Soil–water relationships in the upper soil layer in a Mediterranean Palexerult as affected by no-tillage under excess water conditions – Influence on crop yield

• In soils with a tendency to develop a perched water table close to the surface, no tillage improved some soil hydraulic properties of 0–5 cm layer in such a way that crop development and yield were much higher than that under tillage.

In Mediterranean regions, the performance of conservation tillage under water-deficit conditions has been widely reported, but conversely there exists a lack of studies investigating its effects during periods of water excess, which are common in these regions between fall and spring. Our experiment was established in 2005 on a degraded Palexerult from a raña, a continental detritic formation, of western Spain to study the influence of soil tillage and Ca amendments on soil quality. During high precipitation periods, perched water tables can be formed in very flat raña surfaces with the upper limit close to soil surface due to the presence of Bt horizons with low permeability. In the 2010–2011 and 2012–2013 campaigns, when perched water tables developed very close to the soil surface between November and March, we studied the effects of no tillage (NT) vs. tillage (T) on selected soil hydraulic properties in the 0–5 cm soil layer and on crop yield. We observed the lowest bulk density and the highest soil organic matter content (SOM) for this soil layer under NT. As a result of the higher SOM content and higher total porosity as well as the potential to preserve soil biopores under NT, water content at saturation (SAT), plant-available water capacity (AWC), water infiltration and saturated hydraulic conductivity were also higher in the NT plots compared with those under T. During wet periods, the degree of water saturation (Sr) under T was higher, and sometimes close to saturation. Crop development and yield were strongly affected by near-saturation conditions in the 0–5 cm surface layer, resulting in substantial yield losses under T.