Study: Organic, Sustainable Soils ‘Healthier’ Than Conventional Soils

In a study of soils found on crop-producing N.C. farms, North Carolina State University researchers found that soils on farms that used organic or sustainable production methods had lower levels of Southern blight disease and were overall “healthier” than soils on farms using conventional farming methods.

The study showed that Southern blight disease, a common soil-borne fungus that affects tomatoes, peppers and hundreds of other plants, was three to five times less prevalent on sustainable farms – those where synthetic pesticides were not used – than conventional farms, where synthetic pesticides, synthetic fertilizers and herbicides were used.

Southern blight disease was also less prevalent on organic farms – those where neither synthetic pesticides nor synthetic fertilizers were used – than on conventional farms.

In addition, says Dr. Jean Beagle Ristaino, professor of plant pathology at NC State and the lead author of a paper describing the research, organic and sustainable farm soils contained more helpful chemical nutrients, had higher porosity and water-holding capacity – reducing the need for watering – and contained more beneficial bacteria that contribute to overall healthiness.

The research was published in Applied Soil Ecology.

In the study, conducted from 2001 through 2003, the researchers examined three organic farms and three sustainable farms located in Chatham and Orange counties and four conventional farms located near Clinton, N.C. Besides comparing the incidences of Southern blight disease, the researchers found organic and sustainable farm soils had lower bulk density, which made it easier for plant roots to grow.

They also found that organic and sustainable farm soils had higher water-holding capacity, which translated to higher water content – an important and highly desired characteristic during times of drought.

Chemicals acting as soil nutrients were also more prevalent in sustainable and organic soils, as were tiny organisms that could help suppress soil-borne diseases. The latter finding may have contributed to the reduced levels of Southern blight disease in organic and sustainable farm soils, but further research is needed to gauge whether this relationship was indeed causal, Ristaino says.

The research was funded by the U.S. Department of Agriculture’s Sustainable Agriculture Research and Education Program and NC State’s Agricultural Research Service.

– kulikowski –

Note to editors: An abstract of the paper follows.

“Effect of Organic, Sustainable, and Conventional Management Strategies in Grower Fields on Soil Physical, Chemical, and Biological Factors and the Incidence of Southern Blight”

Authors: Bo Liu, Cong Tu, Shujin Hu, Marcia Gumpertz and Jean Beagle Ristaino, North Carolina State University

Published: October 2007 in Applied Soil Ecology 37:202-214

Abstract: The objectives of our research were to evaluate the impact of organic, sustainable, and conventional management strategies in grower fields on soil physical, chemical, and biological factors including soil microbial species and functional diversity and their effect on the Basidiomycete plant pathogen Sclerotium rolfsii, causal agent of Southern blight. Soils from 10 field locations including conventional, organic and sustainable farms were sampled and assayed for disease suppressiveness in greenhouse assays, and soil quality indicators. Soils from organic and sustainable farms were more suppressive to Southern blight than soils from conventional farms. Soils from organic farms had improved soil chemical factors and higher levels of extractable C and N, higher microbial biomass carbon and nitrogen, and net mineralizable N. In addition, soil microbial respiration was higher in soils from organic than sustainable or conventional farms, indicating that microbial activity was greater in these soils. Populations of fungi and thermophiles were significantly higher in soils from organic and sustainable than conventional fields. The diversity of bacterial functional communities was also greater in soils from organic farms, while species diversity was similar. Soils from organic and sustainable farms had improved soil health as indicated by a number of soil physical, chemical and biological factors and reduced disease.