Transitioning to organic? A three-year project studies the effects of different transitional strategies

Jan. 10, 2019
Tomato plant at an OARDC research field.

Use of compost and a mixed species hay crop are recommended.

For farmers transitioning from a conventional to an organic farming system, decisions made during the three-year transition period can influence important factors of future production, such as soil-borne pathogens, soil fertility, and soil structure. In this study, compost incorporation strongly affected physical, chemical, and biological soil health factors and, overall, the soil food web. Using a mix of perennial hay during the transition was most successful in reducing disease-causing pathogens in the soil. Highest available N and yields occurred in the plots using high tunnel vegetable production.

Materials and Methods

A three-year study was conducted in Wooster, Ohio, to evaluate four common rotational strategies used during transition from a conventional to an organic farming system. The four organic transition strategies evaluated were: 1) tilled fallow, 2) a single planting of mixed species perennial hay, 3) low intensity open field vegetable production, and 4) intensive vegetable production under a high tunnel.

Each transition strategy plot was split in half with 15,000 lbs./ac composted manure applied each year to one half.

At the year of certification, the fields were planted to tomato, with two smaller plots of soybean.

Key Findings

  • Compost treatment increased organic matter of soils in all treatments, lowered bulk density, and increased NO3-N, and microbial biomass-N.
  • The addition of compost boosted plant vigor for tomatoes for all transition strategies, but had an inconsistent effect on suppression of soil-borne diseases.
  • Transition cropping strategy was the main factor influencing bacterial community structure in the soil and the rhizosphere.
  • Bacterial communities involved in disease suppression were more abundant in soil previously cropped with hay compared to tilled fallow and low-intensity vegetable production. This was true for both tomato and soybean crops.
  • Overall, the mixed hay was the most effective in decreasing damping-off for both tomato and soybean crops.
  • Tomato yield during year four was much higher in the high tunnel plot. The hay treatment also showed better yield than the tilled fallow and open field vegetable production.

Why Researchers Think the Hay and High Tunnel Treatments Did Better

Disease suppression might happen in two ways. One involves specific action against pathogen populations. For example, brassicas (cauliflower, kale, turnip, radish, cabbage) suppress soil-borne diseases by exuding sulfur-rich substances that are toxic to many pathogenic soil organisms. And certain species of nematodes eat bacteria and fungi that cause plant diseases. Disease suppression can also occur from high competition for available resources. In both cases, the disease suppression is associated with the overall composition of the microbial community (bacteria, fungi) present in the soil and the rhizosphere.

The hay crop used in this experiment was a combination of Festulolium (a rye fescue hybrid) under-sown with alfalfa, red and white clover, timothy, chicory, orchardgrass, and plantain in equal proportions. Researchers concluded that the above-ground diversity of the hay mix supported an increase in beneficial soil organisms that compete or interfere with pathogens, thus, reducing incidence of disease in future crops.

The highest yields in this study were from the high tunnel plots. While some of the increase resulted from extending the growing season, soil analyses also found a higher level of available N in the high tunnel plots. Researchers think this was a result of maintaining the soil food web in a biologically-active state during the cold early spring months in northern Ohio. The monthly mean soil temperature inside the high tunnels was warmer by 35–41°C from January to May while from July to September it was marginally lower than the outside soil temperature. (Based on top 4 inches.)

For more information on using tunnels in vegetable production, visit the Vegetable Production Systems Laboratory’s Crop Enivronments page.

Prepared by Louceline Fleuridor and Cassandra Brown

Based on summaries of the following papers:

Benítez, MS; Baysal, F.; Rotenberg, D.; Kleinhenz, M.D.; Cardina, J.; Stinner, D.; Miller, S.A.; Gardner, B. B. 2007. Multiple statistical approaches of community fingerprint data reveal bacterial populations associated with general disease suppression arising from the application of different organic field management strategies. Soil Biology and Biochemistry Volume 39, Issue 9, September 2007, Pages 2289-2301

Briar, S.S., Miller, S.A., Stinner, D., Kleinhenz, M.D., & Grewal, P.S. 2011. Effect of different organic transition strategies for peri-urban vegetable production on soil properties, nematode community, and tomato yield. Applied Soil Ecology, 47, pgs 84-91.

Baysal, F; Benitez, MS; Kleinhenz, MD; Miller S.A.; Gardner B.B. 2008. Field management effects on damping-off and early season vigor of crops in a transitional organic cropping system. Phytopathology, Vol. 98, No. 5.