Soil Structure Degradation and Preferential Water Flow in Soil 20 Years after Land-Reclamation.

Soil land reclamation constructions were created 20 years ago in the open-cast ore mining and have been in agricultural use since that time. Land reclamation consisted in creating 60-cm soil chernozem layer above the thick sand layer. Dramatic changes occurred in soil structure of the chernozem layer due to agricultural practice. Typical soil granular aggregates of size 1-5 mm transformed into a prismatic coarse 50-mm peds with flat or rounded surface and columnar 100-mm vertically oriented blocks at the depths of 20-40 and 40-60 cm. Soil textural measurements showed that silt and clay content was less (47.8% and 6.58%) on the surfaces of peds and columnar blocks, compared to content in the inner parts (54.8% and 9.47% respectively). Opposite to silt and clay, contents of Fe and Ca were higher on the surface than inside of the soil blocks. No differences were found in pH (8.5-8.7), organic matter content and its hydrophilic and hydrophobic components in outer and inner parts of the soil blocks. Study of the soil water regime showed formation of temporary perched water above the sandy layer during intensive spring and summer rainfalls. Field starch tracer experiments revealed an existence of preferential water passways through the chernozem layer. The vertical preferential flow occurred along the block surface downward to the low permeable sandy layer that caused creating the perched water. Results of the filed tracer studies were supported by the laboratory breakthrough experiments with Cl and K tracers, and by modeling based on the results of the laboratory measured breakthrough curves. Results of the study assume that the preferential flow and the temporal perched water create favorable conditions for the soil gleization and lead to aggregate transformation from granular structure to the columnar blocks.