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AGRICULTURAL CHEMICALS AND THE SOIL

Governments are funding an army of researchers who are studying the side-effects of the toxic, inappropriate "solutions" to the symptoms of problems while small groups of guerillas are grappling with the causes.

...........S.B. Hill, 1977

GOAL - to provide the reader with a framework for:

  1. examining the problem of agricultural chemicals in soil
  2. designing ecologically sound management strategies for dealing with non-productive soils, pests and diseases.

BEHAVIOURAL OBJECTIVES

- after having read this paper you will be able to understand and accept that:

INTRODUCTION

In a summary of a symposium on pesticides in soil, Professor Audus (1970), pleaded that "we must realize the fantastic complexity of the physical and biological structure of the soil and the dynamic nature of its biological equilibria". He went on to say that "a central characteristic of these equilibria is the intimate interdependence of the various soil organisms". There have been hundreds of papers and dozens of reviews concerning the relationships between chemicals used in agriculture and forestry and the soil (e.g., Guenzi et al., 1974). However, after reading many of these papers I cannot help but agree with Howard Evans' (1970) comment in his book "Life on a Little Known Planet" that "we have learned a great deal....but seem unable to conclude very much from all of it". Joseph Needham's (1932) criticism of biologists as scientists "so busily engaged in accumulating new facts as to be left with no time at all to devote any thought to those [they] already have" seems to apply to many scientists engaged in this aspect of soil research. As Sir Peter Medawar (1969) has noted, there are plenty of analysts among modern scientists but few synthesists. I believe that our poor understanding of soil is closely related to lack of synthesis. This became particularly evident to me some years ago when, with a number of colleagues, I attempted to review the effects of pesticides and fertilizers on soil and its inhabitants (Hill 1972, Weetman et al. 1972, Weetman & Hill 1973, Hill et al. 1975). It was extremely difficult to compare the results of different workers, partly because none of them had measured sufficient variables to draw meaningful conclusions, but more particularly because there is really no established framework for viewing the relationships in soil.

In this paper I will (1) critically review representative examples of studies on the effects of agricultural chemicals on soil organisms, (2) present a case for replacing chemicals with ecologically sound alternatives, and (3) comment on how this might be implemented. The framework for considering these topics will emphasize a normative, rather than extrapolative, approach (cf. Lovins 1976) and collaboration with nature to reach optimal levels of productivity.

1. EFFECTS OF AGRICULTURAL CHEMICALS IN SOIL

As Dr. Clive Edwards is one of the most prolific reviewers of studies on the effects of agricultural chemicals on soil organisms, it is fitting that I repeat one of his conclusions; he states "The most usual effect of agricultural practice is to decrease the number of species of soil organisms and the few species that remain are often able to multiply rapidly until the total numbers are greater than they were originally. The main difference from cultivation is that the effects of chemicals lasts longer. Whereas ploughing or rotation may only change the balance of the soil fauna or flora for a matter of weeks or at most months, persistent chemicals can alter them for months or years". (Edwards 1965; see also Edwards & Thompson 1973, Thompson & Edwards 1974).

However, behind such broad generalizations are the kinds of results summarized in Table 1. It is difficult; if not impossible, to interpret results such as these as soil is very variable and all agricultural practices influence the effects of all others; none of the authors of these studies adequately described or measured the properties of the soil or the agricultural practices that were being employed. Those variables that were largely ignored are listed in Table 2.

Another problem that I encountered was that many authors wrote as if they believed that a) insecticides and fertilizers are the only agricultural chemicals, b) that they only affect soil organisms directly and c) that they are either lethal or without effect. In fact, there are a vast array of agricultural chemicals (Figure 1), most effects and are sublethal rather than lethal (Table 3). Another common misconception is that increases in population density are good whereas decreases are bad. Thus, Harris (1969), after noting that the density of Collembola, a largely beneficial group of soil arthropods, increased after the application of DDT stated, "it is apparent that DDT in this instance changes in species composition, population density be viewed with respect to their long-term influence the balance between mobilization and immobilization has a beneficial influence". Changes in species composition , population density and activity should rather on such relationships as of plant nutrients and their availability to plants. Unfortunately the role of most organisms in soil is too poorly defined to permit such analysis at the present time.

