Fertilizers for food production vs energy needs and environmental quality

ECOTOXICOLOGY

AND

ENVIRONMENTAL

Fertilizers

SAFETY

1,

3 1l-326 (1977)

for Food Production Environmental

vs Energy Quality1

Needs and

R. A. OLSON University

of Nebraska, Received

Lincoln, May

Nebraska

68583

12.1977

The world is experiencing an energy crisis that is restrictive to agricultural requisites production at the same time that food is becoming increasingly short on a global basis. Fertilizers are the most energy demanding of these inputs and have become very expensive and intermittently short in supply with the reduced availability of fossil fuels. They have been indicted, furthermore, as environmental pollutants due to their presumed role in eutrophication and in being a source of excessive NO,-N that may accumulate in some leaf crops and in drinking waters. Exponential growth in fossil fuel consumption cannot continue. Economies can be made in the agricultural sector, which does indeed consume substantial quantities of energy. The energy consumed in this very essential food-producing process, however, is almost insignificant compared with that involved in transport and processing of food beyond the farm and with other energy expenditures in modem society. A shift in priorities will certainly be required in adapting to the real world of the 1970s if man’s first need is to be met. Economies in fertilizer use can be made by adherence to known agronomic principles. Savings in fossil fuel energy can probably be effected also in the production of N fertilizer, by far the most fossil-energydemanding process in the realm of agriculture. Considerable research remains to be done, however, under varied climatic conditions for understanding and controlling processes by which residuals from fertilizers may become environmental pollutants. The various issues in this paper must be resolved promptly in consideration of the now-existing energy crisis and the imminent world food crisis.

The energy crisis of 1973 brought forcible recognition of the fact that man cannot forever have his cake and eat it too. Bountiful as the earth’s resources may be, they are finite, and retrenchment in consumption with serious endeavors toward recycling must be undertaken now if the quality of life for future generations is to be assured. This applies not only to such obvious first-order resources as oil, soil, forests, and the like, but as well to second-generation products resulting from energy input like fertilizers, machines, and even food itself. It is the objective of this paper to survey the role of inorganic fertilizers in world food production in relation to the energy requirement for their manufacture and to their impact on environmental quality. ACCEPTANCE

OF INORGANIC

FERTILIZERS

Inorganic fertilizers have passed through several cycles in their international acceptance, especially in the eyes of those remote from the agricultural production process. ’ This paper represents the context of a lecture presented to the IAEA Secretariat and members of the Vienna scientific community on 4 December 1974. Copyright 8 1977 by Academic Press, Inc. 311 All rights of reproduction Printed in Great Britain

in any form reserved.

ISSN 0147-6513

312

R. A.

OLSON

Tradition dictated that the wastes of animal and people were the natural and only real fertilizers. During the 194Os, when the chemical industry responsible for commercial fertilizer manufacture was first beginning to blossom, much doubt existed concerning the validity of these “chemicals” in the food-producing chain. Commonly heard contentions were that these foreign introductions would sterilize soils, become “habit forming”, and destroy the earthworm population. Experience in a few following years effectively refuted these beliefs by demonstrating that inherent soil productivity could be enhanced by judicious fertilizer use, that earthworms rather thrived on the additional organic material produced and returned to the soil as crop residue, and that fertilizers were habituating only to the extent that, as deficiency persisted of any given element in the soil, application of that element as fertilizer was necessary for most-economic crop returns. General international acceptance of commercial fertilizers came with the 1950s and 196Os, as their role in efficient crop production was elaborated on a worldwide scale. The Green Revolution became reality in the developing countries not only because of the introduced miracle varieties, but equally because of the availability of inexpensive fertilizer nitrogen (N) to feed them. Perspectives were modified again, however, as world attention began to focus on environmental quality from 1969 onwards. But the real crowning blow to fertilizers as the panacea to world food-production needs came with the energy crisis of 1973. The ensuing shortage and high cost of naphtha and natural gas as feedstock for ammonia production created serious shortages especially of N fertilizers, and costs for all kinds of fertilizer materials multiplied. This came as a most serious blow to the developing countries, taking some of the steam out of the Green Revolution at a time when population growth demanded further rapid expansion in food production. FERTILIZER

PERSPECTIVES

IN THE

1970s

The term “fertilizer” is no longer one to be excluded from the parlance of polite company in the 1970s. It is commonly used in front-page newspaper accounts, almost equal in respectability to automobile, refrigerator, and all other manufactured items associated with late 20th century technology. At the World Food Conference of November 1974 the words “food” and “fertilizer” were used almost synonymously. Relation to World Food Needs

