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A Survey of Australian Temperate
Pastures
A survey of Australian
temperate pastures in summer and winter rainfall zones: soil nematodes,
chemical, and biochemical properties.
3/1/2006
Australian Journal of Soil
Research
By G.M. Lodge
Data for soil nematode numbers, total microbial activity, microbial biomass
carbon (C), and various soil chemical properties were collected from permanent
and semi-permanent pastures at 108 locations in 2 contrasting environments: a
summer rainfall zone in northern New South Wales (n = 60) and a winter rainfall
zone in south-east South Australia and western Victoria (n = 48). Nematodes
were also categorised according to their feeding habits and reproductive rates,
and the abundance of various nematode groups was used to compute 3 indices that
indicate the condition of the soil food web [enrichment index (EI), structure
index (SI), and channel index (CI)]. At each location, pasture species herbage
mass (kg DM/ha) was estimated and locations were grouped according to dominant
species (lucerne, subterranean clover and phalaris in both rainfall zones;
perennial ryegrass, winter rainfall zone only) as well as total soil microbial
activity. The objective of the survey was to obtain a general indication of the
biological status of soils used for pasture production in temperate regions of Australia,
compare the soil biology in the 2 study areas, and determine whether it was
influenced by pasture species composition.
The most common plant-parasitic nematode was lesion nematode (Pratylenchus
spp.), which was found at 67% of locations in the summer rainfall zone and 29%
of those in the winter rainfall zone. Generally, there were more free-living
nematodes in the soil than plant-parasitic nematodes. Numbers of free-living
nematodes were highest in the winter rainfall zone, while in the summer
rainfall zone there were more free-living nematodes in subterranean clover and
phalaris pastures than lucerne pastures. Graphical representations of data for
EI and SI indicated that the soil food webs at all sites in the summer rainfall
zone were either structured or degraded. Food webs in the winter rainfall zone
were more variable, with relatively high EI values indicating that more
resources were available to support the soil biology. Climate had a major
effect on CI values, with the mean in the winter rainfall zone being 28
(indicating a bacterial-dominant detritus food web) compared with 72
(indicating fungal dominance) in the summer rainfall zone.
Mean total microbial activity was twice as high (2.6 v. 1.3 [micro]g
fluorescein diacetate/g.min) in soils from the winter than the summer rainfall
zone. Mean levels of total organic C, total nitrogen, and labile C were also
higher for the winter rainfall zone than the summer zone. For both rainfall
zones, mean microbial biomass C was 0.09 mg/g soil, labile C was 9.05% of total
organic C, and microbial biomass C was 3.5% of labile C. In the summer rainfall
zone, values for all measured biochemical properties were lower in lucerne
pastures than in other pasture types.
We concluded that the biological status of soils in the winter rainfall zone
was better than soils in the summer rainfall zone, and that the biology under
lucerne pastures in the summer rainfall zone differed from pastures dominated
by phalaris and subterranean clover. Soils in both study areas were generally
healthy, as they had relatively high levels of total organic C and labile C,
high numbers of free-living nematodes, high microbial activities, and a general
lack of problems associated with plant-parasitic nematodes. However, there were
exceptions, as there was considerable within-site variability for some
biological and biochemical parameters at some sites.
Additional keywords: free-living nematodes, plant-parasitic nematodes,
lucerne, phalaris, subterranean clover, perennial ryegrass, total organic
carbon, microbial biomass carbon, labile carbon, microbial activity.
Introduction
Sown permanent and semi-permanent temperate pastures in high rainfall areas
(>600mm annual rainfall) are an important component of the Australian
landscape, covering 8.26 million hectares, with > 50% of all cattle sales
and nearly 40% of all sheep sales (Australian Bureau of Statistics 1998) being
from this area. Since the productivity and sustainability of these pastures is
dependent on processes that are mediated by soil organisms (e.g. biological
nutrient cycling, formation and maintenance of soil physical properties, and
disease incidence), soil biota are vitally important from an economic, soil
health, and environmental perspective. It is therefore surprising that there
have been few broad-ranging studies of the biology of soils used for pasture
production in Australia.
Much of the literature on the biology of Australian soils under pasture
pertains to specific scientific disciplines. The pathogens associated with
various soil-borne diseases have received particular attention, with most
studies concentrating on important fungal pathogens (e.g. Phytophthora
clandestina and Pythium spp.); diseases of subterranean clover, medics,
lucerne, and white clover; and on pathogens that carry-over to cereal crops in
short-term pasture leys (Stovold 1974; Barbetti and Sivasithamparam 1987;
Burnett et al. 1994; Murray and Davis 1996). Other studies have been relatively
site-specific or have focused on specific components of the soil biology [e.g.
the microorganisms involved in litter decomposition (Hutchinson and King 1989),
soil microbial communities (Banu et al. 2004), nematodes (Yeates and King
1997), microarthropods (King et al. 1985), and earthworms (Baker 1998a, 1998b,
1999)].
A wide range of indicators has been used in more general studies of soil
health and soil biology (e.g. Doran and Safley 1997; Pankhurst et al. 1997),
but we chose to measure total organic carbon (C), total nitrogen (N), labile C,
microbial biomass C, microbial activity, and soil nematodes. Measurements of C
and N provide an indication of the resources available to sustain the soil food
web, labile C is a measure of the C fraction (e.g. sugars, organic acids, and
amino acids) most readily available as a food source for soil microorganisms,
and microbial biomass C is an indicator of the overall size of the soil
microbial community. Enzyme activities are also often used as indicators of
microbial activity (Nannipieri 1994), and we measured the rate at which
fluorescein diacetate (FDA) was hydrolysed by soil esterases, lipases, and
proteases. This is a simple, rapid, and sensitive test that has been used in
several studies to estimate total microbial activity in soil and environmental
samples (e.g. Schnurer and Rosswall 1982; Adam and Duncan 2001).
Soil nematodes were studied because they are useful indicators of
biodiversity and have previously been used to assess the impact of land
management practices on overall soil condition (Yeates and Bongers 1999). From
an ecological point of view, nematodes can be categorised according to their
feeding habits (e.g. plant-parasites, bacterivores, fungivores, omnivores, and
carnivores), and by where they fit on a coloniser-persister (cp) continuum of
1-5 (Yeates et al. 1993; Yeates and Bongers 1999). Bacterivores that multiply
rapidly in disturbed, microbially enriched environments have cp values of l,
while larger omnivorous and carnivorous nematodes, with much longer generation
times, have cp values of 4 or 5 (Bongers 1990). When nematode feeding groups
and cp scales are combined into functional guilds and the data are used to
compute an enrichment index (EI), structure index (SI), and channel index (CI),
nematode faunal analysis becomes a powerful tool for assessing soil health and
making inferences about the condition of the soil food web (Ferris et al.
2001). EI depends on the responsiveness of opportunistic nematode guilds to
food resource enrichment, and therefore indicates whether the soil ecosystem is
nutrient-enriched or nutrient-depleted. SI describes the level of structure and
diversity in the food web, while CI is based on the proportion on
fungal-feeding and opportunistic bacterial-feeding nematodes and indicates
whether the predominant decomposition channels in the food web are fungal or
bacterial.
