Table 1: Summary and time line of experimental protocols.

ActionTime (days)Purpose

Establish perennial grasses60Create suppressive conditions

1st growth cycle: single seed of B. tectorum sown between established perennial grasses (in competition) and alone (without competition)89
1st growth cycle harvest: perennials clipped at 15 cm above soil surface and B. tectorum clipped at soil surface. Dry tissue weights measured1 Quantify the degree of suppression by three perennial grasses in competition with B. tectorum relative to B. tectorum grown without competition

2nd growth cycle: repeat 1st cycle planting protocols78
2nd growth cycle harvest: Repeat 1st cycle harvest protocols1 Clipping perennial grasses simulates the effects of herbivory on suppression. Removal of perennial above-ground mass will test the effect of declining soil resources on suppression

3rd growth cycle: excavate 400 g soil from beneath clipped B. tectorum, mix with 4 g activated carbon, and return to rhizotrons, then repeat planting protocols81
3rd growth cycle harvest: repeat 1st cycle harvest protocols1 Test if activated carbon addition affects suppression via amelioration of allelopathy. Disturbance will create root-free soil space and increase biological soil space, at least initially

4th growth cycle: repeat planting protocols then, after emergence of B. tectorum, top-dress each rhizotron soil with a complete fertilizer solution (Rapid Gro) containing 82 mM N, 6.7 mM P, and 9.0 mM K and micronutrients in a 500 mL solution added in 100 mL increments over 5 weeks84
4th growth cycle harvest: repeat 1st cycle harvest protocols1 Test if suppression is partly due to lack of nutrients

5th growth cycle: perennial grasses cut below growing nodes to kill plant83
5th growth cycle harvest: B. tectorum clipped at soil surface. Soil samples taken1 Test how perennial grass death affects suppression