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ASSESSMENT OF ROOTING INTERACTIONS IN MIXED CROPS
WITH AN HERBICIDE INJECTION METHODOLOGY
Guénaëlle Corre-Hellou and Yves
Crozat Laboratoire dEcophysiologie Végétale et
Agronomie, Ecole Supérieure d Agriculture
d Angers, 55 rue Rabelais BP 30758 49007 Angers
cedex, France
Little information on rooting pattern of
intercropped species is available mainly because
of the difficulty to distinguish roots by species
with commonly used techniques such as trench
profile or soil core techniques. A method based
of herbicide injection was developed to
investigate whether the rooting front advance of
pea, barley and mustard were modified by
intercropping
MATERIALS AND METHODS
Pea, mustard and barley were grown in monocrops
and in alternate row intercrops. Pea-barley and
pea-mustard mixtures were studied pea was sown
at 80 pl m-² and the second component at 40 pl m-²
Herbicide injection technique for the
determination of the rooting front advance of
each species
Herbicide was injected at 3 different chosen soil
depths with 4 replications
The roots absorb the herbicide when they reach
the treated zone
Distinctive symptoms are recorded on leaves
15 days after injection, soil samples were
removed above and under the treated
zone Phytotoxicity symptoms were recorded on
plants brought in contact with the samples
Check of the mobility of the herbicides
(for the study of pea and mustard)
(for the study of barley)
?
RESULTS
Figure 1  Rooting front advance of each species
? pea, ? barley ? mustard in pea-barley and
pea-mustard mixtures in 2001 (----) and 2002
(___) ( ) the variation rate of rooting front
advance between monocropped and intercropped
species significant effect of intercropping
on rooting front advance
barley
pea
mustard
pea
Pea roots advanced at the lowest rate of 1.0 mm
C d-1. The rooting front advance of barley and
mustard were respectively 1.6 and 1.2 mm C d-1.
No significant differences were observed between
intercropped and monocropped pea. In some cases,
a positive effect of intercropping on rooting
front advance was observed for barley and
mustard.
Check of the herbicide mobility
Study of the mobility of the herbicides in the
soil profile expressed as the intensity of leaf
damages on plants grown on 10 cm soil layers
removed 15 days after an herbicide injection at a
given depth (5, 25 or 45 cm depth)
No toxicity symptoms were observed under and
above the treated zone indicating no downward and
upward movement of the herbicides in the soil
profile and no herbicide leakage above the
treated zone for any of the two herbicides during
at least 15 days after injection
CONCLUSION - The herbicide technique is a
reliable, simple and rapid method which is able
to distinguish roots by species in mixture. The
herbicides used are effective on developed
plants, entail clearly symptoms and are of
limited mobility. - Pea has the lower rooting
front advance - Barley and mustard could have a
faster rooting advance in mixture than in pure
stand. It may indicate an increased availability
of plant growth resources for these two species
in the mixture. The root front advance of pea
intercropped was not enhanced due probably to a
decrease of plant growth and an increase of pea
N2 sink strength.