a growing rift in nutrient cycling: most of the nutrients from the soil, transported to cities in the form of foodstuffs, were not returned to the fields. As early as the mid-nineteenth century, Karl Marx described the consequences of such a rift in nutrient cycling:
Capitalist production, by collecting the population in great centers, and causing an ever increasing preponderance of town population … disturbs the circulation of matter between man and the soil, i.e., prevents the return to the soil of its elements consumed by man in the form of food and clothing; it therefore violates the conditions necessary to lasting fertility of the soil.6
Some seventy years after Marx published Capital, U.S. Secretary of Agriculture Henry Wallace wrote that society was pouring “fertility year after year into the cities, which in turn pour what they do not use into rivers and the ocean.”7 This was the first large-scale nutrient cycle rift.
A second rift in the cycling of nutrients developed in the mid-to-late twentieth century. With farm animals raised on large industrial farms far removed from the land that produced their food, crop soils lost large quantities of nutrients that were never replenished with manure. Thus farm products for both human consumption and animal feed, containing large quantities of nutrients removed from soils, are transported long distances from croplands to cities and factory farms. (See Figure 3.2.)
These rifts in the cycling of nutrients have led to the impoverishment of soils, while in cities huge quantities of nutrients accumulate as waste and sewage and as manure on factory farms. Simultaneously, the massive amounts of synthetic fertilizers that are brought in to replace the lost nutrients leach into groundwater and run off into lakes and rivers. This causes water eutrophication: huge algal blooms that deplete the oxygen when they decompose, creating giant low oxygen zones where rivers enter the ocean.
Most pronounced in the United States, the shift to raising beef cows in large feedlots was based on feeding them diets high in corn and soy to fatten them more quickly, shortening the time needed to get them to marketable weight so as to increase profits. But this means that less land is devoted to growing perennial crops for pasture or hay, once the near-exclusive diet of domestic ruminant farm animals. For a year or two following a productive legume or grass-legume hay crop, all the needed nitrogen for grains or vegetables can come from nitrogen stored in soil. Without legume forage crops in rotation, nitrogen fertilizers must be applied annually to supply that key nutrient to grow grains. Less land covered in perennial crops leads to an increase in other problems, such as accelerated runoff of rainfall and soil erosion.
The development and extensive use of synthetic fertilizers was a capitalist attempt to work around the massive loss of nutrients from agricultural soils. Most of the human waste in the cities of the developed world is chemically and biologically treated in sewage treatment plants, ensuring that relatively clean water is discharged back into rivers and oceans. It is estimated that half of the treated sewage sludge (referred to as “biosolids”) in the United States is used for landscaping and on farmland; the remainder is consigned to landfills. Farm fields are the logical destination for the nutrients in human sludge. However, use of sludge on farmlands is a highly questionable practice unless stringent actions are taken to reduce the potential toxic heavy metals and organic chemicals from industry and services such as healthcare (with its use of radioactive test materials), and the chemicals in household products before it is applied to soils.
Figure 3.2: Nutrient and Engergy Flows during Different Eras
Source: Modified from Fred Magdoff, Les Lanyon and Bill Liebhardt, “Nutrient Cycling, Transformation and Flows: Implications for a More Sustainable Agriculture,” Advances in Agronomy 60:1–73 (1997).
The “solutions” to the rupture of nutrient cycling result in their own problems. For example, the large quantity of fertilizer needed to replace the exported nutrients requires a lot of energy to manufacture (especially to produce nitrogen fertilizer) and damage to land and water occurs as phosphorus is mined and refined. With respect to phosphate, its continual application to agricultural soils is not possible indefinitely. By the end of the century, the currently known high-grade phosphorus deposits may be depleted.8
Use of inadequate rotations—either no rotation for a number of years or alternating between corn and soybeans—results in lower yields than would have occurred if the crops had been grown as part of the more complex rotation needed when farm animals and crops are raised on the same farm. Only about half of the applied nitrogen fertilizer is actually used by corn plants. A lot of excess fertilizer, therefore, remains in the soil at the end of the season, and much of it can leach out, causing stream and river pollution with nitrate (NO3−). According to the Environmental Protection Agency, “Forty-six percent of the nation’s river and stream length has high levels of phosphorus, and 41 percent has high levels of nitrogen…. Poor biological condition (for macroinvertebrates) is almost twice as likely in rivers and streams with high levels of phosphorus or nitrogen.”9 Although urban sewage systems and storm runoff make significant contributions, agricultural production is responsible for a huge proportion of nitrogen and phosphorus water pollution. Excess use of nitrogen fertilizer has an additional effect, causing an increase in release of nitrous oxide (N2O) into the atmosphere. N2O is a powerful greenhouse gas as well as the leading cause of depletion of stratospheric ozone (O3), which protects the Earth’s surface from UV radiation.
The magnitude of nitrate losses from cropland in the U.S. Midwest is staggering. The U.S. Geological Survey’s Van Meter continuous monitoring station—in the Raccoon River just upriver from Des Moines, Iowa—samples river flow and nitrate concentrations at fifteen-minute intervals around the clock. Over the span of a year, from April 1, 2015, to March 31, 2016, approximately 100 million pounds of nitrogen (as nitrate and nitrite) flowed down the river on its way to the Mississippi River and the Gulf of Mexico.10
A third rift in nutrient cycling occurred with the drastic reduction in populations of sea birds and large land and sea animals. Migratory herbivores once moved huge amounts of nutrients long distances on grasslands; sea birds and anadromous fish (that live most of their lives in the ocean but return to their home rivers to spawn such as salmon and smelt) carried nutrients from sea to land and whales brought them from the deep ocean to surface waters.
Though extinctions of mammoths and other megafauna happened in precapitalist times, much of the damage to populations of remaining large land and sea animals occurred very recently under the pressures of capitalist resource extraction and land use changes. With regard to the oceans, researchers estimate:
For phosphorus (P), a key nutrient, upward movement in the ocean by marine mammals is about 23% of its former capacity (previously about 340 million kg of P per year). Movements by seabirds and anadromous fish provide important transfer of nutrients from the sea to land, totalling ~150 million kg of P per year globally in the past, a transfer that has declined to less than 4% of this value as a result of the decimation of seabird colonies and anadromous fish populations.11
Three rifts in the natural cycling and flow of nutrients have opened as a result of the functioning of capitalist economies. Trying to remedy the consequences of the first two of these has led to other serious ecological problems. (There has been no attempt to deal with the third rift.)
THE CARBON CYCLE
The preindustrial terrestrial carbon cycle consisted of atmospheric CO2, together with the energy of sunlight and the photosynthetic process of plants, to create carbon-rich organic compounds. Respiration of plants and organisms feeding on plants or other organisms returns CO2
