The Clover Dilemma:Do I have enough?

2020 OFGC Annual Meeting

Dr. Jimmy Henning

University of Kentucky

N222D Ag Science North

Lexington, KY 40546

Legumes

• Better forage quality and animal gains

• Reduce fescue endophyte problems

• Extends grazing season over grass alone

• Reduce N fertilizer cost through N fixation

More Reasons to Love Red Clover

• Isoflavones especially high in red clover (Biochanin A)

• A phytoestrogen mimics the effect of Rumensin/Bovatec in the rumen

• Less de-ammination

• Directly counteracts the vasoconstriction in tall fescue

What is the Clover Dilemma?

• Do I have enough to:• Withhold fertilizer N

and maintain top yields?

• How does N get from clover to grass?

• And When?????

What number have you heard(for enough clover)?• 25 to 30%

• But is that by weight?

• Or Ground Cover?

• Let’s take a look

Nitrogen use Efficiency in legume-grass pastures (West, 1981)

Studied yields and N-transfer in mature alfalfa-grass pastures differing in percent legume

Nitrogen use Efficiency in legume-grass pastures (West, 1981)• Increasing percent

legume increased yield

• Yield increase came from the legume

• Yield is best correlated to percent clover THE YEAR BEFORE

• Little direct transfer from legume to grass

Nitrogen use Efficiency in legume-grass pastures (West, 1981)• Need 30 to 50% legume

by weight year after year to maximize yields

Site 1 – Newly seeded grass clover following cropSite 2 – Long-term stand of grass clover

• “It may be that when we no longer know what to do,

• we have come to our real work

• and when we no longer know which way to go,

• we have begun our real journey.

• The mind that is not baffled is not employed.

• The impeded stream is the one that sings.”

Site 1

Site 2

Clover Content and Total Yield on Two Sites

Rayburn and Green. 2014 Forage and Grazinglands

30%80%

Movement of nitrogen in grass/legume

systems

Adapted with Permission from

2020 AFGC Workshop on

Getting Back to the Basics of Forage Management Workshop

Sponsored by Corteva Agriscience

John Jennings, Professor and Extension Forage Specialist

Nitrogen sources

fertilizer,

litter

rain, snow

legumesorganic matter

The majority of N usually comes from N fertilizer. Legumes can make a

large N contribution if at least 25% of the stand. Organic matter can

provide about 10-30 lbs N per 1% of soil organic matter. Rain/snow

contributes negligible amounts of N. Total of sources, without fertilizer can

provide enough N for about 1 ton of forage per acre per year. Very good

clover stands can contribute much more.

Species Potential N fixed (lbs/acre) Value of N @ $0.40/lb of N

Alfalfa 128-250 $51-$100

White Clover 75-150 $30 - $60

Red Clover 75-200 $30 - $80

Crimson Clover 50-150 $20 - $60

Arrowleaf Clover 50-150 $20 - $60

Hairy Vetch 50-150 $20 - $60

N fixation and Estimated Value

Is this data misleading…..?

Dry matter yield of fescue/clover in response to commercial fertilizer (Huneycutt, et al., 1988)

Fertilizer rate Mean yield (1980-84)

tons/acre

0-0-0 3.01

0-80-80 2.78

0-160-160 3.19

0-240-240 3.40

100-80-80 3.08

100-160-160 3.77

100-240-240 3.66

Symbiotic N Fixation

• In mixed stands legumes fix N for the host plant and release it into the soil for the companion grasses

• What?????

• N fixation is a biologically expensive process for

both rhizobia and host legume

• Legumes do not freely share fixed N with grasses

because symbiotic N fixation allows legumes to

grow in a N-deficient environment

Where is the fixed N?

• Rhizobia bacteriods in root nodules fix N which is used by the host plant. In turn the host provides CHO to the bacteroids.

• The nodules are the factory, but not the warehouse!

• In perennials, 70-80% of the N is in the topgrowth; In annuals up to 90% of the N is in topgrowth

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Topgrowth Root

Ro

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pg

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N Distribution Between Topgrowth and Roots of Crimson CloverG. W. Evers

Texas AgriLife Research & Extension Center, Overton, Texas

Mixed stands with high % legumes can yield like Grass plus N

Total above-ground N content

Fescue plus N(80 lbs N 2X)

Fescue plus Red Clover

Fescue plus Alfalfa

Grass 158 95 77

Legume 0 142 195

Weeds 6 2 5

Total 162 239 277

Total DM Yield (tons/acre)

4.7 4.7 5.8

% Legume Stand 53 59

K. Vines et al. 2006. Plt. Mgt. Network

It takes high % legume to replace fertilizer N and not sacrifice yield

Total above-ground N content

Fescue plus N(80 lbs N 2X)

Fescue plus Red Clover

Fescue plus Alfalfa

Grass 158 95 77

Legume 0 142 195

Weeds 6 2 5

Total 162 239 277

Total DM Yield (tons/acre)

4.7 4.7 5.8

% Legume Stand 53 59

K. Vines et al. 2006. Plt. Mgt. Network

How does the N in legume topgrowth move to the companion

grass??

#1 Grazing

#3 Root contact, fungi#2 Decay

Producing forage from N fixation is a process

Producing forage from N fertilization is an event

Summary

• It takes about 30% legume by weight, year after year, for high yielding mixed stands

• Most of the fixed N is in legume topgrowth

• The 2 main pathways of N transfer from legumes to other forages are cycling through grazing livestock and plant decay

• Total N fixed is dependent on % stand, available free N, and growing conditions

• Transfer of fixed N in grass/legume systems is a process not an event

Common Legumes in Kentucky

Questions?