Evaluation of soil hydraulic parameters for soil water distribution modelsunder drip irrigation

The transient analytical solutions for water distribution from point source are dependent on the soil parameters a from Gardner equation, i.e., k(h) = K-s e(alpha h) and the linearization parameter k=dK(theta)/d theta assumed constant in the derivation of these solutions. Errors in obtaining these p arameters result in failure of the solutions. The objective of this work wa s to evaluate the parameter a and k at different locations in the wetted vo lume under an isolated and a cyclic infiltration process. Matric potential data were collected in several positions of the wetted volume in two situat ions: (i) beginning of irrigation until steady-state, i.e., only during inf iltration process, and (ii) during two irrigation cycles involving infiltra tion and redistribution processes. The results showed that alpha and k para meters vary at different locations of the wetted volume related to the drip per according to the water regime at these locations. The use of inverse me thod for obtaining these parameters requires matric potential data from inf iltration and redistribution during at least two irrigation cycles.