Past and projected world fertilizer use is depicted in Fig. 1. Clearly the growth has been quite phenomenal and could not have so transpired without commensurate outstanding results from fertilizer use in farmers’ fields. The consumption/response data of Fig. 2 are indicative of the observations in most developed countries, where average yields per hectare have doubled and trebled in the past generation. It must be acknowledged in connection with this figure that other technological advances were involved that contributed significantly to the yield trend, including improved crop varieties, better weed control, improved tillage and planting methods, and the like. Even so, yields would almost certainly drop back to half or less of those current after 3 or 4 years if the fertilizer input were curtailed to 1952 levels. Results from introduction of modern fertilizer technology into the developing countries were almost equally spectacular. Even without the complementary inputs in

FERTILIZERS WORLD

1955

313

FOR FOOD PRODUCTION

PLANT

NUTRIENT

1960

1965

CONSUMPTION

1970

I

5

FIG. 1. World consumption of fertilizer nutrients through 1970 with projection onwards (Harre er al., 1971).

all related aspects of production agriculture, the simple introduction of fertilizers to peasant farming accomplished an average 60% increase in production in hundreds of trials in the several countries of FAO’s FFHC Fertilizer Programme (Olson, 1970). The

FIG. 2. Consumption of fertilizer N in relation to average yields of maize grain in Nebraska during the period 1952-1972.

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R. A.

OLSON

average value/cost ratio acquired from economic analysis indicated sufficiently high returns to be very attractive to the farmer. From these and other results, FAO projected a needed annual increase of 14% in fertilizer supplies through 1985 for meeting the food needs of the anticipated population in the developing countries. These needs were being met approximately through 197 1, and, along with the Green Revolution technology being applied in several countries, there was real optimism that any food crisis would be averted in the foreseeable future. As examples, some countries with traditional food grain shortages had become net exporters, such as the Philippines, Mexico, Turkey, and Taiwan, and countries like India, Pakistan, and Indonesia were beginning to visualize self-sufficiency in the relatively near future. By 1974, however, the rosy picture of 3 years earlier was obliterated by unfavorable weather in different regions of the world and by fertilizer shortages. The most critical shortage was of fertilizer N with an approximate l,OOO,OOO-ton deficiency anticipated through 1979 on the basis of planned new plant capacity (Anonymous, 1974). Nor was the short-term outlook bright in view of the spiraling costs for fertilizers at the same time that the quadrupled costs for required petroleum imports were severely depleting foreign exchange earned from exports in a majority of the developing countries. The world suddenly became conscious of the fact that food, fertilizers, and energy are inextricably intertwined. Energy Requirements Modern agricultural production is a highly energy-intensive business very much dependent on fossil fuel energy. It appears further that our modern system of TABLE ESTIMATED AVERAGE

ENERGY

INPUTS

1

FOR THE PRODUCTION

HECTARE OF MAIZE IN THE UNITED DURING 1945 AND 1970”

OF AN STATES

Energy equivalent (kcal x 10m3) Input Electricity Fertilizers Gasoline Grain drying Irrigation Labor Machinery Pesticides Seeds

Transportation Total input Grain output Output/input

1945

1970

80 185 1,357

775 2,640

25 47 30 450 85 50

300 85 12 1,050 55 157 175

2,309 8,567

7,241 20,412

0

3.7

u Adapted from Pimentel et al. (1973).

1,992

2.8

FERTILIZERS

FOR

FOOD

315

PRODUCTION

agricultural technology in producing food expends fossil energy in the same order of magnitude that is realized in output of food energy (Gifford, 1973; Pimentel et al., 1973; Stout, 1974). Excessive as this may seem, however, it is important to realize that six to seven times as much energy is expended thereafter in getting the food to market, processed, packaged, refrigerated, merchandized, cooked, etc. (Gifford, 1973; Stout, 1974). The data of Table 1 provides an estimate of all of the energy inputs involved in the production of a hectare of maize in the United States in 1970 compared with 1945 (Pimentel et al., 1973). The figures are based on country-wide average yields, fertilizer rates, fuel consumption, machinery manufacture/depreciation, etc. They present a somewhat more favorable output/input relationship than others have calculated for the full range of food crop production, perhaps explained by the greater efficiency of maize in converting solar energy per unit area than is achieved by many of the common food crops. A most significant revelation of the data is the tradeoff that has occurred in fossil fuel energy for human labor. Grain yields did increase some 2.4 times during the 25year period, but total energy expenditure tripled such that the efficiency in output relative to input declined almost 25%. But most relevant to the context of this treatise is the fact that fertilizers have come to be by far the largest energy input in the entire system. The major portion of fertilizer materials on the world market has been fabricated for the N, P, or K components, the primary essential elements of plant nutrition, as they are the ones most likely to limit the yields of crops. Among these, N materials are responsible for almost 90% of the energy expenditure expressed in Table 1. This is for the reason that very large amounts of feedstock, usually natural gas or naphtha, are required for generating the elemental H, and the heat and pressure components of the reaction by which elemental N, from air is combined with H, in the synthesis of ammonia, viz., N2+ 3H2 y&i+

2NH,.

