Biology Reference
In-Depth Information
P. minor
density from 40 to 80 plants/m
2
resulted in a corresponding loss of 530
(11%) to 568 kg/ha (13.5%) of wheat yield (Khera et al. 1995).
Much attention is currently focused on exotic invasive weeds that may damage
native biodiversity (Inderjit and Drake 2006; Mack et al. 2000). Noninvasive exot-
ics such as
P. minor
, however, could also cause severe damage in terms of economic
losses. We discuss here the control of
P. minor
with an emphasis on research topics
that deserve more attention.
14.2
Agricultural Practices that Influence the Ecology
and Management of
P. minor
Agricultural practices, such as incorporation of rice straw or application of herbi-
cide mixtures, or both, can play an important role in the successful establishment
and growth of
P. minor
(Kaushik et al. 2005). Farmers in northwestern India often
incorporate unburned and burned stubble/straw into the soil; this practice is fol-
lowed by irrigation and sowing of the next crop. Straw (particularly rice and wheat
straw) is reported to cause allelopathic suppression of crops (Inderjit et al. 2004).
Incorporation of rice straw into the soil followed by irrigation, for example, exerts
a negative effect on the seedling performance of mustard (
Brassica napus
var.
toria
L.)
(Inderjit et al. 2004). After rice harvest, wheat is usually sown next, particularly in
the States of Punjab and Haryana. We studied the influence of rice straw incorpora-
tion on the seedling growth of
P. minor
(Kaushik and Inderjit 2007). Incorporation
of rice straw into soil suppressed the growth of
P. minor
.
Allelochemicals may influence plant growth directly or indirectly by influencing
abiotic and/or biotic factors (Inderjit and Weiner 2001). Although allelopathic
potential of Indian rice cultivars was not examined, several US and Chinese varie-
ties are reported to exude chemicals with potential allelopathic activities (Olofsdotter
1998; Olofsdotter et al. 1999). It would be interesting to explore the allelopathic
potential of Indian rice cultivars and determine if the straw itself (compared with
root exudates) of any rice cultivar is phytotoxic to
P. minor
. We tried to examine
whether inhibition of
P. minor
seedling growth in rice straw-incorporated soil could
be explained by direct effect of allelochemicals or their indirect effect through
altered soil abiotic and/or biotic factors, by using washed, unwashed rice straw or
by amending the unwashed rice straw-incorporated soil with activated charcoal
(Kaushik and Inderjit 2007). Washed rice straw as well as activated carbon did not
ameliorate the phytotoxic effects of rice straw, which ruled out the direct involve-
ment of rice straw allelopathy in growth inhibition of
P. minor
.
Microbes can act as a sink for mineral nutrients (Schmidt et al. 1997). The sup-
pression of seed germination of
P. minor
in straw-incorporated soil, however, could
also be due to immobilization of N by soil microbes, which would be fostered by
carbon-rich straw. We observed higher levels of exchangeable phosphate in soil
amended with rice straw compared with unamended straw, which might result in
higher microbial activity (Kaushik and Inderjit 2007). Om et al. (2002) suggested