This study focuses on the biology of permanent and semi-permanent pastures
used for grazing in temperate regions of Australla. Two areas with similar
pasture species but contrasting climates were surveyed: an area in south-east
South Australla and western Victoria with a
winter-dominant rainfall pattern, and an area near Tamworth and Armidale in
northern New South Wales
with summer-dominant rainfall (Fig. 1). The objectives were to obtain a general
indication of the biological status of soils used for temperate pasture
production, compare the soil biology of the 2 study areas, and determine
whether this biology was influenced by pasture species composition. Studies
detailing soil nematode, chemical, and biochemical properties for pasture
species in 2 contrasting environments in temperate Australla have not
previously been published.
[FIGURE 1 OMITTED]
Materials and methods
Sites
Forty sites, mostly on commercial properties, were selected for sampling on
the North-West Slopes and Northern Tablelands of New South Wales (summer
rainfall zone, Fig. 1 and Table 1) and the south-east of South
Australla and western Victoria (winter rainfall zone, Fig. 1 and
Table 2). A comparison of long-term monthly rainfall and temperature data
(Clewett et al. 2003) for 2 centres within these zones (Tamworth, NSW and
Hamilton, Vic.) showed that although these centres had similar mean annual
rainfall (675 v. 692mm, respectively) their seasonal distribution pattern was
markedly different (Fig. 2a). Also, mean minimum and maximum temperatures
([degrees]C) were lower each month at Hamilton
than Tamworth, except for mean minimum
temperatures in winter (Fig. 2b). Sites with a history of fertiliser
application and no obvious chemical or physical soil constraints to pasture
production were surveyed, but pasture performance was not always optimal.
Winter rainfall zone sites were selected in conjunction with cooperating
producers, and summer rainfall zone sites were chosen after consulting local,
experienced district advisors and cooperating producers. Target species were
subterranean clover (Trifolium subterraneum L.), phalaris (Phalaris aquatica
L.), and lucerne (Medicago sativa L.) in both rainfall zones, and perennial
ryegrass (Lolium perenne L.) in the winter rainfall zone. Perennial grass-based
pastures always had a companion legume.
[FIGURE 2 OMITTED]
In northern New South Wales,
8 sites were located on subterranean clover dominant pastures, 6 on phalaris,
and 6 on lucerne pastures. Subterranean clover occurred in sown pastures (in
association with phalaris), native perennial grass based pastures, and at 1
site (site 9) in conjunction with the invasive perennial grass Hyparrhenia
hirta (L.) Stapf. (Coolatai grass). Native perennial grass based pastures were
dominated by redgrass (Bothriochloa macra (Steud) S.T. Blake) and wiregrass
(Aristida ramosa R.Br.). Phalaris pastures were sown to either cv. Sirosa or
cv. Australlan. Lucerne
pastures were mainly dryland and used for grazing with some intermittent hay
cutting, but 1 (site 7) was used only for irrigated hay production. In South
Australla and Victoria, 10 sites were located on subterranean clover dominant
pastures, 2 on phalaris, 3 on lucerne, and 4 on perennial ryegrass pastures,
with 1 site (site 12) being dominated by tall fescue (Festuca arundinacea
Schreb.) and strawberry clover (T. fragiferum L.). Many sites in the winter
rainfall zone (1, 2, 4, 6, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18) also had a
reasonable presence (>10% on a dry-weight basis) of annual winter-growing
annual grasses [mainly brome grass (Bromus spp.), silver grass (Vulpia spp.),
barley grass (Hordeum leporinum Link), or annual ryegrass (Lolium rigidum
Gaudin)] and capeweed (Arctotheca calendula L.).
For each site, latitude, longitude, and elevation [metres above sea level
(m, a.s.l.)] was recorded and paddock history determined from the cooperating
producer (species sown, date of sowing, and grazing and fertiliser application
history). Soil types at each site were classified according to Isbell (1996).
Herbage mass and species composition
The dry weight rank method of Mannetje and Haydock (1963), and modifications
for tied and cumulative ranks proposed by Jones and Hargreaves (1979), were
used to determine herbage mass (kg DM/ha) and species composition for each site
in both rainfall zones. The data obtained represented the standing herbage mass
(green and dead) of the grazed pastures at the time they were sampled (a 2-week
period in September 2003 for sites in northern New South
Wales, and a 2-week period in November 2003 for South
Australlan and Victorian sites).
At each site, 3 locations (~5 by 5 m) were selected, pasture condition was
visually rated as good, medium or poor and the growth phase (vegetative or
flowering) of the target species was noted. In northern New South Wales, herbage mass and species
rank was estimated in 10 quadrats (0.40 by 0.40m) at each location. Fifteen
calibration quadrats were then harvested with hand-held shears to 10 mm above
ground level and material was dried in a dehydrator at 80[degrees]C for 48h
before weighing. Herbage mass was scored on a continuous 0-5 scale and
converted to kgDM/ha by linear regression (with [R.sup.2] values always
>0.80). For each of the South Australlan and Victorian sites, 3 quadrats
(0.30 by 0.30 m) were harvested to ground level and the material dried in a
dehydrator at 80[degrees]C for 48 h before weighing. Pasture botanical
composition was estimated in 30 quadrats (0.30 by 0.30 m) at each location and
converted to proportions using the rank method of Mannetje and Haydock (1963).
At all sites, species rankings were converted to proportions (%) using standard
multipliers (Mannetje and Haydock 1963; Jones and Hargreaves 1979) and used to
calculate the herbage mass of individual species in each quadrat, before
conversion to percent composition (species herbage mass as a proportion of
total herbage mass).
Soil sampling and analyses
Litter was removed from the soil surface and soil samples collected to a
depth of 0.15 m. In the summer rainfall zone (northern New South Wales sites),
soil was collected in 25 cores (50 mm diameter) at each location and in the
winter rainfall zone (South Australlan and Victorian sites) samples were
collected using a spade in 10 sampling areas (0.15 by 0.15 m) at each of the 3
sampling locations within each site. In mixed pasture types, soil samples were
collected from areas dominated by the target species for that site. Individual
soil samples from each location were mixed and bulked (after removal of large
roots and stones) and stored in sealed plastic bags. Plant and soil samples
were stored and transported to the laboratory in insulated containers and
processed for shipment to various laboratories within 24-48 h of collection.
Gravimetric soil moisture status (%) was determined before samples were
analysed.
Nematodes
A 200-mL sample of field-moist soil was spread on a standard extraction tray
(Whitehead and Hemming 1965), and after 2 days, nematodes were recovered by
sieving twice on a 38 [micro]m sieve. Total plantparasitic (TPPN), total
free-living nematodes (TFLN) and numbers of plant-parasitic nematodes
(identified to genus level) were counted in fresh samples at a magnification of
40X. Nematodes were then fixed in formalln-acetic acid and a sample of at least
100 randomly selected specimens was identified at a magnification of 400X. Each
nematode was assigned a trophic group and cp value, and the data were used to
calculate EI, SI and CI values using procedures described by Ferris et al.
(2001).
