The impact of drip irrigation on soil quality in sloping orchards developed on marl – A case study

The impact of drip irrigation on structural stability of soil aggregates was studied in soils of an apple (Malus domestica Borkh.) orchard, developed on marl. The field study was carried out in a sloping (20%) terrain in the northeastern Slovenia at three slope positions (upslope, mid-slope and downslope), involving a comparison of irrigated versus non-irrigated situations after 6 years of drip irrigation practice. Structural stability was studied in three soil layers (0-5, 5-15 and 15-30 cm) at the end of the irrigation season (in September). In the same samples, soil organic carbon, total carbonates and soil moisture contents were determined. Drip irrigation significantly reduced structural stability and soil organic carbon in the surface soil layer (0-5 cm), while total carbonates increased. Based on the whole set of data, structural stability was strongly positively correlated with total carbonates and negatively correlated with soil organic carbon. This means that the effect of higher level of organic matter mineralisation on structural stability, due to irrigation, is counterbalanced by the increase of total carbonates content in the fine textured calcareous soils. Thus, a negative effect of irrigation on soil organic carbon had less destructive consequences on structural stability than expected.