7. METODOLOGÍA
9.2 BALANCE DEL EJE CINCO DE LA POLÍTICA PÚBLICA DE MUJERES
and
A Z Zo Zobophora Zonga
occurrfug infrequent ly ( S ears and Evans , 19 5 3 ; Wat ers , 195 5 ) . Both A .ca Ziginosa
andL. rube Z Zus
consume dung , deadroots , and dead leaf (Waters , 1955) , reducing the herb age mass o f pas ture .
L . rube Z Zus
has b een reported t o depos i t up to 3 3 t /ha/yr of surface cas t s ( Syerset a Z� l979)
and these cas t s can cover herbage . Al though earthworms can reduce the herb age mass o f pasture by removing large amount s of l it ter , due to imp roved nut rient cyc l ing and improved soil physical propert ies they also improve the environment for plant growth (Bar ley , 19 6 1 ; S t outet a Z� l9 76 ) .
Micro-organi sms (mainly b acteria and fung i ) are involved in the decomposition of lit ter b oth ab ove and b elow the soil surface in pas t ures and t urf (Bear , 19 7 3 ; Hunt , 19 7 7 ) . L i t t er pH , lit ter carbon-nitrogen rat i o , temperature and mois ture are the main fac tors
influenc ing the rate of d ecomposition (Hunt , 19 7 7 ) . L ime app lication and nit rogen fertilizat ion can b oth increase the rat e of l i t ter decompos ition
(Beard , 1 9 7 3 ) . Warmer t emperatures and mo ister condi t ions also increase decompos i t ion (Hun t , 1 9 7 7 ) .
2 . 3 . 2 . 3 Litter and
Although less frequent and less intens ive defoliat ions are exp ected to increase pasture growth , they are als o expected to increas e herbage death and dis appearance . Morris ( 19 70) ·clearly demons t rated the importance of this interaction between gros s aeri al growth and losses from l i t ter disappearance . The maximum harvested yield was obtained by rotational defoliat ion to 3 cm every
4
w eeks , but this was derivedfrom t he minimum gross aerial growth . Maximum g ross aerial growth
occurred unde r the s imulated cont inuous graz ing t reatments maintained at
a high LAI
( 4 . 6 ) .
The d i f ference between gross and harvested yieldwas large ly due t o the death and sub sequent decay of leaves , up to 50%
3 4 .
may b e pref erab le to ob tain less growth , but t o harvest more of the ma terial grown , minimizing the losses through senescence and subsequent
decay .
2 . 4 CONCLUSION
Although defoliat ion intensity and frequency clearly influence pasture growth , the op timum intensity and frequency of gra zing is st ill not c lear from the literature . I t wou ld help if the opt imum graz ing management could be defined in terms of plant physiological parame ters
such as leaf area index , s t age of reproductive growth , reserve s t atus , or s tubb le quality . Recommendat ions could then be made f or farms wi th diff e rent soil types , clima t es , fert ilizer programme s , stocking prac t ic e e t c . T o ob tain satis factory conclusions , inves t iga tions mus t be conducted under graz ing with herbage sampling to ground leve l .
Since net herbage accumulat ion is the result of both growth and herbage disappearance it is necess ary to separa t e dead and live herbage . In this inve s t igat ion defoliat ion intensity and frequency wi l l be defined by p lant physiological parame t ers .
35 .
3
TERMINOLOGY AND DEFINITIONS
The nomenclature.and definitions recently published by Hodgson
( 19 7 9 )
and Thomas( 1980)
are used in this thesis . The more frequently used terms are presented for convenience in this chapter .3 . 1 THE SWARD (Hodgson ,
19 79)
Herbage mass
Herbage growth
Herbage accumulation
Herbage consumed
Herbage harvested
the total mas s of herbage per uni t area of ground , measured to ground level (or to some reference height) .
the development and increase in weight of new leaf and s t em tissue .
(also referred to as net herbage accum ulation) ; the change in herbage mass between succes s ive instantaneous measure ments , summed over time as appropriate . the mass of herbage removed per uni t area by animals at a s ingle grazing or s eries of grazings .
the mass of herbage removed per uni t area by mechanical means at a s ingle harves t or series of harvests .
3 . 2 THE GRAZING PROCESS (Hodgson ,
1979)
Degree· of defoliation
Residual herbage Defoliation interval
the rat io of the amount of herbage consumed or harvested to the original mass . · The equivalent term defoliation is used also .
the herbage remaining after defoliation . the time between successive defoliations of an area . The term defoliation
the number of defoliations per unit time , is also used .
36 .
3 . 3 GRAZ ING MANAGEMENT (Hodgson , 1979)
Graz ing period
Res t period
Graz ing cy cle
3 . 4 THE CANOPY (Thomas , 1980)
Leaf Area Index (LAI )
Tiller
the length of t ime for wh ich a part icu lar area of land is grazed .
the length of time between the end of one graz ing and the st art of the next on a part icular area .
the length of t ime between the beginning of one grazing and the beginning of the next , tha t is , the grazing per iod p lus the rest period .
the area of green leaf ( one side) per unit area of ground that is carried by a canopy . Only lamina was measured .
aerial shoot of a gras s p lant . Tillers
were only counted after they be came apparent to the eye without the d issect ion of the plan t .
Tiller appearance rate (TAR) the rate at which til lers become apparent
to the eye without dissect ion of the p lant .
( i ) Ab solute TAR
( ii ) Proportional TAR
Tiller death rate (TDR)
is given by N2 - N1 where t 2 - t l
t 1 and t 2 are the t ime s at which counts are made of the number of live t i llers (N) .
is given by 1 . N2 - N 1 Nl t 2 - t l
The TAR is
net
if N2 is the number of· live. t i l lers at t 2 , andgross
if N2 = N1 + (number of new t i l lers produced between t1 and t 2) . the rate a t which t illers die . The grossabao lute TDR
andproportiona l TDR
can be3 7 .
calculated when the numb er o f t i llers dying between two dates is measure d . The net TDR is the ne t TAR when N2 < N
1
.3 . 5 REPRODUCTIVE DEVELOPMENT (Thomas ,
1980)
Inf lorescence eme rgence
An thesis
the first app earance of the t ip of a grass inflores cence at the mou th of the
sheath of the flag leaf . Equivalent to
ear emergence or head emergence .
CHAPTER 4
3 8 .