Dan UndersanderPaul Vassalotti

Dennis Cosgrove

A3681

germination & growth

Alfalfa

Understanding alfalfa germination and growth

is important to matching management deci-

sions to alfalfa development. Knowledge of

the germination process will help you under-

stand conditions necessary for good stand

establ ishment and reasons for delayed or

failed establishment. Knowledge of seedling

growth will help you determine when to take

remedial action to control diseases, insects,

and weeds. Understanding the patterns of

spring greenup and regrowth after cutting

w i l l a i d i n de t e rm in i ng the p resence o f

disease problems or winter injury and in

managing weeds. Knowledge of mature stages

of alfalfa will aid in harvest decisions for the

desired forage quality.

As the radicle grows, the portion near-est the seed enlarges and forms ahook. It pushes up through the soilsurface, dragging the cotyledons andseed coat with it. Ó

Once the seedling emerges aboveground and is exposed to light, itstraightens out. At the same time,small root hairs are developing on thelower radicle. The root hairs absorbwater and nutrients from the soil. Ô

Supplying the right conditions foralfalfa seeds will help to assure max-imum germination. Prepare a firm,

weed-free seedbed to minimize competi-tion from weeds and to ensure goodseed-soil contact. Avoid overworking thesoil surface as rainfall following seedingmay crust the surface, preventingseedling emergence. Place seeds 1⁄4- to1⁄2-inch deep in medium and heavy tex-tured soils and 1⁄2- to 1-inch deep insandy soils. These depths cover the seedswith enough soil to provide moist con-ditions for germination while allowingthe small shoot to reach the surface. Soiltemperature must be above 37°F for theseed to begin taking up water. Highersoil temperatures increase the rate ofgermination but do not affect the finalgermination percentage. High soil saltcontent will prevent the plant from tak-ing up water and germinating.

2 A L F A L F A G E R M I N A T I O N & G R O W T H G E R M I N A T I O N & E M E R G E N C E 3

Germination and emergence

The seed on the right is swollen withwater taken up from the soil. Thisprocess marks the first step in seedgermination. Under favorable condi-tions, water uptake begins within 24to 48 hours after planting.

The first part of the seedling toemerge is the root radicle. The radicleanchors the seedling in the soil andalways grows downward, regardlessof the direction it’s pointing in when itfirst comes out of the seed.

Young seedlings are particularly vul-nerable to diseases and herbicidedamage. As the seedlings mature,

they become more resistant to seedlingdiseases and less susceptible to herbicidedamage. Many herbicides have applica-tion restrictions until a specific growthstage is reached. It is important to beable recognize each growth stage so youcan apply treatments at the correct time.

4 A L F A L F A G E R M I N A T I O N & G R O W T H S E E D L I N G D E V E L O P M E N T & G R O W T H 5

Seedling development and growth

The second leaf to appear has three leaflets. This is called atrifoliate leaf. Most subsequent leaves are trifoliate, althoughsome varieties produce leaves with four or more leaflets perleaf that are called multifoliate leaves.

This plant is at the three-leaf stage. Note the three trifoliateleaves in addition to the unifoliate leaf. At this stage, theseedling can manufacture all of its energy through photosynthesis.

The first true leaf to develop on analfalfa seedling has just one leafletand is called the unifoliate leaf.

Cotyledons are usually the first visibleportion of an alfalfa seedling abovethe soil surface.

Even brief exposures to air tempera-tures below 27°F will kill youngalfalfa seedlings. Alfalfa plants sur-

vive cold temperatures by pulling thelowermost buds below ground to form acrown. This process, called contractilegrowth, begins two to six weeks aftergermination. To allow enough time forcrown development, avoid seeding afterthe recommended late-summer plantingdates. Plants that have not formed acrown will not survive the winter.

Crown development has not yet begunon this young plant. The cotyledons,though brown, are still present. Notethe distance between nodes in thispicture compared to those of the plantat right. ÕThe lowermost buds have been pulledbelow ground to form the crown.Crown development on this plant isalready sufficient for winter survival.The crown will continue to enlargethroughout the life of the plant. È

Counting only thefully expandedtrifoliate leaves,this plant is atthe five-leafstage. A leaf isconsidered fullyexpanded whenthe outer edgesof all leaflets areno longer touching.

