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SUBTERRANEAN CLOVERS Trifolium subterraneum, T. yanninicum, T. brachycalcycinum Also called: Subclover Type: reseeding cool season annual legume Roles: weed and erosion suppressor, N source, living or dying mulch, continuous orchard floor cover, forage Mix with: other clovers and subclovers See charts, p. 47 to 53, for ranking and management summary. cool season annual spring seeded reseeding cool season annual fall seeded Subterranean clovers offer a range of lowgrowing, self-reseeding legumes with high N contribution, excellent weed suppression and strong persistence in orchards and pastures. Fall-planted subclovers thrive in Mediterranean conditions of mild, moist winters and dry summers on soils of low to moderate fertility, and from moderately acidic to slightly alkaline pH. Subclover mixtures are used on thousands of acres of California almond orchards,where farmers continue to evaluate some 50 cultivars for optimum combinations. Subclover holds promise in the coastal mid-Atlantic and Southeast (Hardiness Zone 7 and warmer) on sandy loam to clay soils as a killed or living mulch for summer or fall crops. Most cultivars require at least 12 inches of rain per year. A summer dry period limits vegetative growth, but increases hard seed tendency that leads to self-reseeding for fall reestablishment. Subclovers generally grow close to the ground, piling up their biomass in a compact layer. A Mississippi test showed that subclover stems were about 6, 10 and 17 inches long when the canopy was 5, 7 and 9 inches tall, respectively (79). Diversity of Types, Cultivars Select among the many subclover options cultivars that fit your climate and your cover crop goals. Identify your need for biomass (for mulch or green manure),time of natural dying to fit your spring-planting schedule and prominence of seed set for a persistent stand. Subclovers comprise three Trifolium species: • T. subterraneum. The most common cultivars that thrive in acid to neutral soils and a Mediterranean climate • T. yanninicum. Cultivars best adapted to water-logged soils • T. brachycalcycinum. Cultivars adapted to alkaline soils and milder winters Primary differences between these species are their moisture requirements,seed production and days to maturity (15). Other variables include: • Overall dry matter yield • Dry matter yield at low moisture or low fertility • Season of best growth (fall, winter or spring) • Hard-seeding tendency • Grazing tolerance 132 MANAGING COVER CROPS PROFITABLY
Subclover cultivars often are described by their moisture preference and days to maturity, which are closely linked traits. The maturity estimates are set for continuous growing days, and will be greatly lengthened for fall-planted subclovers in the East and Southeast, where winter weather delays flowering for two to three months. • Short season subclovers tend to set seed quickly. Cultivars such as DALKEITH (an improved version of DALIAK) and NUNGARIN need only 8 to 10 inches of rainfall and set seed about 85 days after planting. Early subclovers tend to be less winter hardy (77). • Intermediate types such as TRIKKALA and the new,more competitive GOSSE thrive with 14 to 20 inches of rain and set mature seed in about 100 days. • Long-season cultivars such as KARRIDALE and NANGEELA perform best with 18 to 26 inches of rainfall, setting seed in about 130 days. MT.BARKER was a longtime research standard that is now surpassed by KARRIDALE for forage production, hardseed percentage, re-establishment potential and grazing. KARRIDALE is more prostrate, and is favored for cover crop use (345). BENEFITS Weed suppressor. Subclover can produce 3,000 to 8,500 lb. dry matter/A in a thick mat of stems, petioles (structures connecting leaves to stems) and leaves. Denser and less viny than hairy vetch, it also persists longer as a weed-controlling mulch. Subclover mixtures help West Coast orchardists achieve season-long weed management. In Coastal California, fast-growing TRIKKALA, a mid-season cultivar with a moderate moisture requirement,jumps out first to suppress weeds and produces about twice as much winter growth during January and February as the other subclovers. It dies back naturally as KOALA, (tall) and KARRIDALE (short) come on strong in March and April. The three cultivars complement each other spatially and temporally for high solar efficiency,similar to the interplanting of peas, purple vetch, bell beans and oats in Subclovers thrive in Mediterranean climates of mild, moist winters and dry summers. California vegetable fields where a high-residue, high-N cover is desired (345). In legume test plots along the Maryland shore, subclover mulch controlled weeds better than conventional herbicide treatments. The only weed to penetrate the subclover was a fall infestation of yellow nutsedge.The cover crop regrew in fall from hard seed in the second and third years of the experiment (19). Green manure. In east Texas trials, subclover delivered 100 to 200 lb. N/A after spring plowdown. Grain sorghum planted into incorporated subclover or berseem clover with no additional N yielded about the same as sorghum planted into disked and fertilized soil without a cover crop in three out of four years. The fertilized fields had received 54 lb. N/A (192). Versatile mulch. Subclover provides two opportunities for use as a mulch in vegetable systems. In spring, you can no-till early planted crops after subclover has been mechanically or chemically killed, or plant later, after subclover has set seed and dried down naturally (19). In fall, you can manage new growth from self reseeding to provide a green living mulch for cold-weather crops such as broccoli and cauliflower (165). Conventionally tilled corn without a cover crop in a New Jersey test leached up to 150 lb. N/A over winter while living subclover prevented N loss (99). Mowing was effective in controlling a living mulch of subclover in a two-year California trial with late-spring, direct-seeded sweet corn and lettuce.This held true where subclover stands were dense and weed pressure was low. Planting into the subclover mulch was difficult, but was done without no-till equipment (189). Soil loosener. In an Australian study in compaction-prone sandy loam soil, lettuce yield doubled following a crop of subclover. Without the clover, lettuce yields were reduced 60 percent on the compacted soil.Soil improvement was credited to macropores left by decomposing clover roots and earthworms feeding on dead mulch (323). SUBTERRANEAN CLOVERS 133
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$19.00 Managing Cover Crops Profita
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SUSTAINABLE AGRICULTURE NETWORK THE
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ACKNOWLEDGMENTS This book represent
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FOREWORD Cover crops slow erosion,
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HOW TO USE THIS BOOK Think of this
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BENEFITS OF COVER CROPS Cover crops
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decompose quickly, especially in wa
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Expect excessive field traffic arou
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5. Settle for the Best Available Co
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ORGANIC MATTER ADDITIONS The benefi
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Cover Crops Can Stabilize Your Soil
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generally a good idea to kill a leg
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• For perennial legumes that have
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MANAGING PESTS WITH COVER CROPS By
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The farmers get weed control by fla
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insects. This approach has been use
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• Subterranean Clover (Trifolium
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does no direct tillage, but aggress
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eplace the cover crop before beans,
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as buckwheat, cowpeas, sorghum-suda
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the couple harrows every two to thr
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Start Where You Are In many instanc
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INTRODUCTION TO CHARTS The four com
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pH Preferred. The pH range in which
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Chart 1 TOP REGIONAL COVER CROP SPE
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Chart 2 PERFORMANCE AND ROLES conti
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Chart 3B PLANTING Cost Cost/A Inoc.
