by Carin Ragland
Ten thousand years ago, groups of Homo sapiens began to supplement their hunter-gather subsistence by domesticating plants and animals for the first time in history. The change marked the start of the Neolithic Revolution, commonly called the First Agricultural Revolution because it was truly the first of many (Wikipedia). From 10,000 B.C. to the 19th century societies around the world exploited or extended the habitats of the crops and animals that constituted the foundation of their diets. Of these agricultural endeavors, the most successful incorporated a myriad of complementary organisms, mirrored naturally occurring ecological interactions, and carefully preserved and recycled land, water, nutrients, and other resources for future production. During the Green Revolution, however, farmers became less dependent on ecology and frequent conservation measures due to a variety of new technologies and chemical products that addressed common farming woes such as pests, lack of water, and nutrient deficiency. Farmers began putting more in and getting more out. As a result, it became easier to treat farms as factories, and less like habitats. It became easier—and more profitable—to specialize (Guthman, 62). Thus, farms became larger, outcompeting smaller farms, and growers reduced their variety crops and segregated animal production.
On a large number of farms, land owners rent their land to farmers instead of cultivating the land themselves. Through such agreements, land ownership becomes a source of income, which is provided by the proceeds of the tenants. But in every market there is competition. In the 20th century, the seeds of rapid urban development were sown around urban hubs as the invention of commercial cars and public transit systems pushed suburbs further into the surrounding rural areas (Fainstein, 2014; Rodrigue, 2014). Owners of agricultural land now have a choice: rent their land to farmers or sell it to developers. The decision depends on the highest bidder: tenants may continue to farm the land as long as they can grow and sell enough produce to pay their landlords a sum comparable to potential profits of a land sale to developers.
But as land values rise, so do the levels of required productivity—and all from the same area of land. Consequently, farmers are forced to abandon ecological, conservation practices in order to squeeze out as much from the land as possible to pay the rent and retain profits. The resulting agricultural intensification has unleashed a cornucopia of problems including the contamination of ground water, depletion of water sources, erosion of valuable crop land, widespread hive collapse, and ubiquitous food-safety concerns. By advocating for the introduction of new sustainable practices (and reintroducing traditional ones), today’s Green Movement aims to reverse the environmental, economic, and social harm which has become the legacy of the Green Revolution. But these efforts only partially address the greater issue and ultimate cause of reckless agricultural development: increasing rent pressures.
In this paper I will discuss how constantly increasing rent rates on farm land discourages sustainable agricultural practices—namely those involving symbiotic associations, and why sustainable practices need to be reincorporated in agriculture. Ultimately, this paper will argue that the active promotion of symbiosis in agriculture will mitigate the prioritization of rent over environmental integrity and public health by facilitating the production of more food at lower costs (economic, environmental, and social).
Land is the most important resource in any agricultural enterprise. As Julia Guthman acknowledges in Agrarian Dreams, “all growers…must make payments to land.” The type of payment depends on tenure: those who own land pay property taxes and those who rent land pay according to a lease (also influenced by taxes). Property taxes are based on land value. The value of land governs many factors concerning the viability of an agricultural business; unfortunately, land valuation is determined by past and projected profitability. Such calculations are unfortunate because for decades, profitability has been based on the output potential of exploitive and intensive agricultural practices (Guthman, 178). At the same time, innovations in intensive technologies augment intensification, hence contributing to rising land values.
Omitted from land value calculations are fallowing periods that improve soil fertility, rotations of lower-value crops that foster diversity benefits, minimal tillage practices that conserve water, appropriate wages for a healthy and content workforce, and the possibility of lower yields during transition periods to alternative methods. There are no considerations for long-term investment in the land quality or worker welfare. There is only concern for short-term market fluctuations following the “logic of highest and best use” (Guthman, 168). Accordingly, agriculture must compete with urban development and prove itself highly profitably (Guthman, 68).
In agriculture, the best use is synonymous with cheap, constant production. There is the assumption that one crop will be grown every growing period, and that worker wages will be minimized as much as possible. There is the assumption that yields will be comparable to past harvests and that the same practices will be used to ensure and increase those yields (Guthman, 88). High land costs compel innovations to maximize output in order to meet costs, but increases in output swell land values (Guthman, 68).
