3 2 3 The Effec t Of On Pasture Grcvrth

As discus sed in Sections

3. 2. 1

and

3 . 2. 2, pasture

rearowth depends ·

( 1 )

L. A . I .

i s defined

by Brougham

( 1961 )

as tho area of leaf per unit

area of ground.

(2)

Weather fluc tuations \.Je re

changes

of Heather that occurred Yi t:r..in the week that D . l1 . yield was measured, and accountGd

for

as !auch as 2: 50,� o f the grou:th ra te in ::1 t weelr�.

'l'ot:'�l D . l1. Ilet:;ro\lth

- 35 -

?!!El se IIJ Phase

II

'l'ime

3 . 2

•

.3

The Effe0t Of l1a.,

A .a"3:n ent On Pa.sture

(Continued)

o n the heibht to whic:h pi.l.sture is grazed, the

tL·1e

since grazing , and

l

the clituatic eo.ad:i.tions that

prevail

d.urlng :cegnn-rLh . l�t) l' any given set of climatic fac tors then, the d.;c:ision.s mado by the ;nann.eer o f the grazing system , on

the

hei:;hi:. to v:hich pa� ture is grazed and th0 lent;th of spell beh;ce[l grazirl;_$S will deter·,nin<) the amount of pas tu.ce available

The effec t that tho;.;e grazin� mo.nage�tent dec isions may h...1.v-e

on a-vailable

pasture g,re disc u�sed beloH in a simple exemple and illustrat0d by Fig. 3 . 2 .

Co11si der a _{5 0}

ha.

_{beef w1i t running}

200

_{f a ttening-} a..r:l.i,nals . iil1 area.

of

pasture hs.s been grazed at some time lfk11 day;_;

before

day 11 t11 •

The D . H . pres ent sinc e that grazinG on. day " t ·- k " i s :repres•3nteti by the function a .

On

day 11 tfl

2000

Ki;

D . H . /ha

are present on the p2.s ti.l4e . Giveo. t::ufficient availQblo pasture i t is assuu1ed tha t the anim.s.ls Hi tll�Ln the sys tem 1·1ill

eat 10

Kg

D.�'L/head/d.ay.

In ca s e

I

the JJQUtcger d3cide�:>

to feed. 2�

ha o f p-is !::c1re on day " t.11

(

i . e, _{it will tr'lke 20 cl.:l.)"S} of' fe,;:ci.:Lr�.G

2��

hh of

pas ture/cla.,;r

h0r'o re the pas ture gr.1z ecl on day " t'1 wi ll be graz ed

again) .

Feed available/day Appeti te requirc;amlt Unea te11 pas tu re

Pasture res�due

/ha

:::

= =

(2000

(200

(3000

Kg D

. i-i . /ha

mirrals X

10

Kg ,_ ' D . H. ;�·z X

2 �· ha)

:: 5000

Kg

D

. 1 1 .

Ka

0

D . H /nd)= 2000

:r=g D . i'i . 3v00 Kg D.A. \ 1200 K_u

_{" ' ' ;·}

na )

:::

0 L1 , 1 1 , !ld

In ca::c: e II the decision is to feed only

2

_{ha. of pasture} on day "t "

(

i .e. a

25

d01.y

rotation) .

II

l<'eed availabJ

e/day

Appet:L te requirement Uneaten pasture Pasture

residue/h2.

=

(200l) Kg D.H./ha

x 2

ha)

=

4000 Kg D . i1 .

=

( 200

animals x 10 Kg

D . 1·1 /hd)= 2000

Kg

D.H.

=

2000

Kg

D

. i1 .• =

(2000

Kg

D.H,/2 ha)

=

1 000 Kg D . 1·L

As suming

the pasture regro\vth curves

in Fig.

3.

2 the feed available after a 20 day ro tation

(Case I)

will be

2400 Kg D.H./ha,

while the outcome

To tal

D . H.

(Kg/ha)

2 500

-

_ ...

- -

-- - - -

-

- rl vASE I

- -

- - -

- -- -

- -

-

-- - - -

500

- -

I

- --

- - - - -I

'-

i -

_I

I

I

I

I

I

I

I

I

I

I

I

I

CASE I I 0 � k t + 5 t + 1 0 tl.<?gro,.;tb Period

( d:ws )

t + 1 5 t +

20

t +

25

· �

- .38 -

.3 . 2

•

.3 The

E:ffec t Of On ( Cor1tinued)

of the decision in Cas e :U is that o :1l_y" 2l.JUO Kg D ,J·i . /ha are avai lable

at

the ne:<t erazinc;.

