Agriculture Reference
In-Depth Information
The old, resistant SOM fraction, identified by its resistance to acid hydrolysis,
consists of some aromatics and long-chain aliphatic materials as well as protected
carbohydrates and proteins closely associated with sesquioxides and clays. Mid-IR
spectroscopy that identifies functional groups in both the organic and inorganic soil
constituents clearly shows different functional groups in the inter- and intraaggre-
gate fractions, with higher plant residue components in the interaggregate fraction.
Clay and silt components are also clearly differentiated. Principal Components
Analysis of KBS soil fractions, relative to other soils in our landscape compari-
son, shows more similarities within fractions than between soils, except that the
prairie-derived clays were clearly separated from those in the forest-derived sites,
such as those from KBS.
Microbial biomass, shown in our studies to represent approximately 1.5 to 3%
of the soil C, plays a major role in decomposition and provides the intermediate
products that are stabilized as organic matter. Fungi, which are equal in biomass
to bacteria in many of our agricultural systems, are more variable over time and in
their management responses. They provide a larger proportion of the biomass in
the forested sites, where ectomycorrhizae are important. The soil biota, together
with their breakdown products, are especially significant in the legume-based sys-
tems. Our studies have shown that the use of a clover cover crop in rotation results
in a greater active SOM pool (Nannipieri and Paul 2009). This SOM pool can be
accessed by the rhizosphere organisms of corn, and to some extent wheat, to pro-
vide much of the N required for plant growth. Clover cover crops should thus con-
tinue to be studied and used for their capacity to both fix N and release available N
to succeeding crops (McSwiney et al. 2010).
The challenges of providing a sustainable food supply and a variety of resilient
ecosystem services (Paustian et al. 1996, 1997; Robertson and Paul 1998; Bhardwaj
et al. 2011) in the face of global climate change are closely related to the molecular
composition of SOM and its interactions with physical, biotic, and chemical con-
trols. The studies summarized in this chapter have laid an important baseline for
many years to come as interacting processes and controls continue to be elucidated.
References
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