Abstract
In our previous studies, the phytotoxicity of Ulex europaeus (gorse) and Cytisus scoparius (Scotch broom) was demonstrated in vitro and argued to be caused by the release of volatile and water-soluble compounds from fresh plant foliage. In light of these positive results, there was a need to test the effects ex vitro. In this work, gorse and Scotch broom were used as soil amendments in pot experiments in a glasshouse by incorporating slashed plant material into the soil at a ratio of 1% w/w on a dry mass basis. The phytotoxic effects on the emergence and early growth of maize and five accompanying weed species were analyzed, as were the effect on soil fertility and soil community-level physiological profiles. Thirty days after incorporation, significant decreases in weed density of 32.2% and 59.5% were found for gorse and Scotch broom soil amendments, respectively. Gorse soil amendment was notably effective impairing the establishment of Amaranthus retroflexus and diminishing the plant height of Digitaria sanguinalis and Portulaca oleracea. Scotch broom soil amendment was capable of significantly inhibiting the emergence of D. sanguinalis, Convolvulus arvensis, P. oleracea, and A. retroflexus, with a notable reduction of weed biomass. No undesirable side effects on maize crop or soil quality, including microbial activity, were detected. Our results suggest that the incorporation of gorse and Scotch broom foliage is promising for pre-emergent weed control in maize; however, field trials that support and expand these glasshouse results are essential.
Highlights
The use of allelopathic green manures is gaining attention as a complementary tool for integrated weed management [1,2,3,4,5,6]
The effects on weed emergence were significant from 11 days after foliage incorporation (DAI), and the number of weed seedlings per pot on day 15 was reduced by foliage incorporation (DAI), and the number of weed seedlings per pot on day 15 was reduced by
For Scotch broom-amended pots, the effects were earlier and stronger than for gorse, with significant differences relative to control from 7 DAI, and 72.1% fewer weed seedlings than the with significant differences relative to control from 7 DAI, and 72.1% fewer weed seedlings than the control at 15 DAI (p ≤ 0.001)
Summary
The use of allelopathic green manures is gaining attention as a complementary tool for integrated weed management [1,2,3,4,5,6]. If an allelopathic crop is used for green manuring, when incorporated into the soil such a crop can release phytotoxic compounds capable of inhibiting the germination and growth of weeds in the soil seed bank. Different legume and cereal species have been reported to have suppressive effects on weeds [6,8,9,10,11]. Due to their richness in secondary bioactive metabolites, residues of certain medicinal plants have been assayed as bioherbicidal green manures [12,13].
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