Effects of super-absorbent polymers on the physical and chemical properties of soil following different wetting and drying cycles

Super-absorbent polymers (SAPs), a group of new water-saving materials and soil conditioners, have been widely adopted in agriculture, but little is known about their effects on soil physical and chemical properties under alternating dry and wet conditions. This study assesses soil moisture, bulk density, pH, electrical conductivity (EC) and available P and K after different wetting and drying cycles. Four types of SAPs, labelled BF, JP, BJ and WT, with organic macromolecules were mixed with sandy soils to give concentrations of 0%, 0.05%, 0.1%, 0.2% and 0.3%, with the aim of determining water retention and soil properties after amendment with the SAPs. Soil moisture increased by 6.2-32.8% with SAP application, while soil bulk density was reduced by 5.5-9.4% relative to the control, especially with a moderate water deficit when the relative soil moisture contents were about 40-50%. The largest increase in soil moisture and the greatest reduction in bulk density resulted from the WT treatment. The effects of SAPs on soil pH and EC were contrary. Soil available P increased slightly while available K significantly decreased, except following the first wetting and drying cycle. Available K increased with drying, but the opposite effect was observed for available P. Particular SAPs (JP and WT) seem more suitable under alternating dry and wet conditions. The effects on soil-water retention and other soil properties varied according to the structure of the SAP and soil moisture.