|MARTINS, BRUNO - Agronomic Institute Of New Caledonien|
|REEVES, JAMES - Retired ARS Employee|
|MARTIN-NETO, LADISLAU - Embprapa|
Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 3/10/2015
Publication Date: 8/6/2015
Citation: Martins, B.H., Cavigelli, M.A., Buyer, J.S., Maul, J.E., Reeves, J.B. III and Martin-Neto, L. 2015. Chemical evaluation of soil organic matter structure in diverse cropping systems. In Z. He (ed.). Labile Organic Matter-Chemical Compositions, Function, and Significance in Soil and the Environment. SSSA Special Publication 62:41-65. SSSA, Madison, WI.
Interpretive Summary: Storing carbon in agricultural soils (i.e. carbon sequestration) is an important means of removing carbon dioxide from the atmosphere and thereby helping control global climate change. However, we have a limited understanding of how agricultural management practices foster soil organic carbon (SOC) sequestration, in part because of the complexity of SOC composition. We showed how the composition of SOC, which can impact sequestration, is impacted by tillage, poultry litter application, and crop rotation: 1) SOC fractions at 8-12” depth were more resistant to decomposition in cropping systems that include tillage than in no-till systems; 2) cropping systems that use poultry litter have more resistant SOC than those that rely on mineral fertilizers, and 3) SOC composition is impacted by the specific plant species included in a crop rotation. This information will be of interest to NRCS and other agencies tasked with defining soil management practices that improve SOC sequestration.
Technical Abstract: Soil organic matter (SOM) improves soil structure, nutrient and water retention, and biodiversity while reducing susceptibility to soil erosion. SOM 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 carbon (SOC) sequestration, however, is limited in part by our understanding of the impacts of management on SOC stocks, structure and composition and the relationships among SOM structure, composition and sequestration. Unraveling these connections is challenging because SOM is composed 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) 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), factors that impact SOC structure and composition. Results from mid-IR analyses showed that differences in the C structure of oPOM and fPOM seem related to PL inputs in that degree of humification to 20 cm depth was greater in systems receiving PL. At 20-30 cm the degree of humification of fPOM and oPOM were greater in systems that were tilled than in a no-till system, suggesting that SOC sequestration at these depths may be facilitated by tilling organic matter into soils. PY-GC/MS analyses suggest that fPOM composition is related to particular crops included in a crop rotation. The FSP cropping system that includes a perennial forage (alfalfa) had the most unique set of pyrolysates; a system that included hairy vetch 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.