Total soil microbial activity
Microbial activity was estimated by allowing soil enzymes to hydrolyse FDA
to water-soluble fluorescein, and measuring the end product with a spectrophotometer
(Schnurer and Rosswall 1982). Field-moist soil (5 g dry-weight equivalent),
FDA, and phosphate buffer (pH 7.2) were added to an Ehrlenmeyer flask and
shaken on an orbital shaker for 30 min at 24-26[degrees]C. The reaction was
terminated with acetone, the mixture centrifuged, and the absorbance of the
supernatant measured at a wavelength of 490 nm. Readings were corrected for background
absorbance and appropriate standard curves (Chen et al. 1988) were used to
calculate microbial activity (expressed as [micro]g FDA hydrolysed/g dry
soil.min).
Soil chemical and biochemical properties
For each site and location, a 300-g subsample of soil was air-dried for 7
days and sieved (
Data analyses
For both rainfall zones, data for more than 30 variables were available,
including herbage mass of the target species (kg DM/ha); numbers of TFLN, TPPN,
and various genera of plant parasitic nematodes (Pratylenchus,
Tylenchorhynchus/ Merlinius, Paratylenchus/Gracilacus, Heterodera, Meloidogyne,
Rotylenchus, Helicotylenchus, and Paratrichodorus); CI, SI, and EI values;
total microbial activity; microbial biomass C; labile C; total organic C and
total N; pH (Ca[Cl.sub.2] and water); EC; PRI; P, K, and S (mg/kg of soil);
DTPA Cu, Zn, Mn, and Fe (mg/kg), and exchangeable Ca, Mg, Na, K, and Al
(cmol/kg).
The pastures sampled were typical of those in each of the rainfall
environments and so were highly variable in their species composition and the
spatial distribution of species within a site. Hence, there was considerable
variation among sites dominated by the same species as well as the locations
within a site. To account for this variation, data were examined by calculating
mean values and their 95% confidence interval (standard error times the value
for [t.sub.0.05] for n-1 degrees of freedom; Snedecor and Coehran 1969) for
summer and winter rainfall zones and all sites. These confidence intervals were
used to provide a conservative estimate of differences in mean values among
sites and groupings of data (e.g. environments, species composition, or
microbial activity), while acknowledging the variable nature of the data.
Data for each variable were also plotted to identify any outlying points.
Data for winter rainfall site 12 were excluded from these analyses because this
site was dominated by tall fescue, which was not one of the target species.
Also, data for winter rainfall site 8 (location 3) and site 19 (location 2)
were excluded because the samples were mislabelled. Since chemical analyses
indicated that total organic C levels were unusually high (> 100 mg/g of
soil) at winter rainfall sites 5 and 6 (Organosol soil type, Table 2) and 7
(location 2, Percalcic Black Dermosol soil type, Table 2), these sites were
also excluded from the final analyses. Thus, there were only 17 sites and 48
locations in the final dataset for the winter rainfall zone, with all sites
having a total organic C content of 3.0 [micro]g FDA/g.min (winter rainfall
sites only)] and their mean and 95% confidence interval values were calculated.
For summer and winter rainfall sites, data for each variable and within each
of the target species groups and soil microbial activity groups were also
examined by correlation analyses (using GENSTAT version 7.1) to determine
relationships among variables.
Results
At the time of sampling (September 2003, summer rainfall zone; November
2003, winter rainfall zone), most lucerne and perennial grass plants were
vegetative, whereas subterranean clover and annual ryegrass plants were
flowering. At most sites, plant condition was recorded as medium to good,
reflecting the amount of rainfall received in both zones during the
winter/spring period before sampling. Rainfall was above average in spring 2003
at Hamilton in the winter rainfall zone, and
about 9 mm above the long-term average of 91 mm at Tamworth
in July and August 2003 (Clewett et al. 2003). These rainfall differences were
broadly reflected in the gravimetric soil water content of the soils at the
time of sampling. Most sites (except those with sandy textured soils) in the
winter rainfall zone had soil moisture contents of 18-30%, while soil moisture
in the summer rainfall zone generally ranged from 10 to 16%.
Soil nematodes
The most common plant-parasitic nematode was lesion nematode (Pratylenchus
spp.), which was found at 40 of the 60 summer rainfall locations and 14 of the
48 winter rainfall locations. Populations were generally low (Table 3), with
only 3 summer and 3 winter rainfall locations having relatively high population
densities (e.g. > 1800 Pratylenchus/200 mL soil, which is equivalent to
about 10 Pratylenchus/g soil). Lesion nematodes were found in association with
all pasture types (Tables 4 and 5). P. thornei and P. neglectus appeared to be
the most common species, but it is likely that at least 3 other species were
also present.
Root-knot nematodes (Meloidogyne sp.) and cyst nematodes (Heterodera spp.)
were found in both rainfall zones, but mean population densities were low
(Tables 3, 4 and 5), largely because both nematodes occurred at
Ectoparasitic nematodes found in the survey included pin nematode
(Paratylenchus and Gracilacus), stunt nematode (Tylenchorhynchus and Merlinius,
commonly M. brevidens), spiral nematode (Rotylenchus and Helicotylenchus), and
stubby root nematode (Paratrichodorus). Pin nematode was common in both
rainfall zones and occurred at high population densities (> 2000
nematodes/200 mL soil) at several summer rainfall sites (sites 3, 13, 15, and
19), but population densities of other nematodes were relatively low (Tables 3,
4, and 5).
Except for sites with high numbers of pin nematodes, there were always many
more free-living nematodes in the soil than plant-parasitic nematodes, and this
was reflected in the mean population densities of both groups (Tables 3, 4, and
5). Numbers of free-living nematodes were highest in the winter rainfall zone
(Table 3), while there were more free-living nematodes in subterranean clover
and phalaris pastures than in lucerne pastures in the summer rainfall zone
(Table 4).
Indices derived from nematode community analyses indicated that the soil
food webs under these pastures were moderately structured and enriched (Tables
3, 4, and 5). However, values for EI and SI were lower in the summer than the
winter rainfall zone (Table 3), and were influenced by pasture species (Tables
4 and 5). There were even larger differences in CI values between the 2 zones,
with high indices in the summer rainfall zone indicating that decomposition
channels were primarily fungal, and lower indices in the winter rainfall zone
indicating that bacterial decomposition was predominant (Table 3).
Graphical representations of structure and enrichment indices showed that
mean values for all sites in the northern rainfall zone (Fig. 3a) were
centrally located around E1 and SI values of 50. Based on the interpretation of
Ferris et al. (2001), the condition of the soil food webs at all sites was
considered to be either structured or degraded. Food web condition was more
variable in the winter rainfall zone, as there was more variation in the
structure trajectory and some sites were more highly enriched than in the
summer rainfall zone (Fig. 3b). When the data for individual locations were
plotted (Fig. 3 c, d), it was apparent that there was considerable variability
in food web condition within each rainfall zone. The soil food web was degraded
(low EI and low SI) at more than one-third of locations in the summer rainfall
zone, whereas only a few food webs of this type were observed in the winter
rainfall zone.
[FIGURE 3 OMITTED]
Correlation analysis for all locations (n = 108) indicated that few of the
nematode parameters were closely related to other chemical and biochemical
properties. TFLN numbers were significantly (P< -0.40) with each other and
weakly correlated (r < 0.38) with all of the biochemical and chemical
properties, except for SI values with labile C (r = 0.48) and CI values with
TFLN (r = -0.53), labile C, (r = 0.67), total organic C (r = 0.62), total N (r
= -0.57), and DTPA Fe (r = -0.49).
