Effect of carbon amendment in old-field restoration
Disturbed lands (either for natural or anthropogenic reasons) tend to have an elevated level of nitrogen in the soil, which alters mineralization and immobilization and facilitate the growth of exotic species. Removing invasive species chemically or mechanically are unlikely to limit reinvasion in many ecosystems, while soil legacy effects remain. A nitrogen immobilization experiment was conducted in collaboration with US scientists to restore sand grassland at abandoned arable fields. The concept was to induce microbial activity by carbon amendment that results in N immobilization in the microbial biomass and a lack of soil available N for vascular plants. This way late-seral species gain competitive advantage against early-seral ones that require high nutrient levels.
We immobilized nitrogen over six growing seasons (1998-2003) on three ex-arable fields with poor sandy soils in the Hungarian lowland in order to restore endemic sandy grassland. Sucrose and sawdust were applied at rates based on previous laboratory experiments using local soils. We tested the efficacy of carbon amendment on soil nitrogen availability, microbial biomass and activity and vegetation.
Carbon amendments resulted in significant increase in soil microbial biomass C and reduced soil nitrogen availability after 2 years. Total vegetation cover and cryptogam cover were reduced by reducing soil nitrogen availability, but total species richness and species composition was not or only slightly impacted. The differences between treatment and control became visible only four-five years after the first application and disappeared three years after the cessation of treatments. This study supports the efficacy of carbon amendment as a tool to immobilize available soil nitrogen in the upper soil layers. However, the desired impact on vegetation was not fully achieved despite application over several years. Carbon amendment did not speed up the recovery of sand grasslands, however, the reduction of cover (vegetation and cryptogam) can be a window of opportunity for other species to colonize that can be used as a complement to other treatments.
Halassy, M., Kövendi‐Jakó, A., Reis, B., Szitár, K., Seyidova, Z., & Török, K. (2021): N immobilization treatment revisited: a retarded and temporary effect unfolded in old field restoration. Applied Vegetation Science, e12555.
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