A new study shows organic production outperforms conventional in crop yield, soil fertility, pest reduction and economic return. Rhea Gala reports
Increasing public demand for organic products attracts premiums for the certified organic farmer, causing hard-pressed conventional farmers to consider going organic.
In the US, a 20% annual growth rate caused sales of organic produce to reach $8 billion in 2001; and incentives to farmers to go organic are offered in the 2002 Farm Bill, including cost sharing, and direct payments for conservation practices, such as longer crop rotations.
Scientists Kathleen Delate of Iowa State University and Cynthia A. Cambardella of the US Department of Agriculture assessed the agroecosystem performance of farms during the three-year transition it takes to switch from conventional to certified organic grain production. Strategies for lowering the risk of yield loss during this period have been researched, as productivity has been found to decrease initially when fertilizer and pesticide applications are withheld. But productivity generally improves in successive years under organic management to equal that in conventional farms. The study found that organic grain crops can be successfully produced in the third year of transition and that additional economic benefits can be derived from expanded crop rotation.
The experiment, lasting four years (three years transition and first year of organic certification), tested the hypothesis that organic systems relying on locally derived inputs are capable of providing stable yields while maintaining soil quality and plant protection compared with conventional systems with less diverse crop rotations and greater levels of external, fossil-fuel based inputs. The experimental design involved a completely randomized four replications of four different cropping system treatments.
The researchers looked at the effects of organic farming practices, including crop rotation, cover cropping, compost application, and non-chemical weed control on soil fertility, crop yield, and grain quality compared with the conventional system. They assessed pests and plant response under various crop rotations, and determined which certified organic drop rotations reduced the risks from low yield and improved soil properties and economic returns.
During the four-year period, corn yield in the organic system averaged 91.8% of conventional corn yield and soybean yield in the organic system averaged 99.6% of conventional soybean yield. By year three, there was no significant difference between organic and conventional yields; and both organic corn and soybeans exceeded conventional yields in the fourth year (the first year after certification).
In the initial year of transition, an economic advantage could be gained by planting legume hay crops or crops with a low nitrogen demand in fields with low productivity, to increase fertility for the following corn crop. In the second year, yield differences were mitigated by rotation effects and compost application, providing sufficient nutrients for the organic grain crop. The yields in year three were similar, but the importance of a soil-building cover crop, or legume grass mixture such as the oat-alfalfa mixture used in this study was apparent in the fourth year when organic corn and soybean yields out-performed the conventional crops.
The researchers thought that timely weed management and sufficient levels of nitrogen, phosphate and potassium in the organic system contributed to good yields during transition. Yield increases were obtained after three years because of available nitrogen due to organic amendments, such as composted pig manure and the inclusion of forage legumes and other green manures in extended crop rotations.
Soil fertility depends on the constant renewal of biologically available nitrogen to replenish the organic nitrogen pools for plants to absorb. Total nitrogen levels showed an increase of 457 kg per hectare in organic soil over four years, or an average increase of 114 kg N per ha per annum, sufficient to maintain organic nitrogen pools in this system. Total organic calcium increased 9% in organic soil over the transition period, with no significant increase in non-organic soil.
The researchers found weed pressure in the organic corn and soybean systems was manageable, and that it was less in organic soybean than in corn plots where rye was not used as a cover crop. In the soybean-rye rotation, weed densities were equivalent to conventional systems in the first two years, and significantly less in the third year. Grass and broadleaf weed populations varied between the organic and conventional systems each year, but the impact on yield was considered negligible. Corn borer and bean leaf beetle populations were similar between systems, again with no effect on yield.
Economic returns in the organic corn-soybean-oats/alfalfa and the organic corn-soybean-oats/alfalfa-alfalfa rotations were significantly greater than those in the conventional corn-soybean rotation, as organic soybean commands premium prices in the organic rotation due to increased demand.
A previous study had found enhanced soil fertility and higher biodiversity were correlated with less dependence on inputs in the organic systems, reducing fertilizer and energy inputs by 44% and pesticide by 97%.
This study is ongoing, and will continue to examine the effect of crop sequence and length of rotation on long-term pest disruption and attraction of beneficial insects into the organic systems. Earlier work by Miguel Altieri at University of California, Berkeley, showed that greater biological control should occur in organic systems that maintain diverse biota through minimal pesticide use (see "Agroecology vs ecoagriculture", ISIS report www.i-sis.org.uk).
Potential food quality changes will also be monitored over time, so that assessments of the advantages of organic production over conventional systems can be brought more to the foreground of the debate on organic versus conventional production. As organic farmers produce high quality food without conventional inputs from agribusiness, agribusiness has a vested interest in denigrating organic systems on any account. This research is essential in countering the corporate disinformation campaign.
Article first published 09/12/04
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