Design and evaluation of saline irrigation schedules to cope with drought and scarce fresh water

The aim of the work is to describe for two different coastal pedo-climatic areas of Southern Italy and one area in NW China the effects that saline water and drought have had on the soil physical properties. On these soils the observed changes in soil physical properties after long-term salt accumulation will be reported. The observed differences in soil hydrological properties of saline soils may have a significant impact on the temporal variability of soil water content, e.g. on frequency and duration of soil water con-tent lower than a pre-defined critical threshold. To this end the soil water balance calculations will be per-formed for a range of different meteorological conditions, in particular when a dry, wet and normal cli-matic year occurs. To do that the SWAP numerical model (vers 2.0.7d) has been used. The water balance calculations will be used to evaluate the water storage in the profile through the year. At Torre Lama the h(θ) curve of the 1% saline water treatments had lower values of θ than the 0% treatments at the same pressure head. Different behaviour was observed for Vitulazio, the total porosity for the I0 treatment is around 0.55 against 0.58 of the I1 treatment, in contrast with what observed for the Torre Lama site. Such difference could depend from the shorter duration of saline-sodic water application at the Vitulazio (2 years) site than Torre Lama (5 years). Moreover the difference between Torre Lama and Vitulazio might depend from the difference in the type of clay minerals. In fact at Vitulazio there is an abundance of smectite-type clay in the soil. Despite the difference in total porosity of the two sites the soil water available (AW) calculated in the range of 100 cm and 104 cm pressure head, for a layer of 100 cm depth, show a similar trend at the two sites. At Torre Lama for all the irrigation frequencies and depths considered, the non-saline treatment had lower AW-values than the saline treatments. At Vitulazio, even if the total porosity was in contrast with Torre Lama, the calculated soil water available had the same trend. In fact the I0 treatment at Vitulazio had an AW-value of 128.1 mm against the 178.4 mm of the I1 treatment. The total porosity at Torre Lama changes from about 29% (I0 treatment) to 20% for the I1. Moreover for the Vitulazio site the total porosity changes from a value of 21% for the I0 treatment, to 15% for the I1 treatment. The numerical experiments have shown that the already clear difference in h(θ) and K(h) of the I0 and I1 treatments is reflected in significantly higher AW values of I1 against the I0 throughout the year. The persistence of soil water deficit is also lower for the I1 than for the I0 treatment, as shown by the lower number of days with AW < soil water retention capacity.