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Agronomic and Economic Performance Characteristics of Conventional and Low-External-Input Cropping Systems in the Central Corn Belt

^a Dep. of Agronomy, Agronomy Hall, Iowa State Univ., Ames, IA, 50011
^b Dep. Hortofruticultura, Botánica y Jardinería, Univ. de Lleida, Av. Alcalde Rovira Roure 191, 25198 Lleida, Spain
^c Iowa State University Extension, 720 7th Avenue SW, Tripoli, IA, 50676
^d Dep. of Land Resources and Environmental Sci., Leon Johnson Hall, Montana State Univ., Bozeman, MT, 59717
^e USDA-ARS Invasive Weed Management Unit, 1102 S. Goodwin Ave., Urbana, IL, 61801
^f Dep. of Statistics, Snedecor Hall, Iowa State Univ., Ames, IA, 50011. Funding for this work was provided by the USDA National Research Initiative (Projects 2002-35320-12175 and 2006-35320-16548), the Leopold Center for Sustainable Agriculture (Project 2004-E6), and the Iowa State University Agronomy Endowment

View larger version (27K): [in this window] [in a new window]   Fig. 1. (A) Synthetic N fertilizer and (B) herbicide active ingredients used in each rotation system, by year. The values shown represent the sums of the mass of materials applied per unit area in each of phase of each rotation system, divided by the length, in years, of the rotation.

View larger version (28K): [in this window] [in a new window]   Fig. 2. Change in viable seed densities of (A) giant foxtail and (B) velvetleaf between November 2002 and April 2006 in each rotation system, in the top 20 cm of soil. Means and their standard errors are shown. Negative values indicate a decline in mean seed densities over time. Asterisks indicate a significant difference (P < 0.05, two-tailed test) between the value shown and 0. Within a species, values represented by columns not underwritten with the same lowercase letter are significantly different (P < 0.05).