Spatial variability for some properties of the wastewater irrigated soils

Composite surface soil samples (236 samples) were collected from three fodder farms irrigated for a long period with the treated sewage effluents or well water through a center pivot system. The soil of the 1st farm was loamy sand in texture while it was sandy loam for the other two farms, all were calcareous containing more than 10% of (CaCO3). The average values of EC for the 1st, 2nd and 3rd farms showed to be 3.48, 2.20 and 2.21 dS m−1, respectively. The concentration of Zn was found to be 28.87 mg kg−1 in the 1st farm, while it was 45.96 and 19.51 mg kg−1 in the 2nd and 3rd farms, respectively. The Zn, Cu, Fe and Ni concentrations were higher in the farms irrigated with the treated sewage effluent than their concentrations in those irrigated with well water. The values were 28.87, 16.95, 4225, and 72.26 mg kg−1 for Zn, Cu, Fe & Ni in 1st farm and 42.4, 60.5, 11215, and 180 mg kg−1 for the 2nd farm. The Pb in the soil of the 1st, 2nd and 3rd farms reached 63.01, 37.10 and 27.69 mg kg−1, respectively. It can be concluded that all soil properties except pH had high coefficients of variation, indicating strong variability over space. The data of geo-statistical analysis showed that only TDS and ESP in the 1st farm as well as OM in the 2nd farm had weak spatial dependency while other properties had moderate or strong spatial dependency. Moreover, the TDS and CaCO3 parameters of the 1st and 2nd farms had stronger nugget effects.