Preferential water flow, local soil biota and structure degradation in chernozem 20 years after land-reclamation.

摘要

Technogenic soils (technozems) were created nearly 20 years ago in open-cast ore mining and have been in agricultural use since that time. Land reclamation consisted in creating a 60 cm chernozem soil layer above a thick sand layer. Dramatic changes occurred in the soil structure of the chernozem layer: typical granular soil aggregates of 1-5 mm in size transformed into coarse prismatic 50 mm peds with flat or rounded surface and columnar 100 mm vertically oriented blocks covered with brown coatings. The coatings on ped faces at the depths of 20-40 and 40-60 cm had an increased content of Fe and Ca ions, and the soil texture became coarser under conditions of alkaline medium. Study of the soil water regime showed the formation of temporary perched water above the sandy layer during intensive spring and summer rainfalls. Field starch tracer experiments revealed the existence of preferential water passageways through the chernozem layer. The vertical preferential flow occurred along the block surfaces downward, saturated the blocks and created favourable conditions for the soil gleyzation inside the ped, and for anaerobic microbiota formation (Clostridium limosum, Cl. supterminal and others); after a period of the preferential flow functioning the period of ped draining began and aerobic microbiota (Rhodococcus terrae) were developed on the surface of the ped. Such a distribution and functioning of soil biota favour the movement of Fe-ions to the surface of peds, the appearance of coatings, and the formation of prismatic coarse peds.