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Chart 4B POTENTIAL DISADVANTAGES Sp
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ANNUAL RYEGRASS Lolium multiflorum
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prolonged heat, cold or drought.Tha
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crop for establishing a forage or l
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arley plants from fungus, armyworm
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can increase the fertilizer replace
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cultural and local considerations t
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(339), and by 99 percent in a Calif
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Killing & Controlling Nutrient avai
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ye/vetch/crimson clover,for example
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• In the Corn Belt and northern U
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Wheat Offers High-Value Weed Contro
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BUCKWHEAT Fagopyrum esculentum Type
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Rotations Buckwheat is used most co
Page 83 and 84: plants fractured subsoil compaction
Page 85 and 86: press some species of nematodes. Sp
Page 87 and 88: Incorporated sorghum-sudangrass res
Page 89 and 90: lodge soil particles. Sunlight is u
Page 91 and 92: Crimson-Berseem Clover Combo Works
Page 93 and 94: in water-use efficiency in the tria
Page 95 and 96: Microorganisms mineralize, or conve
Page 97 and 98: COWPEAS Vigna unguiculata Also call
Page 99 and 100: control if you go with rows, using
Page 101 and 102: drought-tolerant sorghum-sudangrass
Page 103 and 104: several winter annual legumes that
Page 105 and 106: In Ohio, crimson clover mixed with
Page 107 and 108: FIELD PEAS Pisum sativum subsp. arv
Page 109 and 110: Chill tolerant. Austrian winter pea
Page 111 and 112: In a “Flexible Green Manure” cr
Page 113 and 114: values from 13 to 34,but were gener
Page 115 and 116: year Maryland study that also inclu
Page 117 and 118: possible, but remember that hairy v
Page 119 and 120: especially in winter grains. With w
Page 121 and 122: less biomass than overwintering sta
Page 123 and 124: Jess Counts on GEORGE for N and Org
Page 125 and 126: after mid-April planting in souther
Page 127 and 128: second cutting. Regrowth comes from
Page 129 and 130: RED CLOVER Trifolium pratense Also
Page 131 and 132: MANAGEMENT Establishment & Fieldwor
Page 133: it function more like a biennial th
Page 137 and 138: trample in the seed. Subclover ofte
Page 139 and 140: Crop Systems Interseeded with wheat
Page 141 and 142: SWEETCLOVERS Yellow sweetclover (Me
Page 143 and 144: difficult to establish annual cover
Page 145 and 146: Spring seeding provides yellow swee
Page 147 and 148: enhances soil fertility, texture an
Page 149 and 150: WHITE CLOVER Trifolium repens Also
Page 151 and 152: for several freeze-thaw cycles. Mak
Page 153 and 154: COMPARATIVE NOTES • White clover
Page 155 and 156: Fall planting. Most growers seed at
Page 157 and 158: combining with a belt-type rubber p
Page 159 and 160: Then seed the remainder while walki
Page 161 and 162: screening, a number of farmers have
Page 163 and 164: the seed is relatively expensive. B
Page 165 and 166: Dyer, David A. 1998. Conservation L
Page 167 and 168: OTHER RESOURCES Cover Crops On The
Page 169 and 170: Cal/West Seeds Box 1428 Woodland, C
Page 171 and 172: Pick Seed Canada P.O. Box 304 1 Gre
Page 173 and 174: SARE Northeast Region Office Univer
Page 175 and 176: APPENDIX F REGIONAL EXPERTS These i
Page 177 and 178: David W. Wolfe Cornell University 1
Page 179 and 180: Bob Burdette Southern Seed Certific
Page 181 and 182: Shiou Kuo Washington State Universi
Page 183 and 184: 20 Bird, George. 1997. Personal com
Page 185 and 186:
59 Clark,A.J. 1993. Managing hairy
Page 187 and 188:
102 Fernholz, Carmen. 1997. Persona
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141 Helm, J.L. and Dwain Meyer. 199
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186 Koume, C.N. et al. 1988. Screen
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226 Mohler, Charles L. 1994.A livin
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267 Plumer, Mike. 1997. Personal co
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309 Shrestha,A. et al. 1996.“Annu
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352 Varco, J.J., J.O. Sanford and J
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Bulk Discounts: Except as indicated
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INDEX A Alfalfa, 10, 42, 84, 88, 94
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performance and roles, 48-49 planti
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sorghum-sudangrass hybrids, 85 subt
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subterranean clovers, 133, 137 swee
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comparative notes, 71 crop systems,
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crimson clover for, 102, 103 crop r
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