Correlations between herbage mass and TFLN (Table 6) indicated that these
parameters were always positively correlated. However, the 2 most widely
distributed plant-parasitic nematodes differed in their relationship with
herbage mass, with Pratylenchus generally being positively correlated and
Paratylenchus/Gracilacus negatively correlated. Two of the indices derived from
nematode community analyses (EI and SI) showed no consistent trends, whereas
the negative correlation between CI values and herbage mass indicated that bacterial
decomposition channels became more predominant as herbage mass increased.
When data were grouped according to soil microbial activity (Table 7), TFLN
responded in the same way as total organic C, labile C, and microbial biomass
C, increasing as microbial activity increased. EI and SI values also tended to
increase with microbial activity, whereas CI values declined markedly as
microbial activity increased (Table 7).
Soil biochemical properties
Mean total microbial activity was twice as high (2.6 v. 1.3 [micro]g
FDA/g.min) in soils from the winter rainfall zone than in those from the summer
rainfall zone (Table 3). Similarly, mean levels of total organic C, total N,
and labile C were higher for the winter than the summer rainfall zone (Table
3). For both rainfall zones, mean microbial biomass C was approximately 0.09
mg/g soil (Table 3) and for all locations, labile C was 9.05% of total organic
C, and microbial biomass C was 3.5% of labile C.
In both rainfall zones, values for all measured biochemical properties were
lower in lucerne pastures than in other pasture types (Tables 4 and 5). Since
30% of the surveyed pastures in the summer rainfall zone were dominated by
lucerne (compared with only 12.5% in the winter rainfall zone), this was one of
the main factors associated with the biological differences observed between
the 2 zones.
For the summer rainfall zone, there were no major differences in any of the
measured soil biochemical properties between pastures dominated by subterranean
clover and phalaris (Table 4). However, subterranean clover pastures in the
winter rainfall zone tended to have lower total organic C and N values than
perennial ryegrass and phalaris pastures (Table 5). Herbage mass (kgDM/ha) of
lucerne pastures in the summer rainfall zone was significantly (P < 0.05)
and positively correlated with total organic C, labile C, and microbial biomass
C (r > 0.60, Table 6). In contrast, herbage mass of subterranean clover
pastures in the winter rainfall zone was significantly and negatively correlated
(r >-0.44) with all of the measured biological properties, except microbial
biomass C (Table 6).
When sites were grouped on the basis of soil microbial activity, means of
the 5 groups ranged from 0.4 to 3.4[micro]g FDA/g.min (Table 7). Over all
locations, total organic C and N, and labile and microbial biomass C, tended to
increase with total microbial activity (e.g. r > 0.42 for the latter
comparison, Table 8). Locations in the summer rainfall zone comprised all of
the sites in group 1 (< 1.5 [micro]g FDA/g.min), whereas in the winter
rainfall zone they were located in groups 2 and 3 (3.0[micro]g FDA/g.min) were
all in the Victorian component of the winter rainfall zone and were associated
with subterranean clover or perennial ryegrass pastures on Sodosol soils.
Hence, total microbial activity groupings were confounded by both pasture
species and rainfall zone.
For all locations (n = 108), both total microbial activity ([micro]g
FDA/g.min) and microbial biomass C (mg/g) were significantly (P< 42% of the
variation in both total organic C and labile C, except for the correlation
between total microbial activity and total organic C in the winter rainfall
zone (r = 0.76, Table 8). Although labile C was also significantly correlated
with microbial biomass C and total microbial activity in the summer rainfall
zone and at all locations (Table 8), [R.sup.2] values were always
In both rainfall zones and at all locations, the only relationship that was
significantly and positively correlated (Table 8) and had high (>0.80)
[R.sup.2] values was that between total organic C and labile C. The correlation
between these properties was r = 0.96 (Table 8; [R.sup.2] = 0.9194) in the
summer rainfall zone (n = 60) and r = 0.92 (Table 8; [R.sup.2] = 0.8434) in the
winter rainfall zone (n = 48). Microbial biomass C was significantly correlated
with total organic C and labile C in the summer rainfall zone (r = 0.64 and r =
0.66), but accounted for
Soil chemical properties
Soils from the summer rainfall zone had higher mean pH(Ca[Cl.sub.2]),
pH(water), K, exchangeable K and Ca, and DTPA Cu, Zn, and Mn values than those
from the winter rainfall zone (Table 3). In contrast, soils from winter
rainfall sites had higher mean EC, DTPA Fe, and exchangeable Al values (Table
3).
For the summer rainfall zone, soils from lucerne-based pastures had higher
mean pH(Ca[Cl.sub.2]), pH(water) and lower DTPA Zn, DTPA Mn, DTPA Fe, and
exchangeable Al compared with those from subterranean clover and phalaris-based
pastures (Table 4). Soils from phalaris pastures tended to have higher S levels
than those from subterranean clover pastures (10.9 v. 4.6mg/kg of soil, Table
4) and higher DTPA Cu than those from lucerne pastures (3.1 v. 2.1 mg/kg, Table
4). Subterranean clover-dominant pastures tended to have lower exchangeable Ca,
Mg, and Na than lucerne pastures (Table 4). Lucerne herbage mass (kgDM/ha) was
significantly (P < 0.05) correlated with P and S levels (r = 0.69 and r =
0.51, respectively, Table 6), while subterranean clover herbage mass was only
significantly correlated with the level of exchangeable Ca (r=0.43). Phalaris
herbage mass (Table 6) was significantly correlated with EC (r = 0.48), PRI (r
= 0.58), DTPA Mn (r = 0.78), and K and exchangeable K (r = 0.96). Regressions
between phalaris herbage mass (PHM) and K or exchangeable K (Ex. K) were: PHM =
4.08 K - 36.7, ([R.sup.2] = 0.91) and PHM = 1722 Ex. K - 19.9, ([R.sup.2] =
0.92).
For the winter rainfall zone, mean values for S, DTPA Mn and exchangeable Al
were lowest for lucerne pastures and mean values for K, DTPA Cu, and
exchangeable Mg, Na, and K were highest for phalaris-based pastures (Table 5).
Mean EC values were lower for lucerne than phalaris pastures (0.05 v. 0.28
ds/m) and mean PRI was higher for phalaris and subterranean clover, than
lucerne pastures (163.7 and 108.7, respectively v. 36.4, Table 5). Subterranean
clover pastures had higher mean DTPA Fe levels than lucerne pastures (468.7 v.
159.6 mg/kg), but lower exchangeable Ca levels than phalaris pastures (4.8 v.
20.2 cmol/kg, Table 5).
For the total microbial activity groups, group 5 had the lowest K values and
group 1 the lowest DTPA Fe values, whereas total microbial activity and
exchangeable Al were highest in group 5 (Table 7). Mean pH(Ca[Cl.sub.2]) was
higher for total microbial activity group 1 than groups 4 and 5, and mean DTPA
Cu and Zn, and exchangeable Mg and K were also higher for group 1 than group 5.
