...population.

About the human driving forces changing land use, Meyer and Turner wrote, ``The role given to population ... reflects less conflicting evidence than conflicting interpretations of the same evidence." They nevertheless examined multiplicity of causes and the difficulty of proof fairly (Meyer and Turner, 1992,citeMeyer:92 51-56).

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...1990[#USDC:90##1#]

The scale of $55 billion total or $232/ca can be discerned by comparison to per capita expenditures of $141 for reading; $306 for alcoholic beverages; $371 for television, radios, and sound equipment; and $3,477 for food.

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...(1982[#Higgins:82##1#])

They cite the following nonagricultural  uses of hectare land per capita, location, and authorities:

The very low values found by Hyde et al. (1980) were ``potentially cultivable land occupied by habitation."

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...11).

Per ha the yield of carp and catfish range from 350 to 5,000 kg during the six-month growing season of the Gulf Coast; because production depends on feed, area yields have little meaning. Lovell (pers. com., 1993) reported that feed conversion is consistent among species but varies with diet. Feed conversion ratios have changed little with time.

During 1989-1991, 80 million t fish were captured from oceans, 7 captured inland, and 12 cultured. (The contribution of fish can be judged by comparing it with the production of 179 million t of meat by agriculture in 1991.) The FAO opines that the total of captured fish can only be maintained, not increased. On the other hand, the FAO believes the slowing of the expansion of aquaculture, which was rapid from 1984-1990, is temporary and prospects for expansion of marine aquaculture are good (Food and Agriculture Organization of the United Nations, 1993,[FotUN93] 187).

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...soybeans.

Nutrients in the edible portion of food as purchased (Watt and Merrill. 1963[WM63])

The 3,500 cal/ca that the 1991 grain and oilseed would provide the present 5.3 billion people of the world exceed the 2,697 cal that the FAO estimates reach consumers in food because, among other things, my calculation shares no calories with animals or manufacturing. Similarly, the protein in all the grain and oilseeds today would provide an average 123 g/day to each of the present 5.3 billion people of the world, exceeding the 71 g that reaches them according to the FAO.

A few words about units and conversions help relate diet to crop yield. People commonly think of dietary requirements in cal/day and yields in kg/yr. If for easy figuring I use 3,650 cal/kg as an approximate caloric content of grain, then a person's annual or 365-day requirement in kg equals one-tenth their daily consumption in calories. 8o 2,000 to 4,000 cal/day/ca equals 200 to 400 kg grain/yr/ca. And a grain yield of 2 t/ha would support ten people with the slim diet of 2,000 cal/day whereas a yield of 4 t/ha would support the ten with the abundance of 4,000 cal/day.

Pursuing conversions further and using 4,000 cal/kg, I note that the 1,927 million t of grain and oilseeds produced by the world's farmers in 1991 contained 8 quadrillion cal, an astronomical quantity that can be expressed as 8,000 tera or 8 peta cal.

Lest the astronomical number suggest that humanity is gobbling up the global biomass, I compare the energy content of the world crop of grain and oilseeds with all the photosynthesis on the planet's land. The biota on land takes in 110 billion t of carbon (Moore and Bolin, 1986[MB86]). Because the carbohydrate of a plant is about twice its carbon, I assign a content of 8,000 cal to each kg of carbon. Then the annual intake of carbon into biomass is about 800 peta cal, fully 100 times the calories in the grain and oilseed crop.

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...1993a[#Parikh:93a##1#]).

Parikh estimated quantities of cereal, meat, dairy products, other animal products, protein feeds, oils and fats, and sugar. I transformed quantities of produce for his Medium Population-Low Growth scenario, using energy and protein contents from Appendix A. Assuming meat, dairy, and other animal products would be produced from the crops, I omitted them to avoid double counting. I lumped the other categories like oils and fats in the single category crops.

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...(1993[#Seckler:93##1#])

I analyzed the world disappearance (carryover for year 1 + production in year 2 - carryover in year 2) of cereals and oilseeds (U.8. Department of Agriculture, 1993). From 1960-1973, disappearance rose exponentially at 4.3% per year; from 1978-1991, however, it rose only linearly at 32.6 Mt per year.

