Using organic matter with chemical amendments to improve calcareous sodic soil

Kangping soil in northeast China is a sodic soil characterized by a high pH and excessive sodium. The high pH and excessive sodium in sodic soils generally cause loss of soil structure, reduce hydraulic conductivity (HC), increase soil hardness, and make the soil unproductive land. After we mixed organic matter (rice straw) and chemical amendments (H2SO4, CaSO4, and FeSO4), a column experiment was conducted to evaluate the physical and chemical properties of the soil influenced by the changes in HC, penetrability of soil surface, pH, electrical conductivity, CO32- HCO3-, Ca2+, Na+, sodium adsorption rate (SAR), available phosphorus (P) and iron (Fe), and leached P. Organic matter decreased the concentrations CO32-, HCO3-, and Na+ in soil solution and increased the total volume of the leachate. Organic matter also reduced the amount of available Fe and increased the available P. However, organic matter did not affect the penetrability of the soil surface as much as soil hardness, HC, and SAR within the short period of this experiment. Among the chemical amendments, H2SO4 and FeSO4 were more effective than CaSO4 to restore HC, electrical conductivity, Na+, and SAR. The chemical amendments, compared with organic matter, significantly leached P from the soil in this study, but the leaching was independent of the concentration of available P in the soil. The CaSO4 had the strongest effect in increasing leached P from the soil without changing the concentration of available P in the soil. Organic matter with added CaSO4 leached P from the soil more than all other treatments.