Field phytometers and lab tests demonstrate that rock dust can outperform dolomite and fertilisers for acid forest soil restoration

Abstract

Background and aims

Soil amendments with rock dust have been proposed for restoring regeneration on ultra-acidified forest soils. Rock dust is a poorly defined amendment, and its mode of action remains unclear. This study was set up to identify rock dust properties that predict plant responses in the field.

Methods

A field experiment with sycamore maple (Acer pseudoplatanus L.) saplings in two sites in the Campine region (NL) was constructed, both at a clearcut (soil pH = 3.5) and under the canopy of Pinus sylvestris L. (pH = 3.1). Treatments included six rock dusts and four reference treatments (TSP, dolomite, KCl, their combination). Rock dusts were amended in the planting pit and broadcast after being characterised for chemical composition and tested for dissolution in accelerated laboratory tests. Sapling growth was monitored for 40 months.

Results

Tree growth was affected by the site and rock dust type. The highest tree volume increases relative to the unamended control were with phonolite that increased volume by a factor 2 (clearcut) and by a factor 8 (under-canopy). On the clearcut, these increases were larger than the reference conventional dolomite and fertilisation treatments. Here, growth was only explained by rock dust’s water retention, which was superior for a zeolite-containing rock dust. Under-canopy, both growth and foliar nutrition were best related to liming and nutrient release by rock dust inferred from an 8-week laboratory-based soil + rock dust suspension test.

Conclusion

Rock dusts are effective to regenerate acid forest soils and laboratory tests of accelerated weathering can inform their potential.