Neglect of mowing and manuring leads to slower nitrogen cycling in subalpine grasslands

Published source details Robson T.M., Lavorel S., Clement J.-C. & Roux X.L (2007) Neglect of mowing and manuring leads to slower nitrogen cycling in subalpine grasslands. Soil Biology & Biochemistry, 39, 930-941.
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Summary

Farmers in Europe are increasingly abandoning traditional hay making and grazing in subalpine grasslands. Hay making and grazing enable herbs to flourish and reduce grass dominance. A study was undertaken in the upper Romanche valley (45.04ºN 6.34ºE) of the central French Alps to assess if neglect of traditional mowing for hay and manuring in subalpine meadows has led to a reduction in nitrogen (N) availability and influenced changes in plant communities.

Study sites comprised 15 fields i.e. 3 replicates for each of five management regimes: 1) terraced fields fertilised with manure and mown for hay, 2) terraces mown but not fertilised, 3) terraces lightly grazed, and 4) unterraced fields mown or 5) unmown.

Soil nitrate and ammonium contents were assessed by analysis of soil core samples collected in 2003 and 2004, and assays of microbial nitrifying and denitrifying enzyme activities were made.

A difference in pH between the two field types (terraced 6.5- 7; unterraced 5.5-6) due to historical ploughing was apparent. This facilitated greater N availability in terraced than unterraced fields.

Manuring and mowing abandonment caused a reduction in N availability. This was correlated with a shift in the plant community towards greater dominance by certain grasses. This further reduced available soil N, reduced microbial activity and led to a loss of characteristic herbaceous subalpine-meadow plants.

On the terraces with no manuring or mowing, floristic changes were primarily a greater dominance of grasses and later-growing species. On the unterraced fields, the dominant tussock grass, Festuca paniculata, where unmown formed large tussocks thus reducing light availabile to other species; this fescue produces N-poor litter (as N is stored into pseudobulbs).

Neglected grasslands are likely to succeed towards shrub or tussock-grass dominated communities.

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