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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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Winter cover crops might reduce nutrient loss to leaching in the Upper Midwest. New oilseed‐bearing cash cover crops, such as winter camelina (Camelina sativa L.) and pennycress (Thlaspi arvense L.), may provide needed incentives. However, the abilities of these crops to sequester labile soil nutrients are unknown. To address this unknown, N in shoot biomass, plant‐available N and P in soil, and NO3−–N and soluble reactive P in soil water collected from lysimeters placed at 30, 60, and 100 cm were measured in cover crop and fallow treatments established in spring wheat (Triticum aestivum L.) stubble and followed through a cover crop–soybean [Glycine max (L.) Merr.] rotation. Five no‐till cover treatments (forage radish [Raphanus sativus L.], winter rye [Secale cereale L.], field pennycress, and winter camelina) were compared with two fallow treatments (chisel till and no‐till). Pennycress and winter camelina were harvested at maturity after relay sowing of soybean. Winter rye and radish sequestered more N in autumn shoot biomass, ranging from 26 to 38 kg N ha−1, but overwintering oilseeds matched or exceeded N uptake in spring, ranging 28 to 49 kg N ha−1 before soybean planting. Nitrogen uptake was reflected by reductions in soil water NO3−–N during cover crop and intercropping phases for all cover treatments (mean = 4 mg L−1), compared with fallow treatments (mean = 31 mg L−1). Cash cover crops like pennycress and winter camelina provide both environmental and potential economic resources to growers. They are cash‐generating crops able to sequester labile soil nutrients, which protects and promotes soil health from autumn through early summer. Core Ideas Alternative, easily established winter‐surviving covers are needed in the Upper Midwest. Cover crops sequestered N and reduced soil and soil water NO3−–N in autumn compared with fallow. Winter oilseed crops reduced soil water NO3−–N in autumn through soybean planting. Novel winter oilseeds provide environmental and economic incentives to enhance adoption.

The Midwestern U.S. landscape is one of the most highly altered and intensively managed ecosystems in the country. The predominant crops grown are maize (Zea mays L.) and soybean [Glycine max (L.) Merr]. They are typically grown as monocrops in a simple yearly rotation or with multiple years of maize (2 to 3) followed by a single year of soybean. This system is highly productive because the crops and management systems have been well adapted to the regional growing conditions through substantial public and private investment. Furthermore, markets and supporting infrastructure are highly developed for both crops. As maize and soybean production have intensified, a number of concerns have arisen due to the unintended environmental impacts on the ecosystem. Many areas across the Midwest are experiencing negative impacts on water quality, soil degradation, and increased flood risk due to changes in regional hydrology. The water quality impacts extend even further downstream. We propose the development of an innovative system for growing maize and soybean with perennial groundcover to recover ecosystem services historically provided naturally by predominantly perennial native plant communities. Reincorporating perennial plants into annual cropping systems has the potential of restoring ecosystem services without negatively impacting grain crop production and offers the prospect of increasing grain crop productivity through improving the biological functioning of the system.

No abstract

Agricultural management practices that enhance C sequestration, reduce greenhouse gas emission (nitrous oxide [N₂O], methane [CH₄], and carbon dioxide [CO₂]), and promote productivity are needed to mitigate global warming without sacrificing food production. The objectives of the study were to compare productivity, greenhouse gas emission, and change in soil C over time and to assess whether global warming potential and global warming potential per unit biomass produced were reduced through combined mitigation strategies when implemented in the northern U.S. Corn Belt. The systems compared were (i) business as usual (BAU); (ii) maximum C sequestration (MAXC); and (iii) optimum greenhouse gas benefit (OGGB). Biomass production, greenhouse gas flux change in total and organic soil C, and global warming potential were compared among the three systems. Soil organic C accumulated only in the surface 0 to 5 cm. Three-year average emission of N₂O and CH was similar among all management systems. When integrated from planting to planting, N₂O emission was similar for MAXC and OGGB systems, although only MAXC was fertilized. Overall, the three systems had similar global warming potential based on 4-yr changes in soil organic C, but average rotation biomass was less in the OGGB systems. Global warming potential per dry crop yield was the least for the MAXC system and the most for OGGB system. This suggests management practices designed to reduce global warming potential can be achieved without a loss of productivity. For example, MAXC systems over time may provide sufficient soil C sequestration to offset associated greenhouse gas emission.