Above- and Below-ground Biomass Production in Corn and Prairie Bioenergy Cropping Systems

The Comparison of Biofuel Systems (COBS) project is a long-term, 20-acre field experiment designed to provide quantitative, side-by-side comparisons of corn- and prairie-based biofuel feedstock production systems with respect to biomass yields, liquid fuel potential, and multiple environmental impacts. Here, we report on above- and below-ground biomass production from selected treatments

Plant Litter Quality Affects the Accumulation Rate, Composition, and Stability of Mineral-associated Soil Organic Matter

Mineral-associated organic matter (MAOM) is a relatively large and stable fraction of soil organic matter (SOM). Plant litters with high rates of mineralization (high quality litters) are hypothesized to promote the accumulation of MAOM with greater efficiency than plant litters with low rates of mineralization (low-quality litters) because litters with high rates of mineralization maximize the synthesis of microbial products and most MAOM is microbial-derived. However, the effect of litter quality on MAOM is inconsistent. We conducted four repeated short-term incubations (46-d each) of four plant litters (alfalfa, oats, maize and soybean) in two low-carbon subsoils (sandy loam and silty loam) with and without nutrient addition. Our short-term incubations focused on the initial stage of litter decomposition during the time when litter quality has a measureable effect on mineralization rates. Plant litter quality had a much greater effect on litter-C mineralization rate and MAOM-C accumulation than did soil type or nutrient addition. Soils amended with high-quality oat and alfalfa litters had greater MAOM-C accumulation than soils amended with low-quality maize and soybean litters. However, soils amended with high-quality litters also had greater litter-C mineralization than soils amended with low-quality litters. As a result, the accumulation of MAOM-C per unit of litter-C mineralization was lower in soils amended with high-vs. low-quality litters (0.65 vs. 1.39 g MAOM-C accumulated g−1 C mineralized). Cellulose and hemicelluose indices of accumulated MAOM were greater for maize and soybean than oats and alfalfa, however, most carbohydrates in MAOM were plant-derived regardless of litter quality. At the end of the incubations, more of the accumulated MAOM-N was potentially mineralizable in soils amended with high quality litters. Nevertheless, most of the litter-C remained as residual litter; just 12% was mineralized to CO2 and 13% was transferred to MAOM. Our results demonstrate several unexpected effects of litter quality on MAOM stabilization including the direct stabilization of plant-derived carbohydrates

Linking crop- and soil-based approaches to evaluate system nitrogen-use efficiency and tradeoffs

Increasing nitrogen (N)-use efficiency (NUE) is key to improving crop production while mitigating ecologically-damaging environmental N losses. Traditional approaches to assess NUE are principally focused on evaluating crop responses to N inputs, often consider only what happens during the growing season, and ignore other means to improve system efficiency, such as by tightening the cycling of soil N (e.g. with N scavenging cover crops). As the goals of improving production and environmental quality converge, new metrics that can simultaneously capture multiple aspects of system performance are needed. To fill this gap, we developed a theoretical framework that links both crop- and soil-based approaches to derive a system N-use efficiency (sNUE) index. This easily interpretable metric succinctly characterizes N cycling and facilitates comparison of systems that differ in biophysical controls on N dynamics. We demonstrated the application of this new approach and compared it to traditional NUE metrics using data generated with a process-based model (APSIM), trained and tested with experimental datasets (Iowa, USA). Modeling of maize-soybean rotations indicated that despite their high crop NUE, only 45% of N losses could be attributed to the inefficient use of N inputs, whereas the rest originated from the release of native soil N into the environment, due to the asynchrony between soil mineralization and crop uptake. Additionally, sNUE produced estimates of system efficiency that were more stable across weather years and less correlated to other metrics across distinct crop sequences and N fertilizer input levels. We also showed how sNUE allows for the examination of tradeoffs between N cycling and production performance, and thus has the potential to aid in the design of systems that better balance production and environmental outcomes.This is a manuscript of an article published as Martinez-Feria, Rafael A., Michael J. Castellano, Ranae N. Dietzel, Matt J. Helmers, Matt Liebman, Isaiah Huber, and Sotirios V. Archontoulis. "Linking crop-and soil-based approaches to evaluate system nitrogen-use efficiency and tradeoffs." Agriculture, Ecosystems & Environment 256 (2018): 131-143. doi:10.1016/j.agee.2018.01.002. Posted with permission.This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License

The Future of Agriculture and Society in Iowa: Four Scenarios

Iowa is a leader in crop and livestock production, but its high productivity has had concomitant negative environmental and societal impacts and large requirements for fossil-fuel-derived inputs. Maintaining agricultural productivity, economic prosperity and environmental integrity will become ever more challenging as the global demand for agricultural products increases and the resources needed become increasingly limited. Here we present four scenarios for Iowa in 2100, based on combinations of differing goals for the economy and differing energy availability. In scenarios focused on high material throughput, environmental degradation and social unrest will increase. In scenarios with a focus on human and environmental welfare, environmental damage will be ameliorated and societal happiness will increase. Movement towards a society focused on human and environmental welfare will require changes in the goals of the economy, whereas no major changes will be needed to maintain focus on high throughput. When energy sources are readily available and inexpensive, the goals of the economy will be more easily met, whereas energy limitations will restrict the options available to agriculture and society. Our scenarios can be used as tools to inform people about choices that must be made to reach more desirable futures for Iowa and similar agricultural region

The future of agriculture and society in Iowa: four scenarios

Iowa is a leader in crop and livestock production, but its high productivity has had concomitant negative environmental and societal impacts and large requirements for fossil-fuel-derived inputs. Maintaining agricultural productivity, economic prosperit