University of Minnesota
By Jim Riddle, Organic Outreach Coordinator

Data presented by University of Minnesota Extension Corn Agronomist Dr. Jeff
Coulter during the U of M’s Organic Field Day, held July 8, 2010, at the SWROC near
Lamberton, demonstrates the long‐term productivity of organic cropping systems.

In 1989, the Variable Input Crop Management System (VICMS) trials were initiated on 40 acres of the Elwell Agroecology Farm at the SWROC to evaluate zero‐externalinput;
low‐external‐input; high‐external‐input; and organic‐input management strategies in a 2‐year soybean‐corn rotation and a 4‐year oat/alfalfa‐alfalfa‐cornsoybean rotation. Crop yields, yield variability, and yield stability were measured over time for these cropping systems.

According to Dr. Coulter, many long‐term trials have demonstrated the value of
including forage legumes in crop rotations, and this was confirmed in the VICMS
research.

Forage legumes, such as alfalfa and clover in crop rotations can: supply nitrogen for
grain crops; increase soil organic matter; improve soil structure and tilth; and
reduce weed pressure. Presently, short‐term rotations without forage legumes
dominate the Midwest, with lost rotation effects being offset with purchased
fertilizers and pesticides.

In the organic plots of the VICMS study, crop rotation, manure, and mechanical weed
control practices were used to eliminate the use of synthetic fertilizers and
pesticides. Beef manure was used as fertilizer. Weeds were controlled through
delayed planting, rotary hoeing, and row cultivation.

In the zero‐input plots, no external inputs were used except seeds. Weeds were
controlled through delayed planting, rotary hoeing, and row cultivation.

In the low‐input plots, banded herbicide and synthetic fertilizer were applied for
realistic yield goals. In the high‐input plots, broadcast herbicide and synthetic
fertilizer were applied for yield goals 10% above expected. Row cultivation was
used in the low‐input and high‐input plots.

The VICMS trials began in 1989, but time was needed to establish crop rotation
background and allow fertility and weed pressures to reach levels representative of
the various systems. Because of this, analysis conducted by Dr. Coulter ignored the
first 4 years of data and focused on 17 years of data from 1993 to 2009.

Oat Yield 1993 to 2009

Oat yield and variability in yield were similar among organic, low‐input, and high-input systems, due to similar agronomic management for oats in the different systems (only differed in nutrients, with beef manure used in the organic plots.) According to Dr. Coulter, manure in organic system may have increased soil water holding capacity, but oat yield is generally determined before the onset of very dry conditions, so yields were similar for all the production systems studied.

Alfalfa Yield 1993 to 2009

Alfalfa yields were less variable and 16 to 28% higher with organic management
than low‐ and high‐input systems, respectively, possibly due to greater soil water
holding capacity under organic management, which is especially important for the
3rd cut of alfalfa.

Soybean Yield 1993 to 2009

Soybean yields were less variable and 6% higher in the 4‐year rotation than the 2‐
year rotation. They were highest and least variable with the high‐input system, and
lowest and most variable with the organic and zero‐input systems, likely due to the
fact that the organic and zero‐input soybeans were planted about 12 days later than
low‐ and high‐input systems. In addition, the food grade soybeans planted on the
organic and zero‐input plots have lower yield potential; there was more weed
competition; plus the yields were reduced in 2006 and 2008 due to soybean aphids.

Corn Yield 1993 to 2009

Corn yields were less variable in the 4‐year rotation than the 2‐year. In the 4‐year
rotation, there was no difference in corn yield between organic‐, low‐, and high-input
systems.

Summary

This study substantiates the long‐term productivity of organic systems. Alfalfa
yields were highest and least variable with organic management. Oat yields and
yield variability were similar for organic and high‐input systems. Corn yields with
the 4‐yr organic rotation were among the highest and least variable. The challenge
in organic management will be to increase soybean yield and reduce variability in
soybean yield across years.

To view Dr. Coulter’s presentation, including graphs of crop yields and variability,
visit www.organicecology.umn.edu.

For more information on this research, contact Dr. Coulter at: [email protected]

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