Each 4 m x 4 m plot is subdivided into 45 subplots

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RS

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° Little bluestem

* Kentucky bluegrass

* Quack grass

Competition treatments

-- No neighbours

R- Root competition

RS Root and shoot competition

Fig. 10.11. Illustration of the experimental design used by Wilson and Tilman (1991). They examined the effect of three levels of nitrogen (high, medium and low) and three competition treatments (-, no neighbours, R-, root competition; RS, root and shoot competition) on three species of grass (little bluestem, Kentucky bluegrass, quack grass).

Four types of competition experiments

Density effects complicate the experimental design, as the selected density will determine, to some extent, competitive outcome.

To circumvent this, four basic types of experimental designs with different density combinations are used (Fig. 10.12). Each experimental design has advantages and disadvantages (Silvertown and Lovett Doust,

(a) Partial additive w 'o

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