Negative allelopathy which plants tend exude or release chemicals to prevent other plants to grow near them.
For a field survey, finding the dominant species of plant (common for grasses) could be useful identification in a grassland ecosystem.
Another good potential indicator of negative allelopathy of plant using visual survey, when a certain plant does not have neighboring plants or only few plant species thrive near the potential plant with allelopathy.
You need to obtain leachate from the relevant plants and test these against seed germination at varying concentrations of leachate since different concentrations can be either stimulatory or inhibitory
1-choose the plant ( alelopathetic plant) such as Eucalyptus or any plant
2-chose different seed of plant such as Triticum sp., Brassica sp., .....
3-prepared the pot whichis contain soil and seed
4-add the dry of alelopathetic plant to the pot by different %
5- do irrigation
6-germination
6-get your data such as germination %, length root and shoot, dry wt. of shoot and root, chemical content such as chlorophyll , carbohydrate ,...protein,......
In the field survey of the plants that are allelopathy to other plants species, one has to identify the plant first observation its area of growth whether other plants are growing or not. If other plants are not growing around it u can suspect the plant being allelopathy plant that inhibits growth of others. So u can take the seed of the plant and germinate,grow in small scale labs and large scale in field for its bio-active components in comparison to the well known alellopthy plants species of eucalyptus tree components.