EAGER: Self-Protection of Organic Carbon in Soil Pores under Organic Agricultural Practices

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1220731 (Zhuang). In agricultural food production, organic farming practice is an engineering approach that applies various methods, such as crop rotation, crop residue return, no-tillage and others, to realize goals of nutritional food, ecosystem health, and high soil productivity. This project will provide insightful information and evidence including evaluation criteria that helps farmers make optimized decisions on what agricultural engineering practices or their combinations should be adopted to maximize soil carbon sequestration and how climate and soil properties affect the effectiveness and potential of organic practices. Soil organic carbon sequestration has many benefits to soil health and food productivity. Due the dependence of agricultre on soil health, this resource is vital important to society. Adoption of organic or conservation practices in crop production can increase the input of organic matter (OM) into soil and thereby create great potential for prioritizing soil quality and preserving organic carbon (OC) in soils. Unfortunately, the mechanisms controlling the rate and capacity of OC accrual remain unclear. This research will use a novel integrated approach to examine an untested but potentially very important mechanism that controls the capacity and stability of carbon sequestration in nano-/micro-sized soil pores. It is hypothesized that a pore-mediated feedback between soil organic colloids, water, and nitrogen dominates the fate and storage of soil carbon in organic farming systems. Research objectives are to: (1) quantify the extent of OM pore-filling (encapsulation) under different organic or conservation practices as well as water hysteresis as affected by the size distribution of OM-filled soil pores; (2) evaluate the biodegradation of encapsulated OM and its contribution to soil respiration at different temperatures, nitrogen availabilities, and water contents; and (3) incorporate OM pore-filling, water hysteresis, and carbon-nitrogen interactions into a soil respiration model. Studies will be conducted using soil samples collected from two organically-managed agricultural sites that have different climatic and soil conditions. Research will focus on soil microaggregates because of their critical role in protecting OC against decomposition over the long term. Also examined will be bulk soil and silt/clay fractions for comparison. Pore-filling very likely represents a critical mechanism governing the potential of soil carbon sequestration in ecological systems (particularly in biomass-productive systems). This study will be the first to characterize pore-mediated carbon-water-nitrogen interactions in soils by using the complementary advantages of state-of-art small-angle scattering (SAS) technique and isotope-based molecular signature technique. The obtained results will clarify whether a feedback effect between soil OM and water with respect to the accessibility of biochemical agents that play a key role in controlling long-term soil carbon preservation in nano-/micro-sized pores. Data on dynamic changes of OM distribution in differently sized pores under different environmental conditions (e.g., temperature and water) will reveal relative susceptibility of soil OM to decomposition. Evaluation of the relationships between OM pore-filling and soil respiration will add new mechanistic information to a latest soil respiration model and clarify the conditions under which soil carbon accrual can be expected within affordable production costs. Comparative analysis of results obtained from a spectrum of agricultural sites in the U.S. and China will make this research applicable beyond the borders of the particular study sites. The research will benefit farmers by providing strategic guidance on adoption of organic or conservation practices for the purpose of simultaneously optimizing food production and quality, soil carbon sequestration, and resistance of crops to adverse environment. The project will provide education and technical training opportunities to at least three undergraduate students through bold thinking and hands-on experience in using novel techniques at national laboratories and in China. The multidisciplinary, international aspects of this research will prepare undergraduate students for graduate study and enhance their capacity and commitment in developing scientifically-sound strategies for sustainable agriculture and climate change mitigation. The project will facilitate future large-scale US-China collaboration on environmental sustainability research.