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Individual study: Effects on soil nitrogen of prescribed fire versus vegetation removal by mowing and raking at a restored prairie, Murphy Lake Prairie, Minnesota, USA

Published source details

Tix D., Hebberger J.A. & Charvat I. (2006) Influence of aboveground biomass removal on nitrogen mineralization in a restored tallgrass prairie. Restoration Ecology, 14, 561-568


Native prairies tend to have soils of low nitrogen (N) availability, an important factor that maintains plant diversity. Periodic burning is a common prairie management practice which influences soil N. This experiment compared soil N properties after a prescribed fire with that following vegetation removal by mowing and raking at Murphy Lake, a 38 ha restored mesic tallgrass prairie in Minnesota (44°42′N, 93°20′W; north USA).

Restoration began in 1995 on an agricultural field. At the commencement of the experiment it was dominated by two native prairie grasses, big bluestem Andropogon gerardii and Indian grass Sorghastrum nutans. The most recent burn was in spring 1997.
In summer 2000, 28 (10 x 10 m) plots were established. Three treatments were applied in spring (4-9 May) 2001 and (23-30 April) 2002, plus an untreated control, assigned randomly to each plot within a block (7 replicates/treatment). In each block, one plot was burned, and two were mowed and raked (one with lime added in year one to mimic deposition of basic cations via ash during a fire, which increases soil pH).

Aboveground plant biomass removal by the two treatments had similar effects on soil moisture, temperature and inorganic N, and created warmer and drier soil than in the control plots.
Net N mineralization after raking was unaffected by lime addition. In the first year (low rainfall), the two treatments had N mineralization rates similar to controls. During the second year (heavy rainfall), mineralization rates were significantly higher (and similar) in removal plots. After fire, soil pH temporarily increased slightly (attributed to ash deposition). Plant productivity (biomass) was also significantly greater on burned than control plots during 2002.
Aboveground biomass removal was the primary factor leading to changes in net N mineralization following burning. The authors suggest that for prairie restorations on nutrient-enriched soils (e.g. previously fertilized agricultural land), frequent burning will likely decrease soil N and thus benefit plant diversity.
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