Soil carbon cycling and storage of bioenergy cropping systems across a heterogeneous agroecosystem

Emerging markets for cellulosic bioenergy feedstocks provide opportunities for implementing soil conservation practices that restore soil carbon (C) stocks within agricultural landscapes. Conservation strategies--including conversion to no-till, using cover crops, and establishing perennial vegetation--alter belowground C cycling processes and increase soil C storage through protection of soil organic matter (SOM). In particular, marginal sites less suited for conventionally tilled annual row crops are being targeted as appropriate locations for conversion to perennial bioenergy crops. However, the effects of topography and variations in soil properties on belowground C cycling processes remain largely unknown. The goal of this research is to quantify impacts of variation in topography and edaphic conditions on mechanisms driving short-term (three years) soil C pools under bioenergy crops. I address this goal through studies conducted as part of the Landscape Biomass Project, located in Boone County, IA, using three bioenergy cropping systems (switchgrass, continuous corn, and triticale /sorghum double crop) replicated across five landscape positions along a topographic gradient. Measurement of annual root productivity of cropping systems showed the highest productivity in switchgrass, while continuous corn was the lowest. Annual cropping systems showed no response to topography or soil properties. Switchgrass productivity was lowest on the floodplain and increased with higher soil sand content, suggesting model predictions of root production may be improved by incorporating information on soil texture. Over three years, soil aggregation changes were positive, and were highest under switchgrass. However cropping system effects on aggregation differed between landscape positions. Although total soil C stocks did not change, C physically protected within soil aggregates increased along with unprotected C pools, suggesting that adoption of no-till and conversion to perennial switchgrass increases stored C pools; increases in both pools were greatest under switchgrass. Structural equation modeling of C cycling processes revealed variation in soil properties influenced changes in aggregation and root C inputs, which affected shifts in soil C pools over time. Contrary to previous studies indicating the primary importance of roots and root-associated microbes, these results indicate that soil properties are the main drivers for change in soil C pools over landscapes

Factors Influencing Soil Aggregation and Particulate Organic Matter Responses to Bioenergy Crops across a Topographic Gradient

Bioenergy crops have the potential to enhance soil carbon (C) pools fromincreased aggregation and the physical protection of organicmatter; however, our understanding of the variation in these processes over heterogeneous landscapes is limited. In particular, little is known about the relative importance of soil properties and root characteristics for the physical protection of particulate organic matter (POM). We studied short-term (3-year) changes in aggregation and POM-C pools under three cropping systems (switchgrass, a triticale/sorghumdouble crop, continuous corn) replicated across five landscape positions along a topographic gradient in Iowa, USA.We isolated POMassociated with three aggregate fractions (N2mm, 0.25–2mm, and 0.053–0.25mm) to determine the relative influence of ten soil and three root properties. Aggregation increased in all cropping systems andwas greatest under switchgrass; however cropping systemeffectswere not consistent among positions. Total soil organic C stocks did not change, but Cwithin both physically protected (iPOM-C) and unprotected (frPOM) C pools increased. Shifts in iPOM-C were concurrently influenced by soil properties and root traits. Soil texture had the strongest influence (65% relative importance), with finer-textured soils showing greater gains in total iPOM-C, while greater root biomass influenced (35% relative importance) accrual of total iPOM-C. Aggregate fractions varied in their iPOM-C response to soil and root variables, however individual pools similarly showed the importance of soil texture and root biomass and annual root productivity (BNPP). Changes in frPOM-C were strongly correlated with BNPP. Our data suggest that macroaggregate formation drives short-term responses of POM, which are influenced by both soil and root system properties. Crops that maximize root biomass and BNPP will lead to the largest increases in protected soil C stocks. However, C storage rates will vary across landscapes according to soil conditions, with texture as the primary influence

Understanding soil organic matter change: Modeling root and soil interactions across agricultural landscapes

What are some options for enhancing organic content and carbon storage in soils that have been used in intensive row-crop production? The project looked at bioenergy feedstocks and how they might be employed to improve soil properties

Beyond planning tools: Experiential learning in climate adaptation planning and practices

In the past decade, several dedicated tools have been developed to help natural resources professionals integrate climate science into their planning and implementation; however, it is unclear how often these tools lead to on-the-ground climate adaptation. Here, we describe a training approach that we developed to help managers effectively plan to execute intentional, climate-informed actions. This training approach was developed through the Climate Change Response Framework (CCRF) and uses active and focused work time and peer-to-peer interaction to overcome observed barriers to using adaptation planning tools. We evaluate the effectiveness of this approach by examining participant evaluations and outlining the progress of natural resources projects that have participated in our trainings. We outline a case study that describes how this training approach can lead to place and context-based climate-informed action. Finally, we describe best practices based on our experience for engaging natural resources professionals and helping them increase their comfort with climate-informed planning

Midwest

The Midwest is home to over 60 million people, and its active economy represents 18% of the U.S. gross domestic product. The region is probably best known for agricultural production. Increases in growingseason temperature in the Midwest are projected to be the largest contributing factor to declines in the productivity of U.S. agriculture. Increases in humidity in spring through mid-century are expected to increase rainfall, which will increase the potential for soil erosion and further reduce planting-season workdays due to waterlogged soil