In thi s example then, the grn zinG m::tna.gement in Case I tends to build up feed, vJhile the grazing marngera ent in Cas e IJ ter1cls to main"t-:1in available _{pas ture D . i·i .}

Althou($h

_th.is exw!l�Jle _{is an} o versim,;;lifi c :!. tiol.:.

of the roal-W')l'lcl si tuation, i t do es ilhw trate the way in Hhich 5 razing manaeement can

affec t pasture

p ro duc tio n .

Brougham

( 1970)

has sbowa the impo rh.nc e of graz ing height and length of spell be �weea grazing

at

t·..;o times of the year. ln late

a

utumn a mix ed rycgro.ss

/::

lovc r pastur8 was defoliated , The

tbree

treat-- ments impo s ed follo,,ing that grazin5 on 1�pril Jrd were :

i)

Gra z e aJain in

18 \-!0)eks

ii

)

Two grazings at

9

in tenrs.ls iii ) Three crazinss at 6 Heek interval.s

T:1e D . l1 . yi elds ov2r tha. t eit:;htee<1 \Jeek v:inter peri o d Here 2 1 20 ,

.3290 , a..'1d .3620

lb D . H./acre

rcs;)ec tively. i-Jhile this rep resented a

70-fo

inc r-eus e in

D .

··1 . pro due tion fo r the three- grazing trea trnen t over the one-graz ing trea tf.:,ent, the pG. s ture grazed. three timc.s o ver the winter also ho:td n higher c lo ver conten t in the s p ring , due to

increased

illwr.i­ na

t

ion a t the base o f the sward, und hif:ll.-::r sprinJ D , ,'l , pro duc tio."1 ,

B rougham (

1970 )

found that grazi11U height v:as partic ularly

c ri tical over the summer perio

d

in the

Palmerston

lio rth envi ronment.

In earl_y" sUJIJrncr a pas ture that had be0n wnfo rmly grazed fo r the previous

18

months

was subj ected

to three grazin�s at three weekly

intenra.ls .

Half the pasture

was

grazed hard while the other half

was

grazed only

to Y' .

Follo"..�.i..n�

these t.reat•nents the \.,rho le pa.sturt3 was erazed uni.fo nnly .

The grazing heights following the period of treatment, although no t

specified, were considered by Bro ugham to be such that pa

s

ture produc tio:-1· was maximised over the

rest

of the yea r. The advantage in daily D . i'1 . increments to th e lax grazed pasture w:::1s in the order o f

50 -

10U%

over

the res t of the summer and the autw11n period. Bro ugham at.tnbllted this

effect to

inc reased soil moi s ture leYels due to the

incre�sed

pas ture

- 39 -

cover over the summer peri o d, and to i nc H�3.sed survival of grass tillers

under the lax grazing -crca tment.

Bece.use of

the interactiou beti.ieCn gra zing 1(1.3-.Ylageu1ent, va s i.,ure speciE:s prr::sent �md climate , and the r.ecd to meet �tniu:al requi rements , defini tion of a.n optiun.1m gra zing s;ys tc:t is a coru.plRX task.

From th e results o f his trial Hork, Bro Ll[;h<-L.l

( 1970)

b.s sue&est�:d

grazing management recomrrtendatio11s fo r mi:.<:c::d

rycgn:tss/\o.'h.i.

te

c.lo·.rcr

pa;;tures in the l'aL·ners ton No rth region. These recon;;;tcnda tivns

are

pre� ented in Table 3.

I c:.nd

are s tated by Brougham to freC'�uently pro duc e

1 6- 1 7000

lb ll .H. per ac re . Grazj_nc; Graz i�1g Interv.s.l

( "'eek s )

8

Hei [;ht

(L1chcs)

1

2

§R!i.flJ..:

3

it

1

3 Sucu:r,.�.r

4

·�

5

3 -

4

l-19 rdgrctz o

_/,.

- 6

1

1

-

2

Many expe riments e.re repo rted in the literature as havinrs UJeasun�d pas ture production under different s tocking rates ( c.ni.mals/uni t area )

and differt-mt types of s tock .

Campbell (

1 969)

measured the annual D . r1 . produc tion of pastures grazed by sheep at 10 and 1 5 ewes

/

ac re . In both treatments the spell

T.!:le lo�er s tc -::king rate tredme!l.t outyielded the high stocking rate treatments, in terms of D .H . produced, : by 25% over

2

years . Hull .?.t. .511.

(

1 961 ) who grazed beef cattle at

5

stocking rates (1 . 3 to /,._. 7 aDimals/a c r� ..

)

on i rriga ted pas tures , also found tha t pasture produ.c tion declined wi th increased stocking rate .

- 4D -

Carnpbell 1 s experiment hoHever,

included

a further treatment in which pas turo grazed by the r...igher s tocking rate

( 1 5

ewes/ac re ) was spelled fo r

28

days betMeen grazin�s . Pas ture produc tion

in

this c a s e

was 50% higher than that obts.ined w;.der th e same s tocking rate and a seven day ro tation.

