Structure Lime as a Soil Amendment: Impacts on Nutrient Loss Risk and Soil Health

We investigated the impact of structure lime (SL) on soil structural stability and phosphorus (P) loss risk from fine-textured mineral soils, as well as its effects on soil fertility, bacterial and fungal communities, and soil carbon (C) dynamics. Effects on erosion and P loss risks were studied utilising rainfall simulation after laboratory incubation of 14 soils with three SL addition levels and untreated control. In addition, soil samples were collected from six fields that had received a single SL treatment between 1 and 6 years prior to sampling and were compared with adjacent untreated control areas. Soil samples from the plough layer of SL-treated fields were analysed for plant-available nutrient contents and subjected to DNA sequencing. Further, the total C content as well as bulk density (BD) were determined down to 40 cm. Rainfall simulation of the laboratory incubated soils showed that SL effectively reduced turbidity and particle-associated P (PP) concentration of the drainage water, and the reduction was largest in soils with a high risk for colloid dispersion due to low electrical conductivity. Dissolved reactive P (DRP) concentration of the drainage water was unaffected by SL treatment. However, in SL-treated soils, an increase in dissolved organic matter (DOC) concentrations in rain simulation, and higher C content at 30–40 cm depth in field soils were observed. As expected, the microbial communities differed according to soil depth, but they did not exhibit community-level changes due to SL; only a few taxa-specific alterations in bacteria and fungi were observed. Treatment with SL decreases particle dispersion on clay soils with low EC but may increase DOC losses.