Comparisons of applications of sand and polyacrylamide for separating the impact of the physical and chemical properties of sodic soils on the growth and nutrition of cotton ('Gossypium hirsutum' L.)

Abstract

In Vertosols sodicity can affect the nutrition of cotton crops. However it is not known whether this results indirectly through the effects of poor soil structure on root growth and activity, or more directly as an effect of soil solution sodium ions on nutrient uptake. To separate these factors we investigated whether adding sand (25, 50 and 75% w/w) or polyacrylamide (PAM) (0.00005%, 0.001% and 0.2% w/w) to sodic and non-sodic soil would overcome the impacts of sodicity on soil physical characteristics in a pot experiment. Treatment effects on soil chemical properties were assessed through in situ measurement of soil solution composition. Soil physical properties were assessed by measurement of bulk density and water stable aggregates. As the proportion of sand in the soil increased, total soil solution nutrient concentrations decreased significantly and soil bulk density increased. This indicates that the addition of sand to sodic soils is an unsuitable method of counteracting the impacts of sodicity on soil physical characteristics in pot experiments. In contrast, increasing PAM application did not significantly affect the soil solution nutrient composition, except in the case of P, which showed a small decrease as PAM increased. Also, increasing PAM application to the soil increased the percentage of water stable aggregates, and increased infiltration and soil hydraulic conductivity. This indicates that the addition of PAM to sodic soils may be a suitable method of overcoming the impacts of sodicity on soil physical characteristics in pot experiments, although care is needed when interpreting P results.