From the above discussion the reader might conclude that I am advocating that a vast army of soil physicists, chemists and biologists be assembled to study all the variables and relationships that I indicated were largely ignored in previous studies. This would certainly be the logical thing to do if there were no alternatives but to continue to use agricultural chemicals. On the other hand, if there are viable alternatives-it would make more sense to direct the army of scientists to work on them.

In the following section I will indicate why I consider that "ecological" alternatives must be developed.

2. ECOLOGICAL ALTERNATIVES TO AGRICULTURAL CHEMICALS

In my opinion the scientific evidence available indicates that in most instances the use of agricultural chemicals is inappropriate.

Developing and maintaining fertile soils

With respect to soil fertility it is relevant to review how soil is formed (Figure 4). The process requires two material inputs, rock (the earth's crust) and dead organic matter, these being converted to soil largely through the process of decomposition.

There is certainly no shortage of rock and in temperate countries there should be no shortage of dead organic matter, as the optimum temperature for its production is nearer the annual mean temperature than is the optimum temperature for its decomposition (Figure 5). This, in fact, is the main reason why we find a deep litter layer in most of our forests whereas there is usually no litter layer in lowland tropical forests. The biological decomposition process is carried out largely by bacteria and fungi. However, at least six factors limit their activity (Figure 6). This is where the soil fauna play such an important role because through their feeding and movement they are continually removing the limiting factors for the microflora, particularly through their ability to distribute the spores of the latter. Thus, if certain members of the fauna are killed or reduced by agricultural chemicals, the activity of the bacteria and fungi species will decline (Figure 7). Increases in the population density of certain groups of soil organisms can also lead to problems through imbalance.

While our detailed knowledge of these processes is poor, it is sufficient to know that by taking into account the organisms in the soil, and catering to their needs, soil fertility can be built-up and maintained. The primary requirement is that organic materials taken from the land be returned. This follows from the law of ecology concerning cycles given in Table 4.

Rather than forcing the resident "decomposer industry" out of business by applying synthetic chemical fertilizers, or killing some of them by applying biocides, we should be investigating their productive potential within each soil type and developing management strategies whereby it can be realized. Such strategies are likely to save money, energy, and avoid damage to the support environment and to human and livestock health (figure 8). This contrasts with our current approach, which involves the removal of several dozen minerals at harvest time followed by the replacement of only a few of them as chemical fertilizers (Figure 9).

Preventing outbreaks of pests and diseases

Pests and diseases are symptoms of poor management (Figure 10). Pesticides, antibiotics and drugs have generally been regarded as "magical bullets" that can eliminate problems (Figure 11). The real situation is that we do not suffer from pests because of a deficiency of pesticide in the environment just as we do not get a headache because of a deficiency of aspirin in the blood.

The use of pesticides and antibiotics to control pests and pathogens leads to the development of a long list of serious secondary problems (Figure 12, Table 5,6).As most pesticides are synthetic organic compounds that have no counterpart in nature they are likely to accumulate in the environment (Table 4, Figure 13, 14).

Moore (1967) has pointed out that we really only have three alternatives with respect to controlling pests (Figure 15). The pesticide approach predominates largely because most of the costs (e.g., environmental, human health) are not taken into account in our cost:benefit analysis (Figure 16) As a member of the British labour party once explained, "we encourage private, short-term gain at public long-term expense".

In order to treat pest problems at the causal level, it is necessary to examine more closely the relationships between agricultural practices and pest damage (Figure 17). Th is approach has been used to generate the strategies outlined in Table 7. These must be designed for each unique situation; consequently the particular strategies employed should ideally be selected by the farmer himself, or someone else who is familiar with the area and the operation of the particular farm. While these approaches could be considerably refined if the money and effort currently directed towards pesticides were used to develop such ecological strategies, I believe that most pests could be brought below the economic threshold with the knowledge that we posses right now: we just need to use it! The history of pest control (Figure 15) indicates that this ecological approach comprises the only means to achieve long-term control of pests and diseases. It is significant to note that the use of pesticides has not decreased the percentage loss of crops to pests, it remains at about 33% (May 1977).

