Figures (2)  Tables (1)

    • Figure 1. 

      Rates of N inputs and transformations in low and high N-input rice paddies, including N fertilization rate (kg urea: N·ha−1·d−1), N2 fixation rates (kg N2: N·ha−1·d−1), dissimilatory nitrate reduction to ammonium (DNRA) rates (kg NH4: N·ha−1·d−1), and denitrification rates (kg N2: N·ha−1·d−1). The values associated with each N cycling process above represent the activity during the active tillering stage of rice when the measurement was conducted.

    • Figure 2. 

      The optimal N application to maximize economic and environmental performance in (a) monsoon and (b) dry seasons for achieving ROI-100 and ROI-0. ROI-100: 100% return on investment; ROI-0: marginal revenue equals marginal cost for additional N fertilizer input.

    • N fertilizer strategy N fertilizer rate
      (kg·N·ha−1)      		 Yield benefit
      (US$\boldsymbol{\$} $·ha−1)      		 Social costs
      (US$\boldsymbol{\$} $·ha−1)      		 NEBa
      (US$\boldsymbol{\$} $·ha−1)      		 NEEBb
      (US$\boldsymbol{\$} $·ha−1)
      FPc (survey) Monsoon 77 833 111 607 496
      Dry 77 817 186 600 414
      DoAd Monsoon 90 852 113 616 503
      Dry 90 842 201 615 414
      ON-ROI-0e Monsoon 83 847 109 617 507
      Dry 202 972 501 661 160
      EON-ROI-0f Monsoon 66 832 102 614 511
      Dry 48 769 140 574 434
      a NEB: the net economic benefit, which is calculated as the yield income minus all on-farm costs, including the cost of synthetic N fertilizer, input costs for seeds, pesticides, variable costs for hired labor (land preparation, establishment, weeding, pesticide application, and harvesting), and fixed costs for renting tractors and harvesters. b NEEB: the net ecosystem economic benefit, which is calculated as the NEB minus all Nr damage costs. c FP from the household survey, interviewing approximately six hundred farmers from the villages where fertilizer yield response trials took place in 2018[32]. d DoA: the national recommendations from Myanmar Department of Agriculture[29]. e ON-ROI-0: economic optimal N rate in this study.f EON-ROI-0: ecological optimal N rate in this study.

      Table 1. 

      The economic and environmental performance of different nitrogen fertilizer application strategies for dry and monsoon season rice in Myanmar