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...years)[#USDA:62##1#]

The book for 1972 tabulates the annual diet from 1909 to 1970. Changing production also gives clues to changes in diet. For example, during the 17 years from 1975 to 1992, the quantity of catfish processed increased about 20% per year, an astounding rise indicating a change in diet. Data from Mike Barker, National Agricultural Statistics Service, USDA.

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...Asia

Several lines of evidence of wheat consumption gaining on that of rice in Asia are cited by Crosson and Anderson (1992,[CA92] 7-9).

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...spectacularly.

Heilig (1993[Hei93]) emphasizes that ``The carrying capacity of the earth is not a natural constant-it is a dynamic equilibrium, essentially determined by human action. Removing constraints, farmers overwhelm soil inventories that do not distinguish between serious soil constraints and simple ones removable by management. Heilig emphasizes his point with the example of Indian farmers.

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...maize.

. For wheat, ; and for maize, .

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...mm/day.

See observation by Arkin et al. in Figure 13-1 in Stewart and Nielson (1990[SN90]).

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...half.

See observations of wheat by Cole and Mathews and of sorghum by Slabbers et al. in Figure 14-4 and 14-5 in Stewart and Nielson (1990[SN90]).

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...efficiency.

An FAO handbook encapsulates agronomic and engineering experience with many crops in relative decreases in yield per decrease in water: Doorenbos and Kassam (1986[DK86]). The handbook tabulates yield response factors ky, a high ky reflecting a crop sensitive to drought. Table 24 of the handbook shows ky larger for maize than wheat, and ky larger for wheat than sorghum. Let yield be y, ET be evapotranspiration, m denote the maxima. Then

Although practical for planning irrigation, the equation concerns relative yield and relative evapotranspiration. It does not, therefore, serve my purpose of calculating absolute values.

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...figures.

Peixoto and Oort's (1992[PO92], 271) value of agrees with Eagleson's 410 mm evaporation: ( evaporation) divided by (, or 410 mm evaporation. Eagleson shows 720 mm for average precipitation on land (Eagleson, 1970[Eag70], 7).

The estimate of flux of carbon into biota on the land is from Moore and Bolin (1986[MB86]).

Another check on consistency is comparing the 1 to 6 g biomass/kg evaporation to the high yields of 20 to 45 t biomass/ha used to explore the limitation of solar energy. If the ratio of biomass to evaporation is then the corresponding evaporation is (20 to 45 t)/( )/( t biomass/ water).

Compared with the average precipitation of 720 and evaporation of 410 mm given by Eagleson, these estimates of 500 to 1,100 mm of evaporation are high, corresponding to high yields.

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...envisioned.

The yield produced by 410 mm of evaporation: (0.41 m evaporation) () (1 t/) (0.004 t biomass/t water) = 16 t/ha. The earth's 13 billion ha of land would produce 208 billion t of biomass or about 100 billion t of cereal. Because cereal contains about 4,000 cal/kg, a diet of 3,000 cal/day requires about one quarter ton of cereal per year. Although other values of parameters produce other estimates, the order of magnitude seems clear: 100 billion t times 4 people per t means that the global water supply for crops places a ceiling at feeding about 400 billion.

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...use.

In Iowa, nitrogen rate for corn rose to about 160 kg/ha in 1985 but then declined. In Illinois, the rate continued to rise. Iowa's yields, however, have kept in step with those of Illinois and the region, too (Hallberg et al., 1991[HCC91]).

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...1.5%

Rates calculated from areas, populations, and food supply tabulated in Food and Agriculture Organization of the United Nations (1992[FotUN]).

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...attained.

Maintenance research encompasses coping with physical changes like salinization, economic adjustments as to rising price of water relative to crops, and biological surprises like the appearance of more virulent pests. The relation between aggregate resource productivity in the United States and other factors suggests that most recent expenditures on research and extension went to maintain productivity (Blakeslee, 1987[Min87], 67-83).

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...equation

The logistic equation is attributed to Pierre-Francois Verhulst, who called the equation logistic in 1845 in a mathematical paper about the increase of population. Hutchinson explained the equation in clear words. In beguiling footnotes, he recounted its history and related it to people from William of Ockham and Thomas Malthus down to A. J. Lotka and R. Pearl (Hutchinson, 1978[Hut78]).

