Critics of organic agriculture claim that it is based more on ideology than on environmental or economic merit. Lim Li Ching reviews the evidence and turns the table on the critics.
Organic farming largely excludes synthetic inputs - pesticides, herbicides and fertilisers – and focuses instead on biological processes such as composting and other measures to maintaining soil fertility, natural pest control and diversifying crops and livestock. Organic agriculture give priority to long-term ecological health, such as biodiversity and soil quality, contrasting with conventional farming, which concentrates on short-term productivity gains.
Organic farming has been denigrated for being less efficient in land use and having lower yields than conventional farming, and even accused of posing potential health risks. According to a commentary in Nature by Anthony Trewavas, Fellow of the United Kingdom Royal Society, "Although its supporters assert that organic agriculture is superior to other farming methods, the lack of scientific studies means that this claim cannot be substantiated" [1].
But he is wrong, there are scientific studies, peer-reviewed and published, documenting organic agriculture’s positive outcomes. Furthermore, certified organic production is just the tip of the iceberg in terms of land managed organically but not certified as such. De facto organic farming [2] is prevalent in resource-poor and/or agriculturally marginal regions where local populations have limited engagement with the cash economy (see "Ethiopia to feed herself", this issue). Farmers rely on locally available natural resources to maintain soil fertility and to combat pests and diseases. They are showing the way towards sustainable agriculture through sophisticated systems of crop rotation, soil management, and pest and disease control, based on traditional knowledge.
The charge that organic farming is lower-yielding is misleading. Because comparisons of conventional and organic agriculture show differences in biological, chemical and physical characteristics that may affect yield, studies simply evaluating the reduction or elimination of inputs in conventional systems may not accurately represent conditions in alternative systems. Furthermore, abstract comparisons made when farms have just turned organic do not tell the whole story, as it takes a few years for yield to increase. Thus, it is necessary to make long-term comparisons.
A study on conventional and alternative farming systems for tomatoes [3] over 4 years indicate that organic and low-input agriculture produce yields comparable to conventional systems. Nitrogen (N) availability was the most important factor limiting yield in organic systems, and can be satisfied by biological inputs.
Another experiment examined yield, vitamin and mineral content of organic and conventional potatoes and sweet corn over 3 years [4]. Results showed that yield and vitamin C content of potatoes was not affected by the two different regimes. While one variety of conventionally grown corn out-produced the organic, there was no difference between the two in the yield of another variety of corn or the vitamin C or E contents. Results indicate that long-term application of composts produces higher soil fertility and comparable plant growth.
A review of replicated research results in seven different US Universities [5] from Rodale Research Center, Pennsylvania and the Michael Fields Center, Wisconsin over the last 10 years showed that organic farming systems resulted in yields comparable to industrial, high input agriculture.
The most remarkable results of organic farming, however, have come from small farmers in developing countries. Case studies of organic practices show dramatic increases in yields as well as benefits to soil quality, reduction in pests and diseases and general improvement in taste and nutritional content [2]. For example, in Brazil the use of green manures and cover crops increased maize yields by between 20% and 250%; in Tigray, Ethiopia, yields of crops from composted plots were 3-5 times higher than those treated only with chemicals; yield increases of 175% have been reported from farms in Nepal adopting agro-ecological practices; and in Peru the restoration of traditional Incan terracing has led to increases of 150% for a range of upland crops.
Projects in Senegal involving 2000 farmers promoted stall-fed livestock, composting systems, use of green manures, water harvesting systems and rock phosphate. Yields of millet and peanuts increased dramatically, by 75-195% and 75-165% respectively. Because the soils have greater water retaining capacity, fluctuations in yields are less pronounced between high and low rainfall years. A project in Honduras, which emphasized soil conservation practices and organic fertilisers, saw a tripling or quadrupling of yields.
In Santa Catarina, Brazil, focus has been placed on soil and water conservation, using contour grass barriers, contour ploughing and green manures. Some 60 different crop species, leguminous and non-leguminous, have been inter-cropped or planted during fallow periods. These have had major impacts on yields, soil quality, levels of biological activity and water-retaining capacity. Yields of maize and soybeans have increased by 66%.
The world’s longest running experiment comparing organic and conventional farming pronounced chemical-free farming a success [6, 7]. The 21-year Swiss study found that soils nourished with manure were more fertile and produced more crops for a given input of nitrogen or other fertiliser. Nutrient input in the organic systems was 34 to 51% lower than in the conventional systems, whereas mean crop yield was only 20% lower over a period of 21 years, indicating efficient production and use of resources. The ecological and efficiency gains more than made up for lower yields. In the long term, the organic approach was commercially viable, producing more food with less energy and fewer resources.