Table 2 gives an indication of the magnitude of the energy involved for the material used in a representative 150 kg of N/ha field application of fertilizer. It should be clarified that the values presented are for anhydrous ammonia manufacture only in a representative plant of the early 1970s. Further conversion to the solid compounds of ammonium nitrate and urea more conventionally used in production agriculture entails

TABLE 2 ENERGY

ASSOCIATED WITH THE CONVENTIONAL PRODUCTION AMMONIA USING NATURAL GAS AS FEEDSTOCK

Energy source andunits Natural gas(m3) Britishthermalunits Kilocalories

Energyconsumedin producingI kg of NH,-N 4.3 43,000 10,831

OF ANHYDROUS

Energyconsumedwith 150kgofNasNH, 645 6,450,OOO 1,625,OOO

316

R.

A.

OLSON

substantially more energy input for supplying the additional reactant and for granulation and conditioning of the resultant hygroscopic materials, e.g., 2NH, + CO,

2

pressure

H,O + CO(NH,), urea

+ drying, granulation, conditioning. In the United States, around 1.5% of the annual consumption of natural gas goes toward fertilizer N production (Stout, 1974). With the present energy shortage, production in winter months has been somewhat curtailed necessarily due to the first priority given to home heating. Much of the further expansion in absolutely essential fertilizer N production capacity for meeting world needs in the short term will thus have to come in the oil-exporting countries. If these energy inputs for fertilizers seem exorbitant, they should perhaps be regarded in the light of some other energy expenditures in modern society. The total energy requirement for agriculture in supplying the food for one person for a year in the United States has been estimated at the equivalent of 112 gallons of petrol (Pimentel, 1973), of which 40 gallons could be charged to the fertilizer input. By contrast, one United States automobile as an average will consume around 700 gallons per annum. It thus becomes a question of where our priorities should be placed-the fertilizer energy requirement doesn’t look so bad in these terms. Impact on Environmental Quality Increasing amounts of fixed N in the air, rainfall, streams, and lakes have been observed with each year in recent times (Feth, 1966; Oden, 1972). The source of the N is manifold without question, but the recorded geometric growth in fertilizer production has made N fertilizers suspect in the eyes of world citizenry. Indeed, it has even been suggested that fertilizer N represents an unacceptable intrusion on the “balance of nature” and that there should be a lo-year moratorium on fertilizer N! Phosphorus fertilizers, too, have been suspect in particular consequence of the role that P plays in the fertility of surface waters. As a result, worldwide attention has been focused on the impact of intensive fertilizer use on the human environment (FAO, 1973). Eutrophication of surface waters. There has been much lament and apprehension concerning the accelerating eutrophication of inland waters in recent years. Investigation into the phenomena that trigger the process reveal the dominant role of the nutrients N and P in supporting the growth of the algae and other plants responsible. Of course, other factors like nonturbid and sufficiently warm water, a readily degradable organic source for supplying CO,, etc., are equally involved. Given the other conditions at satisfactory levels, only about 0.3 ppm mineral N and 10 ppb soluble P in the water are needed to support eutrophication, with larger amounts supporting more thrifty algal blooms (Viets, 1971). The majority concensus to date of those seriously investigating the eutrophication process is that the increasing amounts of urban wastes and the recent concentration of animals for feeding and dairying operations have been primarily responsible. Phosphorus concentrations of drainage waters have been particularly influenced by the cleaning detergents from households that are disposed through sewage systems. The animal excrement that used to be distributed rather uniformly over the landscape is now largely concentrated in a limited

