This paper considers the local, field-scale sustainability of a productive industrial maize agrosystem that has replaced a fertile grassland ecosystem. Using the revised thermodynamic approach of Svirezhev (1998, 2000) and Steinborn and Svirezhev (2000), it is shown that currently this agrosystem is unsustainable in the U.S., with or without tilling the soil. The calculated average erosion rates of soil necessary to dissipate the entropy produced by U.S. maize agriculture, 23-45 t ha-1 yr-1, are bounded from above by an experimental estimate of mean soil erosion by conventional agriculture worldwide, 47 t ha-1 yr-1, (Montgomery, 2007). Between 1982 and 1997, US agriculture caused an estimated 7-23 t ha-1 yr-1 of average erosion with the mean of 15 t ha-1 yr-1 (USDA-NRCS Database). The lower mean erosion rate of no till agriculture, 1.5 t ha-1 yr-1 (Montgomery, 2007), necessitates the elimination of weeds and pests with field chemicals - with the ensuing chemical and biological soil degradation, and chemical runoff - to dissipate the produced entropy. The increased use of field chemicals that replace tillers is equivalent to the killing or injuring of up to 300 kg ha-1 yr-1 of soil flora and fauna. Additional soil degradation, not calculated here, occurs by acidification, buildup of insoluble metal compounds, and buildup of toxic residues from field chemicals. The degree of unsustainability of an average U.S. maize field is high, requiring 6-13 times more energy to reverse soil erosion and degradation, etc., than the direct energy inputs to maize agriculture. This additional energy, if spent, would not increase maize yields. The calculated "critical yield" of "organic" maize agriculture that does not use field chemicals and fossil fuels is only 30 percent lower than the average maize yield of 8.7 tons per hectare (∼140 bu/acre) assumed here. This critical yield would not likely be achieved and sustained by large monocultures, but might be achieved by more balanced organic polycultures (Baum et al., 2008).
ASJC Scopus subject areas
- Plant Science