Changes in some physical properties of Mollisols induced by supplemental irrigation

Supplemental irrigation is becoming a common technique in the State of Santa Fe (Argentina). Irrigation water is characterized by the prevalence of bicarbonate and sodium ions, and by the low saline content. As soils have the exchangeable complex dominated by calcium, and high levels of exchangeable potassium and exchangeable acidity, we hypothesized that the negative effects of supplemental irrigation with such kind of waters on soil aggregation and water transmission would be little intense. The objectives of this research were to verify the effects of alternating supplemental irrigation and rainfall on some physical properties in superficial horizons of Mollisols. Eleven places, each one with an irrigated area (SI) and a non-irrigated area (NI), were studied. Superficial (0–7 cm) undisturbed soil samples (n = 20) were taken with a shovel at each site. Soil samples were used to measure dry-aggregation degree, wet-aggregate stability, and water infiltration rate. SI has negatively affected these soil properties. However, the effects of SI on such properties have depended on soil intrinsic factors, i.e. organic carbon, clay, silt, and exchangeable ion contents, and extrinsic factors, i.e. raindrop impact. Water infiltration was more reduced in the unprotected than in the protected treatments. Destruction of soil aggregates by dispersion and slaking were mainly responsible for the decrease of water infiltration. The results indicated that, even in soils with such special characteristics, the cumulative effects of SI on their properties should be considered when assessing irrigation strategies.