Reclamation of a calcareous sodic soil with combined amendments: interactive effects of chemical and organic materials on soil chemical properties

Concerns about population growth and producing adequate and nutritious food from the limited available resources have made soil conservation a top priority worldwide. This study assessed the effects of alfalfa residue (AR), sugarcane-bagasse biochar (SBB), and walnut-shell biochar (WSB) with or without gypsum (G), aluminum sulfate (AlS), and mixture of both chemical amendments on the chemical properties of a carbonated sodic soil. The organic and chemical ameliorants were added to the soil at rate of 2.5% (w/w) and the soil gypsum requirement, respectively. After a 4-month incubation, amended soils were measured for pH, electrical conductivity of saturated extract (ECe), sodium adsorption ratio (SAR), and exchangeable potassium (K) and available phosphorus (P) concentrations. Both chemical and organic amendments significantly lowered soil pH through enhancing CO2 partial pressure and/or dissolution of native soil calcites. The combined chemical and organic amendments performed more effectively than organics alone to increasing soil EC; the highest EC value was obtained by the application of G+AR (11.0 dS m−1). A synergistic effect of organic and chemical ameliorants on the replacement of exchangeable sodium by calcium was observed, which was reflected by the increased SAR values in treated soils compared with the control. Of the applied amendments, AR-alone has the best efficacy to improve soil available P by enhancing soil P concentration from 4.05 mg kg−1 in the control to 11.87 mg kg−1. Irrespective of chemical amendments, the most increase in soil exchangeable K concentration (from 45.16 mg kg−1 in the control to 274.00 mg kg−1) was obtained by applying WSB-alone to the soil. These results suggest that the partly degraded sodic soils could evolve for agricultural use by amending soils with specific kind of biochars and combined with best soil management practices.