The Role of Soil Organic Matter and Manures in Sustainable Nutrient Cycling - Sustainable Management of Soil Organic Matter - page 269

Fig. 4.6.1. Relationship between the change in DOC extractability and respiration during
incubation of non-sterile and re-inoculated soil samples at different temperatures.

20 ° C can bind almost three times more Cu. At 35 ° C, Cu complexation

ability is lower than at 20 C.

Since the reduced DOM extractability at higher temperatures in
the non-sterile soils is attributable to increased mineralization activity
(Fig. 4.6.1), one would expect an accumulation of recalcitrant soluble
compounds. However, our data indicate that a much larger proportion
of DOM extractable after incubation at 20 and 35

° C but still elevated in comparison with 5 °

° C is utilizable by soil

microorganisms, reaching almost 80% at 35 C (Table 4.6.1). DOM from

sterile samples also shows some incubation effects, but they were small and
not consistent with temperature.
When biologically active soil samples were incubated over a longer time
period, DOC extractability declined rapidly but, even after five extractions
in 12 weeks, soluble organic compounds were not depleted but remained at
a similar level to that in the third extract (Table 4.6.2). DOM quality, as
determined by its molar absorptivity, was affected mainly during the first
4 weeks, when

°

ε 280 increased by ~60% and later only declined slightly. In
contrast to the fairly stable DOC concentrations and ε 280 values after the

4th week, the Cu complexation ability of DOM continued to increase with
incubation time to reach a maximum in the 12th week that was almost three
times higher than in the initial extracts (Table 4.6.2).

Discussion

Soil sterilization by -irradiation proved to be an effective measure in

eliminating microbial activity without interfering greatly with other
properties of the soluble organic matter fraction. DOM extractability and

γ