Ultimately, the paradigm regulating land valuation protocol necessitates destructive, intensive practices: the more growers have to pay toward land, the more they have to produce to make those payments; the more they produce, the higher their land costs. A vicious cycle indeed! If growers adopt sustainable practices, which may produce less, they can’t afford the land. Clearly, this is an untenable system.
In Cuba where global embargos necessitated organic farming and other alternative practices, the government has created a host of rent-eliminating institutions that have reduced the need for intensified agriculture—mostly through usufruct agreements (Funes et al., 52-54). Cuba’s policy makers recognized that no rent is paid within the most successful farm systems (Funes, 9). While the United States is highly unlikely to adopt usufruct policies, it is worthwhile to analyze the ways in which private property laws doom sustainable practices and induce farmers to exploit and abuse their most essential resource, in order to pay the bills.
Applications of Symbiosis in Agriculture
Monoculture dominates the agricultural landscape, however more diverse systems are stable systems because if an infliction plagues one element of the ecosystem, other constituents are present to account for the loss. In this same way, farms are ecosystems and they are best managed in the interest of the future when treated as such. Ecosystems feature a motley of interdependent organisms and habitats that interact within a larger network energy flow and recirculation. Almost all interactions can be characterized as symbiotic—whether they be mutualistic, parasitic, amensalistic, communalistic, or predatory—and the more interactions maintained farm management the more resilient the farm. Crop rotations, intercropping, animal-crop integrated operations, and integrated pest management are notable practices that foster symbiotic associations, reduce expenditures on inputs, and augment the farm’s resiliency and long term productivity.
Initially, when embargos reduced imports by 75%, Cuban officials knew to look toward customary methods and consult traditional farmers during its transition to decreasing input dependence (Funes et al., 6, 51). One of agriculture’s oldest practices is polyculture. Subsistence farmers naturally needed to grow more than one crop to feed themselves. They quickly realized that regularly alternating where certain crops were grown sustained crop quality. This is because different crops modify soil in unique ways: affecting the texture and composition—adding what others take, taking what others add (Wikipedia). Therefore, careful planning and crop scheduling allows farmers to prepare ideal conditions for a certain crop. Crop rotation can also include fallowing, a process in which plants that contribute nutrients to the soil are grown. Notable contributors to soil nutrients are legumes because of their exceptional ability to fix nitrogen—the primary source of nitrogen before 1950 (NRC, 231). Although most legumes are not palatable to humans, some species such as sweet clover, red clover, and sainfoin are suitable for stock feed (Kopp, 2003).
In addition to soil amendment, agricultural experts affirm that crop rotations are the most important measure in combating pests, weeds, and disease (Funes et al., 127). Rotations that omit a crop for some time period interrupt pest and disease reproduction by temporarily removing the host plant (Funes et al., 145). Consequently, rotations have been particularly successful against nematodes. In Cuba, specific planting schemes are used to out-compete specific weeds; for example, to manage mugwort (Parthenium hysterophus) a maize or sorghum-potato-maize-sorghum rotation is effective. Also, it is general knowledge that weed incidences are much lower in crops planted after sweet potatoes (Funes et al., 128).
With proper planning, crop rotations decrease dependence on fertilizers and can be used to suppress weeds. However, rotations violate the USDA’s cross-compliance provision and penalize farmers for self-sufficiency and for improving the quality of their land. Instead the government should encourage crop rotations by requiring farmers to apply for a commodity crop rotation program instead of a program under a single crop. This way, farmers can simultaneously save money on fertilizers and herbicides simply by producing different crops.
With production costs lowered, subsidies would also lower since target prices are calculated based on (over) projected production costs. Also, if unsynchronized, commodity crop rotation programs could prevent surplus and render farmers more responsive to market demands by making substitutions—which are possible in planting schemes because some plants have similar nutrition needs and effects on soil qualities. Thus, crop rotations have the potential to save the government money by keeping farms productive and avoid paying farmers to do nothing in order to address surplus.
The main disadvantage of crop rotations stems directly from specialization. Commodity program farms usually possess an assortment of crop specific machinery that may be useless or damaging in the treatment of other crops. But through commodity crop rotations, the USDA would alert farmers to how soil is affected by crop plans and encourage them to veer from debilitating practices such as constant monoculture.
