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Chemical and Biological Characteristics of Physically Uncomplexed Organic Matter

^a Agriculture Canada, Central Experimental Farm, Ottawa, ON, Canada, K1A 0C6
^b New Zealand Institute for Crop & Food Research, Christchurch, New Zealand
^c CSIRO Land and Water, Adelaide Lab., PMB 2 Glen Osmond SA 5064 Australia

View larger version (11K): [in a new window]   Fig. 1. Physically uncomplexed organic matter is an intermediate between plant residues and soil organic matter. Its quantity and composition in soil are affected by factors that regulate: (1) quantity and type of residue (e.g., amount, composition, and accessibility) and/or (2) microbial activity (e.g., environmental conditions).

View larger version (15K): [in a new window]   Fig. 2. Carbon to N ratio of physically uncomplexed organic matter isolated at different (a) solution densities (n = 535 fractions) and (b) particle sizes (n = 363 fractions). Values on X-axis are (a) the upper end of the solution density range and (b) the midpoint of the size range. Error bars represent standard deviations. Data are from published studies of agricultural, forest, and grassland ecosystems; 43 studies using density fractionation; and 24 studies using particle size fractionation methods.

View larger version (15K): [in a new window]   Fig. 3. Solid-state 13C NMR spectra of a particulate organic matter fraction containing no charcoal (a) and containing charcoal (b). (J. O. Skjemstad, unpublished data, 2004).

View larger version (17K): [in a new window]   Fig. 4. Relationship between the C/N ratio and alkyl/O-alkyl C ratios of plant tissue, particulate organic matter, and particle-size fractions. (Adapted from Leifeld and Kögel-Knabner, 2004).

View larger version (15K): [in a new window]   Fig. 5. The quantity of light fraction-N (left axis–diamond symbols and dashed line) and the quantity of total N (right axis–square symbols and solid line) in the surface 30 cm of soil as a function of the amount of N fertilizer applied in a Saskatchewan grassland. (Drawn from data presented by Malhi et al., 2003).