Use Cover Crops, Manure for Best Soil Quality

LEXINGTON, Kentucky – Producers looking to build soil structure, and ultimately, soil quality through the use of organic amendment inputs may find success with cover crops or manure, according to the results of a University of Kentucky study.

Shawn Lucas, a PhD student majoring in soil microbiology and soil ecology in the Department of Plant and Soil Sciences,found that hairy vetch residue and dairy manure had the greatest impact on soil microbial growth by stimulating greater fungal activity, which promoted greater macro-aggregate formation.

The study, “Effects of Organic Amendments onAggregation and Microbial Community Dynamics in Soils,” was funded by a $10,000 Southern Sustainable Agriculture Research & Education (SARE) Graduate Student Grant.

“Soil aggregation is the foundation for surface soil structure, affecting processes such as water infiltration and movement, oxygen diffusion, and plant nutrient availability,” said Lucas. “I suspect the hairyvetch and the dairy manure did well because vetch and undigested components inmanure consist of complex plant materials which are more easily broken down by fungi, thus stimulating fungal growth in the soil ecosystem.”

Lucas also compared the vetch and the manure with a vegetable compost and non-amended soil. He found that the vegetable compost had little to no affect on the soil microbial community. In some cases, the non-amended soils out-performed the vegetable compost.

“The compost used neither enhanced soil structure nor did it significantly alter the microbial community, even relative to non-amended soils,” said Lucas. “ I suspect it’s because the compost has already been broken down once through the composting process so it doesn’t create an environment for rapid microbial development.”

In the two-year lab study, Lucas destroyed the native soil structure by forcing the soils through a sieve. He then applied the organic amendments and monitored the formation of soil macro-aggregates over aperiod of five, 12, 30 and 82 days.

Lucas found that vigorous fungal growth occurred within days with the hairy vetch and persisted beyond the 82-day treatment.

“I had a visible mat of fungal growth over the surface of the vetch treated soil during the first 2 weeks of the study and indicators of fungal activity remained elevated throughout the study” said Lucas. 

Lucas cautions that lab treatments don’t necessarily translate to real-world situations.

“Field experiments would also need to be conducted,”said Lucas, “but the idea here was to determine how the soil microbial community responds to different organic materials, and which ones stimulate greater fungal activity leading to greater levels of stable macro-aggregates.”

The study is a starting point for producers to determine which organic amendments to use for a specific soil type to build soil structure and soil quality using minimal chemical in puts.

The final report of the study (GS08-065) can be found on the national SARE database and searching by the project number. Other project participants included advisers Elisa D’Angelo with the University of Kentucky Department of Plant and Soil Sciences, and Mark Williams with the University of Kentucky Department of Horticulture.

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Published by the Southern Region of the Sustainable Agriculture Research and Education (SARE) program. Funded by the USDA National Institute of Food and Agriculture (NIFA), Southern SARE operates under cooperative agreements with the University of Georgia, Fort Valley State University, and the Kerr Center for Sustainable Agriculture to offer competitive grants to advance sustainable agriculture in America's Southern region.