Trifolium subterraneum L.

NZ subclover pasture - Jo Grigg
Symbol: 
TRSU3
Group: 
Dicot
Family: 
Fabaceae
Uses: 
Pasture
Mixture
Soil Improvement (Green manure)
Seed
Wildlife
Description: 

Herbaceous, prostrate growing, reseeding, winter annual legume valued as forage in temperate summer moisture deficit areas. Oversown into low quality, low productivity pastures or seeded with perennial ryegrass, orchardgrass, or tall fescue. Provides high quality biomass during late winter and early to mid-spring. Particularly of value to lactating ewes and cows. Unlike most clovers, sub clover is self-pollinated. After self-fertilization, peduncles bend over and florets turn downward. Several sterile, spiny florets emerge at the end of the peduncle, enclosing 2-4 ripening seeds in the dried-out corolla and calyx. These seed burrs become buried in the upper layer of the soil during summer for subsequent germination in autumn.

Identification Characteristics

Type: 
Legume
Growth Season: 
Cool
Identification Characteristics: 

Inflorescence is composed of three or four white florets. Corolla (petal) is usually white; calyx color varies with cultivar, often red banded. Buries its seed pods before the onset of summer drought, hence its name. Pubescent, prostrate runners (stems) do not root at nodes. Long petioles support palmately trifoliolate pubescent, leaves with heart-shaped leaflets displaying cultivar-specific markings that vary with seasonal temperatures. Stipules have green or red veining. Short taproots (~6 in, 15 cm) and laterals with nitrogen fixing nodules. Seeds are oval with a pronounced hilum. They bare about 10 times heavier than white clover seeds (55,000-70,000 per lb, 121,000-154,000 per kg) and vary in color and weight with sub-species and cultivar; subspecies yannicum seeds are cream-colored, subterraneum and brachycalcycinum are black.

Growth Habit and Stand Life

Prostrate growth habit to 6 inch (15 cm) height. Runners (stems) do not root at the node.

Life Cycle: 
Winter annual

Yield Potential and Production Profile

Produces rosette in autumn following late summer seeding or reseeding germination. Primary production is spring to early summer with later maturing cultivars providing forage into early summer if soil moisture is available.

 

Cultivars

Subterranean clover has three sub-species: subterraneum, yanninicum, and brachycalycinum. Subspecies subterraneum is the most common and widely grown. Yanninicum is adapted to spring waterlogged soils. Brachycalycinum tolerates more calcareous soil.

Cultivars differ in persistence, productivity, flowering time, seed maturity, hardseededness, pest and disease resistance, and estrogen content. Select late flowering cultivars if moisture extends into summer, early flowering types for early spring biomass. Low growing - hardseeded types tolerate low temperatures; use small-leaved prostrate types for set stocking grazing management.

Climate and Soil Suitability Zones

Climate Tolerances: 

Grown extensively in coastal hills and pastures west of the Cascade Mountains in Oregon and California. Sub clover mixtures are used as a cover crop in California almond orchards. Suitable for coastal mid-Atlantic and Southeast US in USDA Plant Hardiness zones 7 and greater for forage or as a living or killed mulch. Early flowering cultivars suited to low rainfall areas (less than 20 inches, 500 mm); later flowering cultivars suited to higher rainfall (greater than 30 inches, 700 mm).

Soil Tolerances: 

Grows best in moderately to well-drained loamy to clay-loamy soils that are moist through late spring. Tolerates strongly acid soils to medium alkaline soils: pH 5.1-8.4.

Quantitative Tolerances: 

 

Subterranean Clover Suitability Tolerance Values

Suitability Class

Ave Ann Extreme Min (°C/°F)*

July Mean Max

C/°F)

Annual PPT

WET (mm/in)**

Annual PPT

DRY (mm/in)**

Soil

pH***

Soil Drainage 

Soil Salinity (dS/m)#

Well-suited

-12/10.4

30/86

1524/60

650/26

5.8-7.5

MWD-WD

<2

Moderately suited

-15/5

31/88

1270/50

550/22

5.5-8.0

SPD-SED

2-3

Marginally suited

-18/-0.4

32/90

1016/40

400/16

5.0-8.5

SPD-ED

3-4

**Precipitation requirement: Early flowering cultivars are suited to areas with low rainfall (less than 20 inches, 500 mm) while the later flowering cultivars are suited to higher rainfall (greater than 30 inches, 700 mm). The two columns (WET and DRY) represent current use and potential use, respectively.*USDA Plant Hardiness Zones 7-9 for reseeding cool-season fall seeded; 4b-7b as spring-seeded annual.