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...1980[#Mitchell:80##1#])

Recent statistics from Food and Agriculture Organization of the United Nations Year Books.

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...1-7)

The likelihood that pest control will lead the parade of practical biotechnology is seconded by Fraley (1992[Fra92]). Expenditures on research and the distance from fundamental discovery to actuality are reported by Hodgson (1992[Hod92]).

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...1991[#Ruttan:91##1#])

A European move to keep bovine hormone off the market and reduce surplus was reported by Aldous (1993[Ald93]).

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...peak.

Expenditures and budget 1972-1994 furnished by Ralph Cummings, Jr., U.S. Agency for International Development and adjusted to 1983 dollars by the U.S. consumer price index.

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...(1985[#Hayami:85##1#])

The accompanying figure is copied from Council for Agricultural Science and Technology (1992[fAST92]). Since publication about induced innovation in 1971, its importance has become clear, and naturally its precise meaning and validity have been debated; the debate of a score of years was recently reviewed by Hayami and Ruttan (1993[HR93]).

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...agriculture.

Irrigated area is reported in the FAO production Year Books. The area purposely is provided with water, including land irrigated by controlled flooding. The area is counted only once whether it is irrigated once or several times during the year or grows multiple crops. Beginning in the 1978 Year Book, a consistent series is reported; inconsistently large areas were reported before 1978. 1 copied the 1961 area, which seems consistent with later FAO areas, from a citation of Higgins et al. (1987[HDA87]). In the Last Oasis, Postel called the FAO areas net irrigated area. Somewhat wider areas have been reported by Rangeley as gross irrigated area, which may include areas within irrigation projects and may be increased to acknowledge double cropping (Rangeley, 1987[Ran87]). The FAO and Rangeley areas were compared by Jensen et al. (1990[JRD90]). I have discussed the comparison with M. E. Jensen in person.

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...51)

Lester Brown emphasized the area per capita in Brown (1993[Bro93]).

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...(1990[#WB:90##1#])

Cited by Crosson and Anderson (1992[CA92]).

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...efficiency.

I show the role of the threshold in water use efficiency WUE in the terms used to analyze Figure 6.3.2 and estimate the g grain produced per kg of water. The yields y can be represented as a function of evapotranspiration ET and a threshold :

Because WUE is the ratio of yield y to evapotranspiration ET,

As expected, increasing b, grain produced per water consumed, raises WUE so long as . A higher ET and a lower threshold cause b to lift WUE more.

The unexpected, however, lies in greater evapotranspiration improving water use efficiency. The derivative of WUE w.r.t. ET is positive: . If is zero, WUE equals b regardless of ET. But if is not zero, higher ET increases WUE until . The thresholds in Figure 6.3.2 make water use more efficient when ET loss is greater. The causes of the paradox lie first in the relation of yield to ET, , and then in the threshold .

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...wind

``Take a straw and throw it up into the air,-you may see by that which way the wind is." (Selden, 1689[Sel89])

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...1992[#Rabbinge:92##1#])

Their names for scenarios and my mnemonics are: A = Trade, B = Employ, C = Nature, D = Biocide. Robert Sevenhuysen's lecture at the First International Seminar on Agribusiness (Integer, Monterrey, Mexico, 1 July 1993) prompted me to use the Dutch scenarios.

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...instinct

The title of a book shows the feet of clay: The Experts Speak: The Definitive Compendium of Authoritative Misinformation (Cerf and Navasky, 1984[CN84]).

When the U.S. president appointed distinguished scientists and engineers to report on technology that would matter to the nation during coming decades, they missed antibiotics, radar, rockets, space exploration, and jet engine aircraft. ``In fact, if you were to ask what were the exciting things that happened over the next several decades, they missed all of them, every one." (Townes, 1991[Tow91], 17)

I copied my table of bloopers during the last century from a table compiled by Ausubel (1993[Aus93]).

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...clothes

Although I don't have the reference, I recall Winston Churchill wrote something like this.

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...decade

I could refer to Sports Illustrated, the Intergovernmental Panel on Climate Change, and the National Research Council.

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