2020 Volume 62 Issue 1 Pages 51-59
Forestation in drylands has been progressing to prevent desertification and mitigate climate change. Aiming to improve the water holding capacity of soils and increase survival and growth of tree seedlings, superabsorbent polymers (SAP) are sometimes used in dry and semi-dry climates. We reviewed the basic knowledge of the physical, chemical, and biological properties of soils amended with SAP. We also discussed the effective usage of SAP in forestation. Soils amended by SAP have the following characteristics: 1) increased water holding capacity, which is evident in sandy soils rather than clayey soils; 2) soil water potential in SAP-amended soils mostly applies to water below pF 2.5 (readily available water), and to a lesser extent to water over pF 4.2 (unavailable water); 3) water retention and absorption curves show a hysteresis, indicating that a greater volume of water is held during the desorption process; 4) SAP application is not effective in high salinity water; 5) the large size of SAP improves pore characteristics of heavy-clay soils by creating coarse pores in the soil; 6) SAP expansion by water absorption decreases water permeability in the soil; 7) cation exchangeable capacity (CEC) of soil increases by SAP application; 8) soil microbial biomass increases due to the soil moistening by SAP; 9) no harmful effect on the environmental contamination is detected after SAP application. We recommend limiting the effective use of SAP to sandy or stony soils with coarse pores and soil with relatively low salinity in drylands. Further study is needed to develop the combined use of fertilizers and SAP in order to improve the quality of degraded infertile soils.
