ECOTOXICOLOGY

AND

ENVIRONMENTAL

SAFETY

Agroecosystem-Chemical F.P. Chemical Energy

Residues Agency

and Pollution and the Food

3, 219-235 (1979)

Interactions

and Trends’

W. WINTERINGHAM Programme, Joint Division and Agriculture Organization Vienna, Austria

Received

August

of the International Atomic of the United Nations,

16, 1978

The complex of biotic communities and their common abiotic environment which constitutes a modem “agroecosystem” must increasingly be sustained by intensified practices, artificial inputs of agrochemicals, irrigation, etc. These trends are dictated by growing world food and energy demands and by the consequences of progressive urbanization, deforestation, industrialization, and agricultural mechanization. They have not only created problems of “ecotoxicology” but represent significant disturbances of the natural ecological cycles of water, carbon, and nitrogen on a global scale. Much attention is given to the side effects of pesticides (e.g., the appearance of residues in food webs and the emergence of pesticideresistant populations of pests) and to those of environmental chemicals such as atmospheric pollutants (e.g., the effects of acid precipitation). Review of agroecosystem-chemical interactions as a whole, however, suggests that the disturbances in the natural nutrient cycles and macronutrient levels of atmosphere, soil, and water may be the far more significant interactions within decades. Moreover, these changes are not only due to growing agrochemical usage but to agricultural intensification and deforestation as a whole.

1. INTRODUCTION 1.1. Current Estimates

and Trends

Population is greater, and increasing faster, than at any time in recorded history. The world population of 3.7 x IO9 in 1972 increased to 4 x log in 1975 and is expected to exceed 6 x log by the year 2000. In 1975 some 0.75 x log people were living in “absolute or relative poverty” and “present food production needs to be multiplied by four if the basic needs” of the population estimated for 2000 are to be met (UNEP, 1976). Studies by FAO (1970) suggest significant changes in population distribution. There is a decline in the proportion of the populations of developing countries (excluding China) directly concerned with agriculture as shown in Table 1. Table 2 illustrates corresponding trends in relative farm size. Statistics quoted by UNEP (1977) in relation to soil loss and reclamation confirm these trends and suggest that between 1975 and the year 2000 world population will increase from 4 to 6 x log, and that cultivated land per head of population will effectively fall from ca. 0.3 to 0.15 ha per head of world population. Another trend of global significance is the overall decline in natural forest biomass due to deforestation. The abundant geologic and fossil evidence of a decline of forest area during the entire Cenozoic era (the past 20 million years) is familiar to all students of biology (e.g., see Villee, 1951). Woodwell (1978) 1 Paper presented at IAES Meeting, Vienna, August 16- 18, 1978. Viewpoints are those of the author and are not intended to represent either views or polices of the UN agencies mentioned. 219

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0 1979 by Academx Press, Inc. of reproduction in any form reserved.

220

F. P. W. WINTERINGHAM

TABLE

1

TRENDS IN THE“AGRICULTURAL"AND"NONAGRICULTURAL" POPULATIONSOF DEVELOPINGCOUNTRIES (EXCLUDING CHINA) Agricultural population (X 106)

Year 1962 1975 1985

935 1175 1388

Nonagricultural population (x 106) 459 773 1126

Total (x 106)

Agricultural population (% of total)

1394 1948 2514

67 60 55

has indicated the more recent trends on the basis of the limited quantitative data available: These indicate a dramatic decline in the forest cover of Western European and Mediterranean countries from 90 to 20% during the last millenium; a 30% reduction in the forest area of Western Hanos, Venezuela, during the past 25 years may be typical of the Amazon basin area as a whole. “Forests had completely disappeared from most of China” by the 1940s though recent years have witnessed some planned reforestation whereas in India “forests are still rapidly declining” (UNEP, 1977). The remains of at least five cities of the Fezzan area of the Sahara stand witness, for tourists if not others, to long-lost floral cover; “. . . here is proof that, once upon a time, this was a land of forests and rivers, inhabited by wild beasts long since moved” (Portway, 1978). The significance of these trends, despite the frequent substitution of agriculture for forest, lies in the estimate that “Forest areas . . . hold 90% of all the carbon held in vegetation . . . contribute more than 60% of the net primary production. . . . All the cultivated land . . . accounts for about 8% of the total net primary production and for less than 1% of the standing mass of carbon” (Woodwell, 1978). Moreover, these trends seem likely to continue into the next decades. 1.2. Agricultural

Zntensi$cation

Agricultural intensification has within decades involved dramatic increases in, and apparent dependence upon, agrochemical usage (fertilizers and pesticides), mechanization, and artificial irrigation. These in turn have generated or contributed to a host of problems-some local but serious, others global but potentially sinister. For example, soil degradation and loss of plant nutrients, erosion and rising salinity, TABLE 2 TRENDSIN RELATIVE SIZEOFFARMANDFOOD BURDEN

Year

Average arable farm size (ha)

Average size of farm family

Numbers of personsto be fed by average farm family in addition to itself

1962 1975 1985

2.9 2.3 2.0

6.4 6.4 6.4

2.7 3.5 4.1

AGROECOSYSTEMS-GLOBAL

221

CHEMISTRY

the widespread emergence of pesticide-resistant strains of arthropod and even rodent pests, eutrophication and rising nitrate levels of some derived groundwaters and surface waters, and slowly rising concentrations of atmospheric carbon dioxide (FAO/UNEP, 1978; Woodwell, 1978). I .3. Role of Isotope

Techniques

Isotope techniques play a powerful and sometimes unique role in studying the particular problems of agroecosystem-chemical interactions. Thus, by “labeling” or “tagging” a mineral or organic nitrogen fertilizer with the stable isotope nitrogen-15 it is possible to follow its fate specifically and quantitatively in the presence of the large excess of soil or atmospheric nitrogen already present under field conditions. These techniques are playing a vital role in the FAO/IAEA/ GSF nitrogen residue studies (see below). The accurate measurement of the environmentally stable and radioactive isotopic ratios of the carbon of carbon dioxide enables that derived from the combustion of fossil fuels (which contains no radioactive isotope) to be distinguished from that due to the natural oxidation or artificial combustion of timber or plant carbon. Similarly, both added and “environmental” isotopic tracers play an established role in studies of the hydrological cycle, rates of recharge of groundwaters, etc. (Moser, 1976; Salati et al., 1978). 2. NITROGEN 2. I. Nitrogen

