Over geologic time spans, water passing through soil leaches or removes plant nutrients. In climates where there is barely enough rain to grow cereal crops, soils retain their minerals and the food produced there tends to be highly nutritious. In verdant, rainy climates the soil is leached of plant nutrients and the food grown there is much less nutritious. That's why the great healthy herds of animals were found on scrubby, semi-arid grasslands like the American prairies; in comparison, lush forests carry far lower quantities of animal biomass.
Some plant nutrients are much more easily leached out than others. The first valuable mineral to go is calcium. Semi-arid soils usually still retain large quantities of calcium. The nutrient most resistant to leaching is potassium. Leached out forest soils usually still retain relatively large amounts of potassium. William Albrecht observed this data and connected with it a number of fairly obvious and vital changes in plant nutritional qualities that are caused by these differences in soil fertility. However obvious they may be, Albrecht's work was not considered politically correct by his peers or the interest groups that supported agricultural research during the mid-twentieth century and his contributions have been largely ignored. Worse, his ideas did not quite fit with the ideological preconceptions of J.l. Rodale, so organic gardeners and farmers are also ignorant of Albrecht's wisdom.
Albrecht would probably have approved of the following chart that expresses the essential qualities of dryland and humid soils.
Soil Mineral Content by Climate Area
Plant Nutrient Dryland Prairie Soil Humid Forest Soil nitrogen high low phosphorus high low potassium high moderately high calcium very high low pH neutral acid
Dryland soils contain far higher levels of all minerals than leached soils. But Albrecht speculated that the key difference between these soils is the _ratio _of calcium to potassium. In dryland soils there is much more calcium in the soil than there is potassium while in wetter soils there is as much or more potassium than calcium. To test his theory he grew some soybeans in pots. One pot had soil with a high amount of calcium relative to the amount of potassium, imitating dryland prairie soil. The other pot had just as much calcium but had more potassium, giving it a ratio similar to a high quality farm soil in the eastern United States. Both soils grew good-looking samples of soybean plants, but when they were analyzed for nutritional content they proved to be quite different.
Soil Yield Calories Protein Calcium Phosphorus Potassium
Humid 17.8 gm High 13% 0.27% 0.14% 2.15%
Dryland 14.7 gm Medium 17% 0.74% 0.25% 1.01%
The potassium-fortified soil gave a 25 percent higher bulk yield but the soybeans contained 25 percent less protein. The consumer of those plants would have to burn off approximately 30 percent more carbohydrates to obtain the same amount of vital amino acids essential to all bodily functions. Wet-soil plants also contain only one-third as much calcium, an essential nutrient, whose lack over several generations causes gradual reduction of skeletal size and dental deterioration. They also contain only half as much phosphorus, another essential nutrient. Their oversupply of potassium is not needed; humans eating balanced diets usually excrete large quantities of unnecessary potassium in their urine.
Albrecht then analyzed dozens of samples of vegetation that came from both dryland soils and humid soils and noticed differences in them similar to the soybeans grown under controlled conditions. The next chart, showing the average composition of plant vegetation from the two different regions, is taken directly from Albrecht's research. The figures are averages of large numbers of plant samples, including many different food crops from each climate.
Average Nutritional Content by Climate