The Role of Soil Organic Matter and Manures in Sustainable Nutrient Cycling - Sustainable Management of Soil Organic Matter - page 268

Results

With increasing incubation temperature, DOC extractability from
non-sterile soil samples is greatly reduced (Table 4.6.1). There was a
reduction of 89% in DOC following incubation for 2 weeks at 35

C. A
similar temperature dependence was found in the re-inoculated samples
(not shown) and, for both treatments, the decrease in DOC is clearly
related to the increased respiration rates at higher temperatures (Fig.
4.6.1). The slope of the fitted regression shows that CO 2 evolution exceeds
the change in extractable DOC by a factor of 1.85. Assuming that all DOC
lost during incubation was completely mineralized, 54% of the total
soil

°

respiration could be attributed to this process. In the extracts

from -irradiated samples, initial DOC values were higher than from

non-irradiated samples (Table 4.6.1). Temperature effects on DOC
extractability were also observed, but declines were only significant at
35

γ

C and still amounted to ~60% of DOC extractable before incubation.
With decreasing DOC extractability in the non-sterile samples, their
molar absorptivity increases significantly at incubation temperatures above
20

°

C. The opposite is the case in the sterile samples, where the initially
lower

°

ε 280 values are reduced further during incubation, with a minimum at

20 C.

The Cu complexation ability of DOM was affected by incubation and
temperature only in the non-sterile samples. Compared with initial extracts
and the sterile samples, DOM from biologically active soils incubated at

°

Table 4.6.1. DOC extractability and DOM characteristics in extracts from sterilized and
non-sterile soil samples before and after incubation at different temperatures. For each soil
treatment, significant effects of incubation temperature on solution parameters are indicated by
different letters following the values in the columns (Duncan test).

DOC
(mmol kg − 1 )

ε 280 1
(l m − 1 mmol − 1 )

Cu complexation
(mmol mol − 1 DOC)

DOM degradability
(%)

Non-sterile
Before 30.9 a 25.6 a 4.4 a 15 a

5 ° C 21.3 b 26.2 a 5.7 b 11 a

7.0 c 31.0 c 12.3 d 63 b

20 ° C

35 ° C 3.4 d 29.8 b 8.1 c 80 b

Sterile
Before 46.5 a 18.4 a 4.7 a

b 24 ab

46.6 a 14.6 b 4.7 a 18 b

5 ° C

20 ° C

b 35.8 ab

11.8 c 4.5 a 32 a

35 C 27.3 b

b 12.8 bc

5.3 a 19 b

°

1 UV absorption at 280 nm.