Gordon e t al

( 19oG)

cons ide red _thc.t the neglec t of g1·az ing

pre ssure raeas ure::1ents

( 1 )

_{co uld be a maj o r reason fo r the hcrge errors} and poor repeatabili ty o f pasture experir:wntation. L11 view of Brougham 1 s

results ( discu s s ed in Sec tion

J . 2 . J)

regarding the effect

s

o f defol:i.a.ti.on height _{G l'ld} t.he i ntera c tions b e t�•e en

this,

_{length of spell cmd the} season ,

i t s eems loGical that S0r.rl'2 meas 11re of gra �:i.r:g pressure

and

the result3.nt

gra zing hei_ght are nec es s ary befo re t,he results from s tocking ra te and length of spell experitnen ts c c..n be _{very meaning;ful.}

Hull Q_!,_ a l (

1961 )

also sho'v-red. that '<Jhile pasture reerowth from hard grazed pas tu res

(those

grazed by higi2er stocking rater; ; \·ras

higher

in pro tein content, loHer in lignin content, and henc e hi[�he!' i n enere::y

value, the ac tual pas ture C 01ls umcd by animals at thE' hi;;b cr s wcking

ra tes V£.:.S loHe r in ene_{rgy value than} pasture consumed by a.'1irnals at

I

lov1er s tockin.; ra tes . This resu_{lt \.Jas explained by the reduced}

oppo rtuni ty fo r s elec tive grazing at the higher s tocking rates .

Campbell

( 1966a)

has shown that higher grazing pres sure allows � les s dead fo rage to accumulate in the pas ture . The results o f Hull

et al hoHevcr, su;:;Jes t that differeoc es

in

pas ture quali t.r

(

eller.:;y value

)

bet,,1een pastures grazed at v:1 rio us gr.-i�inz pressures may no t be a true represent3.tioa o f the differences in t�e quality o f pasture actually consu:ned at those grazin;:; pres sures .

The p resenc e of grazine animals also affec ts pas ture pro duc tion

by mechanical damage

callsed

by treading.

Hull

( 196 1 )

found that D . il1.

yield frolll

a trea ttnent cut

(1)

Grazing pressure here means the relationship between f eed avai lable ,

- 41 -

fo r sihge in their expcriw.ent, and henc e no t s ubj ec.: ted to the

damage

caused by an:i_mal

hoove s , .

was about 35�6 higher than the treatment sub- j cc ted to the hi ghest :�rl.l.zi:o.;

pres sl<rL:,

Somn of thi.s e ffect ho weve r ,

could have bc ::m attributod to differenc es in the defoliatioa heic;ht

betiveen the cu ttin.e ann graziL18 tr eab1ents .

EdJllOtld ( 1 974.) has shown tlv-t t treadi

..

1g h;v sheep

(at 49" 4

equi

vali3Llts/ha )

( 1 )

does

reduc e pas ture yield by up to 30/� .

Clover

plants Here .no re susce;)tibh� than ryegrass in a lJixed 3\·!L�.�·d, and treading effec ts were greatest when the so il was at o r above fi eld capacity.

Camp

bell (

1966b)

has examin,)d tc,.e effe:; t of t.ccadi,J.C by du.i ry

COio/S 011 autur!ln- saved pa s ture graz ed in late winter, TiJO stock:i.ae rates were ussd,

60

co�Js/acre/day and

120

cows/ac re/day , and pasture wc

..

s movm as a con tro 1. The pas tL1res Here clo ;;; e to field

capacity

a t the tio t::: o f _{grazi�e and h<m:ine. )1.f ter trEJa t:uen t, pas tu re}

y:Leld

Has measured as the diffe rc�1ce betwe<:'tl ;?Os t-gri:lzi.'1G :::ec;j.du0 r:.nd the

amount of pas ture presetlt

before

the next grdZL"lg , Differenc e m easure- ments co:1ti.1uE.:d fo r the re.nai(lder of t..'fJ.e Hi."lt�r a•ld

the'!

fo llO\·Jint;

sprine an.d

SUlll,-•ler,

duri.nc· which timG all treo.t.ne:1t� were subj ec·i::;ed to

the s ame crazi!16 trei:i

t:uon t.

Thre e

years da t':i Here coll€'c t.::d,

Little va riatio n iLl pasture yi eld vms illen.s ured be Lreer1 the

trea t·nen ts , al t!wugh large variations in pas tu re yield '.o/L�l'•3 1neasur-:3d be tween years .

Camp

bell concludosd tha t the SI!lR.ll los ses as s o c iated

with treadine wo uld no t affec t aniJlal produc tion .