However, the PRI was lower for total microbial activity groups 1 and 2 than for
group 5 and mean S levels were lower for group 1 compared with group 5 (Table
7). Again these differences need to be interpreted with some caution because of
the confounding of rainfall zone, soil type and pasture species with microbial
activity.
Discussion
Plant-parasitic nematodes
Lesion nematode (Pratylenehus) was widely distributed and is potentially the
most important nematode pest in the 2 study areas. Several species of
Pratylenchus are known pathogens of lucerne (Griffin
1985), responses to nematicide have been obtained in Pratylenchus-infested
pastures in New Zealand
(Cook and Yeates 1993), and P thornei and P neglectus are serious pathogens of
cereal crops in both northern and southern Australia (Thompson et al. 1995;
Taylor et al. 1999). Interestingly, however, populations of lesion nematode on
pastures rarely reached the levels observed following susceptible wheat crops,
either because pasture species are less supportive of populations of this
nematode or mechanisms of suppression are more effective in pasture soils than
cropped soils.
The other plant-parasitic nematodes found in our survey were probably not
economically important, except perhaps in specific, localised situations. Cyst
and root-knot nematodes are generally considered the most damaging nematodes on
grassland and forage crops (Cook and Yeates 1993), but in both our study areas,
their population densities were low and the nematodes were not widely
distributed. Pin nematodes (Paratylenchus, and the closely related genus
Gracilacus) were more widespread, but they are rarely considered important
pathogens (Cook and Yeates 1993).
Free-living nematodes
Yeates and King (1997) found >8 x [10.sup.6] free-living
nematodes/[m.sup.2] in the upper 30 cm of soil in an improved, but ungrazed
pasture located near Armidale in our summer rainfall zone. Our data from grazed
pastures showed much lower numbers of free-living nematodes (mean values of 1.5
x [10.sup.6] and 2.7 x [10.sup.6] nematodes/[m.sup.2] to a depth of 15 cm in
summer and winter rainfall zones, respectively). Lower numbers of nematodes in
our northern samples may have been associated with sampling time (end of the
winter growing season in our study, compared with end of the summer season in
the study of Yeates and King 1997), climatic differences in the years before
sampling, or the effects of grazing on the quantity and quality of organic
residues returned to the soil. Nevertheless, populations of free-living
nematodes in pastures were much higher than are usually found in soils from
agricultural and horticultural crops in Australia (based on counts from
samples processed for nematode diagnostic purposes; G. R. Stirling, unpublished
data).
Although complete nematode faunal analyses were undertaken in this study,
our detailed dataset is not presented in this paper. Instead, the data were
simplified by calculating indices that are useful for inferring food web
condition (Ferris et al. 2001). In doing this, we recognise that there is a
loss of ecological information when incidence data for more than 20 nematode species
is combined into a single index, that there is uncertainty about the allocation
of some nematodes to particular feeding groups, and that reproductive rates of
nematodes may vary considerably within cp groups (Yeates 2003). Nevertheless,
the calculated indices provided a useful way of demonstrating biological
differences between climatic zones, pasture species, and individual sites.
The value of EI is influenced by the number of bacterial-feeding enrichment
opportunists (predominantly Rhabditidae), and indicates the level of resources
available for soil microorganisms (due to disturbance, organism mortality,
turnover, or favourable shifts in the environment). In our study, this index
was affected by both climate and pasture species. In the winter rainfall zone,
EI values were highest at site 1 (a subterranean clover pasture), and
relatively high in the 2 lucerne pastures that were sampled. Thus when N inputs
are available from legumes in a cool, moist environment, the food web is
dominated by bacteria and nematodes in the family Rhabditidae are an important
component of the nematode community. These nematodes were rarely seen in the
summer rainfall zone, and this was reflected in the relatively low EI values
for this zone. Interestingly, EI was lower in lucerne and subterranean clover
pastures in the summer rainfall zone than it was in phalaris pastures,
indicating that there were fewer resources in legume-based pastures to sustain
the soil food web.
The soil environment under a pasture is relatively stable and generally not
subject to periodic disturbance, and so its soil food web is usually highly
structured. It was therefore surprising that only 2 pasture types in our survey
(perennial ryegrass and phalaris, both in the winter rainfall zone) had a mean
SI >70. In most other cases, mean SI values ranged from 44-56, with the
relatively low SI values reflecting a lack of omnivorous nematodes
(Dorylaimida). This group of nematodes is particularly sensitive to
perturbations caused by cultivation, heavy metals, acidification and N
fertiliser (Tenuta and Ferris 2004), and so it is possible that unknown stress
factors were operating on the soil food web at some sites, particularly those
in the summer rainfall zone. The level of stress appeared to be relatively high
in some situations, with 5 locations in the summer rainfall zone and 3 in the
winter rainfall zone having SI values
The CI was determined from the proportion of fungivores and opportunistic
bacterivores (Rhabditidae), and indicates whether the primary decomposition
channel in the soil food web was bacterial (low CI) or fungal (high CI). Our
data showed that climate (in the period before sampling) had a major effect on
this parameter, with the mean CI value in the winter rainfall zone being 28
(indicative of bacterial decomposition) compared with 72 (indicative of fungal
decomposition) in the summer rainfall zone. Since bacterial-feeding nematodes
have a greater effect on short-term N availability to plants than
fungal-feeding nematodes (Ingham et al. 1985), the level of biological nutrient
cycling would therefore be expected to be different between the 2 zones.
Reasons for differences in EI and CI between the 2 rainfall zones were not
investigated, but soil moisture was probably a major determining factor.
Rhabditidae feed on bacteria in water films that surround soil particles and
are an important component of the nematode community in moist European soils
(Bouwman and Zwart 1994). They were relatively common in a similar environment
in southern Australia
(winter rainfall zone), but their population densities were probably limited by
periodically dry conditions that commonly occur in the summer rainfall zone. In
the latter environment, fungi and fungal-feeding nematodes were relatively more
important components of the biology, as fungi are the primary decomposers of
plant residues on the soil surface (Hendrix et al. 1986) and fungal-feeding
nematodes are well adapted to survive in dry soil (Freckman et al. 1977;
Bouwman and Zwart 1994).
Effects of climate and pasture species on soil biology
Our results clearly showed that levels of total organic C, total N, and
labile C were higher in the winter rainfall zone than the summer rainfall zone.
The quantity and quality of organic residues available to soil organisms was
therefore highest in the winter rainfall zone, and this was reflected in the
general biological properties (e.g. total microbial activity and total numbers
of free-living nematodes) of these soils. These differences between study areas
were probably related mainly to climate and its effects on pasture productivity
and litter decomposition rates, although factors such as stocking rates and the
presence of soil inverterbrates (e.g. dung beetles) may also be involved.
Climate is one of the main factors controlling levels of soil organic C (Burke
et al. 1989), and both Sanford et al. (2003) and Graham et al. (2003) have
shown higher herbage mass and herbage accumulation rates for pastures in the
winter rainfall zone compared with those in the summer rainfall zone. In
southern Australia,
winter rainfall is relatively consistent and so pasture production is high, and
litter breakdown is limited by dry conditions in summer and low winter
temperatures. In northern New South Wales,
winter rainfall is not as reliable and winter pasture production is lower than
in southern Australia.
