Forage Clover

Trifolium spp.

1. Identification and origin

Forage clover (Trifolium spp.) includes several herbaceous leguminous species of the Fabaceae family, widely distributed throughout Europe, Asia and temperate regions of other continents. In Portugal, the species most used in forage systems include Trifolium repens L., Trifolium pratense L., Trifolium subterraneum L. and Trifolium incarnatum L. They are used in permanent pastures, temporary meadows and rotation systems, valued for their capacity for biological nitrogen fixation.

2. Economic importance

Forage clover is fundamental in extensive and semi-intensive livestock systems, contributing to pasture productivity, improvement of soil fertility and reduction of the need for nitrogen fertilisation. Clover species have high nutritional value, good palatability and capacity to persist in pasture mixtures. They are widely used in Mediterranean pastures, rainfed meadows and organic production systems.

3. Botanical characterisation

The plants of Trifolium spp. are herbaceous, annual or perennial, with characteristic trifoliate leaves. The inflorescences are globose or ovoid heads, with flowers of variable colouring (white, pink, purple or red). The root system is taproot or fasciculate, depending on the species, with symbiotic nodules of Rhizobium spp. responsible for the fixation of atmospheric nitrogen. Seed production varies between species and is influenced by climatic conditions and management practices.

4. Soil and climate requirements

Clover adapts to temperate and Mediterranean climates, with good tolerance to cold and sensitivity to prolonged droughts (except Mediterranean annual species such as T. subterraneum). It prefers well-drained soils, with a pH between 5.5 and 7.0, rich in phosphorus and potassium. Productivity is favoured by adequate autumn-winter rainfall and moderate temperatures. Competition with grasses must be balanced to maximise persistence.

5. Main pests

• Clover weevils (Sitona spp.) — root damage and reduction of nitrogen fixation
• Aphids (Aphis craccivora, Acyrthosiphon pisum) — sap sucking and transmission of viral diseases
• Defoliating caterpillars (Spodoptera spp., Autographa gamma) — reduction of aerial biomass
• Thrips (Frankliniella occidentalis) — damage to young leaves and flowers
• Nematodes (Ditylenchus dipsaci) — deformations and necrosis in vegetative tissues

6. Main diseases

• Anthracnose (Colletotrichum trifolii) — leaf necrosis and death of young plants
• Powdery mildew (Erysiphe trifolii) — white coating and reduction of photosynthesis
• Root rots (Rhizoctonia solani, Pythium spp.) — establishment failures
• Rust (Uromyces trifolii) — leaf pustules and loss of vigour
• Clover mosaic virus (CMV) — mosaics and reduction of productivity

7. General crop management

Management of forage clover is based on the selection of species and cultivars adapted to the climate and the grazing system. Inoculation with adequate strains of Rhizobium spp. improves nitrogen fixation. Crop rotation reduces pressure from soil diseases. Grazing must be controlled to avoid overgrazing and allow vegetative recovery. Phosphate and potassium fertilisation is essential to maintain productivity. Harvesting for hay or silage should take place at the beginning of flowering to maximise quality.

Bibliographic references

• EPPO Global Database – Trifolium spp.
• CABI – Crop Protection Compendium – Trifolium spp.
• Frame, J. (2005). Forage Legumes for Temperate Grasslands. FAO.
• Annicchiarico, P. et al. (2015). White clover and red clover improvement: state of the art and future prospects. Grass and Forage Science, 70, 1–19.
• Nichols, P. G. H. et al. (2014). Genetic improvement of subterranean clover. Crop and Pasture Science, 65, 1132–1146.