The biggest bonus was improved quality of the soil under organic cultivation. Organic soils had up to 3.2 times as much biomass and abundance of earthworms, twice as many arthropods (important predators and indicators of soil fertility) and 40% more mycorrhizal fungi colonising plant roots. Mycorrhizal fungi are important in helping roots obtain more nutrients and water from the soil [8].
The increased diversity of microbial communities in organic soils transformed carbon from organic debris into biomass at lower energy costs, building up a higher microbial biomass. The findings support the conclusion that a more diverse community is more efficient in resource utilisation. The enhanced soil fertility and higher biodiversity is believed to render the organic plots less dependent on external inputs and provide long-term environmental benefits.
Indeed, organic agriculture is helping conserve and improve farmers’ most precious resource – the topsoil. To counter the problems of hardening, nutrient loss and erosion, organic farmers in the South are using trees, shrubs and leguminous plants to stabilise and feed soil, dung and compost to provide nutrients, and terracing or check dams to prevent erosion and conserve groundwater [2].
Field experiments conducted at three organic and three conventional vegetable farms in 1996-1997 examined the effects of synthetic fertilisers and alternative soil amendments, including compost [9]. Propagule densities of Trichoderma species (beneficial soil fungi that are biological control agents of plant-pathogenic fungi) and thermophilic microorganisms (a major constituent of which was Actinomycetes, which suppresses Phytophthora) were greater in organic soils. In contrast, densities of Phytophthora and Pythium (both plant pathogens) were lower in organic soils.
While the study recorded increased enteric bacteria in organic soils, the researchers stressed that this was not a problem, as survival rates in soil are minimal. Critics of organic farming have disingenuously pointed to the possible human health effects of using manure [1]. But untreated manure is not allowed in certified organic culture, and treated manure (known widely as compost) is safe - this is what is used in organic farming. Unlike conventional regimes (where manure might be used), mandatory organic certification bodies inspect farms to ensure standards are met [10].
Little yield difference was observed. In the first year, corn and melon yields were no different in soil amended with either synthetic or organic amendments at four of six farms. In the second year, tomato yields were higher on farms with a history of organic production, regardless of soil amendment type, due to the benefits of long-term organic amendments. Mineral concentrations were higher in organic soils whilst soil quality on conventional farms was significantly improved by the addition of organic fertiliser.
Another means by which soil fertility is restored in organic systems is through legumes. A 15-year study compared three maize/soybean agro-ecosystems [11, 12]. One was a conventional system using mineral N fertiliser and pesticides. The other two systems were managed organically, depending on legumes for N fixation. One was manure-based, where grasses and legumes, grown as part of a crop rotation, were fed to cattle. The manure provided N for maize production. The other system did not have livestock; N fixed by legumes was incorporated into soil.
Amazingly, the 10-year-average maize yields differed by less than 1% among the three systems, which were nearly equally profitable. Soil organic matter and N content (measures of soil fertility) increased markedly in the manure system (and, to a lesser degree, in the legume system), but were unchanged or declined in the conventional system. The latter also had greater environmental impacts - 60% more nitrate leached into groundwater over a 5-year period than in the organic systems.
In Honduras, the mucuna bean has improved crop yields on steep, easily eroded hillsides with depleted soils [13]. Farmers first plant mucuna, which produces masses of vigorous growth that suppresses weeds. When the beans are cut down, maize is planted in the resulting mulch. Subsequently, beans and maize are grown together. Very quickly, as the soil improves, yields of grain doubled, even tripled. Mucuna produces 100 tonnes of organic material per hectare, creating rich, friable soils in just 2-3 years. Mucuna also produces its own fertiliser, fixing atmospheric N and storing it in the ground where it can be utilised by other plants.
Because organic procedures exclude synthetic pesticides, critics claim that losses due to pests would rise. However, research on Californian tomato production found that the withdrawal of synthetic insecticides does not lead to increased crop losses as a result of pest damage [14]. There was no significant difference in pest damage levels to tomato on 18 commercial farms, half of which were certified organic systems and half, conventional operations.
Arthropod biodiversity was on average one-third greater on organic farms than on conventional farms. There was no significant difference between the two for herbivore (pests) abundance. However, densities of natural enemies were more abundant on organic farms, with greater species richness of all functional groups (herbivores, predators, parasitoids). Thus, any particular pest species in organic farms would be associated with a greater variety of herbivores (i.e. diluted) and subject to a wider variety and greater abundance of potential parasitoids and predators.
At the same time, research has shown that pest control is achievable without pesticides, reversing crop losses. For example, in East Africa, maize and sorghum face two major pests – stemborer and Striga, a parasitic plant. Field margins are planted with ‘trap crops’ that attract stemborer, such as Napier grass and Sudan grass. Napier grass is a local weed whose odour attracts stemborer. Pests are lured away from the crop into a trap – the grass produces a sticky substance that kills stemborer larvae [15]. The crops are inter-planted with molasses grass (Desmodium uncinatum) and two legumes: silverleaf and greenleaf. The legumes bind N, enriching the soil. But that’s not all. Desmodium also repels stemborers and Striga.
