MEASUREMENTS AND MATHEMATICAL MODELING OF WATER FLUXES IN AN AGRO-ECOSYSTEM OF MAIZE.

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During the agricultural seasons 2010 and 2011, monitoring work was carried out in maize field in the experimental farm “A. Menozzi” (Landriano-Pavia) of the University of Milan. Measurements of water balance components on field scale (soil humidity, evapotranspiration, soil water potential, groundwater table depth etc.) were used to build enriched database to be utilized in this study. Water retention characteristics are crucial input parameters in modeling of water flow and solute transport. Several field methods, laboratory methods and theoretical models for such determinations exist, each having their own limitations and advantages (Stephens, 1994). Comparisons between estimated, field and laboratory results is vital to test their validity under different conditions. This study attempts to evaluate and compare those methods. The soil water retention characteristics were determined in two representative sites (PMI-1 and PMI-5) located in Landriano field, in Lombardy region, northern Italy. In the laboratory, values of both volumetric water content (θ) and soil water matric potential (h) were measured using the tensiometric box and pressure plate apparatus. In field soil water content was measured with SENTEK probes, and matric potential with tensiometers. The retention curve characteristics were determined by common and recent PTFs that use soil properties such as particle-size distribution (sand, silt, and clay content), organic matter or organic carbon content, and dry bulk density. Field methods are more representative than laboratory and estimation methods for determining water retention characteristics (Marion et al., 1996). Therefore, field retention curves were compared against retention curves obtained from laboratory measurements and PTFs estimations using root mean square error (RMSE) and bias. The laboratory measurements showed the highest ranking for the validation indices. The second best technique was the PTF Rosetta (Schaap et al. 2001). The lowest prediction accuracy was observed for the Rawls and Brakensiek (1985) PTF which is in contradiction with previous finding (Calzolari et al., 2001), showing that this function is well representing the retention characteristics of the area. We conclude that the Rosetta PTF developed by Schaap et al (2001) appears to be well suited to predict the soil moisture retention curve from easily available soil properties. Modeling water dynamics in the Soil-Plant-Atmosphere (SPA) continuum is an important aspect of crop water management and water transfer through the unsaturated zone is a key hydrological process connecting atmosphere, surface water and groundwater. Many simulation models of water dynamics in the SPA and/or soil crop system have already been developed. Therefore, the use of simplified agro-hydrological models may represent a useful and simple tool to simulate water fluxes VI in the SPA. A physically based approach model SWAP (Van Dam et al., 1997) and a conceptual model IDRAGRA (Gandolfi et al., 2011) were selected to evaluate their performance in…