AS AN AGRICULTURAL

RESOURCE

Cycle

Modern intensive agriculture represents a major disturbance to the natural nitrogen cycle. This cycle is illustrated in Fig. 1 in the context of agriculture. Some parameters and estimated trends in relation to agricultural nitrogen are summarized in Appendix 1. Deforestation and native grassland ploughing for agriculture tend to increase losses by leaching and harvest, resulting in a decline in the soil nitrogen (see below). Under native grassland or forest cover, soil organic matter and its constituent nitrogen tend slowly to accumulate or at least to remain at a steady state, natural fixation from the atmosphere being balanced by losses from the soil. Land deprived of forest cover without adequate floral protection is especially prone to soil erosion and to nutrient losses by leaching and/or runoff (e.g., see Likens et al., 1969). Under conditions of intensive cultivation, tillage, etc., soil nitrogen tends to decrease with a growing need for additions of artificial nitrogen in the form of fertilizer and “unfertilized soils no longer can provide the food necessary to meet the needs of expanding populations” (Nelson, 1972). Table 3 illustrates current usage and trends (Nelson, 1972). Total world consumption of nitrogen fertilizers increased from ca. 15 million metric tons per year over the quinquennium 1961-1965 to ca. 33 million in 1971, ca. 35 million in 1972, and ca. 39 million in 1973 (FAO, 1974, p. 253). Rosswall (in Frissel et al., 1977, p. 229) has indicated from recent data (1976) that the average rate of biological nitrogen fixation from the atmosphere by all terrestrial ecosystems (149 x IO8 ha) amounts to 9.3 kg N ha-’ year-‘. Industrial N fixation for fertilizer amounted to 3.5 kg N ha-’ year-‘, i.e., about one-third of that of the natural global fixation. In 1974 some 50 x lo6 tons of N, were fixed industrially compared with 175 x IO6 tons fixed biologically (90 x lo6 tons in agri-

222

F. P. W. WINTERINGHAM

N,O+N,

ptz

N

BY MAINLY

AkEROBlC

DENITRIFICATION

IN (PRECIP(TATION( IRRIGATION

OR

WATER

I ATMOSPHERIC

I

N,

(ADDED! BY LEGUMES

ANIMAL

DRAINAGE HORIZON OR GROUND WATER TABLE

x

FIG. 1. Essential features of the nitrogen cycle in the context of agricultural o Inputs; [:I losses. Net losses by animal ingestion are not shown (Appendix 1).

-

residue studies.

cultural soil) and with 45 x IO6 tons fixed by natural abiological processes such as lightening (Hardy et al., in Brown et al., 1975, p. 136). The relative mobility of added soil nitrogen combined with worldwide reports of high or rising mineral nitrogen levels in groundwaters and derived surface waters has prompted concern at the UN level (FAOSIDA, 1972; FAO/IAEA, 1974; UNESCO-MAB, 1974). In particular it has prompted an international cooperative research program, largely financed through the generosity of the Federal Republic TABLE GLOBAL

3

FERTILIZER(AS N + K,O + P,O,) USAGE ANDTRENDS Amount

(x lo6 metric tons) Total usage 1954 1969 1975 Estimated usage in 1980

17.4 59.3 90.0 115.0

AGROECOSYSTEMS-GLOBAL

CHEMISTRY

223

of Germany and coordinated by the author on behalf of the Joint FAO/IAEA Division (Winteringham, 1977a). 2.2. FAOIIAEAIGSF The objectives

Nitrogen

Residue Program

of this program are stated in the following.

To contribute to the control of the pollutant potential of fertilizer nitrogen residues as undesirable nitrate in food, feed or water, and to improve their conservation in soil as useful plant nutrients. . . . To recommend . . measures designed to attenuate the problem in the context of environmental quality without impairing essential agricultural production.

This program has been effectively running for 3 years and is expected to continue into 1980 or beyond. In addition to a range of complementary activities within the Federal Republic of Germany the program has so far involved collaboration by experienced scientists in 20 other countries (Australia, Austria, Arab Republic of Egypt, Brazil, Canada, Chile, Denmark, India, Israel, Japan, Mauritius, Netherlands, New Zealand, Pakistan, Peru, Romania, Trinidad, United Kingdom, United States, Yugoslavia). 2.3. Long-term

Trends in Total Soil Nitrogen

The scientific studies and information collection through the Joint FAO/IAEA/ GSF nitrogen residue program (above) have shown that, according to climate, soil, agricultural practice, etc., variable proportions of fertilizer nitrogen are indeed irreversibly lost to the crop root zone, sometimes reach groundwater, and sometimes are returned to the atmosphere as a result of denitrification. Losses of added nitrogen by downward leaching tend only to become serious when optimum fertilizer application rates are exceeded, or when the precipitation or irrigation/ evapotranspiration rate ratio exceeds unity, or when even small increases in yield by additions of fertilizer become the dominant farmer objective. However, they have also shown that the downward movement or loss of crop-available nitrogen is not only a function of fertilizer and irrigation practice but also of cultivation, crop rotation, and deforestation generally. Moreover, the few cases where quantitative observations have been made over a sufficient period of time suggest that after disturbing native grassland, or after deforestation for the purposes of intensive crop cultivation, there is often a slow but sure decline of total soil nitrogen and of the soil organic matter of which it is part. There is, therefore, an even more rapid decline in the plant-available nitrogen since the various forms of the total soil nitrogen pool are not equally available to the crop, the more available or labile forms of nitrogen being lost first (Campbell et al., 1976; Smith et al., 1978). The importance of this lies in the fact that the total soil nitrogen in the root zone is usually many times larger (x 100 is typical) than the nitrogen added as fertilizers in any one year (100 kg ha-’ is typical). It represents a large natural reservoir for plant or tree growth and under natural conditions tends to be maintained by the return of animal waste and dead vegetation and by the natural processes of atmospheric dinitrogen fixation. This does not mean, of course, that initially poor soils cannot be improved by fertilizer and appropriate crop rotation (FAO/UNEP, 1978). Indeed, as authoritatively reviewed by Frissel et al. (1977), there are many cases where ongoing farming is associated with an increase in the soil N, P, and K pools, but even here a gain in the total soil N pool was sometimes apparently associated with a net loss in the

