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Application of a residue allelopathy model in the field management of Vulpia phytotoxicity

Min An, Jim Pratley and Terry Haig

EH Graham Centre for Agricultural Innovation, Charles Sturt University, Wagga Wagga, NSW 2678, Australia. Email man@csu.edu.au

Abstract

A mechanistic model of residue allelopathy was applied to overcome the negative effects of vulpia residues on pastures as a component of integrated weed management strategies. Successful pasture establishment was achieved and the vulpia population was minimized. A productive sward of pasture has been in place for several years.

Media summary

Residue allelopathy modelling has great application potential in the managing of plant residues for weed control and in overcoming the negative effects of plant residues.

Key Words

Modelling, residue allelopathy, vulpia, weed control

Introduction

An et al. (1996) developed a mechanistic model to simulate allelopathic phenomena caused by decaying plant residues. This model provides an integrated view of the allelopathic pattern of plant residues during decomposition and indicates two aspects to bioactivity of allelochemicals: stimulation and inhibition. The extent of each over the whole course of residue decomposition is not balanced. The most severe inhibition occurs at the early stages of residue decomposition, while at later stages plants gradually recover from high inhibition and move towards stimulation, eventually returning to 'control' levels of response.

Vulpia (Vulpia spp.) is a notorious annual weed in pastures and cereal crops in southern Australia. Pasture establishment often fails due to the presence of vulpia residues which possess strong allelopathic potential. There are limited options available for controlling vulpia.

The above-mentioned model, together with the knowledge of vulpia residue phytotoxicity, was applied to control Vulpia residues in the field.

Background and Method

A paddock, severely infested with vulpia was chosen as a case study for allelopathy management (Plate 1). The soil was of medium pH at the surface (pH 5.5 H2O) and seasonal conditions were favourable for plant growth during the period of the study. The farmer had determined the need to re-establish pasture on the site because of the infestation of vulpia. In the first year, the area was sprayed with the "knockdown" herbicide SpraySeed (paraquat/diquat mix) and a pasture mix of subterranean clover, phalaris and cocksfoot was sown. Lime had previously been applied. The establishment of pasture was not successful due to the regeneration of vulpia which produced a high level of biomass. In the following year, the farmer sprayed the area with knockdown herbicide (SpraySeed) and resowed at that time by direct drilling. The herbicide however was not particularly effective and much of the vulpia persisted, again restricting adequate pasture establishment.

In the third year, the area was again sprayed with knockdown herbicide, and then was cultivated with a scarifier twice resulting in vulpia residues being mixed with surface soil layers. Based on previous findings (An et al. 1993) and the residue model prediction, sowing was delayed for three weeks post-spraying to enable allelochemical breakdown and the same species mixture was used.

Plate 1. The paddock was dominated by vulpia, where attempts to establish pasture failed. (a) Overview of the paddock; (b) Close-up view.

Results and Conclusion

Successful pasture establishment was achieved (Plate 2) and the vulpia population was minimised. A productive sward has been in place for several years (Plate 3). Direct drilling into vulpia pastures would appear to be a poor option since decomposition needs to occur to allow allelochemicals leached out of residues to breakdown. The use of cultivation and then delayed sowing for certain period of time enabled the allelochemicals to dissipate, avoided the peak inhibitory period from vulpia residues, and allowed successful pasture establishment to follow. These results indicate that when there are limited options for controlling vulpia, proper application of the knowledge of residue allelopathy can provide an alternative. It is simple, economic, and effective.

Application of residue modelling can play a significant role in the managing of plant residues for weed control and in overcoming the negative effects of plant residues. Such application meets the increased demand for conservation and no-tillage farming systems through management of the inhibition and stimulation periods. Such an approach should be considered as a component of integrated weed management strategies.

Plate 2. After spray, cultivation and delayed sowing for three weeks, the pasture establishment was successful. (a)Overview of the paddock pasture; (b) Close-up view.

Plate 3. The established pasture. (a) Overview of the paddock; (b) Close-up view.

References

An, M., Pratley, J.E. and Haig, T. (1993). The effect of soil on the phytotoxicity of residues of Vulpia myoros. In ‘Proceedings of the 7th Australian Agronomy Conference’ pp. 162-164, Adelaide, South Australia. (Australian Society of Agronomy).

An, M., Johnson, I. and Lovett, J. (1996). Mathematical modelling of allelopathy: I. Phytotoxicity caused by plant residues during decomposition. Allelopathy J. 3, 33-42.

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