Project ID



Comparisons across the three research sites, with histories ranging from 5- to 19-years-old, allowed for an examination of the effects of crop rotation history (short vs. longer) and system (organic vs. conventional) on weed management, crop productivity, soil quality and soil microbial communities.

Key Question

What impact does crop rotation history and management system (conventional vs organic) have on weed management, crop productivity, soil quality and microbial communities?


Over all years, despite lower yields in times of excess rain and loss of N from composted manure fertilization, organic returns have averaged twice those of conventional returns. The weather in 2015 and 2016 was extremely challenging, with 10 inches above normal rainfall in June 2015 and drought in 2016. As a result of these extreme weather conditions and late planting, weed management and yields were affected in all plots, pointing out the need for constant on-site management and timeliness in planting, rotary hoeing and cultivation for weed control for successful organic yields. Subsurface drainage water nitrate-N loss for a 3-year period at the OWQ site from the conventionally managed C-S system (79.2 kgN/ha) was nearly twice as much as from the organically managed C-S-O/A-A (39.9 kgN/ha). The pasture system (16.5 kgN ha-1) lost the least amount of N over the 3 years. At the LTAR site, soil quality was consistently higher in the organic rotations relative to the conventionally managed corn-soybean rotation from 2012 to 2016. In 2015 and 2016, soil quality the organic soils had more microbial biomass C and N, higher P, K, Mg and Ca concentrations, and lower soil acidity than conventional soils.

Principal Investigator(s)

Kathleen Delate


Cynthia Cambardella; Matt Bakker; Ann Johanns

Year of Grant Completion