Another symbiotic practice that benefits production by increasing diversity is intercropping. This involves planting more than one type of crop in the same area at the same time. Intercropping is an effectual strategy in controlling pests and weeds for several reasons. Firstly, some intercropping schemes incorporate a plant that can act as a barrier. The executive director of Natural Environmental Ecological Management (NEEM), Jeffrey Ensminger, reported that Cuban farmers often use a maize wall—a line of corn bordering the perimeter of the fields—to fight pests. The wall acts as a barrier preventing pest movement between crop rows and curtailing reproduction. The combination of smells and colors of different crops may also confuse pests (Funes et al., 145).But most importantly, the corn attracts predatory insects that feed on pests. Maize is the crop used most in Cuba for this purpose (Funes et al., 130).
Secondly, by increasing crop density, intercropping decreases the ecological niche for weeds thus reducing their occurrence. Successful crop pairs include a plant with rapid grow or shading foliage. Popular intercropping schemes include cassava-maize, sugarcane-soybean, and maize bean. The constituent with rapid growth makes nutrients less available to weeds; broad leaves starve weeds of sunlight (Funes et al., 130).
To assess how intercropping compares with monoculture, agronomists calculate the land equivalent ratio (LER). The value depicts the relative area of monocultural land needed to produce an intercropping output thus, if the LER of an intercropping system is greater than one, monoculture is less efficient. A collection of studies on thirteen intercropping pairs all resulted in LER’s greater than one; it revealed that intercropping was more efficient in every case—sometimes by a near factor of two— (Funes et al., 148-149). Intercropping practices share crop rotation’s disadvantage regarding a possible lack of specialized equipment for secondary crops. However, increased production and lower pesticide and herbicide expenditures may compensate for machinery related inconveniences in the long-term.
Animal-Crop Integrated Systems
Besides monocultural ubiquity, another striking feature of conventional agriculture vis-à-vis traditional agriculture is the absence of animal-crop integration. Before the development and commercialization of synthetic fertilizers, livestock production was almost inseparable from crop production. Also, livestock were pasture-fed and feed production occurred on the farm site. Now, most livestock producers purchase corn or soy feed or produce hay for feed and use intense confinement (Schiere et. al, 2001). However, the reintegration of livestock in crop operations has the potential to offer many benefits.
On orchards for example, livestock can aid in weed management and are less likely to be able to reach crops or find the crop of interest palatable (Funes et al., 200). Depending on the size of the orchard and the number of animals used, herbicide expenditures could decrease significantly and animal maintenance would require a relatively small percentage of the savings. On large-scale farms, the use of on-site animals for manure is impractical because collection, preparation, transportation, and application are costly and labor intensive (Funes et al., 205, Schiere et. al, 2001). The practice is considerably more viable on small to medium farms; however farms of this scale may produce insufficient crop waste to sustain many animals (Hesterman, 79, Schiere et. al, 2001). Nonetheless, the incorporation of livestock in crop production is an economically viable means to convert fallowing crops and plant waste into valuable products (manure) and to accelerate nutrients availability (Schiere et. al, 2001).
In addition to livestock, other animal integrations in crop production include crawfish in rice production (which requires no feed and yields an additional, high value food) and worm cultivation (an optimal source of manure, also requiring no feed), (Funes et al., 177). Overall, these systems require minimal labor and inputs while boosting both profit and yield.
In livestock production, the incorporation of crops and pasture-feeding tremendously reduces the costs of grain feed and prophylactics. Pasture feeding entails a more spacious and better ventilated environment, which prevents disease outbreaks. Additionally, crop integration creates a self-sustaining system. For example, in 1990, a Michigan dairy farmer that purchased feed and grew hay for his cows was unable to keep up with the monthly costs of feed, equipment, and fertilizer. In an effort to save his farm, he adapted a popular method used in New Zealand which involves the use of an electric fence that can be moved around by one person. Today, this farmer grows a variety of grasses (including varieties with nitrogen fixing properties) and moves the fence periodically by himself. The cows feed on the grasses and fertilize as they graze—eliminating costs for feed, fertilizer, pesticides, and equipment for hay production. New Zealand produces only 2% of the world’s milk but almost 25% of dairy products. Its dairy farmers also boast the world’s lowest production costs (Hesterman, 98-101). Without a doubt, this is an example for the United States to follow, and federal financial support for the purchase of high-tensile electric fencing could lead the country’s meat industry toward sustainability.
