Gf. Becker et al., EFFECTS OF DEFOLIATING STIPA-TENUIS AND PIPTOCHAETIUM NAPOSTAENSE AT DIFFERENT PHENOLOGICAL STAGES - ROOT-GROWTH, Journal of arid environments, 35(2), 1997, pp. 269-283
During 1991-1993, root growth after a single annual defoliation at dif
ferent phenological stages (vegetative or during early, late or post-i
nternode elongation) to 5-7 cm stubble height was determined on field-
grown plants of Stipa tenuis and Piptochaetium napostaense, two import
ant forage grasses in the semi-arid, temperate rangelands of Central A
rgentina. Nondefoliated plants served as controls. Root growth was est
imated by root length density measurements obtained through destructiv
e harvesting, and by using a root periscope to monitor changes in the
number of roots intercepting glass tubes buried in the soil. The root
periscope allowed registration of the angle of each root interception,
which made it possible to measure the root system dynamics (root appe
arance and disappearance). The effects of defoliating S. tenuis and P.
napostaense at different phenological stages on root growth varied wi
th the methodology used. Root growth of both species was not reduced b
y defoliation when it was estimated from root length density determina
tions. However, it:was lower (p < 0.05) on plants which were defoliate
d late compared to those not defoliated during the growing season when
it was estimated using the root periscope. Lack of agreement in the r
esults obtained by the two methods could be associated with various pr
oblems inherent in the use of the root periscope. This instrument was,
however, useful in providing a rapid evaluation of root system dynami
cs (through root appearance and disappearance) in both species. A grea
ter cumulative root appearance and disappearance, for example, occurre
d after plants were defoliated early rather than late in the growing s
eason. This may have contributed, at least in part, to the overcompens
ation in forage production which was observed on plants defoliated at
the vegetative stage during 2 consecutive years of study. (C) 1997 Aca
demic Press Limited.