Non Technical Summary
Globally, intensification of agriculture has lead to a degradation of soil organic matter (SOM) in agroecosystems. SOM is an important indicator of soil health, as SOM acts like a pantry for crops. It is able to hold onto the water and nutrients that plants need, reducing the need for excessive irrigation and fertilization. This study is investigating the mechanisms of SOM formation under cover crop management. Specifically, we are interested in quantifying the contribution of volatile organic compounds (VOCs) to the formation of SOM, and identifying the soil microorganisms linked to increasing VOC derived soil organic matter. Increasing SOM in agroecosystems has the potential to increase food production and food security in the United States, while also mitigating climate change. SOM also protects soil from some of the negative effects of drought. Thus, increasing SOM can increase resistance to drought, which may become increasingly important as changes in precipitation regimes are expected to change dramatically in some places. Furthermore, SOM may contribute to national security by mitigating the destabilizing effects of climate change and food scarcity.We will measure the effects of cover crops on soil health by conducting litter decomposition experiments in a managed agroecosystem and we will measure changes in soil organic matter, microbial community composition, and ecosystem function. Specifically we will use stable-isotope probing, a technique that uses a natural label, to track carbon from cover crops to the soil; and we will use next-generation sequencing to characterize the soil microbial community. We will use these data to establish links between cover crops, soil health, and the soil microbial community. We will distribute our findings through academic and non-academic pipelines, including conference presentations, peer-reviewed publications, and white papers.Ultimately, we expect this project to produce results that will inform farm managers how to effectively manage cover crops for maximum soil organic matter production, and increased soil health. Ultimately, this should result in greater crop yields, bolstering the United States agricultural industry, and reducing food insecurity. We also intend to contribute significantly to our understanding of the contributions of volatile carbon, and soil microorganisms to the production of soil organic matter, which could be used to inform models of soil organic matter formation.

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
102	0110	1070	100%

Knowledge Area
102 - Soil, Plant, Water, Nutrient Relationships;

Subject Of Investigation
0110 - Soil;

Field Of Science
1070 - Ecology;

Goals / Objectives
The overall goal of this project is to use stable isotope probing methods to directly study the effects of cover crop litter residues on the transformation and retention of both carbon and nitrogen (the primary constituents of SOM) in a model cropping system in Kentucky, USA. Specifically, we will: characterize the amount and type of VOCs emitted during the decomposition of aboveground and belowground cover crop litter; assess the impact of litter derived VOCs on soil health indicators such as soil organic matter (SOM) formation and nitrogen (N) retention; identify soil microbial taxa present in agricultural soils that are correlated with soil health and VOC metabolism.

Project Methods
For the above ground litter decomposition we used a litter bag approach to measure decomposition of cover crop residues, and transfer of cover crop derived carbon to the underlying soil horizons. We created litter bags with or without the addition of activated charcoal. We will quantify thecontribution of VOC-C to soil organic matter formation by subtracting 13C enrichment of treatments receiving activated charcoal from 13C enrichment of the treatments without activated charcoal.During the experiment we used an infrared gas analyzer to measure fluxes of green house gases.We labled cover crop residues by pulsing the growing cover crops with13CO2. We will quantify13C enrichment using an IRMS connected to an elemental analyzer. We will characterize the microbial communities by sequencing extracted DNA using an Illumina miseq.For the below ground litter decomposition we directly added13C labeled cover crop roots to the soil. We will quantify the loss of13C in the particulate organic matteras a proxy for root litter decomposition. This method will not be able to directly quantify VOC-C from the root residues. However, this study will more accurately represent transfer C from decomposing root residuesto soil C pools.During the experiment we used an infrared gas analyzer to measure fluxes of green house gases.We labeled cover crop residues by pulsing the growing cover crops with13CO2. We will quantify13C enrichment using a IRMS connected to an elemental analyzer. We will characterize the microbial communities by sequencing extracted DNA using a Illumina miseq.