Potential of Carbon Dioxide Biosequestration of Saline-Sodic Soils during Amelioration under Rice-Wheat Land Use

Potential for carbon dioxide (CO2) biosequestration was determined during the reclamation of highly saline-sodic soils (Aridisols) after rice (2003) and wheat (2003-2004) crops at two sites in District Faisalabad, Pakistan. Two treatments were assessed: T-1, tube-well brackish water only; and T-2, soil-applied gypsum at 25% soil gypsum requirement+tube-well brackish water. The irrigation water used at both sites had different levels of salinity (EC 3.9-4.5 dS m(-1)), sodicity (SAR 21.7-28.8), and residual sodium carbonate (14.9 mmol(c) L-1). Composite soil samples were collected from soil depths of 0-15 and 15-30 cm at presowing and postharvest stages and analyzed for pH, ECe, and sodium adsorption ratio (SAR). After rice harvest, there was no significant effect of gypsum application on ECe, pH, and SAR at both sites, except pH at 0-15 cm depth decreased significantly with gypsum at site 1. After wheat harvest, ECe, pH, and SAR decreased significantly with gypsum at site 1, whereas the effect of gypsum on these parameters was not significant at site 2. Compared to initial soil, ECe and SAR in soil decreased considerably after rice or wheat cultivation, particularly at site 1, whereas pH increased slightly due to cultivation of these crops. For rice, the total CO2 sequestration was significantly increased with gypsum application at both sites and ranged from 1499 to 2801 kg ha(-1). The total sequestration of CO2 was also significantly increased with gypsum application in wheat at both sites and ranged from 2230 to 3646 kg ha(-1). The amounts of CO2 sequestered by crops due to gypsum application were related to seed and straw yield responses of rice and wheat to gypsum, which were greater at site 1 than site 2. Also, the yield response to applied gypsum was greater for rice than wheat at site 1, whereas the opposite was true at site 2. Overall, the combined application of gypsum with brackish water reduced soil ECe and SAR compared to brackish water alone, particularly at site 1. Our findings also suggest that the reclamation strategies should be site specific, depending on soil type and quality of brackish water used for irrigation of crops. In conclusion, the use of gypsum is recommended on brackish water-irrigated salt-prone soils to improve their quality, and for enhancing C biosequestration and crop production for efficient resource management.