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19The use of lay-flat polyethylene pipes for microirrigation of horticultural crops has been 20 receiving a widespread attention in the last few decades. The industry has made significant 21 improvements in the hydraulic performance of lay-flat pipes, so that their use is still expected to 22 increase, mainly because of the enhanced competition for water worldwide, that imposes the use of 23 irrigation systems with potentially high application efficiencies and characterized by a limited 24 installation costs. for the three pipes to 0.11 mm, 0.19 mm and 0.10 mm, resulted higher than those obtained with the 37 photographic method, whose values resulted generally lower than 0.06 mm. At the same time, the 38 tests allowed to identify that most of the changes of the pipe dimensions occur in the range of 39 pressure from 0 kPa to about 30 kPa, being the dimensions quite similar at higher values, when the 40 pipes tend to assume a round cross section. When water pressures increase over a certain limit, p lim , 41 both vertical width and horizontal height still tend to rise, because of the pipe deformation due to 42 the elasticity of the material, with a trend that resulted more marked for the pipe with the lowest 43 thicknesses. According to the experimental data, the relationships between the pipe effective 44 diameter, to be used to evaluate pipe friction loss, and the water pressure, were then determined on 45 the three considered pipes. 46On the other side, based on measured friction losses and on pipe effective diameters, it was verified 47 that the relationship between the Darcy-Weisbach friction factor, f, and the Reynolds number, R, 48 can be still described with a power equation in which, by assuming a value of -0.25 for the 49 exponent, the coefficient resulted lower than the theoretical and equal to c=0.285. 50For the three investigated pipes the errors associated to estimated friction loss per unit pipe length 51 were finally evaluated by considering: i) the experimental relationships between friction factor and 52

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Abstract. Irrigated agriculture is threatened by soil salinity in numerous arid and semi-arid areas of the world, chiefly caused by the use of highly salinity irrigation water, compounded by excessive evapotranspiration. Given this threat, efficient field assessment methods are needed to monitor the dynamics of soil salinity in salt-affected irrigated lands and evaluate the performance of management strategies. In this study, we report on the results of an irrigation experiment with the main objective of evaluating time-lapse inversion of electromagnetic induction (EMI) data and hydrological modelling in field assessment of soil salinity dynamics. Four experimental plots were established and irrigated 12 times during a 2-month period, with water at four different salinity levels (1, 4, 8 and 12 dS m−1) using a drip irrigation system. Time-lapse apparent electrical conductivity (σa) data were collected four times during the experiment period using the CMD Mini-Explorer. Prior to inversion of time-lapse σa data, a numerical experiment was performed by 2D simulations of the water and solute infiltration and redistribution process in synthetic transects, generated by using the statistical distribution of the hydraulic properties in the study area. These simulations gave known spatio-temporal distribution of water contents and solute concentrations and thus of bulk electrical conductivity (σb), which in turn were used to obtain known structures of apparent electrical conductivity, σa. These synthetic distributions were used for a preliminary understanding of how the physical context may influence the EMI-based σa readings carried out in the monitored transects as well as being used to optimize the smoothing parameter to be used in the inversion of σa readings. With this prior information at hand, we inverted the time-lapse field σa data and interpreted the results in terms of concentration distributions over time. The proposed approach, using preliminary hydrological simulations to understand the potential role of the variability of the physical system to be monitored by EMI, may actually allow for a better choice of the inversion parameters and interpretation of EMI readings, thus increasing the potentiality of using the electromagnetic induction technique for rapid and non-invasive investigation of spatio-temporal variability in soil salinity over large areas.

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