Floristically rich grassland tends to occur on infertile soils, conservation management should thus aim to maintain low fertility. It has been suggested that during succession to scrub, fertility increases. A study was undertaken at Knocking Hoe (grid reference TL 131308), Bedfordshire (central England). The effects of several management treatments (including allowing scrub development) applied for 22 years on nitrogen (N) and phosphorous (P) status (i.e. elements most likely to control plant growth) in chalk grassland soils under vegetation, were investigated.
This experiment compared the effects of different annual cutting frequencies (with and without removal of clippings) with unmanaged plots (allowing scrub development) and adjacent grazed area.
In 1965, the following four treatments were applied randomly to plots (2.4 × 1.5 m) in each of four replicate blocks: 1) unmanaged; 2) cut once/year (May); 3) cut twice/year (May and June); 4) cut 3-time/year (May, June, July). The cut plots were divided into two; one half had clippings returned, the other had clippings removed. (No details of the grazing regime are given in the original paper).
In June 1987, soil samples were collected. Concentrations of inorganic N, rates of nitrogen mineralization and nitrification were estimated, and phosphate adsorption curves calculated.
There were no significant differences in NO3-N concentration between any treatments (including the unmanaged plots). Effects were detected in two measures of soil fertility:
1) highest N mineralization rate occurred in unmanaged plots, but this was significantly greater than only two treated plots (those cut once and 3-time/year with clippings returned); N mineralization is the main limiting factor controlling N supply to plants;
2) the most consistent result was a reduction in P sorption in plots where clippings were returned implying greater P availability; if this trend continued, changes in species composition might be expected.
It was also apparent that successional change to scrub led to a change in grass species from mixed Bromus erectus/Festuca ovina grassland towards one mainly dominated by B.erectus.
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