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Book of Abstracts

11th IFOAM
Scientific Conference
11-15 August 1996
Copenhagen, Denmark

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Subject index
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Rodale's Farming System Trial: First 15 Years S19

Drinkwater, L. E. ; Fiorina, L. J. & Wagoner, P.

Rodale Institute, Kutztown, Pennsylvania, 19530, USA

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Since 1981, a conventional corn/soybean cropping system has been compared to two organic systems in a replicated experiment. The three cropping systems also differ from one another in terms of source and amount of nutrients supplied, amount of carbonaceous residues returned to the soil, tillage frequency, proportion of the year with growing plants, and sometimes varietal selection. The organic systems add leguminous cover crops and small grains to the rotation and do not use synthetic fertilizers or pesticides.

The intent of this study is to compare cropping systems under differing management regimes in order to examine management effects on agronomic and ecological properties. Now in its sixteenth year, the experiment offers a unique opportunity to study three well-defined agricultural systems that are clearly diverging in terms of soil organic matter dynamics, nitrogen cycling and overall soil quality. During the first 15 years, a majority of the work has focused on carbon and nitrogen cycling. Both organically managed cropping systems retained more nitrogen and carbon in the soil compared to the conventional system resulting in accumulations of soil organic matter. Despite having received two-fold more nitrogen than the legume-based system, the conventional system showed a net loss of soil nitrogen. Annual above-ground net primary productivity has increased only slightly over time in the conventional system. In contrast, both organic systems have shown significant increases in net primary productivity since 1981 resulting in greater residue inputs in the later years of the experiment.

While the conventional and manure-based system were comparable in terms of the balance between nitrogen inputs and crop exports of nitrogen, nitrogen loss through leaching was two-fold greater in the conventional system, averaging 17.9 kg ha-1 yr-1. We will discuss the strengths and weaknesses of the experimental design as well as highlight some of the more interesting findings.