Influence of soil hydraulic variability on soil moisture simulations and irrigation scheduling in a maize field

Hydrological models play a crucial role for their ability to simulate water movement from soil surface to groundwater and to predict onset of stress conditions within agricultural fields. However, optimal use of mathematical models requires intensive, time consuming and expensive collection of soil related parameters. Typically soils to be characterized exhibit large variations in space and time as well during the cropping cycle, due to biological processes and agricultural management practices: tillage, irrigation, fertilization and harvest. This paper investigates the variability of soil hydraulic properties over a cropping cycle between April and September 2015, within a surface irrigated maize field (6 ha) located in northern Italy. To this aim, undisturbed and disturbed soil samples were collected from different locations within the study area and at different depths, during three measuring campaigns, at the beginning, in the middle of the cropping season and after the harvest. For each soil sample, several parameters were monitored: organic matter and bulk density together with soil hydraulic parameters. Soil parameters of Soil water retention curve parameters were measured following the evaporation method, while the saturated hydraulic conductivity was determined in the laboratory using the well-known falling head method. Results show that soil properties, mainly the saturated hydraulic conductivity, are subjected to significant variations. The variability of these parameters was taken into consideration when simulating soil moisture using FEST-WB model. An improvement in soil water content simulations was observed as compared to field measurements with implications on prediction of water stress conditions that is fundamental for irrigation scheduling.