FERTILIZERS

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317

number of corrals representing major point sources of organic and nutrient pollution as runoff events to stream or lake occur. Unquestionably there is an agricultural contribution to surface water enrichment that encourages eutrophication. The streams of Switzerland appear to carry nutrient N and P in direct proportion to the amount of land area cultivated in the stream watershed, with seeming implication of fertilizers (Jaag, 1972). Much of the nutrient so supplied is largely the consequence of suspended particles carried in the erosional process, N in organic colloids, and P adsorbed to soil sediments. It is by no means all fertilizer since native nutrients of the soil system are very much involved, and if accelerated erosion were controlled, the sediments responsible would not be transported to the water body. Nebraska studies make quite clear the dominance of human and animal concentrations over crop production agriculture on nutrient N and P carried in streams of the state (Muir et al., 1973). The greatest livestock and human population densities exist in the eastermost counties of the state, and here the stream nutrient loads correspondingly reach maximum levels. Throughout the central portion of the state, where crop production is most intensive and the largest amounts of fertilizer are used, only nominal amounts of N and P are being carried in the streams. A further observation that implicates population density and associated industries is the growth in nutrients carried in the Missouri River, viz., an approximate doubling from the first contact with the state’s northern boundary to a point just below Sioux City and the further trebling effected below the city of Omaha. In confirmation of the above observations, correlation studies relating nutrient levels with county statistics for the respective sites revealed highly significant relationships with human and animal population densities and no relation whatever with fertilizer use. An interesting sidelight to the Nebraska river flow data is the radical drop in N and P carried in the Platte River downstream from a major dam and reservoir which clearly serves as a sink for the two nutrients by reason of aquatic life utilization. No serious eutrophication of the 3 x lo6 ha-dm lake has occurred to date, but it appears to be only a matter of time unless the river above can be depolluted of its nutrient load. Similar “sink” effects are observed at other major stream impoundments in Nebraska. The Nebraska water studies revealed marked seasonal fluctuations in the concentration and flow of N in the streams. Both the concentration and flow were at a maximum during the spring and fall months, periods when the rainfall received is most likely to give rise to runoff events. Analysis of rainfall samples during the 3-year period indicated an average mineral N content (NH, and NO,, the former predominating) of around 2 ppm, whereas average stream N concentration was only about 0.7 ppm or about onethird as much. Thus, good indication exists that rainfall runoff is a major contributor to the N carried in streams, and accordingly a portion of the blame for nutrient N in waters must be ascribed to N oxides from the internal combustion automobile engine and those industries that allow NH, and NO, escape to the atmosphere. Fallout of NO,-N in rainfall of Europe has been noted to be of a similar magnitude and growing perceptibly with each passing year (OdCn, 1972), while the amounts in New England downwind from New York are notably higher (Feth, 1966). Nutrient contamination offoods and groundwaters. The only real toxicity hazard for humans likely to be encountered with the elements N and P is in respect of NO,-N that may accumulate in excess in some leaf crops and in waters to be used for drinking.

318

R. A.

OLSON

Phosphorus is quite unlikely to concentrate in food crops to a toxic level even when applied as fertilizer at rates far in excess of that which is economic. Nor does the element penetrate significantly below the point of its placement as fertilizer in most soils due to its strong adsorption by soil colloids and its conversion to low-solubility forms within the soil system. Any N compound applied as fertilizer, however, is likely to be oxidized ultimately to the NO,-N form by natural soil processes prior to its absorption by plants. Nitrates being highly soluble will move in the direction of water flux, and along with excessive water percolation may escape the rooting zone and ultimately reach the groundwater below. When concentration of such waters reaches the level of 10 ppm NO,-N they are regarded hazardous for human consumption by public health authorities. Especially is there danger of methemoglobinemia to the very young infant supplied this water, with similar hazards existing for adults and for animals at higher levels. Very high levels of unassimilated NO,-N have been found in some of the leaf crops like spinach accompanying heavy rates of N fertilization. Processing of such products into baby foods and ultimate consumption by babies, especially in households with limited refrigeration, has given rise to severe circulation troubles and methemoglobinemia of the infants (Schupan, 1972). The probability exists also that concentrations of NO,-N and NO,-N in food materials may interact with secondary amine compounds in a way to produce nitrosamines, which are known to have possible carcinogenic, teratogenic, and mutagenic properties (Anonymous, 1972). There is very good reason, therefore, to maintain surveillance over NO,-N accumulation in certain food crops beyond the usually ascertained most-economic fertilizer rate for yield response. Care must also be exercised in the pasturing of animals on the stalks of plants that have been killed prematurely by drought or freezing because of potentially excessive NO,-N content of the forage. Nebraska studies on groundwater NO,-N accumulation suggest that irrigation extensity and the amount of fertilizer used are significant causative factors (Table 3). Cattle density seems to have some small influence, but there is little or no impact of human population density. A major passive factor is the clay content of soil material above the water table; the more clay, the less NO,-N in the water, and conversely. Also, the shallower the water table, the more NO,-N is likely to be found in the groundwater. These correlations do not explain a major portion of the variability, presumably in part because the agricultural statistics with which the individual irrigation well water NO,-N values are equated exist only on a gross county basis, while the water under a specific farm is characteristic of that precise locality. Even more important are the highly intangible factors of varied geologic NO,-N in the mantlerock above the water table and the amounts of NO,-N that have been in transit to the groundwater from decay of surface soil organic matter since the time of native sod breaking. In any case, there does appear to be rather strong evidence that fertilizer N is at least contributing to the groundwater NO,-N accumulation. Nitrate in groundwater in Nebraska has been increasing during the past 10 years. A series of 480 irrigation wells sampled during the peak of the irrigation season in 196 l1962 was again sampled in 1971-1972 and analyzed for several nutrient components. As would be expected, there was no perceptible change in soluble phosphate of the

FERTILIZERS

FOR

FOOD

319

PRODUCTION

TABLE 3 CORRELATION BETWEEN NO,-N CONTENTS OF NEBRASKA GROUNDWATERS AND SEVERAL FACTORS THAT MAY HAVE

CONTRIBUTED~

Independentvariable

r Value

1. Soil profileclay content 2. Irrigation welldeqSity 3. Total fertilizer use 4. Irrigation welldepth 5. Water pH 6. Cattledensity 7. Humandensity

