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Assessment of Root Zone Nitrogen Leaching as Affected by Irrigation and Nutrient Management Practices

^a Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto, Japan, 606-8502
^b Dep. of Land, Air and Water Resources, University of California, Davis, CA, 95616
^c National Institute of Vegetable and Tea Science, Kanaya, Shizuoka, Japan, 428-8501
^d Division of Agriculture, Osaka Prefecture University, 1-1 Gakuen-cho, Sakai, Osaka, Japan, 599-8531

View larger version (29K): [in a new window]   Fig. 1. Schematic diagram of the soil column.

View larger version (28K): [in a new window]   Fig. 2. Ammonium adsorption isotherms for sand and an Andosol. Symbols are measured data from the batch tests. Solid lines are obtained by fitting measured data using the Freundlich type equation. r2 is the coefficient of determination.

View larger version (44K): [in a new window]   Fig. 3. Temporal changes in the concentrations of (a) total NH4–N and (b) NO3–N in sand batch tests and (c) total NH4–N and (d) NO3–N in Andosol batch tests. Values in figures represent applied NH4–N concentration (mg N kg–1). Dotted lines are fitted by using a first-order rate reaction formula for nitrification.

View larger version (36K): [in a new window]   Fig. 4. Water retention curves of sand and the Andosol. Symbols represent measured data for drying; dashed lines are interpolated from measured data. Solid and dotted lines were optimized using HYDRUS-1D for Exp. 1 and 2, respectively.

View larger version (45K): [in a new window]   Fig. 5. Measured (symbols) and calculated (lines) changes in the volumetric water content (top), NH4–N (center), and NO3–N (bottom) profiles in (a) sand and (b) Andosol columns in the case of Exp. 1 and 2 at the time points just before each solution application and at the end of experiments.

View larger version (32K): [in a new window]   Fig. 6. (top) Measured and calculated temporal changes in the cumulative seepage flux for sand and the Andosol in the case of Exp. 1 and 2. Solid lines represent calculated changes for sand and dotted lines calculated changes for Andosol. Square and circular symbols are measured values for sand and Andosol, respectively. (bottom) Calculated temporal changes in the cumulative seepage NH4–N and NO3–N fluxes for (a) sand and (b) Andosol in the case of Exp. 1 and 2. Solid lines represent NH4–N and dotted lines NO3–N.

View larger version (62K): [in a new window]   Fig. 7. Temporal changes in the precipitation and irrigation (cm d–1) and simulated temporal changes in the cumulative seepage N fluxes for sand in Model A. Heavy solid, heavy gray solid, thin solid, and thin dotted lines represent the case of lumped (S-1), two-split (S-2), three-split (S-3), and six-split (S-6) applications, respectively. Symbols represent the timing of NH4–N applications for each scenario. See Table 2 for scenario numbers.

View larger version (61K): [in a new window]   Fig. 8. Temporal changes in the precipitation and irrigation (cm d–1) and simulated temporal changes in the cumulative seepage N fluxes for the Andosol in Model A. Heavy solid, heavy gray solid, thin solid, and thin dotted lines represent the case of lumped (A-1), two-split (A-2), three-split (A-3), and six-split (A-6) applications, respectively. Symbols represent the timing of NH4–N applications for each scenario. See Table 2 for scenario numbers.

View larger version (33K): [in a new window]   Fig. 9. Grouped quartiles of N leaching fraction computed from nine samples (1992–2000) for (a) sand and (b) Andosol in Model A (top) and Model B (bottom). Scenarios represent lumped (S-1, A-1), two-split (S-2, A-2), three-split (S-3, A-3), and six-split (S-6, A-6) applications.

View larger version (50K): [in a new window]   Fig. 10. Relationship between the N leaching fraction and the total amount of precipitation during the growing season obtained by nine samples (1992–2000) for each scenario in Model A. Solid lines represent the linear regression curve. r2 is the coefficient of determination. Scenarios represent lumped (S-1, A-1), two-split (S-2, A-2), three-split (S-3, A-3), and six-split (S-6, A-6) applications.