Within four weeks after germination, ifRhizobium bacteria is present, roundstructures called nodules will form onalfalfa roots. The bacteria help theplant use nitrogen from the air in aprocess known as nitrogen fixation.

6 A L F A L F A G E R M I N A T I O N & G R O W T H C R O W N F O R M A T I O N & D E V E L O P M E N T 7

Crown formation and development

The plant on the left has suffered win-ter injury while the plant on the righthas not. Injured plants are less vigor-ous and slow to recover. In addition, ifcrown buds have been killed, the plantmust form new buds to replace them. Õ

Uneven (asymmetrical) growth is asymptom of winter injury. The crownbuds on the right side of this planthave been killed by cold temperatures.Such damage is often found on older,diseased plants. This plant will be lessvigorous and lower yielding than ahealthy plant. È

Spring growth ideally comes fromcrown buds formed the previousyear during late summer and fall.

Greenup occurs when buds located onthe crown begin to grow in response towarm spring temperatures. In additionto weather, the timing of spring greenupdepends on plant health, the genetic falldormancy of the variety, and theamount of dormancy developed in theplants during the fall (determined by fallweather conditions). If plants areinjured or slow to greenup, considerplanting more winterhardy varieties.

This well-developed crown showshealthy crown buds growing to produce the season’s first cutting.

8 A L F A L F A G E R M I N A T I O N & G R O W T H S P R I N G G R E E N U P 9

Spring greenup

Forage yield, quality, and stand persis-tence are considerations for decidingwhen to cut. Forage yield increases

until the plant reaches full flower, whileforage quality decreases continually dur-ing growth or regrowth (see figure). Theoptimum balance between yield andquality depends on the cutting and for-age quality desired. Early in the growingseason, plants may not flower normallyand quality may decline even thoughthe plant is not flowering. Therefore,take the first cutting of the season basedon quality or by date (if quality infor-mation is not available). Take later cut-tings based on growth stage or by timeinterval (35 to 45 days).

The optimum yield and foragequality for milking dairy cows rangesfrom vegetative to early bud on the firstcutting to 10% flower on the secondand third cuttings to full flower on alate-fall cutting. For animals with lowernutritional requirements, later stagesmay be harvested. The pictures on thefollowing pages depict growth stagescommonly referred to when discussingcutting management.

Regrowth after cutting arises fromcrown buds and from axillary buds.Axillary buds are found in leaf

axils, where the leaf joins the stem. Theideal cutting height is at least 2 inchesabove the soil surface. This height leavesaxillary buds for regrowth. Lower cut-tings will force regrowth to come fromcrown buds only, reducing yield of thenext cutting. Short cutting intervals (lessthan 35 days) will also reduce the num-ber of axillary buds. Moisture stressimmediately after cutting will reducethe number of crown and axillary budsand, therefore, stem density and yieldavailable for harvest, even if rain occurslater in the growth cycle.

Regrowth from axillary buds andcrown buds.

1 0 A L F A L F A G E R M I N A T I O N & G R O W T H W H E N T O C U T 1 1

Growth after cutting When to cut

forage yield

first-cut forage quality

late-season forage quality

vegetative bud first flower full-flower post-flower

Forage yield and quality at various stages of growth

Late budAt the late-bud stage, flower buds arelarge and lengthening rapidly. Budsbegin developing at three or more leafaxils lower on the stem.

W H E N T O C U T 1 3

Early budThe flowering process begins whensmall buds form in the top one or twoleaf axils. These buds are detectableas small swellings in the axils of theleaves. Forage cut at this stage will bevery high in quality. However, yieldwill be reduced. Cutting several timesper season at this stage will decrease persistence.

Mid budAt the mid-bud stage, flower buds arelarger and easier to detect. Some budsare beginning to lengthen. Additionalbuds are forming lower on the stem.

1 2 A L F A L F A G E R M I N A T I O N & G R O W T H

10% flowerAt this stage, 10% of the stems haveopen flowers. Allowing one cutting togrow to this stage during the year willimprove stand persistence. Late-seasonharvests at this stage may still providedairy-quality hay.

W H E N T O C U T 1 5

FlowersAlfalfa flowers grow in clustersattached to a stem (raceme). The mostcommon flower color is purple.Purple-flowering plants come fromMediterranean stock and have highyield and quick recovery. Plants withyellow flowers are from more winter-hardy stock. A small percentage offlowers may also be blue, cream, orwhite.

