Field production of ornamental shrubs results in significant topsoil removal and degradation of soil chemical properties. We amended field soils with compost to evaluate effects on soil chemical properties and shrub biomass production. We applied either duck manure-sawdust (DM), potato cull-sawdust-dairy manure (PC) or paper mill sludge-bark (PMB) composts to a silt loam soil as a) incorporated 2.5 cm (1 in) of compost tilled into the top 15 cm (6 in) of soil or b) incorporated + mulched 2.5 cm (1 in) tilled into soil + 2.5 cm (1 in) applied over the soil surface. We grew Spirea japonicum ‘Gumball’, Juniper chinensis ‘Pfitzeriana’ and Berberis thunbergia ‘Atropurpurea’ seedlings and measured total and plant available nutrients and shrub biomass production and nutrient contents over two growing seasons. Total soil C was 15–21% higher in all mulched treatments compared to incorporated-only and no-amendment control treatments. Total soil N, P and Cu, available P, S, Ca, Mg, K, pH and EC increased with increasing TC. Mulched DM compost produced significantly higher DTPA-extractable Zn relative to other treatments. In the second growing season, mulched DM compost produced 39–42% greater total barberry biomass than all other treatments. Among all shrub species, the best soil chemical predictors of plant growth were TC, TS, soluble P, exchangeable Ca and K and DTPA-Zn. The best tissue nutrient-content predictors of plant growth were total shoot N, P and Zn and root Zn. The unique growth response of barberry to mulched DM compost suggests that all shrubs may not respond to compost amendments, particularly over the short term.
2Former graduate student. Current address: Guápiles, Costa Rica.
3Assistant Professor and corresponding author.