Microorganism Integration: Arbuscular Mycorrhiza and Rhizobium Symbiosis
A fairly undemanding and beneficial incorporation is fungal and bacteria integration. Soil houses the array of macro and micro nutrients required for crop development, but in reality many of these nutrients are largely out of reach or otherwise unavailable to the plants. However, symbiotic associations between plants and rhizobial bacteria and mycorrhiza fungi can remedy nutrition barriers.
The symbiotic association between plants and mycorrhiza fungi is called arbuscular mycorrhiza (AM). About 80% of angiosperms can form AM, and it is considered one of the most ubiquitous symbioses on earth (Gust, 2012; Gutjahr, 2013). Once it locates a root, the fungus penetrates the epidermis and enters cells in the cortical layer to form highly branched structures called arbuscules. The plant produces an intracellular membrane, the periarbuscular membrane, to accommodate the arbuscules and to house peripheral proteins that control the exchange of nutrients (Gust, 2012). The fungus supplies water, phosphorus, and other nutrients to the plant and receives carbon in return (Gutjahr, 2013). If either organism ceases to benefit from the interaction, the arbuscules collapse and the association within the cell is dissolved.
AM symbiosis research has the potential to address several issues related to agricultural productivity, phosphorus conservation, and water pollution. The use of AM in agriculture increases the amount of nutrients and water accessible to crops, enables smaller, more effective applications of phosphorus fertilizers, decreases water requirements, increases growth and biomass, and decreases growing time (Funes et al., 173; Roy-Bolduc & Hijri, 2010). AM fungi help soil retain phosphorus, which is often leached from the soil. Reduction of agricultural phosphorus applications would help conserve global phosphorus resources as well as water resources by preventing run-off pollution in waterways (Roy-Bolduc & Hijri, 2010).
While mycorrhiza fungi simply transfer nutrients from the soil to the plant, most rhizobial bacteria occupy small spaces in plants roots, called nods, and fix nitrogen from the atmosphere to exchange for carbon. But not all rhizobia operate via nods. The bacteria azotobacter, widely cultivated in Cuba, lives on crop leaves, absorbs water vapor, and fixates nitrogen in the atmosphere. The leaves act as a substrate, and eventually the compounds formed are available to the plant. Up to 50% of needed nitrogen can be provided by the bacteria. Azotobacter increases crop growth rate and quality by aiding the following processes: nitrogen fixation, respiration, and photosynthesis (Funes et al., 170-173).
Other beneficial microorganisms include trichoderma which act as a bio-fungicide—attacking pathogens, facilitating abundant root growth, decomposing organic matter, and stimulating the plant’s defense mechanisms (Muniappan, 2012); and Cyanobacteria which fixates atmospheric nitrogen and produces ammonia. Although these systems don’t produce additional products for harvest, the benefits for crops are tremendous because of mutualistic, symbiotic propensities. However, organisms such as fungi and rhizobia are generally destroyed by soluble fertilizers, but the preservation of these organisms has proved exceedingly advantageous (Guthman, 124).
Integrated Pest Management
Pest problems tend to bug farm management. They are reoccurring, persistent, and costly to handle. Pesticides and herbicide use, burning, and flooding are often effective in killing pests and weeds for a short while but these practice are intensive, put farm workers and consumers at a higher risk of illness, pollute the environment, burden budgets, and also kill beneficial bugs (Kowalski, 2013). Integrated pest management (IMP) is a preventative strategy that assesses when to implement remedial measures based on whether approaching pest levels will cause significant yield decreases. IPM includes a broad range of practices; crop rotations, intercropping, and animal integrated systems are all examples of IPM. It is the ultimate incorporation of symbiosis in agriculture, exploiting predatory relationships, crop-pest relationships, genetic defense mechanisms, unfavorable pest habitats, and time periods when pest development and reproduction are most susceptible.
IPM can include the preservation natural predators or the introduction of new predators and pest-affecting diseases. For example, certain bacteria, fungi, nematodes, protozoa, and viruses are lethal to pests, and onsite bee cultivation facilitates pollination, produces honey, and reduces some pest populations (NRC, 122). Additionally, releasing a combination of lady beetle, parasitic flies, and parasitic wasps can address out breaks of any of the following: aphids, carpentervworms, caterpillars, slugs, spider mites, mealybugs, psyllids, scales, lace bugs, elm leaf beetles, giant whiteflies, eucalyptus longhorn borers, and glassy-winged sharpshooters (Dreistadt, 2014). However, the purchase of predators or pathogens can exceed the affordability of some farmers (Funes et al., 112, 126-127). Resistant crop varieties, pheromone traps, and the release of sterile pests present a similar issue of affordability.
