The Long-Term Agro-ecological Research (LTAR) experiment: Ecological benefits of organic crop rotations in terms of crop yields, soil quality, economic performance and potential global climate change mitigation

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Project Description: 
The Long-Term Agro-ecological Research (LTAR) Experiment was established in 1998 at the ISU Neely-Kinyon Farm in Greenfield to compare conventional and organic cropping systems. The proposed research evaluates alternatives to the traditional corn-soybean rotation in Iowa, and investigates production processes based on agroecological principles, designed to reduce off-farm energy demand and to increase the internal resilience of agroecosystems, which consequently increases their adaptability to potential climate changes.
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Lead Investigator: 
Kathleen Delate
Lead Investigator Affiliation: 
ISU Agronomy and Horticulture
Lead Investigator Bio: 

Kathleen Delate's research lab conducts projects across the state at Iowa State UniversityResearch Farms and as on-farm trials. These include the following: research/demonstration plots of organic agronomic crop production with various crop rotations; organic soybeans following CRP land; variety trials; production of organic herbs (St. John's Wort and catnip), fruits (grapes and apples) and vegetables (peppers, tomatoes, edamame soybeans and sweet corn). The lab also maintains long-term agroecological plots that compare conventional and organic systems.

Cynthia Cambardellais a Research Soil Scientist with the USDA-ARS at the National Laboratory for Agriculture and the Environment (NLAE) in Ames, IA, and Associate Professor of Soil Science in the Department of Agronomy at Iowa State University. She works at multiple scales across space and time to define impacts on critical ecosystem services such as C sequestration, nutrient cycling, water storage, and erosion mitigation.

Craig Chase is a farm management specialist for Iowa State University Extension. His interests include, business planning and business start-ups, also insurance and risk management tools and techniques, organic and food-based alternative agricultural enterprises, regional food systems, sustainable agriculture and water quality issues, and whole farm and enterprise financial analysis and decision-making.

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Cynthia Cambardella, USDA-ARS National Laboratory for Agriculture and the Environment; and Craig Chase, ISU Farm Management Extension

Work continues in Year 16 of a long-term experiment comparing organic and conventional crop rotations. Adverse weather conditions in 2013 affected the production and performance of several crops in the rotations being studied. As a consequence of extended wet weather in spring, poor stands, delayed weed management and subsequent high weed populations, organic soybean yields were 26 percent lower than 2012. Organic corn yields were, however, greater than conventional corn, even when re-planting occurred on June 8.

Key Question: 

How can we gauge the viability of organic cropping systems in relation to the agronomic, economic and soil quality effects in conventional cropping systems?


The project measured various parameters and determined that, even with reduced yields, organic crops were more lucrative because of lower costs of production coupled with higher premium prices compared to conventional crops. Soil quality effects were evaluated every fall after harvest by quantifying a suite of biological, chemical and physical soil properties. Researchers measured soil organic C, total soil N, microbial biomass C, N mineralization, macroaggregation, extractable NO3-N, NH4-N, P, K, Mg, and Ca, electrical conductivity, and bulk density.

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