Managing soil salinity with permanent bed planting in irrigated production systems in Central Asia

Land degradation due to water logging and its influence on secondary soil salinization processes pose a major threat to the sustainability of irrigated agriculture in the semi-arid production ecologies of Central Asia. In rainfed conditions, conservation agriculture (CA) practices, i.e., reduced tillage, residue retention and crop rotation, have proven to have substantial scope for arresting or reversing soil degradation. Previous research findings suggest that CA can be beneficially applied to irrigated croplands as well, but influences on salinization processes are insufficiently documented. This study investigates the effect of CA practices on soil salinity dynamics in irrigated production systems in the Khorezm region, Uzbekistan, Central Asia. The study was conducted under a cotton-wheat-maize rotation system, typical for the region, from 2007 to 2009 with two tillage methods ('CA' - permanent raised beds (PB); conventional tillage (CT)) combined with two residue levels (residue harvested (RH); residue retained (RR)). Compared to pre-experiment levels, salinity in the top 30 cm soil increased significantly during cotton (May-October), while a negligible change occurred during wheat (October-June) and maize (July-September) season. In absence of crop residues, soil salinity on top of the beds increased compared to CT without crop residue retention. When retaining crop residues, the soil salinity under PB was reduced by 32% in the top 10 cm and by 22% over the top 90 cm soil profile compared to CT without crop residue retention. Thus, PB + RR seems a promising option to slow down on-going soil salinization in salt-affected agro-ecologies such as those in the irrigated arid lands of Central Asia. (C) 2015 Elsevier B.V. All rights reserved.