Besides the obvious benefit of not using harmful pesticides in organic agriculture, Korean researchers recently reported that avoiding pesticides in paddy fields encourages the muddy loach fish, which effectively control mosquitoes that spread malaria and Japanese encephalitis [16]. Fields in which no insecticides were used had a richer variety of insect life. But actual larvae numbers of the mosquito vectors were significantly lower in organic sites.
Maintaining agricultural biodiversity is vital to ensuring long-term food security. Organic farms often exhibit greater biodiversity than conventional farms, with more trees, a wider diversity of crops and many different natural predators, which control pests and help prevent disease [2].
Proving with stunning results that planting a diversity of crops is beneficial (compared with monocultures), thousands of Chinese rice farmers have doubled yields and nearly eliminated its most devastating disease, without using chemicals or spending more [17]. Under the direction of scientists, farmers in Yunnan implemented a simple change that radically restricted the incidence of rice blast. Instead of planting large stands of a single type of rice, as they typically have done, they planted a mixture of two different kinds of rice: a standard rice that does not usually succumb to rice blast disease and a much more valuable sticky rice known to be very susceptible.
The hypothesis is simple. If one variety of a crop is susceptible to a disease, the more concentrated those susceptible types are, the more easily disease spreads. The disease is less likely to spread if susceptible plants are separated by other plants that do not succumb to the disease and that act as a barrier. Rice blast fungus, which destroys millions of tons of rice and costs farmers several billion dollars in losses each year, moves from plant to plant as an airborne spore, which should easily be blocked by a row of disease-resistant plants.
Resistant plants not only blocked the spores, but as more farmers participated, positive effects began to multiply. Not only were spores not blowing in from the next row, they were no longer coming from the next farmer’s field either, rapidly halting the disease’s spread. The sticky rice plants, which rise above the shorter, standard rice plants, enjoyed sunnier, warmer and drier conditions that also discouraged the growth of the fungal rice blast.
Furthermore, empirical evidence from a study conducted since 1994 shows that biodiverse ecosystems are 2-3 times more productive than monocultures [18, 19]. In experimental plots, both aboveground and total biomass increased significantly with species number. The high diversity plots were fairly immune to the invasion and growth of weeds, but this was not so for monocultures and low diversity plots. Thus, biodiverse systems are not only more productive, but are less prone to weeds as well!
Research published in Nature investigated the sustainability of organic, conventional and integrated (combining organic and conventional methods) apple production systems in Washington from 1994-1999 [20, 21]. All three gave comparable yields, with no observable differences in physiological disorders or pest and disease damage.
The organic system ranked first in environmental and economic sustainability, the integrated system second and the conventional system last. A sustainable farm must produce adequate high-quality yields, be profitable, protect the environment, conserve resources and be socially responsible in the long term. Specifically, the indicators used were soil quality, horticultural performance, orchard profitability, environmental quality and energy efficiency.
Soil quality ratings in 1998 and 1999 for the organic and integrated systems were significantly higher than for the conventional system, due to the addition of compost and mulch. Differences in annual yields were inconsistent among the three systems, whilst tree growth was similar. There were satisfactory levels of nutrients among all three. A consumer taste test found organic apples less tart at harvest and sweeter than conventional apples after six months of storage.
Organic apples were the most profitable due to price premiums and quicker investment return. Despite initial lower receipts in the first three years, due to the time taken to convert to certified organic farming, the price premium to the grower of organic fruit in the next three years averaged 50% above conventional prices. In the long term, the organic system recovered initial costs faster. The study projected that the organic system would break even after 9 years, but that the conventional system would do so only after 15 years, and the integrated system, after 17 years.
The environmental impact of the three systems was assessed by a rating index related to the potential adverse impacts of pesticides and fruit thinners: the higher the rating, the greater the negative impact. The conventional system index was 6.2 times that of the organic system. Despite higher labour needs, the organic system expended less energy on fertiliser, weed control and biological control of pests, making it the most energy efficient.
Comparisons between conventional and organic farming are actually not on a level playing field because research input into organics is small compared to the former. Organic research tends to be more diffuse, farm-based and participatory, drawing on local knowledge and tradition. It also focuses on public goods, resources and techniques that are not readily patentable. This explains why organics attract little investment from private sources compared to conventional and biotechnological approaches [2]. As such, higher levels of public funding for organics is needed.
At present, growers of more sustainable systems may be unable to maintain profitable enterprises without economic incentives, such as price premiums or subsidies. But if external environmental and social costs are internalised into economic accounting, currently profitable conventional farming systems may well become uneconomical and unsustainable. Incorporating the value of ecosystem processes would encourage food producers to employ economically and environmentally sustainable practices [20].
Article first published 02/10/02
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