-0.49’1 0.43** 0.28** -0.28** -O-23* 0.18* -0.06

(1Nitrate in water obtained from 480 irrigation wells correlated with countywide statistics, except for items 4 and 5, which were specific to the respective sites. * Significant. ** Highly significant.

groundwater in the lo-year period, but NO,-N increased an average 24%, as reported in Table 4. This average increase would not be particularly alarming, since upwards

of 100 years would be required to bring the average up to 10 ppm in view of the low starting level. There are, however, specific counties, as elaborated in this table, in which

the rate of increase has been notably greater, and at least one (Merrick) has reached a quite unacceptable county-wide level. A deep drilling program was inaugurated to follow the transit of nutrient N and P toward the water table under varied ecosystems in Nebraska. The most significant TABLE 4 CHANGES IN NO,-N CONCENTRATION OF NEBRASKA GROUNDWATERS DURING THE IO-YEAR PERIOD 1961-1962TO 1971-1972”

County Deuel Holt Merrick Seward Furnas Keith 47 Counties

Irrigation wellwaters sampled (No.) 9 5 37 23 9 10

480

AverageNO,-N concentration(ppm) 1961-1962

1971-1972

3.28 2.06 8.70 1.90 2.54 2.64 2.53

4.64 6.48 11.10 3.67 3.50 3.63 3.13

Net change (%I +41 215

28 93 38 38 24

a The same wells were sampled in 1961-1962 as in 1971-1972, all during the peak of the irrigation season.

320

R. A. OLSON

revelations have been the following: (a) P movement downward is nil; (b) mineral N accumulates in the deep mantlerock from land cultivation even without fertilization compared with native range, the native soil organic matter by its mineralization after sod breaking contributing NO,-N that leaches beyond the root zone; (c) irrigation of fine-textured soils causes limited NO,-N movement beyond the rooting zone with apparent implication of denitrification, but substantial NO,-N is found throughout the mantlerock above the water table under irrigated sandy soils; (d) lucerne is a good scavenger for NO,-N that has accumulated below the normal annual crop’s rooting zone, at least to 10-12 m under favorable conditions of moisture and soil physical properties; and (e) there are local vast deposits of geologic NO,-N in the mantlerock below the rooting zone that have major pollution potential with irrigation development. One 26,000-km* area of deep loess deposit is estimated to have of the order of 26 x lo6 tons of NO,-N to a depth of 3 1 m. It exists presently in loess material that is essentially at the 15-bar moisture tension level and has a highly significant inverse relation with the fixed ammonia occurring in the loess. The deposit is found below a 5-m depth under native grassland that has never been fertilized and, as well, under land devoted to dryfarming agriculture for the past 70-100 years. Air contamination. A matter of remaining conjecture with N is related to the denitrification process in soil. In the event of substantially greater release of N,O from soils accompanying increased fertilizer N use, the possibility exists of gradual destruction of the ozone layer in the stratosphere that shields the earth’s surface from much of the ultraviolet light to which it would otherwise be exposed (CAST, 1976). Higher levels of exposure to this radiation could prove inimical to the welfare of plant, animal, and man and might even modify the climatic environment. It goes without saying that much research remains to be done on the nitrous oxide/ozone relationship as well as on fertilizer management practices to increase the efficiency of crop use of the element and to minimize N,O loss from the soil. Mineral resource depletion. Concern has been expressed about certain of the world’s mineral resources that are being consumed at an accelerating rate with fertilizer manufacture. The primary apprehension is with the phosphate rock resource, of which some geologists have suggested there is no more than a loo-year supply. Phosphorus is an absolutely essential element to all life processes and its disappearance would be catastrophic. However, the world is known to have extensive deposits of low-purity rock phosphate not economic to mine at the present time which will eventually become viable. Furthermore, there are undoubtedly major deposits not yet discovered that will one day become source material for the fertilizer industry. Nitrogen fortunately exists in essentially unlimited quantities in the atmosphere and is being continuously replenished by plant and animal residue decay in the rhizosphere. The primary problem with it, as elaborated before, is the large amount of energy required in its fixation from the elemental state. Plentiful supplies of the other known essential elements of plant nutrition apparently exist in the earth’s lithosphere. Moreover, a considerable proportion of the nutrients applied as fertilizer is not immediately used and rather accumulates in the soil, and a substantial part of that actually utilized by crops is returned to the soil as crop residue for recycling. Thus we can find little with which to be greatly concerned in respect to mineral raw material depletion from fertilizer production.

