Use of allelopathy in agriculture

THE AGRICULTURE is considered as the backbone of Pakistan’s economy. The majority of 2/3rd popul
ation residing in the villages of Pakistan have reliance upon agriculture. Fifty percent of labour of the country is concerned with agriculture. In national income the share of agriculture is 23%. But, in crop production weeds are considered as one of the major factors of low yield. The losses caused by weeds have been estimated to be much higher than those caused by insect pests and diseases put together. Generally the yield of most crops is reduced by 30-50 % due to weed infestation.

Hence for economical and profitable crop production, weeds are necessary to be managed. Weeds can be managed mainly by two methods.

Indirect Method of Weed Control

These methods are not employed specifically against a particular weed species but have a more general impact. They do not give the guarantee of complete control of weeds but can reduce the magnitude of weeds up to a significant level. Indirect methods are of 2 types: One is Preventive Method and second is Cultural and Ecological Methods. Preventive Method refers to certain precautions which help to prevent the dispersal of weeds or their seeds. Cultural and Ecological Method of weeds control includes good tillage practices, crop rotation, proper planting time, and optimum plant density, use of recommended varieties, good farm management practices and allelopathy.

Direct Method of Weed Control

Direct method involves Manual Method, Mechanical Method, Biological Method and Chemical Method. Manual Method requires more time and labour. It is also weather-dependent. Mechanical Method is expensive and controls the weeds which are present only the sides of rows. Biological Method although environmentally safe method and has no side effect but it takes long time to identify the natural selective enemy of weeds. It is very costly method and its serious drawback is that it is very difficult to implement it under field conditions.

In Pakistan, mostly Chemical Method is used to kill or inhibit the weeds. However, non-judicious use of herbicides has resulted in environmental and health problems. Surface and ground water used for human and livestock consumption is being continuously contaminated with toxic herbicides. Toxic residues of herbicides from plants or soil get enter in the food chain and may prove hazardous even to future generation. The toxic herbicide residues in the environment and food chain have resulted to cause dangerous diseases not only in humans but also in animals. It has also been found that due to continuous use of herbicides, weeds develop resistance to herbicides. Environment, health and resistance development issues have a significant influence on the development of economical and environment friendly technologies for weed control which may reduce the use of chemical herbicides.

Allelopathy seems to be an effective, economical and natural method as well as alternative of herbicides for weed control. Although we can not eliminate the use of herbicides, their use can be reduced by exploiting allelopathy, as an alternate weed management tool for crop production against weeds and other pests.

Allelopathy has been derived from two Greek words: Allelon means ‘‘each other” and Pathos means ‘‘to harm or affect” i.e. the injurious effects of one plant upon another plant, including microorganisms through the release of chemical compounds into the environment is known as allelopathy. Allelopathy is perceived as a donor-receiver phenomenon where one plant releases chemicals that affect the growth of the neighbouring plants.

Allelopathy is considered as an important environment friendly science because the use of allelopathy can reduce the reliance upon synthetic dangerous herbicides as allelochemicals in the allelopathic plants are natural. They do not affect the quality and quantity of crop and save the environment from pollution.

Allelopathic crop water extract is prepared through following procedure: The respective allelopathic crop is harvested at maturity, dried and chaffed with fodder cutter into 2 cm pieces and then stored under shade. This chaffed herbage is soaked in water for 24 hours in a ratio of 1:10 (w/v). Then the water extracts are collected by passing through sieves. These extracts are concentrated up to 20 times by boiling for easy handling and application. These extracts are known as Allelopathic Water Extracts. Allelopathic effects are concentration dependent. So if these plant extracts are concentrated and used in combination, they may be more effective against weeds.

In plants, the phytotoxic substances or allelochemicals can be produced in almost all the tissues including roots, stems, leaves, flowers and seeds. Under favourable environmental conditions, these allelochemicals may be released into the environment to affect the growth of neighbouring plants (i.e.weeds).

The crop plants that have been reported to have allelopathic effects on weeds are: Sorghum, Sunflower, Brassica, Rice, Maize, Mungbean and Mulberry. The inhibitory compounds present in sorghum plants are mostly phenols. The major constituent of sorghum that causes allelopathic activity is sorgolene (2-hydoxy 5-methyl-3-p-benzoquinone). The allelochemicals present in various organs of sunflower are: chlorogenic acid, isochlorogenic acid, á-naphthol and scopolin. The allelochemicals present in rice are: p-coumaric acid, ergosterol peroxide and 7-oxo-stigmasterol. The allelochemicals present in brassica are isothiocyanates, nitriles and oxazolidinethione.

Allelopathy can be purposeful in following ways:

a. Safe Food Production:

The yield produced by allelopathy is safe and have no danger for health. It is a natural phenomenon as allelochemicals are released from the plants. But on the other hand, the toxic residues of herbicides from plants or soil get enter into food chain and cause different diseases not only in humans but also in animals.

b. Environmental Protection:

Allelopathy is an important environment friendly science because it reduces the reliance upon synthetic dangerous herbicides as allelochemicals in the allelopathic plants are natural. Hence allelopathy protects the environment.

c. Resource Conservation:

Synthetic herbicides are much expensive one. They increase the cost of production. Being the natural phenomenon, allelopathy is the cheapest method and hence conserves the resources.

d. Sustainable Weed Management:

Various experiments have been successfully performed on allelopathy that demonstrate that if different crop water extracts can be tank mixed with one third dose of herbicides, give nearly the same results as full dose of herbicides.

http://www.technologytimes.pk/mag/2011/jan11/issue05/use_of_allelopathy_in_agriculture.php