Summer-growing pasture species contribute to the pool of organic matter, but
their impact is limited by erratic rainfall and by high litter breakdown rates
during periods when soil moisture is adequate following rainfall.
Low EI values, low levels of microbial activity, and low numbers of
free-living nematodes in soils from lucerne pastures in the summer rainfall
zone suggests that their general level of biological activity is lower than for
soils supporting other types of pasture. There are several possible reasons for
this. First, lucerne has a non-fibrous tap root system, and so there is little
root activity near the soil surface, where our samples were collected. Second,
lucerne pastures are generally better utilised by livestock and less litter may
therefore be returned to the soil than with other pasture species. Third, high
water use by lucerne (e.g. Humphries and Auricht 2001; Angus et al. 2001)
reduces competition from other plant species and diminishes litter accumulation
in the area between lucerne plants. Fourthly, lucerne is often grown as a
pasture ley on soils with a long history of soil disturbance from cropping, or
in arable paddocks that have been cultivated for many years. In the summer
rainfall zone, these soils have lower levels of total and labile C (Lefroy et
al. 1993; Blair et al. 1995; Whitbread et al. 1996) than lightly grazed,
undisturbed grasslands.
Although lucerne pastures in the winter rainfall zone had higher EI values
and levels of microbial activity than similar pastures in the summer rainfall,
only 2 sites were sampled in the winter rainfall zone and in both cases lucerne
comprised
Effects of chemistry
Effects of soil chemistry on soil biology are often indirect, as many
chemical parameters can affect the amount of plant residues returned to soil
through their impact on plant growth (Dalal 1998). However, soil pH did not
appear to operate in this way in the 2 study areas, as pH(Ca[Cl.sub.2]) was generally
suitable for the target species: [5.3-6.5 for lucerne, 4.0-6.4 for subterranean
clover, 4.0-6.5 for perennial ryegrass (Helyar and Anderson 1971)], and >5
for phalaris (Ridley and Coventry 1992). Nevertheless, direct effects of pH on
the soil biology may have occurred, as measurements for all locations (n = 108)
showed that pH(Ca[Cl.sub.2]) was weakly correlated with microbial activity,
TFLN and microbial biomass C (r=-0.58, -0.18 and -0.34, respectively).
Although all sites in our survey had a history of superphosphate
application, soil P Colwell levels were
Our data indicated that the mean level of soil S for all locations was 7.3
mg/kg, which was marginally above the critical value (6.5-6.7 mg S/kg)
determined by Blair et al. (1991) and Anderson et al. (1994). However, the mean
concentration of S in lucerne-dominated pastures in the summer rainfall zone
(5.2 mg/kg), was below this critical value, raising the possibility that
indirect effects orS on plant growth may have contributed to the low microbial
activity of lucerne pastures in this zone.
Fleming (1997) indicated that K levels >120mg/kg were adequate for
perennial ryegrass--subterranean clover pastures, and Spencer and Govaars
(1982) indicated a critical limit of 116mgK/kg. However, our data showed that
phalaris herbage mass in the summer rainfall zone was highly correlated with K
Colwell values much higher than these critical limits (range 95-840 mg/kg) and
was also correlated with exchangeable K values ranging from 0.18 to 1.97
cmol/kg. These relationships, and the higher mean K Colwell values for
phalaris-dominated pastures in the winter rainfall zone, (371 mg/kg) indicated
that K nutrition may have indirectly impacted on soil biology by affecting the
productivity of phalaris pastures. There was also some evidence of this in the
summer rainfall zone, with a weak correlation between exchangeable K and both
TFLN and microbial activity (r = 0.36 and 0.34, respectively).
Brennan and Best (1999) cited unpublished data for soils in Western Australia
indicating that growth responses to Cu in subterranean clover pastures could
only be obtained at concentrations
Soil Mn levels were higher in the summer than the winter rainfall zone (53.3
v. 13.2mg/kg). Soil pH and microbial activity can affect the solubility of Mn
in the soil (Uren 1999), but our data from all locations showed that Mn values
were poorly correlated with these soil properties (r < 0.10). However, for
the summer rainfall zone soil, Mn levels were significantly correlated with
microbial activity (r = 0.66, n = 60).
Conclusions
We concluded that from a biological perspective, soils used for pasture
production in the 2 study areas were reasonably 'healthy'. This was based on
the relatively high levels of total organic C and labile C at many of the
surveyed sites, the high numbers of free-living nematodes and high microbial
activities in most soils, and a lack of evidence of widespread problems
associated with plant-parasitic nematodes. An important conclusion was that the
biological status of these pasture soils appeared to be much better than that
of soils used for cropping in Australia.
Total organic C declined markedly in Vertosols under cultivation (Dalai and
Mayer 1986), whereas it was enhanced by grass-legume pastures (Dalai et al. 1995).
Data for red-brown earth soils (Red-Brown Chromosols) in the summer rainfall
zone showed that total C values were ~44% lower in cropped soils, than in
adjacent paddocks of undisturbed grasslands (Lefroy et al. 1993). When our
results were compared with those obtained from cropped soils in the northern
grain-growing region (e.g. M.J. Bell et al., unpublished), numbers of
free-living nematodes and microbial activities were much higher in pastures
than cropped soils. We therefore suggest that perennial pastures, such as those
surveyed in the present study, could be used as standard reference sites when
monitoring the ecological condition of soils used for agriculture. A similar
recommendation has been made in the USA (Neher and Campbell 1994).
The above conclusion does not mean that the biological status of all
surveyed pasture soils was satisfactory, as the soil biology in lucerne
pastures in the summer rainfall zone was generally poorer than in phalaris- or
subterranean clover-dominant pastures. Our data also indicated that there was
some variation in soil biological status among sites that were dominated by the
same pasture species. This variability was possibly related to differences in
soil texture or herbage mass inputs, as both can have a major effect on
microbial biomass (Dalal 1998). In hindsight, relationships between soil
texture, plant herbage mass and our biological and biochemical measurements may
have been strengthened by a more objective measure of soil textural differences
(e.g. particle size analysis), and more comprehensive measures of pasture
productivity (e.g. herbage accumulation rates, as determined by Sanford et al.
2003). At the farm level, our measurements (3 locations at each site) indicated
that there was often considerable biological variability within fields.
Commonly, one of the following parameters (total organic C, labile C, microbial
biomass C, microbial activity, EI, SI, or CI) varied by more than 100% within a
field, and at some sites, this level of variability was observed for several
parameters. Since soil texture and grazing management within fields were
similar, more detailed studies are required to understand the causes of this
within-field variation and quantify its economic and environmental impact.
Given that the grazing industry has demonstrated an interest in soil biology
by commissioning a review of the knowledge of soil biology in pasture
production systems (Gupta and Ryder 2003), our results will raise questions
from graziers about which parameters are the most useful indicators of soil
biological status. We suggest that labile C should be a primary measurement as
it is a key driver of soil biological activity, it can be measured in the field
using a hand-held colourimeter (Weil et al. 2003), and levels vary considerably
within Australian pastures. In the summer rainfall zone, for example, labile C
was low in lucerne pastures at sites 8 and 11 (1.06 and 1.25 mg/g,
respectively) and in a heavily grazed, unfertilised natural grassland at site
10 (1.12mg/g), and relatively high (3.02mg/g) in a phalaris pasture at site 2.