3 . 2 . 4. 3

Effec t Of Fa eces

The faeces

dropped by

animals durine erazing will also affec t pasture

Greenhe.lgh

anc.l Reid

( 1968)

conducted an experime·'lt where d.t."l.i ry ( 'I )

Edri'lond

( 1 958)

has estimated that a grazj_ng sheep

Falis

1 . 7 miles/ day. Sinc e a rac e one rnile

lon

g x L1• 1

1 011

wide equals one ac re ,

Edmond

expresses the treadine effec t of

10

sheep \..ralking through

a

4'

1 0 11 wide race

daily

as equal to 1 0 sheep equi-.ralents/ac re. Si;nilurly

300 sheep 1..ralk.ing th:r>x.lgb. the

race once every 30 days

represents

3

₀

0_/3

_{0 "' 10} s hee!) equ.i vale•J ts,lac re. Th<:: figure

49.,4

equiv&len.ts/ha

desc ribed by Edr:.oad ( 197/+ ) equals 20 she ep/i::!c rej day.

- 42 -

CO\-TS were

gra2ied

at tHo levels of grazing pressure on pas ture that

had previousl,.v been ci tl-J.er mo\m or f,raz ed. The

previously g

raze

d

pasture had

2.

s;; of its area c o ve:: _{red by faeces . By meastu"'ing the}

amount o f pas ture rej ec ted in subsequet1t grf.lzing they concluded that

the presenc e o f faeces affec ted ani::nal intal�.:e over an area

8 -

1 2

times t..'rJ.e size of the actual area

co vered..

3

•

.3

Pasture

Used

In

Thi�_ S"ti._t,y,cr

It has been shO\·T:l that pasture produc tion va.cies Hi th the length of S�)ell between grazi::1;3'S and the severity (height) of gra.zi:a.e . The interactio11 of these t·,:o fac tors t-Ji _{th s easo nal, climatic and ani,ml} fac tu rs can lead to ch.L!11t;es in pas tm.·e co<:lpo s:i_ tion and pas tu

re

pro­ duction thr-ou�hout the year.

( 1 972 ) de:cived a set of regro' .• th curves fo r a mixed S\-Tard ( ryegrao s/clover) growine in the :i?aJ.w;r.s tm1 i{o rth J oca]_i t,>r in an average year.

provided by D . ,::> . I . R . Grassh.nds Dlvis.i.ofl. s taff based on thei r k.:-toHledge

of ho\-1 pas tttre was

li..�cly

to produce under br;Hine

c.onni

tions .

Throu;hout the year defoliation height

was assue1ed.

to c o inc ide wi th _{tho se figures sugges ted by BrouE;htun ( 1 970 ) ( pres :.:;11ted in t.?.ble}

.3 . 1 ) .

Associated vJi _{th this patte ru o f defo liation heigh t. Hould be a pattern} of pas ture cor.J.f)() Si t.ional ch.anee

-

a patten1 thc.'1. t ac

co

rding to Brougham

shou

l

d provide

consis tently high

D . !1 .

yields .

Hright

(197.3b ) using

the data from ?o llards _{s tudy and o ther}

unpublished data simulated a series cf relationships bGtween

D.i-1.

present and pasture growth rate fo r all

weeks

o f the year.

From the s e data i t was po

s

sibl

e

to cons truc t a seri es o f pasture regrm;th c urves wi th the daily D . H .

increments

as a function o f ti�e after defo lia tion a.11d defo liation height.

Individual curves were

construc ted fo r regro�·rth after defoliation in eac_{h week of the year.}

While the data generated by �Jright referred to po tential growth rather tha.n the ac tual growth that may be

expected

in any partic_ular

,

- 43 -

year, they

did give

some idea

of

the effect that grazing height ma;;r have on pasture regro\,th.

As Hell as plo tting D .H . prusont abcne defolia-tion hej.ght as a

func tion of ti:ne after

defolia

t.iou fo r a

rant;e of

grazi..YJ.e sev-eri ties

(hi.�ights) , the actual daily

i..'1.c :ce�ents _{in D . H. pres ent Here also} plo tted.

Gene ralised curves arc sho1m in Fig. 3 . 3 .

As \orould b e CX'_2ec ted fro�::� the HOrk

o f

Brougham

( 1956) ( 1 )

the rnaxi.:.tiUG.l do.iJ.y grrx.,rth rates achi eved _{after defoliation. at a r3..nge}

of

grazing

severi

ti es Y"'.:J.ri ed little .

The

_ti:'lc

take!l

fo r tJ1e pas tur·� to

achieve

ma.nmun daLly groHtl1 rate did vary Hi th defob ation height.

In document Application of linear programming to farm management analysis : intensive beef grazing systems : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Farm Management at Massey University (Page 45-56)