Reclamation of a scalded, red duplex soil by waterponding

Abstract

In semi-arid New South Wales, waterponding is successfully used to reclaim red duplex soils which have been scalded by wind and water erosion exacerbated by overgrazing and drought. Reclamation was studied by comparing profiles under scald, 7 month old and 22 year old ponds, as well as under a sandy hummock and a naturally revegetated patch. The scalded soils were generally bare of vegetation, having crusted, silt loam A horizons over red, silty clay B horizons, which were saline and sodic with well developed structure. Infiltration was slow, causing rainfall to be lost by runoff and evaporation. Under recent ponds, there had been leaching of soluble salts but few other changes. Under older ponds and naturally reclaimed sites, besides leaching, the structure of the B horizon had become massive with the formation of large shrinkage cracks on drying which break open the crust. In thin section, the fabric showed more birefringent clay and there were some pore coatings of dispersed clay. These observations lead to the hypothesis that initial revegetation is a result of reduction in run-off and increased infiltration and possibly leaching of soluble salts. In the longer term, leaching causes reorganization of clay in the sodic B horizon and formation of a massive structure with shrinkage cracks which dramatically improve the infiltration rate. For waterponding to cause revegetation by this process, the soils should have a clay subsoil with shrink/swell potential and high sodicity so that restructuring takes place on leaching.