Similar site-to-site variation also occurred in the winter rainfall zone, with
levels of labile C being lowest in a lucerne pasture at site 2 (1.13-1.63 mg/g)
and highest in a phalaris pasture at site 3 (4.60-5.97 mg/g).
Since labile C was only loosely correlated with microbial biomass C and
microbial activity in our study (Table 8), it may not provide more than a broad
indication of the soil biological status at a particular site. Correlations
between labile C and the biology were weakest in the winter rainfall zone,
probably because there was considerable variability in soil texture within this
zone. Labile C is therefore likely to be a more useful indicator of soil
biological properties in soils with broadly similar physical properties. The
value of labile C as a biological indicator will also improve as we learn more
about the impact of grazing management on levels of labile C, and increase our
understanding of the temporal dynamics of C availability and how it influences
key soil biological processes.
Acknowledgments
This study was jointly funded by Meat & Livestock Australia, Australian
Wool Industries and the Grains Research and Development Corporation, as part of
a Soil Biology Initiative. We gratefully acknowledge the assistance of the
landholders and managers whose properties were surveyed, as they willingly
allowed us access to their properties. We also thank Dale Lewis for sampling
the sites in the winter rainfall zone, Brian Roworth for his help in collecting
and processing the samples from the summer rainfall zone, Marcelle Stirling for
counting many of the nematode samples, Liz Wilson for measuring microbial
activity, Phil Moody for C and N analyses, Gregor Yeates and Jackie Nobbs for
help in identifying flee-living and plant-parasitic nematodes, respectively,
and Lester McCormick, Clare Edwards and Ian Collet for their assistance in
selecting survey sites in the summer rainfall zone. Phil Moody, Gregor Yeates,
VVSR Gupta and Keith Hutchinson made helpful suggestions regarding the
manuscript.
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Manuscript received 21 June 2005, accepted 21 September 2005
G. R. Stirling (A) and G. M. Lodge (B)
(A) Corresponding author. Biological Crop Protection, 3601 Moggill Road, Moggill, Qld 4070, Australia.
Email:
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(B) NSW Department of Primary Industries, Tamworth Agricultural Institute, 4 Marsden Park Rd,
Calala, NSW 2340, Australia.
Table 1. Summary details of the 20 sites sampled in the summer rainfall zone (northern NSW) in September 2003 For each pasture type, the number in brackets indicates the mean dry-weight of the species as a proportion (%) of the total Elevation Site Nearest town Latitude Longitude (m, a.s.l.) 1 Nundle 31:24:45 151:06:35 570 2 Nundle 31:24:55 151:05:10 585 3 Duri 31:15:25 150:49:25 555 4 Bingara 29:56:55 150:24:25 375 5 Upper Horton 30:12:50 150:25:40 440 6 Barraba 30:21:35 150:21:35 840 7 Somerton 30:55:50 150:34:00 300 8 Somerton 30:54:45 150:33:05 320 9 Barraba 30:34:40 150:37:00 520 10 Barraba 30:34:55 150:37:10 510 11 Manilla 30:49:40 150:40:50 400 12 Upper Horton 30:14:35 150:25:30 440 13 Upper Horton 30:13:05 150:25:30 450 14 Armidale 30:36:40 150:36:20 1040 15 Armidale 30:36:40 150:36:20 1040 16 Uralla 30:36:30 150:32:40 1060 17 Uralla 30:36:40 150:32:20 1065 18 Bundarra 30:21:50 151:10:10 685 19 Bundarra 30:21:50 151:10:10 685 20 Manilla 30:49:00 150:42:30 385 Site Pasture type Soil type 1 Subterranean clover (54) Brown Chromosol 2 Phalaris (74) Black Vertosol 3 Lucerne (56) Brown Dermosol 4 Lucerne (90) Black Vertosol 5 Phalaris (61) Brown Chromosol 6 Phalaris (48) Brown Dermosol 7 Lucerne (100) Brown Dermosol 8 Lucerne (63) Red Chromosol 9 Subterranean clover (55) Brown Chromosol 10 Subterranean clover (40) Red Chromosol 11 Lucerne (88) Red Chromosol 12 Lucerne (100) Brown Chromosol 13 Subterranean clover (80) Brown Chromosol 14 Phalaris (63) Grey Chromosol 15 Subterranean clover (58) Grey Chromosol 16 Subterranean clover (66) Red Dermosol 17 Phalaris (100) Red Dermosol 18 Phalaris (71) Yellow Chromosol 19 Subterranean clover (63) Yellow Chromosol 20 Subterranean clover (70) Brown Vertosol Table 2. Summary details of the 20 sites sampled in the winter rainfall zone (south-east South Australia and western Victoria) in November 2003 For each pasture type, the number in brackets indicates the mean dry-weight of the species as a proportion (%) of the total Elevation Site Nearest town Latitude Longitude (m, a.s.1.) 1 Langkoop, Vic. 37:08:54 140:59:28 90 2 Struan, SA 37:05:49 140:47:48 80 3 Struan, SA 37:06:16 140:45:51 50 4 Coonawarra, SA 37:18:16 140:51:14 55 5 Millicent, SA 37:37:60 140:20:17 15 6 Bray, SA 37:14:15 139:58:49 10 7 Greenways, SA 37:10:49 140:11:20 20 8 Wattle Range, SA 37:20:53 140:37:15 50 9 Dergolm, Vic. 37:23:16 141:13:17 100 10 Penola, SA 37:27:28 140:56:50 65 11 Mingbool, SA 37:41:35 140:52:01 70 12 Eight Mile Creek, SA 38:02:11 140:45:50 5 13 Hamilton, Vic. 37:50:30 142:05:19 200 14 Hamilton, Vic. 37:50:31 142:05:21 200 15 Hamilton, Vic. 37:40:19 142:01:38 200 16 Coleraine, Vic. 37:36:05 141:39:40 200 17 Caramut, Vic. 37:59:09 142:35:57 150 18 Caramut, Vic. 37:58:33 142:31:27 150 19 Vasey, Vic. 37:24:32 141:54:01 250 20 Coleraine, Vic. 37:37:13 141:41:57 200 Site Pasture type Soil type 1 Subterranean clover (41) Brown Kurosol 2 Lucerne (18) Bleached