Agronomists take the eating habits of people as fixed and given and raise the yields of the given crops. Diets do change, however, as I have shown for the United States. So going beyond raising the yields of given crops by breeding and management, I shall examine the ability of different species of plants to spare more land for Nature by sustaining more people on a given land area.
The title of Seeds of Change (Hobhouse, 1986[Hob86]) dramatizes and the yardstick of agricultural progress in Table B-1 in Appendix B measures how discoveries and swapping of species during the Age of Exploration revolutionized agriculture and humanity's diet. The introduction of the potato into Ireland exemplifies such change.
Although the tragedy of the Irish Famine obscures this fact, the potato helped the Irish greatly.
The potato, provided it did not fail, enabled great quantities of food to be produced at a trifling cost from a small plot of ground. Sub-division [of the land] could never have taken place without the potato: an acre and a half would provide a family of four to six with food for twelve months, while to grow the equivalent grain required an acreage four to six times as large and some knowledge of tillage as well. Only a spade was needed for the primitive method of potato culture usually practised in Ireland. Trenches were dug and beds--called ``lazy beds"--made; the potato sets were laid on the ground and earthed up from the trenches; when the shoots appeared, they were earthed up again. This method, regarded by the English with contempt, was in fact admirably suited to the moist soil of Ireland. (Woodham-Smith, 1980[WS80], 29-30; 35)
About 1780, the population of Ireland burgeoned, and the rise from 1779 to 1841 has been placed at the astounding figure of 179%. Woodham-Smith wrote that first among the factors favoring the increase was ``an abundant supply of incredibly cheap food, easily obtained, in the potato, and the standard of living of the time was such that a diet of potatoes was no great hardship. With the addition of milk or buttermilk potatoes form a scientifically satisfactory diet, as the physique of the pre-famine Irish proved." In 1841, the Irish numbered 8 to 9 million.
An Irish view in 1840 of a crop of the species Solanum tuberosum compared with a crop of a cereal like Triticum aestivum is reconstructed in Figure 7.5.1. A family of five could be sustained on about 4 million cal/yr. To produce the calories on an acre and one-half, or 0.6 ha, as Woodham-Smith wrote, would require a yield of 11 t/ha of potatoes containing 610 call kg. A contemporary wrote in 1845 that Irishmen grew 5 t of potatoes on a rood, or 0.1 ha (Large, 1940[Lar40], 23), but comparison with Woodham-Smith's report of 11 and modern yields less than 50 make the 1845 report of 50 t/ha iffy.
Figure 7.5.1. About 1840 and today, the calories and protein grown per hectare. The crops about 1840 were potato (spud) and wheat in Ireland reported by Woodham-Smith (W-S) and in Virginia (VA) reported by Jefferson. The 1990 yields were reported by FAO for potato, wheat, and rice in Ireland (lRL), the United States, and Japan (J) (Edwards, 1943; Food and Agriculture Organization of the United Nations, 1992; Woodham-Smith, 1980). [Edw43][FotUN][WS80]
Woodham-Smith (1980[WS80]) wrote that compared with potatoes, `` ...the equivalent grain required an acreage four to six times as large." This implies a yield of 0.4 t/ha of wheat containing 3,300 callkg.
Thomas Jefferson's (Edwards, 1943[Edw43]) letters report yields in Virginia during the same era. In 1793, he wrote George Washington that small grain yielded 1.0 to 1.3 t/ha on good land. In 1795, Jefferson planted a measured acre of wheat and in his farm book recorded a yield of only 0.25 t/ha. In 1815, he modestly wrote Jean Baptiste Say, ``Our best farmers (such as Mr. Randolph, my son-in-law) get from [0.7 to 1.3 t/ha of wheat. ...Our worst (such as myself) from [0.4 to 1.2i, with little or more manuring." (Later I shall show that the average U.S. yield of wheat was 0.7 t/ha in 1869).