 Rooting: short taproot with many fibrous branching roots; to a depth of 1 foot (30 cm).

*** Soil pH tolerance: NRCS Range and Pasture Handbook, Chapter 3 classification for Sub Clover is strongly acid to moderately alkaline (5.1-8.4).

Soil drainage: NRCS Range and Pasture Handbook, Chapter 3 classification for Subterranean Clover is PD-WD. Soil drainage class abbreviations: 1=VPD, very poorly drained; 2=PD, poorly drained; 3=SPD, somewhat poorly drained; 4=MWD, moderately well drained, 5=WD, well drained; 6=SED, somewhat excessively drained; 7=ED, excessively drained. Percent relative yield of sub clover for the 7 class values;   1-7: 5, 20, 55, 100, 100, 55, 20, respectively.

Flooding Tolerance: Brief (3-6 days)

# Soil salinity tolerance: NRCS Range and Pasture Handbook, Chapter 3 classification for clovers (alsike, Berseem, white, red, strawberry) is Moderately Sensitive (1.5-3 DS/m). No specific listing for sub clover; selected Moderately Sensitive.

 

 

 

Suitability Maps

Historically, maps have been drawn based on primary use areas, showing broad geographic areas, e.g. Compendium of Common Forages maps within Forages: An Introduction to Grassland Agriculture, 7th ed. (2018), John Wiley & Sons, Inc.

(Subterranean Clover Adaptation & Use Map.)

(SARE Managing Cover Crops Map. Source: Managing Cover Crops Profitably, 3rd Ed., Sustainable Agriculture Research & Education.)

More highly detailed maps, based on quantitative climatic and soil factor tolerances and using GIS spatial grids, provide information on where species are suitable for a variety of intended uses.

The following collection of maps were developed by a group of Oregon State University scientists, using the PRISM-generated collection of climate factor grids and the NRCS soil characteristics database.

Quantitative Tolerances GIS Maps

Climate Factors Soil Factors Combined Factors

Minimum Temperature Wet

pH Wet

Climate and Soil Wet

 

 

 

 

Climate and Soil Dry

Maximum Temperature Wet

Drainage Wet

All Soil

Precipitation Wet

Salinity Wet

All Climate Wet

Precipitation Dry

 

All Climate Dry

Map designations of wet and dry refer to different precipitation requirements for current use areas (40-60 inch rainfall zones, designated wet) and potential use areas (16-26 inch rainfall zones, designated dry). 

Quality and Antiquality Factors

Quality Factors: 

Highly palatable and digestible forage in late winter and spring.

Anti-quality Factors: 

Older cultivars produce compounds with estrogenic activities that can interfere with livestock breeding. Select low estrogen-containing cultivars. 

Species Selection Characteristics

Annual Precipitation (inches): 
8 to 12
Plant Hardiness Zones (cold tolerance): 
6b
7a
7b
8a
8b
9a
Heat Zone (July Mean Max Temperature): 
< 14 °F
14 to 18 °F
18 to 22 °F
22 to 26 °F
26 to 30 °F
30 to 34 °F
34 to 38 °F
38 to 42 °F
42 to 46 °F
46 to 50 °F
50 to 53 °F
53 to 56 °F
56 to 59 °F
59 to 62 °F
62 to 65 °F
65 to 68 °F
68 to 71 °F
71 to 74 °F
74 to 77 °F
77 to 80 °F
80 to 84 °F
84 to 88 °F
88 to 92 °F
Soil pH Tolerance: 
Strongly acid, 5.1–7.3
Moderately acid, 5.6–7.3
Moderately acid to moderately alkaline, 5.6–8.4
Slightly acid to moderately alkaline, 6.1–8.4
Near neutral, 6.1–7.3
Soil Drainage Tolerance: 
poorly drained
somewhat poorly drained
moderately well drained
well drained
somewhat excessively drained
Flooding Tolerance: 
3-6 days
Soil Salinity Tolerance: 
Moderately sensitive, 1.5–3 dS/m

Management Level Required

Suitable Management Level: 
High
Medium

Image Gallery

Resources

Publications: 

Books and Book Chapters

  • Clover Science &Technology (Agronomy Monograph No. 25, 1985)

Extension Fact Sheets and Circulars

USDA NRCS Plant Profiles

Organizations

Vendors