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A B S T R A C TIn the United States, commercial-scale cellulosic-ethanol production using corn (Zea mays L.) stover has become a reality. As the industry matures and demand for stover increases, it is important to determine the amount of biomass that can be sustainably harvested while safe-guarding soil quality and productivity. Specific study objectives were to measure indices of soil hydrological and aggregate stability responses to harvesting stover; since stover harvest may negatively impact soil hydrological and physical properties. Responses may differ with tillage management; thus, this paper reports on two independent studies on a tilled (Chisel field) and untilled field (NT1995 field). Each field was managed in a corn/soybean (Glycine max [Merr.]) rotation and with two rates of stover return: (1) all returned (Full Return Rate) and (2) an aggressive residue harvest leaving little stover behind (Low Return Rate). Unconfined field soil hydraulic properties and soil aggregate properties were determined. Hydrological response to residue treatments in the Chisel field resulted in low water infiltration for both rates of residue removal. In NT1995 field, Full Return Rate had greater capacity to transmit water via conductive pathways, which were compromised in Low Return Rate. Collectively, indices of soil aggregation in both experiments provided evidence that the aggregates were less stable, resulting in a shift toward more small aggregates at the expense of larger aggregates when stover is not returned to the soil. In both fields, aggressive stover harvest degraded soil physical and hydrological properties. No tillage management did not protect soil in absence of adequate residue.2016 Published by Elsevier B.V.

Arbuscular mycorrhizal fungi (AMF) may play an important role in ecological succession, but few studies have documented the effectiveness of mycorrhizal inoculation at restoration/reclamation sites. At a roadside prairie restoration in Shakopee, Minnesota, we compared AMF root colonization and resulting vegetative cover among four inoculation treatments. After 15 mo of growth, we found that AMF colonization was high in all treatments but was significantly higher in treatments that received AMF inoculum propagated from a local prairie site or commercially available inoculum than the uninoculated control. For the prairie inoculum, this increase in colonization occurred whether the inoculum was applied with seeds in furrows or broadcast with seeds on the soil surface. However, increased colonization did not discernibly affect the restored vegetation; neither total vegetative cover nor the proportion "desired" prairie vegetation differed among inoculation treatments. By the end of the third growing season (27 mo after planting) there were no longer differences in AMF colonization among the inoculation treatments nor were there differences in vegetative cover. It is likely that natural recolonization of the plots by remnant AMF populations at the site limited the duration of the inoculation effect. This natural recolonization, in combination with relatively high soil phosphorus levels, likely rendered inoculation unnecessary. In contrast to previous published studies of AMF inoculation in landscape restorations, this study shows that AMF inoculation may not be warranted under some circumstances.

Cellulosic biofuel production may generate new markets and revenue for farmers. However, residue removal may cause environmental problems such as soil erosion and soil organic matter (SOM) loss. The objective of this study was to determine the amounts of residue necessary for SOM maintenance under different tillage and residue removal scenarios for corn–soybean [Zea mays L.–Glycine max (L.) Merr.] and continuous corn rotations for a site in west‐central Minnesota. We employed a process‐based model (CQESTR) to evaluate management practices and quantify SOM changes over time. Results showed that conventional tillage resulted in SOM loss regardless of the amount of residue returned. Under no‐till, residue amount was important in determining SOM accumulation or depletion. For the upper 30 cm of soil, average annual rates of 3.65 and 2.25 Mg crop residue ha–1 yr–1 were sufficient to maintain SOM for corn–soybean and continuous corn rotations, respectively. Soil OM in soil layers below 30 cm was predicted to decrease in all scenarios as a result of low root inputs. When considered over the upper 60 cm (maximum soil depth sampled), only continuous corn with no‐till was sufficient to maintain SOM. Results from this work are important because they show that, for these management scenarios, no‐till management is necessary for SOM maintenance and that determining whether SOM is accumulating or declining depends on the soil depth considered. At current yields observed in this study area, only continuous corn with no‐till may generate enough residue to maintain or increase SOM.

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