But inexpensive alternatives do exist. In addition to reduced pesticide use, fostering pollinator populations can be accomplished simply by planting flower patches which eliminate “food deserts” in monocultural areas with non-flowering crops (Spivak, 2013). More affordable inputs include neem oil and karanja oil (also available as a “cake”). The two are similar, but neem’s benefits are extensive. Neem reduces the population of many insects, mites, and nematodes that plague crops as well as parasites that affect livestock such as ticks, lice, and fleas (Funes et al., 124). The oil possibly works by disturbing the timing of hormonal processes and shrinks pest populations by disturbing optimal reproductive and developmental periods (Jeffrey Ensminger). Judicious applications are preventative and last up to nine months.
A 1994 study in Cuba examining the costs of biological control agents on a group of crops estimated $339,854 in expenses ($1,172,495 pesos, 3.45 pesos exchange rate, Oanda historical exchange rates). The study estimated a cost of $6,175,345, if synthetic chemicals were used to perform the same amount of control—a 72% greater expense (Funes et al., 134). In addition to cutting production costs, IPM mitigates water pollution, soil erosion, protects pollinators, and reduces risks posed by monoculture.
Diversifying techniques such as crop rotations, intercropping, animal integration, and IMP require farm operators to trade capital-intensive management with knowledge-intensive strategies (Funes et al., 92). By funding transitions to these practices and removing diversity penalties (in the form of loss and lack of subsidies), the USDA would acknowledge farms as ecosystems. Such policy would influence farmers’ perceptions of their land and compel them to strengthen and stabilize the ecosystems fueling farm production.
So far, this paper has proscribed symbiosis-related methods to address the most pressing issues regarding conventional soil agriculture. This section describes a form of agriculture called aquaponics, a method of growing plants that incorporates many forms of symbiosis and has the potential to increase in biodiversity, use of safer agro-inputs, preserve soil, and conserve water.
Aquaponics is the process of growing plants and marine animals in a simulated ecosystem. In this system, effluent produced by the fish, or other marine animal, provides a nutrient food source for the plants, after bacteria convert ammonia in the fish-waste into nitrates. At the same time, waste extraction performed by the plants maintains a non-toxic environment for the fish. Aquaponics exploits the mutualism between plants and fish in order to facilitate self-sufficiency. It is one of the most sustainable agricultural systems because it preserves soil, necessitates the use of fewer and nontoxic inputs, conserves water, and requires biodiversity.
Aquaponics conserves soil because most systems use alternative growing mediums to support the plants such as PVC pipes, coconut fiber, or gravel. Seeds are germinated and brought to seedlings in soil or other media. After the plants have grown to an appropriate size, they are transferred to aquaponic apparatuses and the seed tray media is often reusable. With alternative growing mediums available, operations that choose to grow plants in local soils are less compelled to cultivate to the extent of detrimental intensity. Also, aquaponic companies can operate on marginal lands, further mitigating the pressure on agricultural land to meet food demands (Davis et al., 2013).
Aquaponic systems preserve water because ecological considerations regarding integrated marine organisms limit the number of safe inputs. The effect on water quality and the toxicity of some agro-chemicals can pose more immediate health issues to fish than to humans (Chiang, 2009). At the same time, systems with appropriate crop-fish ratios and properly fed fish can produce enough effluent to nourish crops, eliminating the need for fertilizer. Moreover, aquaponics conserves water by using (a lot) less water. Through direct application to root zones and recycling, aquaponics uses up to 90% less water than conventional systems (Ecotrope, 2012). Due to evaporation and plant absorption, systems required routine water additions amounting to 1-1½ percent of the system’s total volume. But an analysis of lettuce production in the Virgin Islands had revealed that even with regular water additions, one pound of aquaponically-grown lettuce requires less than half the amount of water needed to grow one pound of conventional lettuce (Food & Water Water, 2009).
