Exploitation of Sorghum (Sorghum bicolor L. Moench) allelopathic characteristics in controlling weeds in Sesame (Sesamum indicum L.)

My idea for sustainable crop protection involves the use of plant species to control weeds in crop production systems particularly targeting resource poor farmers practicing Conservation Agriculture (CA). Conservation agriculture is a climate smart technique of growing crops through the simultaneous implementation of three interlinked principles namely minimal soil disturbance, crop rotations and retention of crop residues. The weed control technique described above is commonly referred to as allelopathy. Allelopathy is a plant phenomenon whereby certain plant species can influence the growth and development of other plant species by releasing secondary metabolites known as allelochemicals which can either stimulate or suppress the germination, growth and productivity of other plants.

Currently in Zimbabwe, there has been a widespread promotion of sesame production especially in areas that receive low to moderate rainfall because of the plant’s drought tolerance properties which render it suitable to be grown in drought prone areas. Sesame is mostly grown in rotation with sorghum, a drought resistant cereal crop under CA. Venturing into this enterprise is lucrative to resource poor farmers in marginalised areas but most farmers are failing to derive maximum economic benefits due to poor productivity. Low productivity is attributed to several factors including diseases, insect pest damage but for the most part weeds are a major yield reducing factor. Challenges in weed control have been reported and lack of registered herbicides in the country for use in sesame has not the situation any better. It has led to a labour burden on women and children who spend most of their time hand-weeding and adulteration of any pesticide farmers think works in a dicotyledonous crop.

My research idea is to investigate whether sorghum can be used to control weeds in sesame whilst at the same time checking the compatibility of the two crops to be grown in a crop rotational system. Sorghum is a well-recognised allelopathic crop that has been extensively studied for its allelopathic potential and is widely documented as a source of phytotoxic secondary metabolites. Allelopathic activity of sorghum is particularly attributed to sorgoleone and dhurrin, two important allelochemicals that are produced in the roots and herbage of sorghum, respectively. There several methods of manipulating sorghum allelopathy that can be easily adopted by resource poor farmers or by farmers that are transitioning from conventional agriculture to CA. Exploitation of sorghum allelopathy then comes in as an environmentally friendly and easy to adopt weed control method as it can applied as common cultural weed control methods that farmers already know. The only twist is that sorghum can provide weed control by releasing potent bioherbicidal molecules that can potentially inhibit growth and development of weed species. Some of the methods include the retention of sorghum crop residues as surface mulch, live mulches, inclusion of sorghum into a crop rotational or intercropping system and spraying of aqueous sorghum extracts known as sorgaab in combination with reduced herbicide dosages.

Chlorophyll fluorescence

I started the research work when was doing my MSc research project and conducted laboratory and greenhouse experiments to test on the effect of sorghum on the initial seedling growth and physiological processes of sesame and some selected weed species. I also managed to isolate some allelochemicals responsible for sorghum allelopathy. I now intend on carrying out further investigations but this time using the weed control approaches previously mentioned above because it seems unfair to give recommendations to farmers when research has not be conducted under field conditions. The experiments will mostly focus on field trails and I need at most five seasons, working with two seasons per year. The field trails will be conducted to assess whether sorghum as surface mulches, live mulches, soil incorporated residues and as a rotational crop has the potential of controlling weeds in sesame. The research will also assess the bioherbicidal potential of sorgaab as early post emergence sprays that can be used to control weeds then finally a soil analysis to determine the persistence of sorghum allelochemicals. Since it is widely documented that sorghum is allelopathic, the expected result of the research is that weed control can be achieved using sorghum either as a mulch and or as bioherbicidal spray. The expected outcome would be that allelopathy can be adopted as a tool for weed management as it diversifies control options especially for resource poor farmers practicing CA. The major indicator that will be used to assess whether the project is a sustainable or not is the number of farmers who continue with this idea and so the need to have an end of project evaluation. Apart from my personal research I intend on engaging local farmers growing sesame as part of the research, hoping to have some of the farmers as participants for this investigation. Sesame farmers will be the primary beneficiaries of the project. The stakeholders I am targeting include Welthungerhilfe, Agricultural Partnership Trust which have promoted CA and sesame production in Gokwe and Sidella which is a company that has been encouraging adoption of sesame in the lowveld areas of Zimbabwe on contract farming arrangements.

I am passionate about the use of allelopathic plant species because it is an easy to adopt, environmentally friendly and cost effective weed management strategy that can control weeds and improve crop quality and quantity. There are various methods of exploiting allelopathy which are easily accessible and easy to do even for resource poor farmers in marginalised areas. If crop yield quantity and quality is improved then the livelihoods of farmers is also improved, food and nutrition is secured and the standard of life of women and children is also elevated. Finally, the best thing about the exploitation of allelopathy is that it is sustainable and if used in CA farming systems then it’s a double dose of kindness to the earth!

Juliet Chengetai Murimwa, Zimbabwe

113 comments

    1. Hie Tapiwa.

      Thank you for the comment. Hope such innovations can benefit resource poor farmers in marginalized areas.

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  1. Hey Juliet. This is a great project that you are embarking on and I’m positive it’s going to yeild results. The fact that sorghum is easily accessible it’s going to make it easy for farmers to access. Through the use of this crops will remain organic as no strong chemicals would have been used and this also sounds safe for the environment. This is very innovative.

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    1. Hie Tafadzwa. Thank you for the comment.

      Did you know that sorghum is an economically important crop globally which ranks as the 5th most important crop. In Zimbabwe, it is currently being encouraged to grow sorghum particularly because of erratic weather rainfall patterns that have been experienced as of late. This is because it possesses drought tolerant properties. So with sorghum at the farmers’ disposal, it will be easy and cheap for them to manipulate sorghum’s allelopathic attributes in weed management.

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  2. This is really good for us as a country since we are already experiencing erratic rainfall patterns due to climate change and our Agricultural sector is moving more towards small grains. Thank you for this

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    1. Hie Adolf

      Thank you for the comment. Sorghum will serve two purposes, as a source of food and also source of bio-herbicidal molecules which can control weeds.

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