Tenosol 3 Phalaris (55) Petrocalcic Black Dermosol 4 Subterranean clover (47) Eutrophic Brown Sodosol 5 Lucerne (55) Organosol 6 Perennial ryegrass (6) Brown Chromosol 7 Perennial ryegrass (12) Percalcic Black Dermosol 8 Subterranean clover (60) Calcic Brown Chromosol 9 Subterranean clover (69) Brown Kurosol 10 Subterranean clover (65) Calcic Brown Sodosol 11 Lucerne (7) Eutrophic Brown Chromosol 12 Fescue (67) Organosol 13 Subterranean clover (54) Ferric Eutrophic Brown Sodosol 14 Subterranean clover (8) Eutrophic Brown Sodosol 15 Subterranean clover (43) Brown Sodosol 16 Phalaris (47) Black Vertosol 17 Subterranean clover (43) Ferric Eutrophic Brown Sodosol 18 Perennial ryegrass (67) Ferric Eutrophic Brown Sodosol 19 Subterranean clover (60) Grey Vertosol 20 Perennial ryegrass (40) Brown Sodosol Table 3. Mean and 95% confidence interval (Cl) for total herbage mass (kg DM/ha), soil nematode numbers, indices derived from nematode community analysis and a range of soil chemical and biochemical properties for sites surveyed in spring 2003 for summer and winter rainfall zones, and for all locations Values in brackets are the number of locations for each zone. Values for nematodes are number/200 mL soilFactor Rainfall zone Factor Summer (n = 60) Winter (n = 48) Mean 95% CI Mean 95% CI Herbage mass (kg DM/ha) 1826 276 3387 541 Nematodes Total free-living nematodes 1997 294 3598 504 Total plant-parasitic nematodes 833 312 241 139 Pratylenchus 214 144 205 119 Tylenchorhynchus/Merlinius 17 16 22 27 Paratvlenchus/Gracilacus 535 303 97 50 Heterodera 23 34 0 -- Meloidogyne 36 56 0 -- Enrichment index 42 3 51 5 Structure index 51 4 60 7 Channel index 72 7 28 6 Biochemical Microbial activity 1.3 0.2 2.6 0.2 ([micro]g FDA/g.min) Microbial biomass C (mg/g soil) 0.08 0.01 0.09 0.02 Labile C (mg/g) 1.7 0.2 3.3 0.3 Total organic C (mg/g) 20.2 1.8 34.0 3.4 Total N (mg/g) 1.7 0.1 2.8 0.3 Chemical pH(Ca[Cl.sub.2]) 5.5 0.1 5.1 0.3 pH(water) 6.4 0.1 6.0 0.2 EC (ds/m) 0.05 0.01 0.10 0.03 P retention index 84.3 13.5 100.1 22.7 P (mg/kg) 38.2 6.8 39.2 13.6 K (mg/kg) 356.9 44.5 126.4 35.4 S (mg/kg) 6.7 1.6 7.8 1.2 DTPA Cu (mg/kg) 2.6 0.3 0.7 0.1 DTPA Zn (mg/kg) 21.0 7.5 1.1 0.3 DTPA Mn (mg/kg) 53.3 8.4 13.2 4.1 DTPA Fe (mg/kg) 118.2 21.6 404.9 65.4 Exchangeable Ca (cmol/kg) 11.7 1.7 7.6 2.2 Exchangeable Mg (cmol/kg) 3.2 0.6 2.2 0.8 Exchangeable Na (cmol/kg) 0.2 0.1 0.5 0.2 Exchangeable K (cmol/kg) 0.8 0.1 0.3 0.1 Exchangeable Al (cmol/kg) 0.05 0.02 0.29 0.09 Rainfall zone All locations Factor (n = 108) Mean 95% CI Herbage mass (kg DM/ha) 2525 345 Nematodes Total free-living nematodes 2704 309 Total plant-parasitic nematodes 568 188 Pratylenchus 297 110 Tylenchorhynchus/Merlinius 28 18 Paratvlenchus/Gracilacus 439 183 Heterodera 21 23 Meloidogyne 34 38 Enrichment index 46 3 Structure index 55 4 Channel index 52 6 Biochemical Microbial activity 1.9 0.2 ([micro]g FDA/g.min) Microbial biomass C (mg/g soil) 0.09 0.01 Labile C (mg/g) 2.4 0.2 Total organic C (mg/g) 26.4 2.2 Total N (mg/g) 2.2 0.2 Chemical pH(Ca[Cl.sub.2]) 5.4 0.2 pH(water) 6.3 0.1 EC (ds/m) 0.08 0.02 P retention index 96.2 12.2 P (mg/kg) 56.5 10.9 K (mg/kg) 238.8 37.2 S (mg/kg) 8.2 1.3 DTPA Cu (mg/kg) 1.8 0.2 DTPA Zn (mg/kg) 11.6 4.2 DTPA Mn (mg/kg) 33.9 5.9 DTPA Fe (mg/kg) 235.1 39.2 Exchangeable Ca (cmol/kg) 12.3 2.4 Exchangeable Mg (cmol/kg) 2.8 0.4 Exchangeable Na (cmol/kg) 0.3 0.1 Exchangeable K (cmol/kg) 0.6 0.1 Exchangeable Al (cmol/kg) 0.15 0.04 Table 4. Mean values and 95% confidence intervals (CI) for species herbage mass (kg DM/ha), soil nematode numbers, indices derived from nematode community analysis and a range of soil chemical and biochemical properties for 60 locations sampled in the summer rainfall zone in spring 2003 Values for nematodes are number/200 mL soil Subterranean Lucerne clover (n = 18) (n = 18) Factor Mean 95% CI Mean 95% CI Herbage mass (kg DM/ha) 1143 394 1298 396 Nematodes Total free-living nematodes 1303 411 2198 478 Total plant-parasitic nematodes 251 162 1413 697 Pratylenchus 200 147 270 313 Tylenchorhynchus/Merlinius 9 7 30 39 Paratylenchus/Gracilacus 32 62 973 694 Heterodera 0 -- 14 28 Meloidogyne 9 19 79 138 Enrichment index 36 7 42 5 Structure index 44 7 53 7 Channel index 85 13 71 10 Biochemical Microbial activity 0.6 0.1 1.4 0.3 ([micro]g FDA/g.min) Microbial biomass C (mg/g) 0.06 0.01 0.08 0.01 Labile C (mg/g) 1.3 0.1 1.7 0.3 Total organic C (mg/g) 15.5 1.1 20.2 2.8 Total N (mg/g) 1.3 0.1 1.7 0.2 Chemical pH(Ca[Cl.sub.2]) 6.0 0.3 5.3 0.2 pH(water) 6.9 0.3 6.2 0.2 EC (ds/m) 0.05 0.01 0.04 0.005 P retention index 66.2 8.0 86.3 27.2 P (mg/kg) 29.5 11.7 37.4 9.8 K (mg/kg) 347.6 71.9 382.0 63.4 S (mg/kg) 5.2 1.4 4.6 1.0 DTPA Cu (mg/kg) 2.1 0.2 2.7 0.4 DTPA Zn (mg/kg) 6.4 2.3 20.6 8.8 DTPA Mn (mg/kg) 29.7 7.3 62.0 12.3 DTPA Fe (mg/kg) 48.1 19.4 140.2 37.0 Exchangeable Ca (cmol/kg) 16.3 3.9 9.2 1.6 Exchangeable Mg (cmol/kg) 4.7 0.9 2.1 0.4 Exchangeable Na (cmol/kg) 0.3 0.1 0.1 0.0 Exchangeable K (cmol/kg) 0.8 0.1 0.9 0.1 Exchangeable Al (cmol/kg) 0.02 0.02 0.07 0.03 Phalaris (n = 18) Factor Mean 95% CI Herbage mass (kg DM/ha) 1319 476 Nematodes Total free-living nematodes 2424 574 Total plant-parasitic nematodes 642 320 Pratylenchus 125 209 Tylenchorhynchus/Merlinius 4 3 Paratylenchus/Gracilacus 418 285 Heterodera 52 109 Meloidogyne 0 -- Enrichment index 47 7 Structure index & | 
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