3. IMPLEMENTING CHANGE

Changing from chemical to management strategies will not be easy. Modern agriculture has become dependent on chemicals just as heroin addicts have become dependent on their drug (neither pesticides nor stimulatory drugs treat problems at the causal level). The irrational outbursts experienced on withdrawal of these two "drugs" share certain features in common; such outbursts are a measure of a loss of true freedom, the kind that is unfortunately not protected by any Bill of Rights'.

Because of the addictive nature of the problem, the implementation of alternative ecological strategies will require an enormous cooperative effort involving the general public (consumers), industry and commerce (including producers), researchers (in federal and provincial governments, universities and industry), communicators (media people, educators, and extension agents) and governments (federal, provincial and local) (Figure 18). The alternative to cooperation is to respond to the crises that will undoubtedly occur with increasing frequency if we continue with the kinds of solutions to problems that are exemplified by the use of agricultural chemicals (Whiteside 1977). Some of the strategies available to governments are listed in figure 19.

CONCLUSIONS

1) the long-term disbenefits associated with the production and use of agricultural chemicals, particularly pesticides (resource depletion, environmental damage and health consequences), are such that alternative ecologically sound strategies must be developed and used;
2) in order to make a soil productive and keep it so, it is necessary to cater to the needs of its beneficial biota;
3) outbreaks of pests and diseases are symptoms of poor management and consequently can and should be prevented and controlled by developing and employing ecologically sound management strategies;
4) the replacement of chemical by management solutions will require cooperation between the general public, industry and commerce (including the producers), researchers, communicators and governments).

REFERENCES

AUDUS, L. J. 1970. Symposium summary. Pp. 142-4 in Pesticides in the Soil: Ecology, Degradation & Movement. 144 pp. Michigan State Univ. East Lansing.

CLARKE, L. R., P. W. GEIER, R. D. HUGHES & R. F. MORRIS. 1967. The Ecology of Insect Populations in Theory and Practice. 232 pp. Methuen, Lond.

EDWARDS, C. A. 1965. Some side-effects resulting from the use of persistent insecticides. Ann. Appl. Biol. 55, 329-331.

EDWARDS, C. A. & A. R. THOMPSON. 1973. Pesticides and the soil fauna. Residue Rev. 45, 1-79.

EVANS, H. E. 1970. Life on a Little Known Planet. 318 pp. Deutsch, Lond.

GUENZI, W. D. et al., ed. 1974. Pesticides in Soil and Water. 562 pp. Soil. Sci. Soc. Am., Madison, Wi,

HARRIS, C. R. 1969. Insecticide pollution and soil organisms. Proc. Entomol. Soc. Ont. 100, 14-29.

HILL, S. B. 1972. Effects of agriculture on soil mites. Unpublished paper presented to joint meeting of Entomol, Soc. Am., Entomol. Soc. Que., & Entomol. Soc. Can., Montreal, November 26.

HILL, S. B., L. J. METZ & M. H. FARRIER. 1975. soil mesofauna and silvicultural practices. Pp. 119-135 in B. BERNIER & C. H. WINGET, eds. Forest Soils and Forest Land Management. Pr. Univ. Laval, Quebec.

HOCOMBE, S. D. 1968. Herbicides in soil. Pp. 152-158 in J. D. FRYER & S.A. EVANS, eds. Weed Control Handbook. Vol. 1, Blackwell, Oxford.

LOVINS, A. 1976. Exploring energy-efficient futures for Canada. Conserver Soc. Notes 1 (4), 5-16.

MAY, R. M. 1977. Food lost to pests. Nature 267(5613), 669-670.

MEDAWAR, Sir Peter. 1969. Induction and Intuition in Scientific Thought. 62 pp. Methuen, Lond.

