P-001 Modeling Water Flow and Nitrogen Transport in SRI

MODELING WATER FLOW AND  NITROGEN TRANSPORT IN PADDY FIELD  UNDER THE SYSTEM OF RICE INTENSIFICATION Rudiyanto1, Satyanto K. Saptomo2, Budi I. Setiawan3 Department of Agricultural Engineering, Bogor Agricultural University Kampus IPB Darmaga Bogor 16680, Indonesia e‐mail: [email protected], [email protected] [email protected] 

ABSTRACT The System of Rice Intensification (SRI) in the eastern parts of Indonesia has been reported could increase the averaged yield of 84% compared with conventional method ranging from 3.92 t/ha to 7.23 t/ha. The applied Intermittent irrigation and fertigation have important portrays in the SRI. Herewith, water flow and solute transport models are developed to simulate the fate of nitrogen concentration and its transformation. Richard’s equation coupled with the advection‐dispersion equation along with the first order transformation of NH4‐N to NO3‐N and the equilibrium nonlinear sorption condition were applied by mean of the finite volume method. Those equations were solved using Picard iteration and Newton method, respectively. Soil hydraulic properties of Sadatani paddy field in Cidanau watershed at Serang Regency, Banten Province were used as the studied materials. Two scenario of intermittent irrigation with 10 days wet followed by 5 days dry, and 5 days wet followed by 10 days dry at vegetative stages were simulated. The model could give reasonable explanations of the water flow patterns as well as those for nitrogen behaviors in the soils. The first scenario gave leaching potential of NO3‐N in shallow groundwater higher than the second scenario. However, these models need further elaborations taking into account such as effects of soil temperature in soil layers on solute transport, etc. Keywords: water flow, nitrogen transport, the system rice intensification.

• Schedule of Irrigation and Fertilizer

Introduction Cidanau watershed was covered by paddy field approximately 6,073 ha (28%) in total area of 22,072 ha (Tsuyuki and Baba, 2003) and average yield is 5.1 ton/Ha. The SRI which has high yield (average of 7.2 ton / Ha) is potential to apply in this area. Furthermore, The SRI was also known water saving due to applying intermittent irrigation during vegetative stages. We suppose that the applying intermittent irrigation is not only water saving but also affected on controlling nitrogen leaching in shallow groundwater. Thus, in this study we try to analysis consequence of intermittent irrigation to nitrogen transport by simulating the temporal dynamic of water flow and nitrogen transport in Cidanau paddy field if SRI is applied.

Materials and Method

Results and Discussion

• The Conceptual Model Scenario 1

Scenario 2

• The Governing Equation of Water Flow and Nitrogen (NH4‐N and  NO3‐N) Transport and Transformation ∂θ ∂ ⎛ ⎛ ∂h ⎞ ⎞ K ( h ) ⎜ + 1⎟ ⎟ − E = ∂t ∂z ⎜⎝ ⎝ ∂z ⎠ ⎠

∂C ⎞ ∂ ∂ ∂ ⎛ qCNH 4 − N θ C NH 4 − N + ρ S NH 4 − N = ⎜ De:NH 4 − N NH 4 − N ⎟ − ∂t ∂z ⎝ ∂z ⎠ ∂z − knit −cθ CNH 4 − N − knit − s ρ S NH 4 − N − SCNH − N

(

)

(

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4

∂θ C N 03 − N ∂t

∂C N 03 − N ∂ ⎛ = ⎜ De:N 03 − N ∂z ⎝ ∂z + knit −cθ C NH 4 − N

⎞ ∂ qC N 03 − N ⎟− ⎠ ∂z + knit − s ρ S NH 4 − N − kdenCN 03 − N − SCN 0 −N

(

)

3

• Soil Hydraulic Properties and Nitrogen Transport Parameters

Comparison of Potential of  Nitrate Leaching

During vegetative stages, both scenarios have pressure head profiles higher than air entry value (77 cm). Furthermore, both scenarios also have the same profiles at the end of maturity stages. Nitrate profile shows scenario 1 draw down faster then scenario 2. Thus, scenario 1 have higher potential of nitrate leaching.

Conclusion The model could give reasonable explanations of the water flow patterns as well as those for nitrogen behaviors in the soils. The first scenario gave leaching potential of NO3‐N in shallow groundwater higher than the second scenario. However, these models need further elaborations taking into account such as effects of soil temperature in soil layers on solute transport, etc.

JSPS-DGHE Core University Program in Applied Biosciences: "Towards Harmonization between Development and Environmental Conservation in Biological Production“ 1997/98~2007/08 The University of Tokyo