224

F. P. W. WINTERINGHAM

TABLE4 AGRICULTURALNITROGENINPUTS,~UTPUTS,AND LOSSESIN THEYEAR 2000 (TOP O-30 cm OF SOIL) “New”

cultivated land (ca. 300 x 10” ha)

“Old”

cultivated land (ca. 700 x lOa ha)

kg ha-r year-’ Inputs Precipitation Biological fixation Mean fertilizer N Total outputs Net removal by harvest Denitrification, volatilization Mean loss to the root zone by leaching Loss by erosion and surface runoff Total Net changes in root zone N (O-30 cm) Water pollutant potential from agriculture Global water pollutant potential Global loss to food and agricultural through erosion, runoff, denitrification, volatilization, and leaching

10” Nil 11

10” lb 170’ 181

81”

100’ 10’

lb

I

604 10” 91

10” 180

-80'

+1’

> 10’

70'

>52 X 10” metric tons year-’ >59 x 10” metric tons year-’ l

’ Reported contributions by precipitation (see Winteringham, 1979) ranged from zero (Mauritius) to 17.5 (UK) and suggested an average input of the order given. * Except for certain flooded rice paddy ecosystems (Shanmugam et al., 1978) biological fixation has been estimated to be of the low order given (Vlassak et al., 1973). Harvest of all legume fixed nitrogen assumed (see Winteringham, 1979). p This is based on the conservative assumption of a threefold increase in global fertilizer nitrogen consumption over the current annual rate (see above), i.e., 120 x 10” tons in 2000. One projection (see Brown et al., p. 139) is for 160 x 10” tons in 2000. d Based on soil nnrogen rate loss constant of 0.014 year-’ (i.e., effective half-life of 50 years) which is conservatively consistent with the data of Campbell et al. (1976) and Kolenbrander (1973) and an effective soil nitrogen level in the “A” horizon (O-30 cm) of 5000 kg N ha-‘. This means a loss rate in 2000 of ca. 70 kg ha-’ year-l. However, it is assumed that the rate of loss estimated by Campbell ef al. ignores the precipitation and biofixation input so that the total loss rate will be 70 + 11 = 81. e The proportion of soil nitrogen removed by harvest varies greatly with crop, soil, climate, etc. Bearing in mind predominance of world cereal demand and production (FAO, 1974, p. 35) and relatively high harvest removals in terms of applied fertilizer N (e.g., see Thomas and Gilliam in Frissel et al., 1977, pp. 182-243) the removal of 100 kg N ha-’ is, hopefully, a conservative figure for the year 2000, i.e., a global efficiency of ca. 60% (cf. Frissel and Kolenbrander in Frissel et al., 1977, p. 280). It is interesting to note that of the total N harvested from the old land alone (70 x 10” tons) only one-third would be directly consumed as food by the estimated world population of 6 x log. The daily average intake by man of 60 g protein (Mayer, 1976) is equivalent to ca. 10 g nitrogen or a world annual total of 22 X lo6 tons. Human food nitrogen derives mainly from cereals, less than 3% coming from fisheries (see FAO, 1974; Tont and Delistraty, 1977). ’ Estimate for average based on various reports (see Winteringham, 1979) and on controlled estimates under laboratory and field conditions at fertilizer application rates of the order (see below) of 300 kg N ha-’ year-’ (see Rolston, 1978). u Mean movement of soil nitrogen below the root zone will not be a function of the average fertilizer application rate (170 kg ha-‘) but will be a weighted function of the different rates of application. Under intensive agricultural conditions actual rates tend to be either zero or at some recommended level according to crop, rotation, etc. (e.g., see Frissel et al., 1977). In 2000 it is assumed that of the 700 x lo6 ha of intensively farmed land 400 x 106 ha received nitrogen at 300 kg N ha-’ while 300 x 106 ha receive none. Because of the growing use of supplementary irrigation, water input in 1980 is

AGROECOSYSTEMS-GLOBAL

CHEMISTRY

225

pool of plant-available nitrogen (Floate, in Frissel et al., 1977, pp. 292-295). It does mean, however, that certain large initially rich soil resources have been depleted and, therefore, useful or available soil nitrogen is lost. In the United Kingdom, in relation to organic matter, “Some soils are now suffering from dangerously low levels and cannot be expected to sustain the farming systems which have been imposed on them” (Agricultural Advisory Council, 1970). Kolenbrander (1973) has reported that soil organic matter fell from an initial mean value of 9% to less than half that within 10 years of ploughing up grassland. Studies by Paul and his colleagues (Campbell et al., 1976) of Canadian prairie soils, which represent a major source of the world cereals, have confirmed that the organic carbon content of the soils followed the general trend as that of nitrogen. After “breaking virgin land, soil N was lost at a rate equivalent to a halflife of about 44 years” during the first 14 years, thereafter more slowly (cf. Kolenbrander, 1973). It was also concluded that “prairie soils would lose 40% of their original N in 60 years; thereafter losses would be very low.” Losses in the United States have also been reported where native grassland has been ploughed for subsequent long-term cultivation of crops (Thomas and Gilliam in Frissel et al., 1977, p. 215). Meints and colleagues (1977) studied soil organic nitrogen in selected plots of Illinois over a 36-year period. During the first 30-year period total soil nitrogen decreased by 3-20% with some evidence of a reversal of the trend during a further 6-year period in some cases but not in others, despite heavy fertilizer nitrogen applications. However, the authors stress that the 6-year period was insufficient for reliable data. Interpretation was complicated by changes in ploughing depth, etc. These and many other similar observations demonstrate that the soil organic matter and stored nitrogen content of initially rich or virgin soils can decline slowly, but surely, under certain and widely prevailing conditions of intensive agricultural practice. A new lower steady-state level of total soil nitrogen tends to be achieved (Reinhorn and Avnimelech, 1974). This level can also be approached by appropriate crop rotation and fertilization of initially poor soils, e.g., by fertilizer use combined with appropriate crop rotation including forage legumes (Danceret al., 1977). Unfortunately, the steady-state levels of many soils of the world are neither known or reached; nor are the associated agricultural productivity levels or fertilizer requirements known. assumed to be ca. 1% x evapotranspiration rates. The available data (see Winteringham, 1979) on this basis suggest an average rate of leaching below the root zone of about 60 kg ha-’ year-’ averaged over the whole 700 x IO6 ha. h Based on quoted 1967 survey in USA (EPA/USDA, 1975/1976). ’ This implies annual loss (ca. 80 kg ha-’ year-’ in 2000) of root zone nitrogen from the newly exploited soils with no significant fertilizer additions and, more or less, a steady state for the soil N level of the intensively farmed, fertilized, and longer-used soils. j This figure is based on erosion only. However, there is abundant evidence (see Winteringham, 1978; Campbell et al., 1976; Likens et al., 1969) that ploughing native grassland or deforestation per se immediately encourages the downward movement of mineral nitrogen, and since it is unlikely that the accelerated mineralization of soil root zone nitrogen is entirely recovered in the harvested crop the actual pollution potential is probably greater than 10 kg ha-’ year-’ as indicated. k Erosion losses are included in estimating total pollution potential on the grounds that eroded soil organic nitrogen is likely to undergo nitrification and to reach surface waters ultimately as nitrate. l It might be noted that this conservative estimate of loss to food and agriculture is equivalent to almost one-half of the projected fertilizer N production in 2000 and more than the total current production.

