effect of organic and inorganic amendments on parameters of water retention curve, bulk density and aggregate diameter of a saline-sodic soil

to study the effects of soil amendments on physical and hydraulic properties of a saline-sodic sandy clay loam soil, a field experiment was carried out as a complete block design with three replications. the treatments in this research consisted of control (b), 10 ton ha-1 gypsum (g), 10 ton ha-1 urban solid compost (c), three levels of vinyl alcohol acrylic acid (s1= 0.05%, s2= 0.1%, s3= 0.2%), cs1, cs2, cs3, gs1, gs2, gs3cgs1, cgs2, and cgs3. four months after applying the treatments, water contents were measured at 9 pressure heads for each treatment and data obtained were fitted to van genuchten equation. the parameters of this equation (i.e. θs, θr, α, and n) were determined by the least square error method. also some physical properties including bulk density (bd), mean weight diameter (mwd) of aggregates, plant available water content (pawc), and the slope of water retention curve at inflection point (s index) were measured. the results showed that all treatments increased saturated water content (θs) significantly (p< 0.05) compared with the control (b). a similar trend was observed for residual water content (θr). the highest and lowest values of α were noted in b and s2 treatments, respectively. pawcs increased significantly in all treatments compared with control ones except for g, gs1, gs2,and gs3 treatments (p< 0.05). adding the soil amendments increased the values of s index and mwd and decreased bd, significantly compared with the b treatment. it seems that the mixture of vinyl alcohol acrylic acid at 0.1% with urban solid compost or gypsum is a suitable amendment for increasing awc and improving physical quality of studied saline-sodic soils.