Title: Chemical Evaluation of Soil Organic Matter Structure in Diverse Cropping Systems
Abstract: Soil organic matter (SOM) improves soil structure, nutrient and water retention, and biodiversity while reducing susceptibility to soil erosion. Soil organic matter also represents an important pool of C that can be increased to help mitigate global climate change. Our understanding of how agricultural management practices foster soil organic C (SOC) sequestration, however, is limited by gaps in our knowledge of the relationships among SOM structure, composition, and sequestration. Unraveling these connections is challenging because SOM is comprised of a complex mix of substances with various functional groups in various stages of decomposition, usually bonded with the soil mineral fraction. Recent application of infrared (IR) spectroscopy and pyrolysis-gas chromatography-mass spectrometry (PY-GC-MS) analysis to soil C fractions is helping uncover some of these relationships. In this chapter, we review these methods and our evolving understanding of SOM structure and composition. We use IR and PY-GC-MS data from a long-term agricultural research (LTAR) site in Maryland, USA, to explore management impacts on SOC structure and composition. The diverse cropping systems of the Farming Systems Project (FSP) LTAR differ in tillage, crop rotation, and source of fertility (mineral fertilizers vs. poultry litter [PL] and legume cover crops) as the factors that affect SOC structure and composition. Results from mid-IR analysis showed that differences in the C structure of occluded and free particulate organic matter (oPOM and fPOM, respectively) seem related to PL inputs in that degree of humification to the 20-cm depth was greater in systems receiving PL. At 20 to 30 cm, the degree of humification of oPOM and fPOM were greater in systems that were conventionally tilled than in a no-till system, suggesting that SOC sequestration at these depths may be facilitated by tilling organic matter into soils. The PY-GC-MS analysis suggests that fPOM composition is related to particular crops included in a crop rotation. The FSP cropping system that includes a perennial forage (alfalfa [Medicago sativa L.]) had the most unique set of pyrolysates; a system that included hairy vetch (Vicia villosa Roth) had the second-most unique set of pyrolysates. Combined use of IR spectroscopy and PY-GC-MS revealed different aspects of SOC structure and composition.
Publication Year: 2015
Publication Date: 2015-07-24
Language: en
Type: book-chapter
Indexed In: ['crossref']
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Cited By Count: 5
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