226

F. P. W. WINTERINGHAM

Agricultural intensification combined with artificial irrigation and agrochemical inputs (pesticides, fertilizers, etc.) has led to higher food and fiber production per unit land area. There is evidence, however, that some large and productive areas of soils are becoming slowly but significantly depleted of their natural nitrogen reserves. There appears to be a need to monitor and study the implications of these trends in terms of future productivity potential, agrochemical requirements, and environmental quality criteria. Such trends might appropriately be taken into account by the FAO/UNEP/UNESCO soil monitoring and degradation program (Dudal and Batisse, 1978). In Appendix 1 background information and data are summarized as a basis for estimating agricultural N inputs and losses in the year 2000. The results are shown in Table 4. 3. INTENSIVE AGRICULTURE AS A DISTURBANCE CARBON, HYDROLOGICAL, AND NUTRIENT

OF NATURAL CYCLES

Commoner (1963, 1971, 1976) and others (Eckholm, 1976; Ehrlich and Ehrlich, 1970; Meadows et al., 1972) have identified man’s activities as a growing disturbance of vital natural cycles and as threats to environmental health. They have also indicated trends, especially in the levels of human resources, which hardly leave grounds for complacency. Their publications may be intended for the lay reader but there is considerable evidence of their timeliness. Brown et al. (1975) have very usefully effected an integrated and objective appraisal of world food productivity mechanisms and associated research imperatives. The emphasis, however, was on enhancing productivity without regard to effects on the natural cycles or existing levels of micro- and macronutrients of soil and air. A recent FAO/UNEP project (coordinated on FAO’s behalf by the author) involved an extensive review of “problems, principles and priorities for identifying criteria as a basis for controlling the undesirable effects of contaminants, pollutants, and excessive nutrients on living organisms, excluding man, but which are important to food and agriculture” (FAOIUNEP, 1978). This confirmed that there are indeed many- serious problems of toxic chemical residues such as wildlife and fish kills, effects of atmospheric sulfur dioxide and acid precipitation upon terrestrial flora and aquatic fauna, emergence of pesticide-resistant populations of agricultural pests, etc. But there was also a paucity of data on long-term effects on populations and on species diversity and abundance which take into account adaptation at the biochemical level and selection of resistant or tolerant species at the genetic level (Winteringham, 1977b). These factors are likely to minimize the long-term effects of environmental chemicals on fauna or flora. In the longer term (yet within decades) the more significant interactions appearing are due to the disturbance in natural cycles and in the levels of macronutrients. In the context of agriculture the effects of these are likely far to outweigh those of trace contaminants. 3.1. The Carbon

Cycle and Climate

Reference has already been made to the global trends in deforestation and the associated problems of erosion and desert encroachment which now attract serious international attention and development of countermeasures (UNEP, 1977). Agricultural intensification has inevitably involved deforestation and ploughing of native grassland on a large scale. The problems of soil erosion resulting from

AGROECOSYSTEMS-GLOBAL

227

CHEMISTRY

deforestation to which many vast desert areas stand witness (Eckholm, 1976) are well known. The more subtle effects on soil nutrient resources and the mobility of soil nutrients are more recent in recognition (see above). Woodwell (1978) has now drawn attention to the role of natural forest in the carbon cycle and its maintenance. He has indicated that while deforestation may have reduced the total capacity of terrestrial vegetation to act as a sink for carbon dioxide by photosynthesis, it has more probably resulted in the release of carbon dioxide by the oxidation of resulting humus. Thus, the global increases in atmospheric carbon dioxide seem likely to be due not only to fossil fuel combustion but also to deforestation. This takes into account other aspects of the natural carbon cycle such as atmosphere-ocean exchange, plant respiration, etc. However, two related factors should be mentioned. Primary forests are not only major factors of net primary production (carbon fixation less that released by metabolic respiration) but gradually accumulate and protect the soil pool of carbonaceous and of other nutrients. Substitution of intensive agriculture not only reduces primary production but also removes the protective cover of the stored soil carbon, probably facilitates its oxidation and release as CO, (cf. trends in soil nitrogen above), and reduces soil retentivity of other nutrients. Essential features of the carbon cycle in this context are shown in Fig. 2. Some quantitative parameters and trends are summarized in Appendix 2. In short, deforestation, agriculture, and industrialization tend

FIG. 2. Essential features of the carbon zation, and fisheries (see Appendix 2).