MOHR, E. C. J., F. A. van BAREN & J. van SCHUYLENBORGH. 1972. Tropical Soils: Comprehensive Study of Their Genesis. 3rd edn. 481 pp. Mouton-Ichtiar Baru, Van Hoeve The Hague.

MOORE, N. 1967. A synopsis of the pesticide problem. Adv. Ecol. Res. 4, 75-129

NEEDHAM, J. 1932. Thoughts on the problem of biological organization. Scientia (Milan) 52, 84-92.

WEETMAN, G., R. KNOWLES & 5. HILL. 1972. Effects of different forms of nitrogen fertilizer on nutrient uptake by Black spruce and its humus and humus mesofauna. Pulp. Pap. Res. Inst. Can. Woodl. Rep. 39, 20 pp.

WEETMAN, G. & S. B. HILL. 1973. General environmental and biological concerns in relation to forest fertilization. Pp. 19-35 in Forest Fertilization, Symposium Proceedings. USDA. For. Serv. Gen. Tech. Rep. NE-3.

WHITESIDE, T. 1977. The pendulum and the toxic cloud. The New Yorker, July 25, 30-55.

REFERENCES FOR TABLE 1.

Baudissin, F.G. von, 1952. Zool. Jahrb. Abt, Syst oekol Geogr Tiere 81,47-90.

Bauer, K., 1964. Mitt Biol. Bundesanst. Land-Forstwirtsch Berl. -Dahlem 122, 5-42.

Curry, J.P., 1970. Pedobiologia 0, 329-361.

Davis, B.N.K., 1965. Bull Entomol. Res. 56, 357-366.

Dobson, R.M., 1955. P. 252 in D.K. McE. Kevan, ed. Soil Zoology. Butterworths, London.

Drift, J. van der, 1963. Tijdschr Plantenziekten 69, 188-199.

Edwards C.A., 1965. Pp. 239-261 in G T. Goodman, R.W. Edwards & J.M. Lambert, eds. Ecology and the Industrial Society. Blackwell, Oxford.

Edwards D.A., 1968. Pp. 174-175 in J.D. Fryer & S.A.. Evans, eds. Weed Control Handbook. 1. Principles. Blackwell, Oxford.

Edwards, C.A., 1970. Proc. 10th Br. Weed Control Conf. 3, 1052-1057.

Fox, C.J.S.., 1964. Can. J. Plant Sci. 44, 405-409.

Karg, W., 1965. Nachrichtenbl Dtsch Pflanzenschutzdienst Berl. 19(4), 97-105.

Muller, G., 1972. Pedobiologia 12, 169-211.

Newman, J.F., 1965. Proc. 3rd. Br. Insectic. Fungic.. Con6. 342-357.

Popovici, 1., G. Stan, V. Stefan, R. Tomescu, A Dumea, A. Tarta & F. Dan, 1977. Pedobiologia 17, 209-215.

Prasse, J. 1975. Pp. 469-480 in J. Vanek, ed. Progress in Soil Zoology. Academia, Prague.

Rapoport, E.H. & G. Cangiolo., 1963. Pedobiologia 2, 235-238.

Rothamsted Expt. Sta. Repts. (C.A. Edwards et al.)

Sanocka-Woloszyn, E. & B.W. Woloszyn, 1970. Meded.. Rijksfac. Landbouwmet Gen t 35, 731-738.

Steinbrenner, K., F. Nagutsch. & 1. Schl icht. 1960. Albrecht Thaer.-Arch. 4, 611-631.

Stringer, A., 1966. Long Aston Agric Hort Res. Sta. Rept. (1965) 51-52.

Voevodin, A.V., 1966. Sb. Ref Pred Mez. Konf Herbic., Prague, 105

OTHER POTENTIALLY RELEVANT REFERENCES (NOT SEEN)

Anon, 1976. Versl Meded Plantenzieklenkundige Dienst, Jaarboek 1975, No. 150. 118 pp. Wageningen, Netherlands.

Marcuzzi, G., 1972. Monti Boschi 23(Z), 39-41.

