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Abbreviations: AI, acid insoluble; AS, acid soluble; SOC, soil organic carbon; SOM, soil organic matter.Understanding the interaction between plant components and their subsequent decomposition provides insights on how plant quality differences may infl uence C sequestration within a given management system. Our hypothesis was that decomposition is a function of biochemical composition when all other variables are constant (e.g., particle size, temperature and moisture). Recognizing the challenges of reconciling laboratory and fi eld studies, this study examined the decomposition dynamics of fi ve selected crops with varying composition under controlled temperature and moisture regimes. Residue materials were partitioned into leaf, stem, and root organs to give a clearer indication of compositional control on decomposition. Plant quality varied among species (alfalfa [Medicago sativa L.], corn [Zea mays L.], cuphea [Cuphea viscosissima Jacq. ⋅ Cuphea lanceolata W.T. Aiton], soybean [Glycine max (L.) Merr.] and switchgrass [Panicum virgatum L.]). A two-component litter decomposition model was used to describe decomposition observed during 498 d.Stepwise multivariate regression indicated initial N concentration, starch, total lignin, and acid-insoluble ash (AI ash) were the four best predictors (r 2 = 0.83) of the rate of active component decomposition (k a ); however, initial composition poorly predicted the rate of passive decomposition (k p ). The best four-component model (r 2 = 0.43) identifi ed by stepwise multiple regression for k p included AI ash, hemicellulose, N concentration, and C/N ratio. Rate constants are a function of the incubation period, thus making direct comparison among separate experiments diffi cult. Chemical recalcitrance appears to slow root decomposition; such chemical recalcitrance to decay may partially explain why roots have been found to contribute more C to the SOC pool than surface residues.The use of trade, fi rm, or corporation names in this publication is for the information and convenience of the reader. Such use does not constitute an offi cial endorsement or approval by the United States Department of Agriculture or the Agricultural Research Service of any product or service to the exclusion of others that may be suitable. The USDA is an equal opportunity provider and employer.Soil Sci. Soc. Am. J. 71:155-162

Many environmental benefits accrue from reducing tillage and increasing crop diversity; however, economic factors often encourage the continued use of intensive tillage and specialized crop production. This study examined crop yields, input costs, and economic returns during the transition to a range of cropping system alternatives in the northern Corn Belt region, including different system (organic, conventional), tillage (conventional, strip-tillage), rotation (corn-soybean, corn-soybean-wheat/alfalfa-alfalfa) [Zea mays L., Glycine max (L.) Merr., Triticum aestivum L., Medicago sativa L.], and fertility (no fertilizer/manure, fertilizer/manure applied at recommended rates) treatments. Increasing crop diversity and reducing tillage intensity reduced total costs by $24-102 ha 21 within conventional treatments, and $16-107 ha 21 within organic treatments. Yields of corn, soybean, and wheat were more than 15% lower when using organic vs. the highest yielding conventional practices. Treatments receiving fertilizer or manure had wheat yields more than 0.3 Mg ha 21 and alfalfa yields 2.7 Mg ha 21 higher than treatments that did not receive fertilizer or manure. Within conventional systems, no significant differences in the 4-yr net present value of net returns were detected for tillage and rotation alternatives. Net present values for the organic systems without organic price premiums were at least $692 ha 21 lower than for the best conventional systems suggesting a barrier to the adoption of these systems should organic price premiums decline. However, when organic price premiums were included, most organic treatments had net present values comparable to or exceeding those from conventional treatments.

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