cycle in the context

LXCHANGE

ANAEROBIC

\\

C%

of deforestation,

agriculture,

industriali-

228

F. P. W. WINTERINGHAM

to decrease total plant photosynthesis and increase relative total respiration and combustion resulting in slow increases in the atmospheric CO, pool (Woodwell, 1978). Population growth and energy demands are of course causing a decline in fossil carbon reserves (Meadows er al., 1972). This may have a longer term corrective effect (Woodwell, 1978). Whatever the detailed mechanisms involved there is no doubt about the sign& cant rise in atmospheric carbon dioxide by 0.5- 1.5 ppm annually and its probable continuity for several more decades (Woodwell, 1978). The possible effects of this on climate are complicated by other global atmospheric disturbances due to man’s activities such as the effects of chlorofluoromethanes and nitrous oxide (including that from soil denitrification of added fertilizers) upon the ozone layer (Barrie et al., 1976) but as Woodwell (1978) has suggested “the results of a steadily rising amount of carbon dioxide in the atmosphere will almost certainly be destabilizing” and we are considering changes over “the next several decades.” Despite replanting it seems likely that the pressure for net deforestation will continue. Thus, in Sweden which has a long tradition of forest industry, the annual processing capacity already exceeds the annual growth of forests (Kardell, 1978). Development of the Amazon basin and large-scale alcohol fuel production from sugar cane and other crops (Hammond, 1977) have already prompted concern about the possibility of serious climatic effects at the regional level (Friedman, 1977). However, for a country heavily depending on imported oil such developments would appear not only to be justified but can also be seen as a means of reducing pollution by fossil fuel combustion. Moreover, with rising fossil fuel costs, their diminishing resources and the potential of sugar as an alternative basis for a range of chemical products as well as for ethanol by fermentation (Vlitos, 1977), a growing, demand for the cultivation of botanical sugar seems probable. Fortunately, with commendable foresight at the Federal Government level a timely macroecological research program has been initiated in Brazil on the basis of cooperation between the Centro de Energia Nuclear na Agricultura (CENA) of the University of Sao Paulo in Piracicaba and the Instituto National de Pesquisas da Amazonia (INPA) at Manaus. This will contribute data essential to wise planning and management of Amazonas development. 3.2. The Hydrological

Cycle and Climate

The effects of deforestation and agricultural development will depend on the importance of forest evapotranspiration. in the regional hydrological cycle and on the effects on soil nutrient levels and on soil structure and stability. The Amazon basin of ca. 6 x IO6 km2 represents the world’s largest river catchment and 15% of the world total freshwater flow. Current hydrological research (Salati er al., 1978) involves a study of environmental IsO and 2H fractionation during oceanic surface evaporation and forest evapotranspiration and transport, respectively, and the use of the derived data .to estimate the relative importance of the forest biomass in local climate. Preliminary estimates by other workers (reference cited in Salati et al., 1978) have indicated that “about 55% of the precipitation waters, on the average, are returned to the atmosphere through evapotranspiration while 42-46% are drained by the river.” Essential features of the hydrological cycle are shown in Fig. 3. Some related parameters and estimated trends are summarized in Appendix 3.‘There is evidence

AGROECOSYSTEMS-GLOBAL

TROPOSPHERE

TROPOSPHERE

FIG. 3. Essential features of the hydrological and urbanization (see Appendix 3).

229

CHEMISTRY

TROPOSPHERE

cycle in the context of deforestation,

agriculture,

that deforestation and agricultural substitution tend to decrease the relative terrestrial evapotranspiration resulting in a decline of precipitation over land (see above). There is evidence that relatively small changes in climate might have serious effects on large-scale crop production. There is already a delicate balance of world food supply and demand, and cereal reserves appear to be relatively small (UNEP, 1976; 1977). Accelerated desertification (Friedman, 1977) or cooling (Kukla and Mathews, 1972; Kukla and Kukla, 1974) might significantly affect cereal and other agricultural productivity (Thompson, 1975). 3.3. Population

Constraints

Looking to the future, Nakayama (1977) has indicated that conventional terrestrial agriculture could not support a world population of more than 8 x lo9 (cf. the expected population of 6 x log in 2000). On the other hand he has indicated a considerable theoretical potential for microbiological utilization of organic wastes for food production or for protein synthesis by desert algal forms. A potential for increased marine food sources supplemented by aquaculture has also been suggested by Tont and Delistraty (1977), and Marchetti (1978) has theoretically provided for a human population of lo”! 4. CONCLUSIONS Chemical-biota interactions at the molecular, cell, organism, or population level are of academic interest and often represent acute practical problems. On one hand, there are, for example, the vital and ubiquitous role of living organisms in the degradation of otherwise toxic or undesirable organic chemical residues and the t-emoval of contaminants through bioaccumulation and sedimentation in aquatic ecosystems. On the other hand, there are the effects of environmental chemicals upon the ecosystem: e.g., the eutrophication of inland waters, the effects of acid precipitation and of estuarine and coastal pollution, the emergence of pesticideresistant populations of serious agricultural pests and arthropod vectors of disease.

230

F. P. W. WINTERINGHAM

But in the longer term, yet within decades, there is evidence of far more serious threats to agricultural resources and their productivity deserving higher priority and cooperation at the international level. These are due to the macrodisturbances of natural ecosystem-chemical interactions and cycles as a result of growing deforestation and agricultural intensijication as a whole. The effects may be slower to develop but their scale is already global. Their implications may compare with those of exhausting fossil fuel reserves. The development of suitable controls without impairment of essential agricultural productivity clearly demands international cooperation on an adequate scale. In particular it will require longer term planning than seems to be in favor at national levels today. “It is unusual for a country to have a ten years plan, and unheard of to have a IOO-years plan. . . . Clearly, decisions made now and during the next 30 years will determine the future of mankind” (Foundation for Environmental Conservation, 1977). The United Nations Environment Programme provides some machinery for the required cooperation. The consideration of agroecosystems here certainly emphasizes the burden of population increases and argues for economic stability rather than growth as suggested by Wilson (1977). In any event an integrated scientific approach to these problems seems called for. This must take fully into account the disturbing trends now indicated. It must surely involve close cooperation between environmental scientists and system analysts especially. The recent workshop on the environmental problems of agriculture organized by IIASA (1978) can at least be seen as a hopeful sign. To conclude with a parody on the Nero legend; perhaps too many of us fiddle at the molecular level while the environment bums. APPENDIX 1: SOME PARAMETERS IN RELATION TO AGRICULTURAL

