Hydro-physical characterization of contrasting soils in a semiarid zone of the Ebro river valley (NE Spain)

The arid agricultural lands of the Monegros Desert, in the central Ebro Basin (NE Spain), show contrasting white patches (WPs) and dark patches (DPs), evidencing their different soil composition. The white patches have shallow soils with low or nil crop development in most years. Soil at the dark patches uses to be deeper, and winter cereal attains better development. This paper analyzes soil hydro-physical features in order to identify differences in soil physical properties between white and dark soils. For this purpose, 20 pairs of WP/DP soils were studied on several agricultural plots. Each sampled pair was under the same soil condition. Three soil treatment (ST) were studied: freshly tilled soil (MB), cropped (C), and fallowed soil (F). The gypsum and calcium carbonate content, organic matter (OM) content, and particle size distribution for the 0–10 cm depth soil were determined. Field measurements for the 1–10 cm depth soil layer were soil bulk density (ρb), soil penetration resistance (SPR), saturated hydraulic conductivity (K1–10) and sorptivity (S1–10). The water retention curve (WRC) was determined in the lab on undisturbed soil cores for the 1–10 cm depth soil layer. Additional field measurements of soil surface crust sorptivity (Scrust) and hydraulic conductivity (Kcrust) at saturation were also performed. The results show that WP soils have significantly (p < 0.05) higher contents of gypsum, lower contents of calcium carbonate and OM, and a coarser texture than DP soils. Compared to DP, the WP soils have higher values of SPR but lower ρb, K and S values in both the surface crust and the 0–10 cm depth soil layer. On average, K1–10 in DP was 1.4 times higher than that measured in WP. DP showed a better-defined microstructure and retained more water retention at near saturation conditions than WP. Soil treatments have a significant effect on ρb, SPR, S1–10, K1–10 and on the WRC parameters. Overall, ρb and SPR was the lowest under MB, with maximal S1–10 and K1–10 values under C. Compared to C and F, MB presented the highest volume of structural porosity and the lowest water retention at near saturation conditions.