Soil carbon cycling and storage of bioenergy cropping systems across a heterogeneous agroecosystem

Emerging markets for cellulosic bioenergy feedstocks provide opportunities for implementing soil conservation practices that restore soil carbon (C) stocks within agricultural landscapes. Conservation strategies--including conversion to no-till, using cover crops, and establishing perennial vegetation--alter belowground C cycling processes and increase soil C storage through protection of soil organic matter (SOM). In particular, marginal sites less suited for conventionally tilled annual row crops are being targeted as appropriate locations for conversion to perennial bioenergy crops. However, the effects of topography and variations in soil properties on belowground C cycling processes remain largely unknown. The goal of this research is to quantify impacts of variation in topography and edaphic conditions on mechanisms driving short-term (three years) soil C pools under bioenergy crops. I address this goal through studies conducted as part of the Landscape Biomass Project, located in Boone County, IA, using three bioenergy cropping systems (switchgrass, continuous corn, and triticale /sorghum double crop) replicated across five landscape positions along a topographic gradient. Measurement of annual root productivity of cropping systems showed the highest productivity in switchgrass, while continuous corn was the lowest. Annual cropping systems showed no response to topography or soil properties. Switchgrass productivity was lowest on the floodplain and increased with higher soil sand content, suggesting model predictions of root production may be improved by incorporating information on soil texture. Over three years, soil aggregation changes were positive, and were highest under switchgrass. However cropping system effects on aggregation differed between landscape positions. Although total soil C stocks did not change, C physically protected within soil aggregates increased along with unprotected C pools, suggesting that adoption of no-till and conversion to perennial switchgrass increases stored C pools; increases in both pools were greatest under switchgrass. Structural equation modeling of C cycling processes revealed variation in soil properties influenced changes in aggregation and root C inputs, which affected shifts in soil C pools over time. Contrary to previous studies indicating the primary importance of roots and root-associated microbes, these results indicate that soil properties are the main drivers for change in soil C pools over landscapes.</p

Factors Influencing Soil Aggregation and Particulate Organic Matter Responses to Bioenergy Crops across a Topographic Gradient

Bioenergy crops have the potential to enhance soil carbon (C) pools fromincreased aggregation and the physical protection of organicmatter; however, our understanding of the variation in these processes over heterogeneous landscapes is limited. In particular, little is known about the relative importance of soil properties and root characteristics for the physical protection of particulate organic matter (POM). We studied short-term (3-year) changes in aggregation and POM-C pools under three cropping systems (switchgrass, a triticale/sorghumdouble crop, continuous corn) replicated across five landscape positions along a topographic gradient in Iowa, USA.We isolated POMassociated with three aggregate fractions (N2mm, 0.25–2mm, and 0.053–0.25mm) to determine the relative influence of ten soil and three root properties. Aggregation increased in all cropping systems andwas greatest under switchgrass; however cropping systemeffectswere not consistent among positions. Total soil organic C stocks did not change, but Cwithin both physically protected (iPOM-C) and unprotected (frPOM) C pools increased. Shifts in iPOM-C were concurrently influenced by soil properties and root traits. Soil texture had the strongest influence (65% relative importance), with finer-textured soils showing greater gains in total iPOM-C, while greater root biomass influenced (35% relative importance) accrual of total iPOM-C. Aggregate fractions varied in their iPOM-C response to soil and root variables, however individual pools similarly showed the importance of soil texture and root biomass and annual root productivity (BNPP). Changes in frPOM-C were strongly correlated with BNPP. Our data suggest that macroaggregate formation drives short-term responses of POM, which are influenced by both soil and root system properties. Crops that maximize root biomass and BNPP will lead to the largest increases in protected soil C stocks. However, C storage rates will vary across landscapes according to soil conditions, with texture as the primary influence.This article is from Geoderma 255-256 (2015): 1, doi:10.1016/j.geoderma.2015.04.016.</p

Understanding soil organic matter change: Modeling root and soil interactions across agricultural landscapes

What are some options for enhancing organic content and carbon storage in soils that have been used in intensive row-crop production? The project looked at bioenergy feedstocks and how they might be employed to improve soil properties.</p

Improved forest management as a natural climate solution: A review

Natural climate solutions (NCS), a set of land management, conservation and restoration practices aimed at mitigating climate change, have been introduced as cost-effective strategies to increase carbon (C) sequestration in terrestrial ecosystems. Improved forest management (IFM) has been identified as one NCS for working forests with substantial climate change mitigation potential. However, there is a disconnect between the policy and carbon markets context and the scientific evidence for verifiable C benefits. Further, forest soil C—the largest forest C pool—has largely been excluded from current forest management guidelines and has not been included in the IFM discourse. Herein, we assess the evidence for the potential of specific IFM practices to sequester C in live forest vegetation and store it in both live and dead organic matter, and forest soil. We review IFM approaches that can enhance forest C storage, and links to best management practices and silvicultural systems to offer guidance for practitioners and researchers in the Great Lakes region of the United States. Finally, we discuss the current challenges and opportunities in including soil C in forest C management guidelines and frameworks