1 4 A L F A L F A G E R M I N A T I O N & G R O W T H

50% flowerHalf of the stems have open flowers.Roots have the most carbohydratesstored at this stage. This is beyondthe recommended harvest stage forquality hay.

100% flowerAll stems now have open flowers.Shoots from crown buds for nextgrowth cycle may be visible at thebase of the plant.

Estimating preharvest alfalfa quality

Choose five representative 2-square foot areas in the field. (Sample more timesfor fields larger than 30 acres.) In each area, determine the stage of the mostmature stem (see below). Then measure the height of the tallest stem, NOT

the highest leaf. Note that the tallest stem may not be the most mature stem. Usethe chart to determine relative feed value (RFV) of the standing alfalfa forage. Thisprocedure does not account for changes in quality due to wilting, harvesting, andstorage. These factors may lower RFV by 10 to 20 points.

late vegetative stem is more than 12 inches tall, no visible buds or flowers

early bud 1 to 2 nodes have visible buds; no flowers or seed pods present

late bud more than 2 nodes have visible buds; no open flowers or seed pods

early flower 1 node with at least one open flower

late flower 2 or more nodes have open flowers

––––––––––––––– stage of most mature stem –––––––––––––––

height of late early late tallest stem vegetative early bud late bud flower flower

inches ––––––––––––––––– relative feed value –––––––––––––––––

16 234 220 208 196 18617 229 215 203 192 18218 223 211 199 188 17819 218 206 195 184 17520 213 201 191 181 17121 209 197 187 177 16822 204 193 183 173 16523 200 189 179 170 16124 196 185 175 167 15825 191 181 172 163 15526 187 178 169 160 15227 184 174 165 157 15028 180 171 162 154 14729 176 167 159 151 14430 173 164 156 148 14131 169 161 153 146 13932 166 158 150 143 13633 163 155 147 140 13434 160 152 145 138 13235 156 149 142 135 12936 154 146 139 133 12737 151 144 137 131 12538 148 141 134 128 12339 145 138 132 126 12140 142 136 130 124 118

Source: Derived from equations developed by R.W. Hintz, V.N. Owens, and K.A. Albrecht at theUniversity of Wisconsin-Madison, Department of Agronomy.

Additional informationFor more information on related topics, see the following publications availablefrom your county Extension office.

Alfalfa Analyst (A8CA1018)Alfalfa Diseases I (A7800601)Alfalfa Diseases II (A7800602)Alfalfa Insect Pests (A2156)Alfalfa Management Guide (NCR547)Alfalfa Stand Assessment: Is This Stand Good Enough to Keep? (A3620)Perennial Forage Crop Variety Update for Wisconsin (A1525)

Copyright © 1997 by the Board of Regents of the University ofWisconsin-System doing business as the division of CooperativeExtension of the University of Wisconsin-Extension. Send inquiriesabout copyright permission to: Director, Cooperative ExtensionPublishing, 201 Hiram Smith Hall, 1545 Observatory Dr.,Madison, WI 53706.

Authors: Dan Undersander is professor of agronomy, College of Agricultural andLife Sciences, University of Wisconsin-Madison and University of Wisconsin-Extension, Cooperative Extension. Paul Vassalotti is a master technical service rep-resentative, American Cyanamid Co., Cross Plains, Wisconsin. Dennis Cosgrove isassociate professor of agronomy, University of Wisconsin-River Falls and Universityof Wisconsin-Extension.

Credits: Produced by Cooperative Extension Publishing, University of Wisconsin-Extension. Editor, Linda Deith; designer, Susan Anderson; photographer, B.-Wolfgang Hoffmann. Funding for this publication was shared by AmericanCyanamid Co.

University of Wisconsin-Extension, Cooperative Extension, in cooperation withthe U.S. Department of Agriculture and Wisconsin counties, publishes this infor-mation to further the purpose of the May 8 and June 30, 1914 Acts of Congress;and provides equal opportunities and affirmative action in employment and pro-gramming. If you need this material in an alternative format, contact the Office ofEqual Opportunity and Diversity Programs or call Cooperative ExtensionPublishing at (608) 262-2655.

This publication is available from your Wisconsin county Extension office orfrom Cooperative Extension Publishing, Rm. 170, 630 W. Mifflin St., Madison,Wisconsin 53703. Phone (608) 262-3346.

A3681 Alfalfa Germination and Growth I-09-97-8M-300