FERTILIZERS

SOME

ALTERNATIVES

TO THE

FOR

FOOD

321

PRODUCTION

FOOD-ENERGY-ENVIRONMENT

DILEMMA

There are alternatives for adjusting somewhat to the serious problems that have been posed here. Certainly mankind has mistreated the world’s environmental systems and has continuously accelerated the rate of fossil fuel consumption as though it were an infinite resource. Perhaps even most serious of all is that human population growth continues in geometric proportions with calamatous prospects of famine for the future. Agriculture is strained to its present capacity in feeding the world’s four billions in 1974. In consideration of the vagaries of weather with attendant periodic lost production due to drought, frost, etc., in major regions, together with the recognized energy problem, the projected seven billions in the year 2000 can hardly be expected to enjoy an acceptable quality of life. Who can be so optimistic as to believe that the world’s limited soil, water, and energy resources can withstand such a burden? Utilization of Organic Wastes The current world shortage of fertilizers could be alleviated significantly by full use as fertilizer of those acceptable organic wastes that are now disposed of in the most convenient way possible. Certainly, all animal manures that can be recovered and that are not used for other purposes (like fuel for heating and cooking) should be used to the extent possible. The sewage of cities contains useful amounts of nutrients if it can be pasteurized to prevent spread of disease and if it is devoid of toxic quantities of the heavy metals coming from various industries. And, of course, the return of all crop residues to the soil essentially assures the amount of nutrients needed for the next crop’s vegetative parts. It goes without saying that there is an economic limit in distance to which organic wastes can be transported to serve as fertilizer since the bulk is great for supplying a given unit of nutrient. In the case of major sites of organic waste accumulation like cities and large feedlots, a possibly more feasible procedure would be the conversion of the waste to methane gas and methyl alcohol (Reed and Lerner, 1973) or oil (Steffgen, 1974) and the subsequent utilization of these materials as energy source. Not only would the aesthetic appearance of streams and lakes be enhanced by halting the disposal of such wastes in them, but the by-products so produced would serve as a valuable supplement to the declining supply of fossil fuel energy. It has been suggested, for example, that conversion of crop and forest product residues to fuel energy would take care of 5-10% of the total energy requirement of Australia (Gifford, 1973). Another calculation suggests that 50% of the fossil fuel energy that now goes into electricity production in the United States could be derived from conversion of its billions of tons of recoverable organic wastes into oil (Steffgen, 1974). Caution must be exercised, however, on the extent to which crop residues could be used for this purpose in view of the significant role they serve in feeding soil organisms that assist in maintaining satisfactory soil structure and in consideration of the potential plant nutrients removed. Increased Symbiotic N Fixation Increased legume production will indeed alleviate the present critical world N shortage. Many of the grain legumes like soybeans when properly inoculated are

322

R. A. OLSON

capable of fixing much if not all of the N required by the crop, thus eliminating the fertilizer N requirements of such fields. Of additional benefit is the fact that significantly more food protein, a serious dietary deficiency in many regions, is produced. Unfortunately, grain legumes do not approach the quantity of food calories that can be produced per unit land area by cereals, such that a backward step results in total quantity of food calories with substitution of grain legume for cereal. A traditional method for increasing available soil N levels has been the production of green manure legumes. This procedure normally involved growth of the legume through a season to accomplish a substantial amount of vegetative growth and commensurate N fixation followed by plowing it under and allowing the proteinaceous top and root residues to supply N through microbial nitrification for the subsequent crop. This procedure unfortunately gives little promise for the current tight world food situation since land is tied up growing the legume that might otherwise be producing food grain. An alternative for getting around the problem is to seed the legume into an existing crop as it approaches maturity and obtain as much growth as possible prior to seeding the next crop. Obviously, such a procedure can work only with an assured plentiful moisture sup& since the green manure crop will extract substantial soil water in making its growth. Because of their high water requirement green manure legumes, however managed, have virtually no place in dry farming regions. A matter of utmost interest today is the possibility of achieving significant amounts of N fixation through symbiosis in the cereal grains as has been found to occur in tropical grasses (Dobereiner and Day, 1974). Were it possible to inoculate seed with the appropriate organism (Spirillum or other genus) and achieve fixation of but 10% of the crop’s N needs, there would be no world shortage of this critical fertilizer nutrient today. Major efforts would appear to be warranted toward selection and breeding of crop varieties and selection of efficient strains of organisms capable of N fixation with joint compatibility for the desired symbiotic relationship. Nitrogen supplementation from this source would not necessarily alleviate the nitrate pollution hazard but could be highly significant from the economic standpoint. More eflcient utilization of fertilizers. Significant improvement can be achieved in the efficiency with which fertilizers are used by farmers, thereby reducing rates applied and ultimately the energy requirement per hectare in crop production. When fertilizers were still cheap in the late 196Os, it is not surprising that farmers in highly developed agricultural regions used fertilizers at rather excessive rates as an insurance measure to be sure there was enough of the particular nutrient. Data from Nebraska indicate that approximately 45% more N as fertilizer was being applied than removed in crops in 1968 (Fig. 3). Such practice disregards the native N delivery capacity of soils and the amounts of N added with rainfall and nonsymbiotic fixation and, furthermore, has pollution implications. There is increasing agreement among world agronomists that rate of applied nutrient for any given crop must be adjusted to the soil’s nutrient supply at planting, including the residual from previous years’ fertilizer treatments. The residual mineral N in soil as an indicator of required fertilizer N rate for optimum yield of winter wheat in Nebraska is clearly depicted in Fig. 4. Note that for the fallow-wheat cropping region of semiarid climate 67 kg/ha of supplemental N was needed where soils had <45 kg/ha of residual mineral N in the 180-cm rooting profile, but only 45 kg of N was needed with 45-90 kg