AND TRENDS NITROGEN

Soderlund and Svensson (1976) have compiled a global inventory of nitrogen and have tabulated its distribution in terms of total terrestrial biomass, oceanic biomass, and masses of inorganic forms on land, in water, and in the atmosphere. Global estimates of total denitrification and biofixation have also been given. Total world industrial fixation of nitrogen (1974) has been estimated at 50 x IO6 tons of which 10 x lo6 tons were used for fibers, plastics, explosives, and animal feed, and 40 x 10” tons for fertilizers (see Brown et al., 1975, p. 136). Total world biological fixation of nitrogen has been estimated at 175 x IO6 tons year-l including 90 x lo6 tons to nonlegume crops and 45 x lo6 tons to meadows and grassland. Natural abiological fixation (lightening, combustion, etc.) accounts for 45 x lo6 tons year-’ (see Brown et al., 1975, p. 136). Application rates of fertilizer nitrogen vary from zero to levels as high as 800 kg ha-’ year-’ according to crop, region, etc. (see Winteringham, 1978). Average rates for different regions in 1970 have been reported as follows (see Brown et al., 1975, p. 139): Europe North America USSR Asia Latin America Africa Oceana

66 kg N ha-’ 32.5

19.8 15.9 11.4 3.9 3.3

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CHEMISTRY

Many soil nitrogen balance studies have been based on the assumption of a steady-state or constant organic and mineral nitrogen pool of the soil (e.g., Bolin and Arrhenius, 1977). This has been dictated by the paucity of quantitative data on losses through denitrification and the relatively slow changes in the otherwise large total and variable soil nitrogen pool. However, these changes can become significant over decades compared with fertilizer application rates (see section 2.3). The assumption has probably led to an underestimate of total soil nitrogen losses by leaching and denitrification. Recognizing the limitations of extrapolation into the future (Batisse, 1974) it is nevertheless important to attempt this on the basis of reasonable scenari for planning purposes. The following scenario is adopted for estimating some global parameters for agricultural nitrogen over the period of 1975-2000: World population, 1975 World population, 2000 Increase, 1975-2000

4 x 109 6 x log

SO% (cf. UNEP,

Therefore, increases required in agricultural productivity, existing world levels of nutrition, will also be 50%, Total cultivated land area, 1975 Expected cultivated area, 2000

1977) at least to maintain

1.25 x log ha ca. 1 x log ha

(which will include ca. 0.3 x log ha of new land brought under cultivation (UNEP, 1977)). It is assumed that the new land will become available by forest clearance (e.g., in the Amazon basin) and/or ploughing of native grassland (e.g., tropical Savannah of Africa). Therefore, it is assumed that by the year 2000 the A-horizon (say O-30 cm) of this new land will still be relatively rich in total nitrogen. A conservative level of 1000 ppm by weight (cf. Campbell et al., 1976) in soil of bulk density of 1.5 g cme3 is assumed, i.e., ca. 5000 kg N ha-‘. It is further assumed that over this period yields based on the native soil nitrogen will be acceptable and will not receive significant fertilizer nitrogen inputs. Campbell et al. (1976) have indicated expected net soil nitrogen loss to be roughly exponential with time with a half-life (t& of the order of 50 years (cf. also Kolenbrander, 1973). It follows that the increased agricultural productivity will mainly have to be met by immensely improved productivity from the remaining 0.7 x log ha of older-cultivated land. The diminishing relative yield response with increasing N application rate is well known (e.g. see Nyborg et al., 1976; Olson et al., 1974). In the absence of unforeseen social changes or food production technology this confirms the requirement of greatly increased fertilizer nitrogen usage over current levels. Against this background Table 4 represents conservative estimates of fertilizer N requirements, root zone losses, and pollutant potential in the year 2000. APPENDIX 2: SOME PARAMETERS AND TRENDS IN RELATION TO THE CARBON CYCLE Atmospheric carbon dioxide pool is equivalent Total terrestrial freshwater and marine biota Soil organic matter, humus, biota, etc. Marine carbonate-bicarbonate system

to

700 X lo9 metric tons C 800 x log

ca. 2,000 x log ca. 40,000 x log

232

F. P. W. WINTERINGHAM

Rates have been estimated

as follows:

Fossil fuel combustion Effects of deforestation oxidation

5 x log metric tons year-’ and accelerated

humus 4-8 x log

Net primary production by all world forest areas represents Net primary production by all world Savannah areas represents Net primary production by all world cultivated areas represents

60% of total terrestrial production 12% 8%

All of the above values are from Woodwell (1978). A small additional input to the atmospheric COz pool is due to anaerobic methane production from natural sources such as swamps, sediments, etc. equivalent to 1.2 x log metric tons C year-’ (Maugh, 1972) followed by atmospheric photooxidation. The rising concentrations of atmospheric COz (see section 3) are now believed to be due to a combination of fossil fuel combustion, deforestation, accelerated soil and plant residue carbon oxidation, and the relative reduction of photosynthetic sinks. The rising atmospheric COz is not likely to stimulate terrestrial photosynthetic incorporation since this is not believed to be a “prime factor limiting the rate of photosynthesis in terrestrial communities” (Attiwill, 1971). APPENDIX

3: SOME PARAMETERS AND TRENDS THE HYDROLOGICAL CYCLE

IN RELATION

TO

Global Steady State

Evaporation and transpiration from land Precipitation over land Total drainage from land to the oceans Evaporation from the oceans Precipitation over oceans Atmospheric transport from oceans to land (From Ehrlich and Ehrlich,

160 km3 day-’ 260 100 875 775 100 1970.)