In his farm book in 1795, Jefferson recorded the respectable yield of 9 t/ha potatoes, near the 11 t/ha I inferred from Woodham-Smith's report of 1840 Ireland. In dry 1830, a farmer in Connecticut wrote that 3.4 t/ha was ``not half a crop" (Townshend, 1985[Tow85]).
The left of each pair of bars in Figure 7.5.1 depicts the energy or calories, and the right the protein per hectare. The height of the first pair of bars shows the advantage of the Solanum spp. over wheat, whether the Irish wheat estimated from Woodham-Smith's words or the Virginia wheat reported by Jefferson. Early in the nineteenth century, changing from grain to potatoes either supported more Irish on a rood of land or spared more roods for Nature.
Figure 7.5.1 also compares some modern crops. The yields of energy and protein are calculated from national average crop yields for 1990 (Food and Agriculture Organization of the United Nations, 1992[FotUN]). The great increase in productivity of potatoes in Ireland fulfills expectations. The productivity of 72 thousand ha of Irish wheat today, however, astounds. It exceeds any other national average. Its energy yield slightly exceeds that of the intensive crop of Japanese rice, and because wheat is richer in protein than rice, Irish wheat yields far more protein than does Japanese rice. Yields in Virginia today also show the relative rise in wheat compared with potato yields. In 1990, the average yield of wheat in Virginia was about 10 times Jefferson's 1795 yield on a measured acre, but the 1990 Virginia average for potatoes was only slightly more than twice Jefferson's 1795 yield.
Even in the nineteenth century, wheat gained on potato yields (Figure 7.5.2). National statistics (Mitchell, 1980[Mit80]) beginning in 1847 show area and production of wheat and potatoes in Ireland. Although these statistics show wheat and potatoes producing somewhat more calories than I inferred for Figure 7.5.1, potatoes nevertheless out-yielded wheat in 1847. By the end of the century, however, declining potato and rising wheat yields put wheat in front for many years. After falling behind, especially during World War II, Irish wheat began producing more energy per hectare than did Irish potatoes.
Figure 7.5.2. The changing advantages in energy yield of Irish potatoes and wheat (Food and Agriculture Organization of the United Nations, various years; Mitchell, 1980). [FotUN][Mit80]
The yields of other crops, too, fail to rise like the logistic curve in Figure 7.3.2. For example, the unchanging yield of Japanese rice recently has been emphasized (Holmes, 1993[Hol93]). The stubborn failure of yields to rise dooms, of course, any sparing land for Nature. In some cases, persistent research may succeed in lifting the ceiling now holding down yields of the species. In other cases, Figure 7.5.2 suggests changing species may be the way to feed more people without expanding cropland as population grows. The change could, of course, be to a combination that increased food production during a decade by multiplying the number of crops per time or alleviating a soil problem by rotation.
Changing crops can increase the number of people supported on a given cropland, and reversing the change can increase the number again.
The poor showing in Figure 7.5.1 of the average of the 28 million ha of modern American wheat makes the point that environment as well as species affects yield. In the nineteenth century, Irish wheat yielded more than American (Figure 7.5.3.). Although yield of Irish wheat exceeded that of French in the mid-nineteenth century, both increased somewhat and both exceeded that of American wheat by the end of the century. During the twentieth century, the gap between wheat yields in the two European nations and in the United States widened. Although farmers in some places in the United States grew high yields, weather held back others. Among the 50 United States and their diverse weather, average wheat yields varied almost fourfold in 1990. Environment, especially the unreliability of water in the American Wheat Belt, as well as species, affects yield.
Figure 7.5.3. The course of wheat yields in Ireland, France, and the United States (Edwards, 1943; Food and Agriculture Organization of the United Nations, 1992; Mitchell, 1980; Woodham-Smith, 1980). [Edw43][Mit80][FotUN][WS80]
In wet western Ireland, potato varieties of 1840 in lazy-beds beat grain, but for the national average, the wheat of 1990 beat modern potatoes. In America, likely because water limits wheat yields, the recent rise in wheat yields has been smaller than in Ireland. So changing human diets and crop species to match the era and place can increase the number of people sustained on a given area of land, saving more for Nature.