Polyacrylamide dissolved in low-quality water effects on structure stability of soils varying in texture and clay type

Efficacy of polyacrylamide (PAM), a water-soluble soil conditioner, prepared with poor-quality water (low salinity, higher sodicity) commonly available to farm managers, is unknown. We studied the effects of treating aggregates of four soils with predominant smectitic or kaolinitic clay mineralogy with PAM solution prepared with poor-quality water (low salinity and high sodicity). Impact of PAM on pore size distribution (PSD) and structure stability of the soils and the relations between the stability indices obtained were studied from water retention curves derived at low suction (0–50 hPa). The retention curves were characterized by a modified van Genuchten model that yields (i) the model parameters α and n and (ii) a soil structure index (SI). Applying PAM modified the water retention curve shape, mostly in the smectite soils, and increased α and improved SI up to 3.3 and 1.7 times in the smectitic and kaolinitic soils, respectively, relative to the control. An observed exponential relationship between soil SI and parameter ɑ allowed predicting the effects of PAM addition on soil structure stability. The noted improvement in structure stability was comparable with results for conditions where PAM solution was prepared with good-quality water. Abbreviations: PAM, polyacrylamide; SAR, sodium adsorption ratio; EC, electrical conductivity; HEMC, high-energy moisture characteristic; VDP, volume of drainable pores; MS, modal suction; SI, structural index; PSD, pore size distribution.