149 x lo6 km2 (ca. 15 x log ha) Total land area 361 x lo6 Total ocean area (From Handbook of Chemistry and Physics, Chemical Rubber Publishing Co., Cleveland, Ohio, 1951.) Total arable land (including land under 1.47 x lo9 ha permanent crops) 2.99 x lo9 Permanent meadows and grasslands Forests and woodlands 4.03 x 109 (From FAO, 1974.) Global tropical rain forest (including 0.6 x log ha of the Amazon basin) of 1.7 x log ha is equivalent to net primary production rate of 9.9 tons carbon ha-’ year-‘.

AGROECOSYSTEMS-GLOBAL

Global Savannah of 1.5 x lo9 ha is equivalent tons carbon ha-’ year-‘.

233

CHEMISTRY

to a net primary production

rate of 4.1

Global cultivated land of 1.4 x lo9 ha is equivalent to a net primary production of 2.9 tons carbon ha-’ year-‘. (Primary production rates per hectare calculated from data summarized by Woodwell, 1978.)

rate

If evapotranspiration be assumed to be roughly proportional to net primary production rate per hectare [this assumption is justified by the fact that when water and nutrients are nonlimiting, growth is proportional to transpiration (Penman, 1963)], it follows that evapotranspiration rate per net area of cultivated land is less than one-third of that of primary forest and less that one-half that of Savannah. The hydrological cycle statistics (above) suggest that ca. 60% of precipitation over land is due to recycling evapotranspirated water (cf. Salati et al., 1978). If the projected real world food needs beyond the year 2000 (i.e., four times the present level-UNEP, 1976) were met by only doubling the present area of cultivated land (say 1.4 x IO9 ha) by clearing 0.7 x lo9 ha of tropical rain forest and 0.7 x lo9 ha of Savannah (see 6.1 above), then total precipitation over this new cultivated land might be expected to be reduced by ca. 20%. This might indeed affect climate and accelerate desertification rates (compare Friedman, 1977). REFERENCES Agricultural Advisory Council (1970). Modem Farming and the Soil, pp. i-x, l-119. Her Majesty’s Stationary Office, London. ATTIWILL, P. M. (1971). Atmospheric carbon dioxide and the bioshere. Environ. Pollu?. l(4), 249-261. BARRIE, L. A., WHELPDALE, D. M., AND MUNN, R. E. (1976). Effects of anthropogenic emissions on climate: A review of selected topics. Ambio 5(5, 6), 209-212. BATISSE, M. (1974). Global prospects for natural resources. Nature Resources 10(l), 2-7. BOLIN, B., AND ARRHENIUS, E. (1977). Nitrogen-An essential life factor andagrowingenvironmental hazard. Ambio 6(2, 3), 96-105. BROWN, A. W. A., BYERLY, T. C., GIBBS, M., AND SAN PIETRO, A. (eds.) (1975). Crop ProductivityResearch Imperatives (an international conference organized by M. Lamborg, S. K. Ries, F. H. Tschirley, and S. H. Wittwer), Michigan-Kettering, East Lansing, Mich., and Yellow Springs, Ohio. CAMPBELL, C. A., PAUL, E. A., AND MCGILL, W. B. (1976). Effects of cultivation and cropping on the amounts and forms of soil N. In Proceedings of Nitrogen Symposium, Calgary, Alberta, pp. 9- 101. COMMONER, B. (1963). Science and Survival, pp. 3- 177. Ballantine, New York. COMMONER, B. (1971). The Closing Circle, pp. l-343. Bantam Books, New York. COMMONER, B. (1976). The Poverty of Power, pp. l-297. Bantam Books, New York. DANCER, W. S., HANDLEY, .I. F., AND BRADSHAW, A. D. (1977). Nitrogen accumulation in kaolin mining wastes in Cornwall. I. Natural Communities. Plant Soil, 153-167; II. Forage legumes. Plant Soil, 303-314. DUDAL, R., AND BATISSE, M. (1978). The soil map of the world. Nature Resources 19(l), 2-6. ECKHOLM, E. P. (1976). Losing Ground-Environmental Stress and World Food Prospects, pp. 9-223. Norton, New York. EHRLICH, P. R., AND EHRLICH, A. H. (1970). Populations: Resources: Environment. Freeman, San Francisco. EPA/USDA (197511976). Control of Water Pollution from Cropland, Washington, D.C., Vol. I, pp. I-111; Vol. II, pp. l-187. FAO (1970). Provisional Indicative World Plan for Agricultural Development. Rome, Vols. I and II. FAO (1974). Production Yearbook, Rome, Vol. 28(l), pp. l-328. FAOIIAEA (1974). Effects of Agricultural Production on Nitrates in Food and Water with Particular Reference to Isorope Studies. IAEA, Vienna, STIIPUB1361.

F. P. W. WINTERINGHAM

234

FAO/SIDA (1972). Effects of Intensive Fertilizer No. 16, Rome, 1972. FAOIUNEP (1979). Environmental Chemicals: Context

of Agriculture,

Forestry,

Fisheries

Use on the Human

Criteria and Feed.

Environment.