Melnik, N.M., 1974. Zh Obsch Biol 35(3), 423-428.

Myskow, W. 1973. Zesz. Prob. Pestepow Nank Rolmizych, No. 145, 43-55.

 

TABLE 1

Authors of papers on Effects of Herbicides on Total Population Density of Soil Mites (only first author is given)

Herbicide Decrease No Change Increase
2,4-D Bauer 65 (slight, short-term) Baudissin 52; Edwards 68, 70; Fox 64; Prasse 75; Rapport 63 Bauer 64 (over longer-term)
2,4,5-T   Edwards 68, 70  
Atrazine Popovici 77 Fox 64; Edwards 70  
Benzoyl-Propethyl Rothamsted 74, 75 (slight, short-term)    
Bladex Edwards 70 (esp. predators); Rothamsted 71 Rapaport 63  
Chloropropham Sanocka-Woloszyn 70    
Chlorthiamid Rothamsted 76 (slight)    
Dalapon Curry 70 (top 7.5 cm.) Edwards 68, 70 Fox 64
Diquat   Newman 65  
DNOC Dobson 55; Edwards 68, 70 (esp. predators) Drift 63; Edwards 65 Karg 65
Elbanil Muller 72 (short-term)    
Linuron   Edwards 68, 70; Rothamsted 64  
MCPA   Davis 65; Edwards 68, 70; Rothamsted 64  
Monuron Edwards 70 (large doses); Fox 64; Voevodin 66 (x10 recommended amount) Edwards 68  
Paraquat Curry 70 (top 7.5 cm.) Edwards 70; Newman 65  
Prometryne Muller 72 (short-term); Sanocka-Woloszyn 70    
Propham   Bauer 64  
Simazine Edwards 65, 68, 70; (esp. predators); Muller 72 (short-term); Prasse 75; Rothamsted 64 Voevodin 66 Steinbrenner 60 (slight); Stringer 66
TCA Edwards 70 (large doses) Edwards 68 Fox 64
Tri-allate   Edwards 68, 70; Rothamsted 64  

 

TABLE 2

FACTORS INFLUENCING EFFECTS OF PESTICIDES IN SOIL

Pesticide

  • Type
  • Volatility
  • Solubility
  • Formulation
  • Concentration
  • Application
  • - method
  • - time (of year and day)
  • - frequency
  • -amount
  • Soil/Site

    Climate

    Experimental Variables

     

    TABLE 3

    EFFECTS OF PESTICIDES ON NON-TARGET FAUNA

    LETHAL

    1. Acute toxicity (immediate)

    2. Chronic toxicity (builds up over longer period)

    SUB-LETHAL

    MORPHOLOGICAL, PHYSIOLOGICAL AND PATHOLOGICAL EFFECTS

    Behavioural Effects

     

    Table 4

    Natural Laws and Their Implications for a Normative Food Policy
    Laws Policy Implications
    Survival of all species is based on:
  • needs (food, space, shelter, and for humans, clothing, education and other quality of life factors)
  • availability of the resources on which they depend
  • incidence of mortality factors
  • Identify real needs (as distinct from manipulative wants) and control all other activities that are likely to interfere with their satisfaction over the long-term, e.g., reduce wastage in the food system, of both inputs and outputs.
  • Support the development of lifestyles that depend only on renewable resources and that are environmentally supportive or minimally disruptive, e.g., non-polluting.
  • Establish strict priorities for the use of non-renewable resources.
  • Support the development of lifestyles that prevent premature human mortality.
  • All organisms are subject to certain biochemical constraints.
  • Utilize only organic compounds that have a counterpart in nature, i.e., that will decompose.
  • Relationships in the environment are cyclical.
  • Support the development of cyclical (as opposed to linear) food production systems that depend only on renewable resources, are self-sustaining, and are non-polluting, e.g., those that utilize organic wastes, along with other biological strategies, to maintain soil fertility (facilitated by regional self-sufficiency).
  • Natural systems tend to become more complex/diverse and stable with time, through an increase in the number of species and in the interactions between them.
  • Support the development of "complex" food production systems, e.g., mixed farms, crop rotations, mixed cultures.
  • Support the development of a decentralized food system with minimal handling between producer and consumer.
  • Treat causes of problems rather than symptoms; largely by using a preventative approach based on management strategies. These, in turn, are based on an understanding of the complex interrelationships within the farm environment.
  •  

