Science in Society Archive

Organic Agriculture Enters Mainstream

Organic Yields on Par with Conventional and Ahead During Drought Years

But by far the greatest gains are due to savings on damages to public health and the environment estimated at more than US$59 billion a year. Dr. Mae-Wan Ho puts the nail on the coffin on industrial agriculture

Myths die hard

Scientists who should know better - if only they had kept up with the literature - continue to tell the world that organic agriculture invariably means lower yields, especially compared to industrial high input agriculture, even when this has long been proven false (see for example, “Organic agriculture fights back” SiS 16 [1]; “Organic production works”, SiS 25 [2]).

Researchers led by David Pimenthal, ecologist and agricultural scientist at Cornell University, New York, have now reviewed data from long-term field investigations and confirmed that organic yields are no different from conventional under normal growing conditions, but that they are far ahead during drought years [3]. The reasons are well known: organic soils have greater capacity to retain water as well as nutrients such as nitrogen.

Organic soils are also more efficient carbon sinks, and organic management saves on fossil fuel, both of which are important for mitigating global warming.

But by far the greatest gains are in savings on externalised costs associated with conventional industrial farming, which are estimated to exceed 25 percent of the total market value of United States’ agricultural output.

Long-term field trials at Rodale Institute

From 1981 through 2002, field investigations were conducted at Rodale Institute in Kutztown, Pennsylvania on 6.1 ha. Three different cropping systems: conventional, animal manure and legume-based organic, and legume-based organic. Plots (18 x 92 m) were split into three (6 x 92 m) subplots, which are large enough for farm-scale equipment to be used for operations and harvesting. The main plots were separated with a 1.5 m grass strip to minimize cross movement of soil, fertilizers, and pesticides. Each of the three cropping systems was replicated eight times.

The conventional system based on synthetic fertilizer and herbicide use, represented a typical cash-grain 5-year crop rotation (corn, corn, soybeans, corn, soybeans) that reflects commercial conventional operations in the region and throughout the Midwest. According to USDA 2003 data, there are more than 40 million ha in this production system in North America. Crop residues were left on the surface of the land to conserve soil and water; but no cover crops were used during the non-growing season.

The organic animal-based cropping represented a typical livestock operation in which grain crops were grown for animal feed, not cash sale. This rotation was more complex: corn, soybeans, corn silage, wheat, and red clover-alfalfa hay, as well as a rye cover crop before corn silage and soybeans. Aged cattle manure served as the nitrogen source and applied at 5.6 tonnes per ha (dry), 2 years out of every 5 immediately before ploughing the soil for corn. Additional nitrogen was supplied by the plough-down of legume-hay crops. The total nitrogen applied per ha was about 40 kilograms per year or 198 kg per ha for any given year with a corn crop. Weed control relied on mechanical cultivation, weed-suppressing crop rotations, and relay cropping, in which one crop acted as living mulch for another.

The organic legume-based cropping represented a cash grain operation without livestock. The rotation system included hairy vetch (winter cover crop used as green manure), corn, rye (winter cover crop), soybeans, and winter wheat. The total nitrogen added to this system per ha per year averaged 49 kg (or 140 kg per ha) per year with a corn crop). Both organic systems included a small grain, such as wheat, grown alone or inter-seeded with a legume. Weed control was similar in both organic systems.

Yields no different except under drought conditions

For the first five years of the experiment (1981-1985), the yields of corn grain averaged 4 222, 4 743 and 5 903kg per ha for organic-animal, organic-legume, and conventional systems. After this transition period, corn grain yields were similar for all systems: 6 431, 6 368, and 6 553 kg per ha. Overall, soybean yields from 1981 through 2001 were 2 461,

2 235 and 2 546 kg per ha; the lower yield of organic legume system is attributed to the failure of the soybean crop in 1988, when climate conditions were too dry to support relay intercropping of barley and soybeans. If 1988 is taken out of the analysis, soybean yields are similar for all systems.

The 10-year period from 1988-1998 included 5 years in which the total rainfall from April to August was less than 350 mm (compared with 500mm in average years). Average corn yields in those dry years were significantly higher (28 percent to 34 percent) in the two organic systems: 6938 and 7235kg per ha in organic-animal and organic-legume systems compared with 5333 kg per ha in the conventional system.

During the extreme drought of 1999 (total rainfall between April and August only 224mm), the organic animals system had significantly higher corn yields (1511 kg per ha) than either the organic legume (421 kgper ha) or the conventional (1100kg per ha). Crop yield in the organic legume were much lower in 1999 because the high biomass of the hairy vetch winter cover crop used up a large amount of the soil water. During the 1999 drought soybean yields were 1400, 1800 and 900 kg per ha for organic animal, organic-legume and conventional.

Other advantages of organic systems

Over a 12-year period, water volumes percolating through each system were 20 percent and 15 percent higher in the organic-animal and organic legume systems than in conventional. During the growing season in 1995, 1996, 1998 and 1999, soil water content was significantly higher in the soil farmed using the organic legume system than in the conventional system, accounting for the much higher soybean yields in the organic legume system in 1999.