for the Protection

FAG Soils Bulletin

of Non-Human

Biota

in the

Monographreport,FAO, Rome,~npreparation

for publication. Foundation for Environmental Conservation (1977). The Reykajvik imperative on the environment and future of mankind. Environ. Conserv. 4(3), 161-163. FRIEDMAN, I. (1977). The Amazon Basin, another Sahel? Science 196, 7. FRISSEL, M. J., et al. (1977). Cycling of Mineral Nutrients in Agricultural Ecosystems (M. J. Frissel, ed.), Agro-ecosystems, Vol. 4, Nos. 1, 2; pp. v-viii, l-354. HAMMOND, A. L. (1977). Alcohol: A Brazilian answer to the energy crisis. Science 195, 564-566. IIASA (1978). Environmental Problems of Agriculture. Workshop organized by the International Institute of Applied Systems Analysis, Laxenburg, Austria, June 27-30. KARDELL, L. (1978). Ecological aspects of the Swedish search for more wood. Ambio 7(3), 84-92. KOLENBRANDER, G. J. (1973). Fertilizers, farming practice and water quality. In The Fertilizer Society, London, Proceedings, No. 135, pp. 3-36. KUKLA, G. J., AND KUKLA, H. J. (1974). Increased surface albedo in the Northern Hemisphere. Did satellites warn of the weather troubles of 1972 and 1973? Science 183(4126), 709-714. KUKLA, G. J., AND MATHEWS, R. K. (1972). When will the present interglacial end? Science 178(4057), 190- 191. LIKENS, G. E., BORMANN, F. H., AND JOHNSEN, N. M. (1969). Nitrification: Importance to nutrient losses from a cut over forested ecosystem. Science 163(3872), 1205- 1206. MARCHETTI, C. (1978). On lo’*: A Check on Earth Carrying Capacity for Man, PR-18-7, pp. I- 11. IIASA, Laxenburg, Austria. MAUGH, T. H. (1972). Carbon monoxide: Natural sources dwarf man’s output. Science 177,338-339. MAYER, J. (1976). The dimensions of human hunger. Sci. Amer. 235(3), 40-49. MEADOWS, D. H., MEADOWS, D. L., RANDERS, J., AND BEHRENS, W. W. (1972). TheLimits to Growth, pp. 17-205. Pan Books, London and Sidney. MEINTS, V. W., KURTZ, L. T., MELSTED, S. W., AND PECK, T. R. (1977). Long term trends in total soil N as influenced by certain management practices. Soil Sci. 124(2), 1 lo- 116. MOSER, H. (1976). Nuklear Techniken in der Hydrologie [Nuclear techniques in hydrology]. Kerntechnik 11, 461-469. NAKAYAMA, 0. (1977). World carbon problem. Ecotoxicol. Environ. Safety 1, 249-254. NELSON, L. B. (1972). Agricultural chemicals in relation to environmental quality. Chemical fertilizers: Presence and future. J. Environ. Qual. l(l), 2. NYBORG, M., NEUFELD, J., AND BERTRAND, R. A. (1976). Measuring crop available nitrogen. In Proceedings of Nitrogen Symposium, Calgary, Alberta, pp. 103-127. OLSON, R. A., MUIR, J. H., WESELY, R. W., PETERSON, G. A., AND BOYCE, J. S. (1974).Accumulation of Inorganic Nitrogen in Soils and Waters in Relation to Soil and Crop Management, STIlPUB/361, pp. 19-38. IAEA, Vienna. PENMAN, H. L. (1%3). Irrigation in Britain. J. Roy. Sot. Arts 111(5080), 272-289. PORTWAY, C. (1978). Travel: A taste of timeless beauty. The Times Saturday Review, April 29, p. 15. REINHORN, T., AND AVNIMELECH, Y. (1974). Nitrogen release associated with the decrease in soil organic matter in newly cultivated soils. J. Environ. Qual. 3(2), 118-121. ROLSTON, D. E. (1978). Application of gaseous diffusion theory to measurement of dentrification. In Proceedings of a Workshop on Agricultural Nitrogen in Relation to the Environment (D. R. Nielsen and J. G. Mac Donald, eds.), Vol. II. Academic Press, New York. SALATI, E., DALL’OLIO, A., MATSUI, E., AND GAT, J. R. (1978). Recycling of water in the Amazon basin: An isotopic study. Water Res., in press. SHANMUGAM, K. T., O’GARA, F., ANDERSEN, K., MORANDI, C., AND VALENTINE, R. C. (1978). Control of biological nitrogen fixation. In Proceedings of a Workshop on Agricultural Nitrogen in Relation to the Environment (D. R. Nielsen and J. G. Mac Donald, eds.), Vol. I. Academic Press, New York. SMITH, S. J., CHICHESTER, F. W., AND KISSEL, D. E. (1978). Residual forms of fertilizer nitrogen in field soils. Soil Sci. 125(3), 165- 169. S~DERLUND, R., AND SVENSSON, B. H. (1976). The global nitrogen cycle. Ecol. Bull. (Stockholm) 22, 23-73.

AGROECOSYSTEMS-GLOBAL

CHEMISTRY

235

THOMPSON, L. M. (1975). Weather variability, climatic change, and grain production. Science 188(4188), 535-541. TONT, S. A., AND DELISTRATY, D. A. (1977). Food resources of the oceans: An outline of status and potentials. Environ. Conserv. 4(4), 243-252. UNEP (1976). The State ofthe Environment 2976, pp. l-20. United Nations Environment Programme, Geneva. UNEP (1977). The State of the Environment: Selected Topics--1977, pp. I-14. United Nations Environment Programme, Pergamon Press, Elmsford, N.Y. UNESCO-MAB (1974). Consultative Group on Project 9: Ecological Assessment ofPest Management and Fertilizer Use on Terrestrial and Aquatic Ecosystems (part on fertilizers) MAB Report Series No. 15. VILLEE, C. A. (1951). Biology: The Human Approach, pp. l-580. Saunders, Philadelphia and London. VLASSAK, K., PAUL, E. A., AND HARRIS, R. E. (1973). Assessment of biological nitrogen fixation in grassland and associated sites. Plant Soil 38(3), 637-649. VLITOS, A. (1977). Sweets for starters. Chem. Brit. 13(9), 340-345. WILSON, J. T. (1977). Overdue: Another scientific revolution. Nature (London) 265, 196- 197. WINTERINGHAM, F. P. W. (1977a). Joint FAO/IAEA/Federal Republic of Germany international coordinated programme of research on agricultural nitrogen residues with particular reference to their conservation as fertilizers and behaviouras potential pollutants. Progr. Water Technol. 8(%), 179- 181. WINTERINGHAM, F. P. W. (1977b). Comparative ecotoxicology of halogenated hydrocarbon residues. Ecotoxicol. Environ. Safety 1, 407-425. WINTERINGHAM, F. P. W. (1979). Nitrogen balance and related studies-A global review. In Proceedings and Report of the Fourth Research Coordination Meeting of the FAOIIAEAIGSF of Research on Agricultural Nitrogen Residues, Piracicaba. Sao Paulo, Brazi/, July

Vienna. (in press). WOODWELL, G. M. (1978). The carbon dioxide question. Sci. Amer.

238(l), 34-43.

Programme 1978. IAEA,