Biodiversity is increased and maintained in aquaponics because by definition, the success of the system depends on interspecies relationships. As a result the system requires fewer inputs and yields more outputs: fish in addition to crops. In a 2011 TED Talk presentation, Charlie Price explained how the simply fish-crop system can be expanded to become more self-sufficient and produce more outputs (featured: Ecotrope, 2012). Typical inputs include fish feed, water, energy, seeds, and media for starts.
Four possible outputs of an exceptionally self-sufficient system are as follows. 1) The incorporation worms (vermiculture), allows for the production of several new outputs. Fed by plant waste, the worms produce nutrient-rich “vermicompost” for soil cultivation, their waste can be manufactured into a biofertilizer known as “worm tea,” or the worms themselves can be food for the fish. 2) The incorporation of black soldier flies and chickens enables internal production of fish food. The flies are abundant sources of protein, and can feed on the processing waste from fish (heads, tails, fins etc.). However, animal byproduct laws restrict that flies produced in this matter can be fed back to the fish. Therefore, chickens are necessary to legalize the cycle. If the fish-fed flies are produced as a food source for chickens, chicken-fed flies (given waste from chicken processing) can be fed to the fish. The result is an internally produced input (fish food) and 3) two additional outputs (chickens and eggs)—however, energy losses between trophic levels would require some degree of supplementation. 4) A fourth possible output of an aquaponics system is fresh water prawns. Algae inevitably grow in nutrient-rich water in the presence of sunlight, forming a food source for prawns. Algae consume nutrients and oxygen (at night). Therefore, integrating prawns helps manage algae growth for the benefit of the system (Affnan, 2009).
Lastly Price describes various measures that can further internalize input production. These include the use of solar, photovoltaic equipment for energy, RWH for water supplication, and fish-breeding for continued production after harvest. It is also possible to extract seeds from a portion of the produce, with the same effect as fish-breeding. Consequently, aquaponic systems have the potential to operate sustainably with minimal negative impact on the environment and human health (with the use of all food grade materials).
Conclusion: Is Aquaponics Really Agriculture’s Panacea?
The long-term decline of modern agriculture began when agriculture’s most important practices—crop rotations, intercropping, animal-crop integrated operations, and integrated pest management—were rendered inconvenient and eliminated from the production repertoire. Within soil agriculture these practices increase diversity and foster symbiotic associations that reduce expenditures on inputs, preserve soil quality, conserve water and augment the farm’s resiliency and long term productivity. However, under current rent pressures, the majority of farmers will not simply adopt sustainable practices because it is the right thing to do—nor can most of them afford to. Aquaponic production is the ultimate means to adopt this sustainability regime because its success is inextricably linked to the proper implementation and optimization of inherently sustainable practices.
Aquaponics is a demonstrated, sustainable system with multifarious benefits and production possibilities, but it is not without disadvantages and drawbacks. Rent, fish food, energy, and heating costs are the largest expenditures in the most common systems. Due to general fish sensitivity to pH variation, tilapia is the most popular species cultivated because of its tolerance to pH variation. However, due to low market value, fish harvests usually account for only about 2% of profits and rarely exceed 10% of costs (Newman, 2012). Also aquaponic production is currently practical only for “table vegetables” (Davis et al., 2012). Yet, overall, the self-sufficient aquaponic model described (and practiced) by Price presents a paragon toward which our current, self-destructive agriculture system should aspire.
The success of an aquaponic system is largely independent from the quality of the soil on which the facility is located, so it is possible to implement on marginal lands. Marginal land is often cheap; it is generally characterized by extremely low profit potential, lack of arability, and unattractive features (Investopedia). Aquaponic operations can also thrive in odd spaces, such as rooftops, sides of buildings, and vacant lots (Gaus, 2013). Moreover, aquaponic facilities produce more in smaller spaces and at faster rates. Consequently, aquaponic companies have the potential to circumvent high land and rent expenditures. Without the constant pressure of substantially increasing land prices, rent, or property taxes, these operations can adopt, commit to, and innovate sustainable practices on a large scale.
