The study, conducted for three years, took a look at how much nitrogen and phosphorus leached into the soil under 14 species of trees compared to turfgrass at three Saint Paul city parks. Nitrogen leaching was both more and less than turfgrass during the study, but trees leached less phosphorus than turfgrass in both years.
The study aimed to compare leaching between trees and turfgrass; among tree species and to estimate watershed effects on nutrient leaching. They began with the hypotheses that trees would take up more N and P and provide soil microbes with more organic carbon than turfgrass.
None of the studied locations uses fertilizer. Trees, some 33 of them, were deciduous (23) and evergreen (10). All were mature and did not have mulch or other soil management underneath. Soil water samples were not collected during drought periods.
Tree species tested included: Abies concolor, Acer platanoides, A. saccharinum, Celtis occidentalis, Fraxinus pennsylvanica, Ginkgo biloba, Gleditsia triacanthos, Pinus ponderosa, P. resinosa, P. strobus, P. sylvestris, Quercus macrocarpa and Tilia cordata.
The study was inconclusive on recommending specific tree species, as variation within species was sometimes greater than between species. The authors’ main recommendation from the study is that additional work on nutrient leaching should continue to “test correlations with plant traits and soil assays” for the purpose of developing protocols to be able to asses many tree combinations and management practices.
It’s estimated that Minnesota’s Capital Region has about 33% tree cover, that’s a lot of natural phosphorous removal! Imagine what could be done if we knew more about which trees were best suited to nutrient reduction.
NewTerrain October 17, 2016