Implications of Soil Biodiversity for Sustainable Organic Matter Management - Sustainable Management of Soil Organic Matter - page 351

Catabolic Evenness Under Different Land Uses

Catabolic diversity can provide a robust indicator of the condition of
microbial communities that is independent of soil type effects. In a study of
land uses across 14 soil types, microbial catabolic evenness was consistently
greatest in soils under indigenous vegetation (range: 19.7-22.3) or
long-term pasture (range: 20.1-23.3), but least in long-term cropped soils
(range: 16.4-19.6; Degens et al ., 2000b). Soils under a mixed pasture-
cropping management had catabolic evenness part way between these
extremes (range: 17.7-20.5) but, under pine forest, there was no character-
istic level of evenness (Degens et al ., 2000b). These broad ranges provide a
framework for assessing the diversity in soils without knowledge of soil type
or history.
Within soil types, where land use changes from pasture to cereal crop-
ping or greater cropping intensity, there can also be a concurrent decrease
in microbial catabolic evenness. A change from pasture to wheat cropping
in a sandy loam resulted in a decline in catabolic evenness from 20.2 to
19.2 ( P < 0.05; mean of bulked samples from two plots) over a 12-month
period. In nearby plots under continuous arable cropping, however,
catabolic evenness remained relatively stable (ranging between 18.8 and
19.3; not significantly different at P > 0.05). Similarly, increasing cropping
pressure can result in soils with reduced catabolic evenness (Table 5.1.1),
relative to levels normally found in pastures (20-22). This indicates that
previous land management practices were having a deleterious effect on the
biological condition of these soils. When considering the sizes of different
organic C pools in the soils in isolation (Table 5.1.1), it is difficult to
evaluate the significance of these without comparison with a reference soil
under land use with minimal physical disturbance (e.g. long-term pasture).
Comparison of these soils with a long-term pasture soil confirms that

Table 5.1.1. Microbial catabolic evenness, total organic C, microbial biomass C and potentially
mineralizable organic C (mean of five reps) in soil under different land management histories.

Land management
history

Catabolic
evenness

Total organic C
(mg cm − 3 )

Microbial biomass C
(mg C cm − 3 )

Potentially mineralizable C
( µ g C cm − 3 h − 1 )

8 years crop,
4 years pasture

b 19.1 ab

45 a 1.26 b 1.34 c

10 years pasture,
2 years crop 19.6 b 39 b 0.74 a 0.33 a

5 years crop,
2 years pasture

18.7 a 48 a 0.74 a 0.94 b

Long-term pasture 21.4 c 56 a 1.38 c 1.66 d

After Sparling et al. (2000). Values within columns followed by the same letter are not significantly
different (P< 0.05).