Affnan. “Of Algae and Oxygen.” Affman’s Aquaponics. 29 Jun. 2009. 30 Aug. 2013. <http://www.affnanaquaponics.com/2009/06/of-algae-and-oxygen.html>
Chiang, Richard. “Cost/Benefit Analysis of Aquaponic Systems.” Backyard Aquaponics.16 Nov. 2009. 27 Aug. 2013. <http://backyardaquaponics.com/Travis/CostBenefitAnalysisofAquaponicSystems.pdf >
Farm Workers. “The Bracero Program.” Farm Workers. Dec. 1999. 8 Aug. 2013. <http://www.farmworkers.org/bracerop.html>
Davis, Colle, Phyllis Davis. “Aquaponics Creates New Jobs Based On Food Production and Solar Power.” Portable Farms. 9 May 2012. 24 Aug. 2013. <http://portablefarms.com/2011/jobs_aquaponics-2/>
Davis, Colle, Phyllis Davis. “Warehouse Aquaponics? Yes, Here’s How…” Portable Farms. 14 Jul. 2013. 20 24 Aug. 2013. <http://portablefarms.com/2011/jobs_aquaponics-2/>
Dreistadt, S. H. “Biological Control and Natural Enemies.” UC Statewide IPM Program. University of California, Davis, 2007.
Ecotrope. “Aquaponics: Growing Fish and Plants Without Soil.” OPB. 2 Mar. 2012. 26 Aug. 2013.
Fainstein, Susan. “Urban Planning.” Encyclopaedia Britannica. 11 Feb. 2014. 2 Sept. 2014. <http://www.britannica.com/EBchecked/topic/619445/urban-planning/10805/The-era-of-industrialization>
Food & Water Water. “Water Usage in Recirculating Aquaculture/Aquaponic Systems.” Food & Water Water Newsletter. Aug. 2009. 23 Aug. 2013. <http://www.lanikaifarms.com/Recirculating%20Aquaculture%20Systems%20(RAS).pdf>
Funes, Fernando, Luis Garcia, Martin Bourque, Nilda Pèrez, and Peter Rosset. Sustainable Agriculture and Resistance. Food First Books, Cuban Association of Agricultural and Forestry Technicians, and Center for the Study of Sustainable Agriculture, Agrarian University of Havana, 2002.
Gaus, Roman. “The Farming Technique That Could Revolutionize the Way We Eat.” The Atlantic Cities. 6 Mar. 2013. 9 Aug 2013. <http://www.theatlanticcities.com/arts-and-lifestyle/2013/03/farming-technique-will-revolutionize-way-we-eat/4880/>
Guthman, Julie. Agrarian Dreams: The Paradox of Organic Farming in California. London: Regents of the University of California, 2004.
Hesterman, Oran B. Fair Food: Growing a Healthy, Sustainable Food System for All. Ney York: PublicAffairs, 2011.
Kopp, Juanita. “Feeding Legumes to Cattle.” Alberta Agriculture and Rural Development, 2003.<http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex6516>
Kowalski, Kurt. “Invasive Phragmites – Prevention, Monitoring, and Control Strategies in an Integrated Pest Management Framework.” U.S. Geological Survey, 2013.
Muniappan, R. “Trichoderma in Agriculture.” Office of International Research, Education, and Development, Virginia Tech. 27 Mar. 2012. 9 Aug. 2013. <http://www.oired.vt.edu/ipmcrsp/documents/presentations/Trichoderma-Muniappan-March2012.pdf>
National Research Council, Committee on the Role of Alternative Farming Methods in Modern Production Agriculture, and Board on Agriculture. Alternative Agriculture. Washington, D.C.: National Academy Press, 1989.
Newman, Steve. “Can you make money with aquaponics?” Ghadvisor. 12 Nov. 2009. 27 Aug. 2013. <http://ghadvisor.blogspot.com/2009/11/can-you-make-money-with-aquaponics.html>
Rodrigue, Jean-Paul. “Urban Mobility.” The Geography of Transport Systems. 2014. 2 Sept. 2014.<https://people.hofstra.edu/geotrans/eng/ch6en/conc6en/ch6c3en.html>
Schiere, J.B., Ibrahim, M. N. M., van Keulen, H. “The Role of Livestock for Sustainability in Mixed Farming: Criteria and Scenario Studies under Varying Resource Allocation.” Agriculture, Ecosystems and Environment: 90 (2002) 139–153.< http://agron-www.agron.iastate.edu/Courses/agron515/Schiereetal.pdf>
Spivak, Marla. “Why Bees Are Disappearing.” Ted Global, 2013.<http://www.ted.com/talks/marla_spivak_why_bees_are_disappearing?language=en>
Wikipedia. “Crop Rotation.” 2 September 2014.< http://en.wikipedia.org/wiki/Crop_rotation >