About 5.2 million kilocalories of energy per ha were invested in the production of corn in the conventional system. Energy inputs for the organic animal and organic legume systems were 28 percent and 32 percent less. The energy inputs for soybean production in the organic-animal, organic legume and conventional systems were similar at 2.3 mkcal, 2.3 mkcal, and 2.1 mkcal respectively.

Economic comparison of the organic corn-soybean rotation with conventional corn-soybean systems from 1991-2000 showed that without price premiums for the organic rotation, the annual net returns for both were similar:$184 per ha for conventional, $176 per ha for organic legume (Table 1).

Table 1. Annual costs per ha

 Organic legumeConventional
Fertilizers &Lime$18$79
Hired labour$6$9
Net income$176$184

Soil carbon at start (1981) was not different between the three systems. In 2002, however, soil carbon levels in the organic animal and organic legume systems were 2.5 percent and 2.4 percent versus 2.0 percent in the conventional. The annual net aboveground carbon input (based on plant biomass and manure) was the same in organic legume system and conventional system (~9 000kg per ha), but about 10 000 kg per ha in organic animal system. However, the two organic systems sequester more of that carbon in the soil, resulting in an annual soil carbon increase of 981 and 574 kg in the organic animal and organic legume systems, compared with only 293 kg per ha in the conventional systems (calculated on the basis of about 4 million kg per ha of soil in the top 30cm.). Total soil carbon increase after 22 years was: 27.9 percent, 15.1 percent and 8.6 percent in organic animal, organic legume and conventional systems.

Soil nitrogen levels started at 0.31 percent in 1981. By 2002, the conventional system remained unchanged, while organic animal had increased to 0.35 percent and organic legume system to 0.33 percent. Using 15N to measure retention of N in soil it was estimated that 47 percent, 38 percent and 17 percent respectively of the nitrogen from organic animal, organic legume and conventional was retained in the soil each year after application. This matched the decreased amount leached from the organic soils.

Four herbicides were applied in the conventional system: atrazine (to corn), pendimethalin (corn), metolachlor (corn and soybeans) and metribuzin (soybeans). From 2001 to 2003, only atrazine and metolachlor were detected in water leachates collected from conventional systems at levels in excess of 3 parts per billion, exceeding maximum contaminant level set by US EPA for atrazine (no level has been set for metolachlor).

Soils farmed with the two organic systems had greater populations of spores of the beneficial Arbuscular mycorrhizal fungi, shown to enhance disease resistance, improve water relations and increase soil aggregation.

Large amounts of biomass (soil organic matter) are expected to significantly increase soil biodiversity. Microarthropods and earthworms were reported to be twice as abundant in organic versus conventional agricultural systems in Denmark. Earthworms and insects create holes in the soil that increase the percolation of water into the soil and decrease runoff.

Labour requirements

Each system was allowed 250 “free” family labour per month; while the cost of hired labour was $13 per hour. With organic farming system, the farmer was busy throughout the summer with the wheat crop, hairy vetch cover crop, and mechanical week control but worked less than 250 hours per month). In contrast, the conventional farmer had large labour requirements in the spring and fall, plating and harvesting, but little in the summer months.

Increase in labour input may range from 7 percent to a high of 75 percent in organic compared to conventional systems. But in situations where human labour is not in short supply, this too can be an advantage of organic agriculture in creating employment.

The externalised costs of conventional agriculture not taken into account

By far the biggest gains from organic agriculture arise from the savings on the damages to public health and the environment due to the use of agrochemicals in conventional agriculture.

The National Organic Standards Program in the United States prohibits the use of synthetic chemicals, GMOs and sewage sludge in organically certified production.

As Pimenthal points out [3], the estimated environmental and healthcare costs of pesticide use at recommended levels in the US is about 12 billion every year. According to the National Research Council [3], the cost of excessive fertilizer use is $2.5 billion per year, while the estimated annual costs of public and environmental health losses related to soil erosion greater than $45 billion [5].

The total externalised cost of conventional agriculture per year is $59.5 billion. This represents 27.4 percent of the entire agricultural output ($217.2 billion in 2002 [6]).

Article first published 12/09/05


  1. Lim LC. Organic agriculture fights back. Science in Society 2002, 16, 30-32.
  2. Gala R. Organic production works. Science in Society 2005, 25, 14-15.
  3. Pimental D, Hepperly P, Hanson J, Douds D and Seidel R. Environmental, energetic, and economic comparisons of organic and conventional farming systems. BioScience 2005, 55, 573-82.
  4. BANR/NRC 2003 Board on Agriculture and National Resources, National Research Council, Frontiers in Agricultural Research: Food, Health, Environment, and Communities. Washington DC, National Academies Press, 2003.
  5. Pimental, D et al. Environmental and economic costs of soil erosion and conservation benefits. Science 267, 1117-23.
  6. Chapter 17 Statistical Abstract of the United States: 2004-2005, Section 17 Agriculture, US Census Bureau,

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