply remains unclear. The study assessed whether crop rotation could improve soil N availability by enhancing mineralization and releasing fixed NH₄⁺–N under less-reducing conditions. As a secondary aim the effect of extra organic inputs on soil N supply and the N balance was investigated. A field experiment covering 7 growing seasons (2017–2020) was carried out in the Vietnamese Mekong Delta comparing three crop rotations (rice–rice–rice, sesame–rice–rice, soybean–rice–rice) with or without compost. Soil samples (0–15 cm and 15–30 cm) were collected from the third crop onward, and exchangeable NH₄⁺–N, NO₃⁻–N, fixed NH₄⁺–N, and plant N uptake were measured. Crop rotation did not affect exchangeable NH₄⁺–N but increased soil NO₃⁻–N at both depths, raising the risk of N losses. Crop rotation marginally increased fixed NH₄⁺–N, indicating N conservation. Organic amendments enhanced exchangeable NH₄⁺–N but did not affect topsoil fixed NH₄⁺–N. Neither rotation nor amendments alone increased plant N uptake. Overall, the N balance was negative with an imbalance in soil organic N and a gradual net loss of fixed NH₄⁺–N. Introducing upland crops into rice monoculture requires balancing trade-offs between improved N availability for plant uptake and enhanced susceptibility to N losses, emphasizing the need to develop balanced N management strategies in rice-based systems.</p>

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Effects of Crop Rotation and Organic Amendments on Soil Nitrogen Dynamics in a Rice-based Cropping System in the Vietnamese Mekong Delta

  • 期刊论文

  • 发表日期：

    2026年4月23日

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  • Qui Van Nguyen,
  • Steven Sleutel,
  • Ann Verdoodt,
  • Phuong Minh Nguyen,
  • Khanh Huynh Tran,
  • Tran Thi Thu Vo,
  • Heleen Deroo,
  • Khoa Van Le,
  • Wim Cornelis

摘要

While several studies have shown that soil nitrogen (N) levels decline by introducing upland crops into paddy rice monoculture, the net effect onto soil N supply remains unclear. The study assessed whether crop rotation could improve soil N availability by enhancing mineralization and releasing fixed NH₄⁺–N under less-reducing conditions. As a secondary aim the effect of extra organic inputs on soil N supply and the N balance was investigated. A field experiment covering 7 growing seasons (2017–2020) was carried out in the Vietnamese Mekong Delta comparing three crop rotations (rice–rice–rice, sesame–rice–rice, soybean–rice–rice) with or without compost. Soil samples (0–15 cm and 15–30 cm) were collected from the third crop onward, and exchangeable NH₄⁺–N, NO₃⁻–N, fixed NH₄⁺–N, and plant N uptake were measured. Crop rotation did not affect exchangeable NH₄⁺–N but increased soil NO₃⁻–N at both depths, raising the risk of N losses. Crop rotation marginally increased fixed NH₄⁺–N, indicating N conservation. Organic amendments enhanced exchangeable NH₄⁺–N but did not affect topsoil fixed NH₄⁺–N. Neither rotation nor amendments alone increased plant N uptake. Overall, the N balance was negative with an imbalance in soil organic N and a gradual net loss of fixed NH₄⁺–N. Introducing upland crops into rice monoculture requires balancing trade-offs between improved N availability for plant uptake and enhanced susceptibility to N losses, emphasizing the need to develop balanced N management strategies in rice-based systems.