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<p>Rice production in Asian and African continents relies heavily on urea fertilizer, yet nitrogen use efficiency (NUE) in flooded rice systems remains low because conventional broadcast application of prilled/granular urea results in substantial N losses through different pathways. Urea deep placement (UDP) is a fertilizer application method which involves placement of urea supergranules or urea briquettes below the soil surface, close to the plant root zone, instead of being broadcast on the soil or flooded water surface. UDP has been widely investigated as an alternative strategy to improve rice yields, N uptake and NUE. This review synthesizes evidence on the agronomic, economic, environmental, and operational performance of UDP across rice systems in Asia and Africa, and position UDP relative to other contemporary N-management approaches. A meta-analysis of 34 peer-reviewed studies was conducted comparing UDP with farmers’ practice. Results of the meta-analysis showed that one-time UDP increased grain yield by 14.6% on average, agronomic N use efficiency by 38%, and recovery efficiency of N by 21.3%, although response magnitude varied with soil, climate, season, and management. The evidence further indicated that UDP performs best in flooded transplanted rice grown on medium- to fine-textured soils with relatively low percolation rates, where deep placement favors retention of ammonium in the root zone and reduces exposure of fertilizer N to floodwater. Grain yield and NUE benefits were observed to be greater in wet-season, tropical to subtropical, and moderate- to high-rainfall environments. Compared with approaches such as site-specific nutrient management and real-time N diagnostics, UDP offered a distinct placement-based mechanism for improving NUE and may be deployed either as a stand-alone basal strategy or can be combined with diagnostic tools for in-season adjustment. In addition to improving yield and profitability, UDP consistently reduced NH<sub>3</sub> volatilization, N<sub>2</sub>O and CH<sub>4</sub> emissions, and yield-scaled global warming potential relative to broadcast application of urea. However, wider adoption of UDP remains constrained by labor demand, inconsistent urea briquette supply, and limited access to affordable and reliable mechanical applicators. Overall, the review showed that UDP should be promoted not as a universal recommendation, but as a targeted, ecosystem-specific technology whose successful scaling will depend greatly on mechanization, improved delivery systems, and integration with locally adapted extension strategies.</p>

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Urea deep placement in rice systems of Asia and Africa: a review of yield performance, nitrogen use efficiency, environmental benefits, mechanization and adoption potential

  • 期刊论文

  • 发表日期：

    2026年7月29日

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  • Yashpal Singh Saharawat,
  • Yadvinder Singh,
  • Upendra Singh,
  • Padma Shanthi Jagadabhi,
  • Harminder Singh Sidhu,
  • Chitar Mal Parihar,
  • John Wesley Lowe,
  • Ishrat Jahan,
  • Yam Ghaire,
  • Dharamvir Singh Rana,
  • Mahesh Kumar Gathala,
  • Alison Laing

摘要

Rice production in Asian and African continents relies heavily on urea fertilizer, yet nitrogen use efficiency (NUE) in flooded rice systems remains low because conventional broadcast application of prilled/granular urea results in substantial N losses through different pathways. Urea deep placement (UDP) is a fertilizer application method which involves placement of urea supergranules or urea briquettes below the soil surface, close to the plant root zone, instead of being broadcast on the soil or flooded water surface. UDP has been widely investigated as an alternative strategy to improve rice yields, N uptake and NUE. This review synthesizes evidence on the agronomic, economic, environmental, and operational performance of UDP across rice systems in Asia and Africa, and position UDP relative to other contemporary N-management approaches. A meta-analysis of 34 peer-reviewed studies was conducted comparing UDP with farmers’ practice. Results of the meta-analysis showed that one-time UDP increased grain yield by 14.6% on average, agronomic N use efficiency by 38%, and recovery efficiency of N by 21.3%, although response magnitude varied with soil, climate, season, and management. The evidence further indicated that UDP performs best in flooded transplanted rice grown on medium- to fine-textured soils with relatively low percolation rates, where deep placement favors retention of ammonium in the root zone and reduces exposure of fertilizer N to floodwater. Grain yield and NUE benefits were observed to be greater in wet-season, tropical to subtropical, and moderate- to high-rainfall environments. Compared with approaches such as site-specific nutrient management and real-time N diagnostics, UDP offered a distinct placement-based mechanism for improving NUE and may be deployed either as a stand-alone basal strategy or can be combined with diagnostic tools for in-season adjustment. In addition to improving yield and profitability, UDP consistently reduced NH3 volatilization, N2O and CH4 emissions, and yield-scaled global warming potential relative to broadcast application of urea. However, wider adoption of UDP remains constrained by labor demand, inconsistent urea briquette supply, and limited access to affordable and reliable mechanical applicators. Overall, the review showed that UDP should be promoted not as a universal recommendation, but as a targeted, ecosystem-specific technology whose successful scaling will depend greatly on mechanization, improved delivery systems, and integration with locally adapted extension strategies.