by Whitney Reid
With the human population rising, and available land on Earth dwindling, there has been a growing need in recent decades to utilize more efficient agricultural technologies to meet the growing demand for food and resources. This has led to a surge in the concept of sustainable agricultural, practices which satisfy the agricultural demands of the present without diminishing the ability of future populations to meet their own needs (Renard et al., 2012). Many might believe that meeting this goal will require the revolutionizing of agricultural practices and the development of new technologies, but in fact sustainable methods like wet rice cultivation and swidden-fallow agroforestry have been utilized for thousands of years (Kerr, 2013). It is important to note, however, that although these methods are sustainable, they may still have negative environmental consequences.
Wet rice, grown in flooded fields called paddies, has been sustainably cultivated for centuries, primarily in Southeast Asia (Kerr, 2013). Controlled flooding aids in the transport and deposition of silt which is high in organic matter and nutrients that improve soil fertility (Grigg, 1974). The addition of manure resulting from animal-powered ploughs also contributes to increased soil fertility without the use of chemical fertilizers (Carney, 2009). Rather than exhausting soil nutrients, this cultivation method helps to improve soil fertility, producing relatively undiminished yields each growing season without the need to fertilize or leave fields fallow (Grigg, 1974). However, the difficulty required to plant seedlings and to maintain appropriate water and soil levels in fields requires high labor inputs, making this method unsuitable for large-scale production in many contexts (Grigg, 1974). Perhaps most importantly, these flooded fields provide the ideal habitat for anaerobic microbes which attach to plant roots and produce methane, which in turn is released into the atmosphere (Stokstad, 2015). In fact, studies of air bubbles trapped in Antarctic ice show a sharp increase in atmospheric methane 5000 years ago, corresponding with the time that humans began cultivating wet rice (Kerr, 2013).
Another method known as swidden-fallow agroforestry, or the burning of forests and brush to clear lands for farming, can in fact be sustainable when executed correctly (Curry, 2016). This method relies on a sequence of clearing wooded lands through controlled fires, then allowing these fields to lay fallow and regenerate vegetation after the annual crop, typically over 10-25 years (Nigh & Diemont, 2013). This burning helps to replenish soil carbon, thus improving soil fertility (Nigh & Diemont, 2013). The growth of brush during the fallow period allows the soil to be disturbed and loosened, providing better planting conditions and allowing the soil to regain valuable nutrients (Nigh & Diemont, 2013). One major disadvantage of this system is the long period necessary for the regrowth of vegetation. This requires farmers to shift cultivation by utilizing other parcels of land during this fallow period, meaning 10-25 sections of land may be required while only one section is cultivated and harvested each growing season (Nigh & Diemont, 2013). In addition, the burning of trees releases carbon dioxide into the atmosphere, another infamous greenhouse gas. Evidence of increased concentrations of atmospheric CO₂correspond to dates when humans began clearing forests to create agricultural lands 8000 years ago (Kerr, 2013).
Both wet rice cultivation and swidden-fallow agroforestry present important and sustainable methods of utilizing land to produce agricultural products that are becoming increasingly in demand. However, while each process aids in maintaining soil fertility, thus allowing these soils to be utilized by future generations, they may also offer labor or time constraints that present challenges for large-scale production. While these approaches exploit resources and land in a more sustainable way, the emission of greenhouse gases that results can have negative impacts on a global scale. It is important to realize that even the most sustainable agricultural practices can have consequences and disadvantages, and these should not be overlooked.
References
Carney, J. A. (2009). Black rice: The African origins of rice cultivation in the Americas. Cambridge: Harvard University Press.
Curry, A. (2016). ‘Green hell’ has long been home for humans. Science,354(6310), 268-269. doi:10.1126/science.354.6310.268
Grigg, D. B. (1974). The agricultural systems of the world: An evolutionary approach. London: Cambridge University Press.
Kerr, R. A. (2013). Humans fueled global warming millennia ago. Science,342(6161), 918-918. doi:10.1126/science.342.6161.918
Nigh, R., & Diemont, S. A. (2013). The Maya milpa: Fire and the legacy of living soil. Frontiers in Ecology and the Environment,11(S1), 45-54. doi:10.1890/120344
Renard, D., Iriarte, J., Birk, J., Rostain, S., Glaser, B., & Mckey, D. (2012). Ecological engineers ahead of their time: The functioning of pre-Columbian raised-field agriculture and its potential contributions to sustainability today. Ecological Engineering,45, 30-44. doi:10.1016/j.ecoleng.2011.03.007
Stokstad, E. (2015). New rice variety could feed the planet without warming it. Science. doi:10.1126/science.aac8890
Campus Environmental Center 