Project ID



Comparisons across the three Iowa research sites, with histories ranging from three to 17 years, allowed the research team to examine 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

Do farming systems with histories of long crop rotations, slowly mineralized sources of nitrogen (from natural, recycled materials like composted manure), and cover crops perform better in terms of pest suppression, weed management, and healthy soil microbial communities than two-crop conventional farming systems with synthetic inputs?


By studying and collecting over 25 sets of biological data, researchers are beginning to answer this question by determining equivalent yields where crops are grown on land with a history of longer rotations with oats and alfalfa, and non-synthetic inputs are used. Soil microbial community analysis showed the presence of more than 11,000 distinct bacterial taxa at the Neely-Kinyon Long-Term Agroecological Research (LTAR) site, with bacterial communities within the organic soils different from the bacterial communities in the conventional soil. This suggests that organic management provides a rich resource of food for the soil microbes, which fuels microbial growth, and subsequently increases microbial biomass.

Principal Investigator(s)

Kathleen Delate


Cynthia Cambardella, Matt Bakker, Ann Johanns

Year of Grant Completion