With reference to the Sunday Observer article titled ‘Glyphosate ban to be relaxed’ on June 18, 2017, Dr. Ranil Senanayake who was member of the Glyphosate Evaluation Committee as mentioned in the article has sent the following response.
The following report was also submitted to the committee on Weedicide and Pesticide as there is a large degree of overlap and replication of effort.
The existing situation vis-a-vis the application of agro-toxins must be examined on the national scale and in the current context. It must fairly examine the options and hidden costs, so that any recommendation by this committee can be examined in a transparent manner.
The top soils of the mountains have become barren as a consequence of the type of agriculture that is being practised on it. A healthy soil ecosystem has not been a priority area of research. It must be acknowledged that the condition of the soil ecosystem does have a bearing on the productivity and stability of the land. The diversity of species and trophic levels make soil as complex an ecosystem as a forest.
Trophic level
An effect at one trophic level will have consequences at other levels. Work on pathogenic organisms of forest trees demonstrates that the application of a particular chemical can suppress beneficial bacteria that control plant pathogens, creating increases of plant infections in the treated area; while the application of another chemical can encourage the growth of beneficial bacteria which suppress pathogenic organisms and promote better plant growth in the treated area (Cerra et al., 1987).
Further, it has been shown that the application of herbicides can have either an inhibitory or stimulatory effect on many soil organisms (Anderson, 1978) by changing the nature of the ecological relationships of these organisms.
The critical nature of these interrelationships has been shown by the work done in Russia, demonstrating that the feeding patterns and growth of soil inhabiting saprophagous invertebrates depends on the activity of soil microorganisms, which in turn are stimulated by the activity of the soil-inhabiting saprophagous invertebrates (Ghilarov, 1963).
Agriculture changes the nature of the soil ecosystem, generally, bringing about a loss of diversity and creating a new network of energy flows. As one researcher notes:
“The communities of (microorganisms in) agricultural soils might be regarded as natural communities impoverished in species.
The gradually increasing mechanical effects upon agricultural soils can be tolerated by a small number of species of high ecological valency” (Balough, 1963).
This suggests a loss of species that have specialized ecological functions and a corresponding increase in absolute numbers of a few species, which function as ecological generalists.
This trend of reducing diversity as a consequence of increasing energy input into an ecosystem has been clearly demonstrated in aquatic ecosystems (Margelef, 1963). The current trends, of increasing chemical applications on agricultural soils, can contribute further to soil ecosystem modification.
The organic fraction of soil can sequester, or remove carbon dioxide from the atmospheric pool for periods exceeding 4,000 years through synthetic microbial activity (O’Brien & Stout, 1978).
The type of land management and its effects on the soil biota can help control or exacerbate the current trends in the atmospheric carbon dioxide cycle (Senanayake, 1993)
Influence
The management of soil can have an influence on the rate of cycling carbon dioxide. However, as organically fixed carbon in the soil has to be secured from some prior photosynthetic activity, the residence time of organic carbon in the soil becomes important.
The dynamics of the soil carbon pool can be influenced by management techniques. This feature of the soil can be developed to meet the needs expressed in present concerns about the global ‘greenhouse effect’.
“Soil organic matter is one of our most important national resources; its unwise exploitation has been devastating; and it must be given its proper rank in any conservation policy as one of the major factors affecting the levels of crop production in the future.
The nation should be made aware of the rapid rate at which the organic matter in the soil is being exhausted. Farm-management practices should be adopted that will at least maintain, and in as many cases as possible, increase the supply of this natural resource in the soil.
The maintenance of soil organic matter might well be considered a national responsibility.” While the effects of agrochemicals on soil is manifold, the loss yet to be appreciated.
An example is the case of Glyphosate. Research demonstrated that the Herbicide Glyphosate was innocuous to animals and was only toxic to plants and microorganisms. Direct, toxic effects result from the inhibition of amino acid synthesis via the shikimic acid pathway (Grossbard and Atkinson 1985).
Microorganisms and higher plants are the only organisms known to utilize this pathway, and thus are intolerant of Glyphosate.
This means all plants and microorganisms exposed to it will be killed. However, in the soil Glyphosate stimulates soil microbial activity, in the same groups of microorganisms that are simulated by the addition of fertilizer salts.
Ecosystem
This type of soil management by applying a surge of energy through the ecosystem has tended to simplify the soil ecosystem to such an extent that no long term humic carbon compounds are decanted into the soil. The effect is very clear when soils where there has been a history of Glyphosate use and soils where Glyphosate is not used, are compared.
In Sri Lanka, we still have to appreciate this fact. The colonial experience robbed us of that precious organic matter. The plantations sector at one time had a keen interest in building up good soil, however, the current short term, profit driven processes leave no room for building the biomass and biodiversity of the soil.
This lack of investment in building up the soil had left tea plants that cling to the subsoil and can only produce good crops with artificial fertilizer that we have to import. But, today, a new threat has sprung up.
Irresponsible land use decisions, sanctioned by the officials concerned are rooting out the tea plants that gave some stability to degraded mountains and are replacing it with annual vegetable cultivation that bleeds away the remnant bits and poisons our water sources.
In the drier a stochastic future before us, the country cannot afford to maintain marginal lands that do not produce humic soils.
The current system of land management with chemicals that preclude the formation of a humic soil must be discouraged.