Habitat indicators
Many weed species are confined to certain field communities and soil habitat conditions. In the latter case, the response of weeds can be considered as an indication of natural edaphic conditions and as a response to soil properties, including those changed by agrotechnical measures.
The response of weeds to edaphic conditions is primarily manifested in responsiveness to moisture supply, reaction of soil environment and nutrient supply.
Plants-indicators of soil water regime
In relation to the level of soil moisture there are groups of weeds:
- hygrophytes – occur exclusively in damp, poorly aerated soils: marsh swift-leaf (Gnaphalium uliginosum), frogweed (Juncus bufonius), field broom (Apera spica-venti), field horsetail (Equisetum arvense), field mint (Mentha arvensis), marsh hedgenettle (Stachys palustris), creeping buttercup (Ranunculus repens);
- hygromesophytes – prefer damp well aerated soils: lamb’s-quarters (Chenopodium album), Chenopodium polyspermum, Fumaria officinalis, cleavers (Galium aparine), Tripleurospermum inodorum, stinkweed (Thlaspi arvense), perennial sow thistle (Sonchus arvensis);
- xerophytes – prefer well aerated, warm, sometimes strongly drying, soils: redroot pigweed (Amaranthus retroflexus), prostrate pigweed (Amaranthus blitoides), Stachys annua, storksbill (Erodium cicutarium), smolt-cracker (Silene vulgaris), green foxtail (Setaria viridis), barnyard grass (Echinochloa crus-galli), Common ragweed (Ambrosia artemisiifolia).
Plants-indicators of soil acidity
According to the reaction to the pH value of the soil solution (actual acidity), there are groups of plants-indicators of soil acidity:
- oxylophytes – grow mainly on soils with a pH value < 5.0: small sorrel (Rumex acetosella), corn spurrey (Spergula arvensis), knawel (Scleranthus annuus), toricum of the field (Arenaria arvensis), chamomile non-scented (Tripleurospermum inodorum), wild radish (Raphanus raphanistrum), field broom (Apera spica-venti), frogweed (Juncus bufonius);
- oxymesophytes – grow on soils with soil solution reaction from slightly acidic to neutral: wild oat (Avena fatua), sprawling swan (Atriplex patula), wormseed mustard (Erysimum cheiranthoides), stinkweed (Thlaspi arvense), Black henbane (Hyoscyamus niger), marsh hedgenettle (Stachys palustris), Potentilla anserina, perennial sow thistle (Sonchus arvensis);
- plants indifferent to the reaction of soil solution: lamb’s-quarters (Chenopodium album), shepherd’s purse (Capsella bursa-pastoris), purple cockle (Agrostemma githago), horseweed (Erigeron canadensis), Galeopsis speciosa, Achillea yarrow.
The presence of several species of weeds of the same group gives grounds for assessing the advisability of liming soils. This method often leads to a change in the floristic composition of weeds and reduces the weed infestation of crops.
Plants-indicators of nutritional regime
According to the level of responsiveness to the supply of soil elements of mineral nutrition (nutritional regime), there are “element-positive” and “element-negative” groups of weeds. In the practice of farming it is important to know the indicator plants that respond positively to high content of certain elements of mineral nutrition in the soil.
The group of nitrophiles (nitrogen-loving) includes lamb’s-quarters (Chenopodium album), multiseed (Chenopodium polyspermum), sprawling swan (Atriplex patula), wild radish (Raphanus raphanistrum), wild mustard (Sinapis arvensis), rugged mountain knotweed (Persicaria lapathifolia), conspicuous bunting (Galeopsis speciosa), double-cut bunting (Galeopsis bifida), barnyard grass (Echinochloa crus-galli), annual bluegrass (Poa annua), small sorrel (Rumex acetosella).
Phosphatophiles include the following species: groundsel (Senecio vulgaris), field violet (Viola arvensis), corn spurrey (Spergula arvensis), red broom (Spergularia rubra), apothecary woodruff (Fumaria officinalis), henbit (Lamium amplexicaule).
Potassiumophiles include cleavers (Galium aparine), spreading lambsquarter (Atriplex patula), stinkweed (Thlaspi arvense), perennial sow thistle (Sonchus arvensis).
The above classification of weeds in relation to the various elements of mineral nutrition is not absolute, because with a change in mineral nutrition other conditions of life change. Therefore, the response of weeds to individual elements may also change.
Sources
Farming. Textbook for universities / G.I. Bazdyrev, V.G. Loshakov, A.I. Puponin et al. – Moscow: Publishing House “Kolos”, 2000. – 551 с.