The factors that have been retained for soil diagnosis are fertility, pH, settlement, texture (proportion of sand, silt, clay, etc.) and moisture content. Plants do not respond in the same way to these different factors. Some grow exclusively in acidic soil and have good pH indicators, while others are indifferent to this factor. We must take the time to observe carefully how plants colonize a field. Determine the importance of species density and diversity. Consider their distribution (uniform or sporadic) and their state of health.
For example, the abundance of healthy plantain and bird knots in the field indicates a problem with soil compaction. This diagnosis is reinforced by the presence of wild buckwheat, stinkweed or quackgrass in the field and there is milkweed of Syria, field thistles or barbanes at the edge of the field.
In all cases, indicator plants are a preliminary tool for diagnosing agricultural soils that require confirmation by further analysis. All plants were characterized according to the behavior most often encountered. For example, a sunny plant (major plantain or lamb’s quarters) may occasionally be observed in a shady environment.