The Effect of Chelating Agents on Soil Sodicity

Abstract

Results of laboratory and field tests suggest that chelating agents could be used to alleviate adverse soil properties caused by excess sodium, such as low permeability. Adding multi-dentate carboxylic acid chelating agents to sodic soil, or to mixtures of soil with sodium-contaminated waste, significantly reduced sodium adsorption ratio (SAR) values. Judging from cation concentrations in saturated paste (sat. paste) filtrates, chelating agents act to ameliorate soil sodicity by releasing Ca and to a lesser extent Mg from undissolved compounds. After adding chelating agents to moist soils that contained free lime, measured weight losses were consistent with CO ₂ evolution due to CaCO ₃ decomposition. The electrical conductivity (EC) of the sat. paste filtrate of materials treated with chelating agents increased less than when equivalent Ca or Mg was supplied in conventional, soluble form. Bigger sat. paste vacuum filtration volumes, improved soil permeability and faster field infiltration rates were observed after treatment with chelating agents. The Ca- and Mg-complexes of agents such as citric and malic acid degrade in moist soil; such agents could perhaps be used in a series of applications to improve ease of cultivation and permeability of cropped land. The agent ethylenediamine tetraacetic acid (EDTA) forms stable complexes, and could therefore be used as a one-time treatment for sodic materials that are to be disposed of by burial, following guidelines for soil SAR and EC.

Keywords:

• SAR
• EC
• drilling waste
• EDTA

Notes

* After 50 h, corrected for weight loss from a control vial of soil

** Estimated from the soil's CaCO₃ content, using Eqn. (3)

^†3 determinations (Klute 1965), 95 % conf. Limits.

^†Mean of four determinations, and 95% confidence limits.