    TABLE 5

    EFFECTS OF PESTICIDES

    A Direct Effect on Target Organisms (Pests)

    1. Mortality goes beyond critical level and population dies out (rare).
    2. Population rapidly makes up loss (resurgence) and fluctuates in phase with treatments (this is what usually occurs - it is a density-independent phenomenon).
    3. Population becomes resistant (this is the inevitable result).

    Source: Modified from Clark et al., 1967.

    B. Effects on Non-Target Organisms that have Relationships with Target Organisms (including indirect effects on target organisms.)

    4. Food or commodity is damaged, e.g., pesticide may be phytotoxic to crop.
    5. Secondary pest outbreaks occur, often due to competitors being less affected by pesticide than is major pest or to damage to predators or other controls of competitors.
    6. Damage to organisms that control pests, i.e., to the density-dependent controls (permits resurgence of pests to higher densities than before treatment).

    C. Effects on Non-Target Organisms that have no Obvious Relationships with Target Organisms.

    7. Damage to adjacent desired animals and plants due to drift.
    8.. Damage to pollinators.
    9. Damage to decomposers.
    10. Damage to non-adjacent animals and plants due to persistence and subsequent distribution of pesticides in air, water and via food chains.

    D. Effects on Non-Living Environment

    11. Deposition of pesticides on buildings, etc.; may damage paint work, machinery and necessitate cleaning of windows, etc.

    E. Effects on People

    12. Direct poisoning of applicator and innocent by-stander.
    13. Damage resulting from exposure to persistent pesticides in air, water and food or from fear of exposure.
    14. Short-term private economic benefits associated with temporary control of pests.
    15. Long-term public disbenefits associated with harmful side-effects to required resources.

     

    Table 6

    ECOLOGICAL STRATEGIES FOR PEST CONTROL

    1. Selection of Plant

    2. Selection of Site

    Select site, particularly the soil, for its ability to satisfy all the needs of the plant and to avoid pest damage requires detailed knowledge of plants, soils, and pests

    Consider:

  • soil type, fertility, structure and drainage
  • elevation, slope, aspect
  • location in relation to other features of the landscape
  • climate
  • previous history of site, i.e., crop, tillage, chemicals, pests
  • Modify site, if necessary, to meet needs of crop

    3. Planting

    Complex the planting design by:

  • crop rotation
  • mixed or companion planting
  • management of field borders and other adjacent environments to favour natural controls, e.g., by provision of nursery or trap crops, nesting and overwintering sites
  • Plant at the best time and in the best way-for the plant and the worst time and way for the pest
  • Introduce preventative pest control devices, e.g., tree bands, barriers, pheromone or other traps
  • Design size and shape of plots to discourage pests
  • 4. Maintenance of Site

    General:

  • Create and maintain optimum soil conditions for the plant and beneficial soil and above-ground organisms and unfavourable conditions for pests, e.g., through appropriate tillage, irrigation, drainage and application of organic and inorganic amendments and mulches; inoculation of plant and/or soil with beneficial organisms.
  • Avoid damaging the plant or stressing it with growth stimulants or toxins, e.g., unbalanced fertilizers, hormones, herbicides and pesticides
  • Practice good sanitation
  • Prune and thin where and when necessary
  • Monitor pest populations
  • If Pest Outbreak Occurs:

    5. Harvesting, Distribution, Storage and End-of-Season Chores

  • Time harvesting to avoid late pest attack
  • Store only healthy, pest-free produce in optimal conditions for crop and unfavourable conditions for pest
  • Destroy crop residues and potential over-wintering sites of pest
  • Manage soil over winter to reduce pests and encourage natural controls
  • Copyright 1978 Ecological Agriculture Projects


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