3.3
Crop Rotation
Crop rotation is system in which different plants are grown in a sequence in a specific
field for definite time period. It is important to reduce pest (weeds, pathogens, and
insects) pressure, to overcome autotoxicity, and to sustain soil fertility [6, 43, 92].
Diversified rotation is key for sustainable weed control as it creates unstable conditions for weeds and helps to reduce weed seedbank [44]. Allelopathic crop in a
rotation can potentially suppress its associated weeds and reduce weed infestation
in the crop following in the rotation [45]. Both root exudates and decomposing
crop residues an allelopathic crop in the rotation add allelochemicals to the soil that
help to reduce weed pressure [46]. For example, weed infestation is reduced in wheat
crop if grown following the sorghum crop due to release of allelochemicals from
sorghum [47]. For instance, in sunflower-wheat rotation, the weed infestation in
wheat crop grown after sunflower was considerably reduced [6]. Inclusion of
rapeseed in rotation caused about 40% reduction in weed density in the subsequent
crop in rotation [46].
Weed seed germination inhibition potential of allelopathic crop in rotation can
also negatively affect the seed germination of subsequent crop in rotation. For
example, wheat germination was delayed when it was grown in rotation with
sorghum [48]. However, wise use of allelopathic crops in rotation and tillage timing
can help to reduce the inhibitory effect on crop [49]. Therefore, good crop rotation
with inclusion of allelopathic crop can help to avoid autotoxicity and to reduce weed
problem with minimum dependence on chemical weed control method.
3.4
Mulching and Residue Incorporation
In allelopathic mulching, the crop or weed residues are applied on soil surface or
incorporated in the soil. Mulching with allelopathic crop/weed residues inhibits
weed germination and growth due to release of allelochemicals in the rhizosphere,
physical suppressing and depriving weed seeds from light [50–53]. In addition to
weed control, mulching increases water holding capacity, increases soil fertility,
enhances organic matter, and works as buffer to maintain soil temperature [54–56].
Commonly, farmers use economic parts of the crop while incorporating the
remaining crop parts in the field as organic matter. The allelopathic plant parts left
in the field inhibit the weeds. Recently, many studies have been done to explore the
weed control potential of allelopathic mulches and residue incorporation in field
crops. For instance, application of sorghum crop straw as surface mulch in maize
provided up to 37% weed control [57], while in cotton and rice, about 60% and 50%
weed control, respectively, was achieved with sorghum surface mulch [58] Sorghum
residue incorporation or surface mulches provided effective control of various noxious
weed species including C. rotundus, broad-leaved dock (Rumex obtusifolius L.),
P. minor, C. arvensis, C. album, and scarlet pimpernel (Anagallis arvensis L.)
[59, 60]. In another field study, it was observed that maize residues added in the field
after maize harvest caused significant reduction in weed infestation in the succeeding
510
N. Farooq et al.
Crop Rotation
Crop rotation is system in which different plants are grown in a sequence in a specific
field for definite time period. It is important to reduce pest (weeds, pathogens, and
insects) pressure, to overcome autotoxicity, and to sustain soil fertility [6, 43, 92].
Diversified rotation is key for sustainable weed control as it creates unstable conditions for weeds and helps to reduce weed seedbank [44]. Allelopathic crop in a
rotation can potentially suppress its associated weeds and reduce weed infestation
in the crop following in the rotation [45]. Both root exudates and decomposing
crop residues an allelopathic crop in the rotation add allelochemicals to the soil that
help to reduce weed pressure [46]. For example, weed infestation is reduced in wheat
crop if grown following the sorghum crop due to release of allelochemicals from
sorghum [47]. For instance, in sunflower-wheat rotation, the weed infestation in
wheat crop grown after sunflower was considerably reduced [6]. Inclusion of
rapeseed in rotation caused about 40% reduction in weed density in the subsequent
crop in rotation [46].
Weed seed germination inhibition potential of allelopathic crop in rotation can
also negatively affect the seed germination of subsequent crop in rotation. For
example, wheat germination was delayed when it was grown in rotation with
sorghum [48]. However, wise use of allelopathic crops in rotation and tillage timing
can help to reduce the inhibitory effect on crop [49]. Therefore, good crop rotation
with inclusion of allelopathic crop can help to avoid autotoxicity and to reduce weed
problem with minimum dependence on chemical weed control method.
3.4
Mulching and Residue Incorporation
In allelopathic mulching, the crop or weed residues are applied on soil surface or
incorporated in the soil. Mulching with allelopathic crop/weed residues inhibits
weed germination and growth due to release of allelochemicals in the rhizosphere,
physical suppressing and depriving weed seeds from light [50–53]. In addition to
weed control, mulching increases water holding capacity, increases soil fertility,
enhances organic matter, and works as buffer to maintain soil temperature [54–56].
Commonly, farmers use economic parts of the crop while incorporating the
remaining crop parts in the field as organic matter. The allelopathic plant parts left
in the field inhibit the weeds. Recently, many studies have been done to explore the
weed control potential of allelopathic mulches and residue incorporation in field
crops. For instance, application of sorghum crop straw as surface mulch in maize
provided up to 37% weed control [57], while in cotton and rice, about 60% and 50%
weed control, respectively, was achieved with sorghum surface mulch [58] Sorghum
residue incorporation or surface mulches provided effective control of various noxious
weed species including C. rotundus, broad-leaved dock (Rumex obtusifolius L.),
P. minor, C. arvensis, C. album, and scarlet pimpernel (Anagallis arvensis L.)
[59, 60]. In another field study, it was observed that maize residues added in the field
after maize harvest caused significant reduction in weed infestation in the succeeding
510
N. Farooq et al.