Effects of Rice Husk Biochar and Calcium Amendment on Remediation of Saline Soil from Rice-shrimp Cropping System in Vietnamese Mekong Delta

In a rice-shrimp cropping system in Vietnamese Mekong Delta, more effective techniques are required to remediate the saline soils for lowing salinity to secure rice growth and productivity. The objective of this study was to evaluate the reclamation potential of biochar and calcium in laboratory experiments using a saline soil sample from the rice-shrimp system. Our hypothesis was that the addition of biochar might improve the infiltration rate, so remove salts more effectively, in particular sodium, from the saline soil. The experiment was set up with two kinds of rice husk biochar at rates of 0 and 50 g kg-1 combining with three levels of CaO (0, 0.5 and 2 g kg-1 soil, equivalent to 0, 0.5 and 2 Mg ha-1, respectively). Results indicated that biochar enhanced significantly drainage speed by 4 times compared to the control without biochar application. After leaching, exchangeable sodium percentage (ESP) in the soils was significantly lower in biochar treatments than in the control. Some other chemical indicators (K:Na and Ca:Na ratios) were also higher in biochar treatments. Although both biochars effectively removed salts from the saline soil, biochar with a lower Na+ adsorption capacity, a lower surface area and a higher amount of salts performed better in removing Na+ from soil. Combined application of biochar and CaO at low dose was more effective in improving soil properties related to Na+ leaching and ESP.