Evaluating field measured soil hydraulic properties in water transport simulations using the RZWQM

Better understanding and quantification of infiltration and water movement in macroporous soils is extremely important, both for optimising the use of water in agriculture and for minimising preferential transport of nitrogen and pesticides to groundwater. The methods of measuring soil hydraulic properties by conventional methods do not distinguish between the soil matrix and macropores that may be present in the sampled soil. The objective of this work is to evaluate a two-domain model of infiltration using the conventionally measured soil hydraulic properties considered as soil matrix properties, supplemented by macropore flow capacity measured with a tension infiltrometer. To determine the soil hydraulic characteristics a two step method was used, using field data from an infiltration redistribution experiment and running the Root Zone Water Quality Model (RZWQM) in the inverse mode. The results indicate that there is the need to develop a new technique to determine appropriate soil matrix and macropore properties in macroporous field soils. The hydraulic properties determined by conventional methods are apparently the properties of soil matrix, but seem to miss the effect of larger pores that are below the 1.0 mm diameter assumed to be the lower limit for macropores. The macropore properties determined with a tension infiltrometer apparently do not distinguish between continuous and dead-end macropores, and do not give any indication about the continuity of macropores with depth.