Reclamation of salt-affected soils using pumice and algal amendments: Impact on soil salinity and the growth of lucerne

Abstract

We investigated whether individual or combined additions of either pumice (PU) and/or algae (AL) to a sandy soil could alleviate the impact of irrigation with saline water on the growth of lucerne ( Medicago sativa L. ) under simulated semi-arid conditions. The study included six treatments that received saline water (6.4 dS m −1 ): T1 (sand – positive control), T2 (sand + 3% (v/v basis) PU), T3 (sand + 12% PU), T4 (sand + 3% PU + 2% AL), T5 (sand + 12% PU + 2% AL), T6 (sand + 2% AL). A seventh treatment was T7 (sand – negative control), to which deionised water was added. All treatments underwent 14 cycles of irrigation wetting and drying events (at 27 ± 1 °C/ 16 ± 1 °C day/night). At the end of the experiment and compared with the positive control (T1) (EC: 2.3 dS m −1 ; SAR: 21.8), the two treatments with the largest application rate of PU (T5 and T3) showed the largest (significant at P < 0.05) reduction in soil EC, SAR, and water-extractable ions among those treatments receiving saline water (T1–T6). Lucerne in treatments T1–T6 always had a smaller dry weight (DW) biomass and relative growth rate (RGR) than the treatment receiving deionised water (T7) (DW: 2.29 g m −2 ; RGR: 0.073 mg g −1 d −1 ), but values for treatment T5 (DW: 1.69 g m −2 ; RGR: 0.06 mg g −1 d −1 ) were significantly larger ( P < 0.05) than for treatments T1–T4 and T6 (DW < 1.13 g m −2 ; RGR < 0.056 mg g −1 d −1 ). Overall, the results obtained suggest that, if proven feasible at a field scale, the combined addition of PU (12%), by reducing salinity and contributing to water retention, and AL (2%), by adding nutrients and/or bioactive compounds, could be used to mitigate salt stress and improve plant growth in sandy soils under arid conditions. • Our studies emphasised the benefits of applying pumice to alleviate salinity and sodicity stress in plants. • The benefits of pumice were amplified when this was added along with algae (at a 2% v/v). • Pumice-induced salt trapping could be explained by a breaking of the hydraulic connections within the water column, induced by the formation of entrapped air blocks in the pores during desiccation.