FERTILIZERS

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Replaced ___. 100% -...-.--.-...J

_-.

-

FIG. 3. Fertilizer N, P,O,, and K,O used in Nebraska as a percentage of the nutrients harvested in all crops of the state, 1952-1972.

of residual, and only 22 kg of N with 90-135 kg of residual. With > 135 kg of N residual the trend was one of yield depression for applied fertilizer N! How foolish if all of these 74 fields had had applied to them a uniform 60 kg of N as fertilizer by the

fALLOW

WHEAT

E

+

,-(IO)

10

I /c

eo

/

bi /

=4e 2

9 ---,---------Y(g,)

L 0

tt N

48

ACCLICO,

N~,“A

a7

I 0

46 N

a0 ACCLILD,

I55 N4,“A

lb0

t*

FIG. 4. Yield and protein response of winter wheat after fallow and irrigated maize to increasing rates of fertilizer N as influenced by the residual NO,-N in the 180~cm profile at planting time in Nebraska field experiments of 1962-1968. (*Number of field experiments: a total of 74 on wheat and 17 on irrigated maize.)

324

R.

A.

OLSON

respective farmers. The other half of the figure indicates that the principle applies as well to irrigated maize production, although larger amounts of N are required for achieving the higher yield potential of this crop than are needed for wheat after fallow. The protein percentage of both crops continued to increase in a straight-line function with increasing N rate across all residual levels beyond the N required for maximum yield. Farmers are not commonly reimbursed for elevated protein, nor is the quality of the protein likely to be as high as that in the crop produced with less N fertilizer. Accordingly, it is not economically feasible to program the higher N rates for protein yield enhancement at the present time.

45

PO kg NITRCGEX/

180 ha

FIG. 5. Yield response of irrigated maize to fertilizer N as influenced by rate and time of application (economic analysis based on 1965 prices, but a plot with 1974 prices would be proportionate; average of 14 experiments).

Conservation of fertilizer nutrients can be realized by adjustments in time of application in certain cases. Whereas the nonmobile nutrients like P, Mg, and K must be applied at planting or before to assure their presence in the seedling root zone, the usual N materials are most efficiently utilized by annual row crops with the bulk applied as a midseason side-dressing just prior to the crop’s heavy demand for the element (Olson et al., 1964). In the 14 irrigated experiments shown in Fig. 5, it can be seen that 90 kg of N as a midseason side-dressing gave equal economic return to 180 kg applied before planting. The residual mineral N in the soil rooting zone after a few years of such treatment is also greater than that where planting time applications were made (Herron et al., 1971). Nitrogen conservancy so recorded is the result of an established root system being present that reduces leaching potential and lessens the time of opportunity for ammonia volatilization and denitrification losses to occur. For effecting the economy that this procedure will permit on at least a modest percentage of the land area so concerned, some reversal in the trend toward bulk-blend and spread operation popularized in the 1960s as a labor-conserving measure will be necessitated. The method of application and placement of fertilizers can influence both losses and the etIiciency with which fertilizer is used and thus have bearing on the most-economic

