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An Inverse Method to Estimate the Source-Sink Term in the Nitrate Transport Equation

Dep. of Soil and Water Sciences and Key Lab., of Plant-Soil Interactions, MOE, College of Resources and Environment, China Agricultural Univ., Beijing 100094, China

Renduo Zhang

School of Environ. Science and Eng., Sun Yat-Sen (Zhongshan) Univ., Guangzhou 510275, China

View larger version (30K): [in this window] [in a new window]   Fig. 1. Randomly generated "measured" and fitted NO3––N concentration distributions at different times.

View larger version (24K): [in this window] [in a new window]   Fig. 2. Comparison of the estimated and theoretical distributions of the average source-sink term (SST) in the convection-dispersion equation (CDE) for (a) spatial intervals SI = 5–10, 5–20, 5–30 cm (Ex. 1a); and (b) time intervals T = 5, 10, 15, 30 d (Ex. 1b).

View larger version (16K): [in this window] [in a new window]   Fig. 3. Comparison of the estimated and theoretical distributions of the average source-sink term (SST) in the convection-dispersion equation (CDE) with a time interval T = 10 d and a spatial interval SI = 5–10 cm for a two-layered soil profile (Ex. 2b).

View larger version (23K): [in this window] [in a new window]   Fig. 4. (a) Theoretical, randomly generated "measured," and fitted soil NO3––N concentration distributions; and (b) comparison of the estimated and theoretical distributions of the average source-sink term (SST) in the convection-dispersion equation (CDE), at a time interval T = 10 d and a spatial interval SI = 5–10 cm for different relative error RE = 10%, 20% and 30% of measured nitrate concentrations (Ex. 3).

View larger version (30K): [in this window] [in a new window]   Fig. 5. The average root-nitrate-uptake (RNU) rate distributions during different irrigation periods (DAP: days after planting) (a) estimated using the proposed inverse method; and (b) calculated with the established RNU models and the simulated NO3––N concentrations (Ex. 4).