Degree Type


Date of Award


Degree Name

Master of Science




Sustainable Agriculture

First Advisor

Kathleen Delate


Negative environmental impacts associated with intensive pesticide use and over-fertilization in conventional production have encouraged many producers to investigate organic methods. In the most current (2008) U.S. Department of Agriculture (USDA) statistics on organic agriculture, land under certified organic production increased to 4.8 million acres, with 194,637 acres of organic corn (Zea mays L.), 125,621 acres of organic soybean [Glycine max (L.) Merr.], and 164,888 acres in organic vegetable crops. In order to enter the expanding organic market and meet certified organic requirements, producers must implement a soil-building plan that focuses on preserving soil organic matter. The majority of organic grain production occurs in the Midwestern U.S. where growers are aware of the need to balance meeting increasing demand with maintaining soil health. A countervailing event that affects soil quality in organic systems is weed management, which currently relies extensively on tillage operations. Beginning in 2002, the Rodale Institute (Kutztown, PA) piloted an Organic No-Till system to reduce tillage operations and the carbon footprint of organic production. This system is based on a roller/crimper implement (a large, 10.5 ft. wide x 16 in. diameter, steel cylinder with steel blades welded in a chevron pattern to facilitate a crimping motion) that is used to mechanically terminate fall-planted cover crops the following spring in place of synthetic herbicides, which are disallowed in organic production.

A series of organic no-till experiments was established in Iowa from 2008 to 2011 to examine the effect of cover crops, crop sequences, and tillage operations on organic grain crop growth, weed management and yields. In the first set of experiments (2008-2011) at the Iowa State University (ISU) Agronomy Farm (Boone, IA), organic no-till soybeans in the wheat-rye/soybean-oat-rye/soybean crop sequence produced equivalent yields to tilled organic soybeans in the same crop sequence, averaging 34 bu/acre over two seasons. Weed management mirrored tilled plots until later in the season when rye tillers emerged in no-till plots; these grasses did not affect yields, however. Organic no-till corn in the wheat-hairy vetch/corn-oat-hairy vetch/corn sequence did not achieve acceptable yields in either year, due to competition with hairy vetch re-growth and poor weed management from lack of sufficient cover crop mulch. Tilled corn also suffered from lack of supplemental nitrogen in this experiment, leading to the conclusion that cover crops should not be considered as a sole nutrient source in organic corn production.

In the organic no-till corn experiment at the ISU Neely-Kinyon Farm (Greenfield, IA) from 2010 to 2011, five cover crops, including hairy vetch (Vicia villosa), rye (Secale cereale), winter triticale (Triticosecale sp.), Austrian winter pea (Pisum arvense), and a combination of rye/hairy vetch, were evaluated against a control plot with no cover crop under two main treatments of no tillage (no-till) and conventional tillage (tilled). Tilled corn crops out-performed no-till crops both years of the experiment. In 2010, due to extensive rains and late planting, all corn was harvested as silage, with biomass yields of 25 tons/acre in tilled plots and 6.5 tons/acre in no-till plots. Cover crops were not uniformly associated with increased yields, but higher silage yields were obtained in the hairy vetch treatments in no-till plots compared to rye and triticale treatments. Corn grain yield in 2011 in the legume cover crop treatments in tilled plots averaged 120 bu/acre compared to only 57 bu/acre in the cereal cover crop treatments. Corn in the no-till plots again suffered from lack of N, weed competition and cover crop re-growth, and was harvested as silage, averaging 13.3 tons/acre, with no significant difference between cover crop treatments. Other problems in organic no-till corn included corn borer damage, which may have been associated with greater attraction by insect pests to crops under stress. As a result of these experiments, organic no-till corn is now considered too difficult for Midwest conditions, and a new crop rotation including alfalfa as a cover crop prior to the no-till segment of rye/soybean is currently under investigation. Based on the beneficial effects from increased carbon inputs in long-term organic no-till crop rotations, economic benefits could also be obtained from soil carbon enhancement and greenhouse gas reduction if Clean Energy legislation and carbon markets support such practices in the future.


Copyright Owner

Dan Edward Cwach



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68 pages