Solute transport modeling under cultivated sandy soils and transient water regime

Drainable lysimeters offer the possibility to integrate heterogeneous solute leaching conditions caused by row crops and transient water regime, and to conveniently measure water and solute fluxes at the drainage outlet. To compare solute leaching behavior in and around drainable lysimeters operating under a transient water regime in potato (Solanum tuberosum L.) fields, parameters of the convective lognormal transfer (CLT) function model were fitted using bromide (Br^-) flux concentrations (C^f) measured in lysimeters and from Br^- resident concentrations (C^r) measured in adjacent soil cores. Expected mean values E_z(I) obtained from C^r and C^f CLT parameters were equivalent and well correlated (R² = 0.78). However, estimated median values μ of the CLT function were smaller when derived from Cr (1.05 to 1.28) compared with C^f (1.23 to 2.14). Most μ values were also smaller than previously reported values for a 30-cm reference depth, indicating that 50% of solute mass would leach more readily in these coarse sandy soils. Higher variance and dispersion of C^r compared with those of C^f could be related to a smaller sampling support (sample size/sampling area) in the case of C^r measured by soil coring, or to disruption of solute transport mechanisms in the repacked lysimeter. Retained Br^- in the top soil layer after 12 to 17 cm of cumulative drainage was indicated by measured C^r. Neither CLT function simulated well residual topsoil C^r values, indicating that Br^- plant cycling or preferential flow probably interfered even though tuber Br^- uptake was relatively small.