Tropical Grasslands (2007) Volume 41, 260268
Effect of defoliation interval and height on the growth and quality of Arachis pintoi cv. Amarillo
K. SINCLAIR1, K.F. LOWE2 AND
K.G. PEMBLETON3
1 NSW Department of Primary Industries,
Wollongbar, New South Wales
2 Department of Primary Industries and
Fisheries, Mutdapilly Research Station, Peak
Crossing, Queensland
3 University of Queensland, School of Agronomy
and Horticulture, St Lucia, Queensland, Australia
Abstract
The effect of defoliation on Amarillo (Arachis
pintoi cv. Amarillo) was studied in a glasshouse
and in mixed swards with 2 tropical grasses. In
the glasshouse, Amarillo plants grown in pots
were subjected to a 30/20°C or 25/15°C temperature
regime and to defoliation at 10-, 20- or
30-day intervals for 60 days. Two field plot studies
were conducted on Amarillo with either irrigated
kikuyu (Pennisetum clandestinum) in autumn and
spring or dryland Pioneer rhodes grass (Chloris
gayana) over summer and autumn. Treatments
imposed were 3 defoliation intervals (7, 14 and
28 days) and 2 residual heights (5 and 10 cm for
kikuyu; 3 and 10 cm for rhodes grass) with extra
treatments (56 days to 3 cm for both grasses and
21 days to 5 cm for kikuyu).
Defoliation interval had no significant effect
on accumulated Amarillo leaf dry matter (DM)
at either temperature regime. At the higher temperature,
frequent defoliation reduced root dry
weight (DW) and increased crude protein (CP)
but had no effect on stolon DW or in vitro
organic matter digestibility (OMD). On the other
hand, at the lower temperature, frequent defoliation
reduced stolon DW and increased OMD but
had no effect on root DW or CP. Irrespective of
temperature and defoliation, water-soluble carbohydrate
levels were higher in stolons than in
roots (4.70 vs 3.65%), whereas for starch the
reverse occurred (5.37 vs 9.44%).
Defoliating the Amarillo-kikuyu sward once at
56 days to 3 cm produced the highest DM yield
in autumn and spring (5832 and 7121 kg/ha DM,
respectively), although the Amarillo component
and OMD were substantially reduced. Highest
DM yields (1726 kg/ha) were also achieved in
the Amarillo-rhodes grass sward when defoliated
every 56 days to 3 cm, although the Amarillo
component was unaffected.
In a mixed sward with either kikuyu or rhodes
grass, the Amarillo component in the sward was
maintained up to a 28-day defoliation interval
and was higher when more severely defoliated.
The results show that Amarillo can tolerate frequent
defoliation and that it can co-exist with
tropical grasses of differing growth habits, provided
the Amarillo-tropical grass sward is subject
to frequent and severe defoliation.