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rate of application. For example: (1) With soils only slightly deficient in P, only about one-half as much material is required for optimum yield when row applied as when broadcast; (2) urea must be incorporated immediately to minimize potential for ammonia volatilization loss, especially with alkaline soils; (3) anhydrous ammonia must be injected to depths dictated by shank spacing, soil moisture, and clay content; (4) a small amount of ammonium ion applied in association with fertilizer P enhances crop utilization of the latter; (5) no significant quantity of ammonia or of solid materials with high salt indexes should be placed in close proximity to seed because of likely germination inhibition, etc. Nitrogen balance studies have commonly shown little more than 50-60% utilization of the applied material in the crop grown (Allison, 1955). Clearly, much remains to be learned concerning the efficient use of N fertilizers, from the standpoints of both deriving maximum crop utilization to maximize economic return and restricting the amount escaping the root zone to prevent its becoming a potential environmental pollutant (IAEA, 1974). It is for the purpose of deriving a more comprehensive understanding of this issue that a cooperative nitrogen residues program has been activated between the GSF of the Federal Republic of Germany and the Joint FAO/IAEA Division, which is largely financed by the German Government. Work will be carried out under varied environmental conditions by institutes within the FRG, in developing countries and at the Seibersdorf Laboratory of the IAEA, during the coming 5 years for seeking out the missing links. Electrolytic hydrogen production. A substantial savings in fossil fuel energy may become possible with the production of H, gas for NH, synthesis by the use of electrical energy for electrolysis of water in place of the conventional natural gas or other fossil fuel source of H,. Much of the production of the H, would come during off-peak periods of electrical demand, an alternative that would be especially attractive with nuclear power reactors (Stout, 1974), which should not be reduced from full operating power and increased again in short-time intervals. Other. A number of other modifications can be made in production agriculture that will have limited impact on fertilizer economy but will impart a major reduction in energy requirement compared with conventional practice. One of the most significant innovations is that of the till-plant system, especially where it effects herbicide and pesticide application and any required starter fertilizer treatment simultaneously. This process can eliminate four to six of the conventional trips over the soil surface with heavy equipment, in the process minimizing soil compaction and conserving substantial fuel energy. REFERENCES ALLISON, F. E. (1955). The enigma of soil nitrogen balance sheets.Aduan. Agron. 7,213-250. ANONYMOUS (1972). Accumulation of nitrate. U.S. National Academy of Sciences, Washington D.C. ANONYMOUS(1974). World nitrogen fertilizer market outlook. T.V.A. Circ. Z-50. CAST (1976). Effect of increased nitrogen fixation on stratosphere ozone. Council for Agricultural Science and Technology Report No. 53. Department of Agronomy, Iowa State University, Ames. DOBEREINER, J., AND DAY, J. M. (1974). Associations of nitrogen fixing bacteria with roots of grass species. Latin American Wheat Conference, Embrapa-Fecotrigo-USAID, Port0 Alegre, Brazil. FAO (1973). Effects of intensive fertilizer use on the human environment. Soils Bull. 16, FAO. FETH, J. H. (1966). Nitrogen compounds in natural waters-A review. B’&er Resow. Res. 241-58.

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GIPFORD, R. M. (1973). Energy, food and agriculture. CSZRO Annu. Rep. Plant. Industry. HARRE, E. A., GARMAN, W. H., AND WHITE, W. C. (1971). The world fertilizer market. In Fertilizer Technology and Use (R. A. Olson et al., eds.). Soil Science Society of America, Madison, Wis. HERRON, G. M., Drumsa, A. F., FLOW~RDAY, A. D., COLVILLE, W. L., AND OLSON, R. A. (1971). Residual mineral N accumulation in soil and its utilization by irrigated corn (ZeQ mays L.). Agron. J. 63, 322-327. IAEA (1974). Effects of agricultural production on nitrates in food and water with particular reference to isotope studies. Panel Proceedings Series, IAEA, Vienna. JAAG, 0. (1972). The main sources of eutrophication of inland waters with special reference to the comparative magnitudes of pollution sources. Soils Bull. 16,235-287, FAO. MUIR, J., SEIM, E. C., AND OLSON, R. A. (1973). A study of factors influencing the nitrogen and phosphorus contents of Nebraska waters. J. Environ. QuQZ. 2,466-470. ODIN, S. (1972). The extent and effects of atmospheric pollution on soils. Soils Bull. 16, 179-194, FAO. OLSON, R. A. (1970). The fertilizer programme of the Freedom from Hunger Campaign. In Change in Agriculture (A. H. Bunting, ed.), pp. 599-605. Gerald Duckworth, London. OLSON, R.A., DREIER, A. F., THOMPSON, C., FRANK, K., AND GRABOUSKI, P. H. (1964). Using fertilizer nitrogen effectively on gram crops. Station Bulletin 479. Nebraska Agricultural Experiment Station. PIMENTEL, DAVID, HURD, L. E., BELLOTTI, A. C., FORSTER, M. J., OKA, I. N., SHOLES, 0. D., AND WHITMAN, R. J. (1973). Food production and the energy crisis. Science 182,443-449. REED, T. B., AND LERNER, R. M. (1973). Methanol: A versatile fuel for immediate use. Science 185 12991304. SCHUPAN,W. (1972). Effects of the application of inorganic and organic manures on the market quality and on the biological value of agricultural products. Soils Bull. 16, 1’98-224, FAO. STEFFGEN,F. W. (1974). Energy from agricultural products. Amer. Sot. Agron. Spec. Pub. X2,23-35. STOUT, P. R. (1974). Agriculture’s energy requirements. Amer. Sac. Agron. Spec. Pub. Z&13-22. VIEYS,F. G., JR. (1971). Water quality in relation to farm use of fetilizer. Bio-Science 21,460-467.