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: This email address is being protected from spam bots, you need Javascript enabled to view it

(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                       55        6 

Channel index                         62       13 

                                        Biochemical 

Microbial activity                   1.8      0.3 

  ([micro]g FDA/g.min) 

Microbial biomass C (mg/g)          0.10     0.02 

Labile C (mg/g)                      2.1      0.3 

Total organic C (mg/g)              24.9      3.7 

Total N (mg/g)                       2.0      0.3 

                                        Chemical 

pH(Ca[Cl.sub.2])                     5.2      0.1 

pH(water)                            6.1      0.1 

EC (ds/m)                           0.06     0.01 

P retention index                   99.6     27.1 

P (mg/kg)                           48.0     15.1 

K (mg/kg)                          332.7    111.4 

S (mg/kg)                           10.9      4.8 

DTPA Cu (mg/kg)                      3.1      0.7 

DTPA Zn (mg/kg)                     36.2     21.3 

DTPA Mn (mg/kg)                     65.5     18.7 

DTPA Fe (mg/kg)                    159.1     34.2 

Exchangeable Ca (cmol/kg)           10.5      3.0 

Exchangeable Mg (cmol/kg)            3.1      1.4 

Exchangeable Na (cmol/kg)            0.2      0.1 

Exchangeable K (cmol/kg)             0.8      0.3 

Exchangeable Al (cmol/kg)           0.06     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                       55        6 

Channel index                         62       13 

                                        Biochemical 

Microbial activity                   1.8      0.3 

  ([micro]g FDA/g.min) 

Microbial biomass C (mg/g)          0.10     0.02 

Labile C (mg/g)                      2.1      0.3 

Total organic C (mg/g)              24.9      3.7 

Total N (mg/g)                       2.0      0.3 

                                        Chemical 

pH(Ca[Cl.sub.2])                     5.2      0.1 

pH(water)                            6.1      0.1 

EC (ds/m)                           0.06     0.01 

P retention index                   99.6     27.1 

P (mg/kg)                           48.0     15.1 

K (mg/kg)                          332.7    111.4 

S (mg/kg)                           10.9      4.8 

DTPA Cu (mg/kg)                      3.1      0.7 

DTPA Zn (mg/kg)                     36.2     21.3 

DTPA Mn (mg/kg)                     65.5     18.7 

DTPA Fe (mg/kg)                    159.1     34.2 

Exchangeable Ca (cmol/kg)           10.5      3.0 

Exchangeable Mg (cmol/kg)            3.1      1.4 

Exchangeable Na (cmol/kg)            0.2      0.1 

Exchangeable K (cmol/kg)             0.8      0.3 

Exchangeable Al (cmol/kg)           0.06     0.03 

Table 5. 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 48 locations sampled in the winter rainfall 

                                                     Subterranean 

                                        Lucerne         clover 

                                        (n = 6)         (n=28) 

Factor                              Mean   95% CI    Mean   95% CI 

Herbage mass (kg DM/ha)              258       66    1700      395 

                                              Nematodes 

Total free-living nematodes         4408     3122    3535      672 

Total plant-parasitic nematodes      125      149     197      113 

Pratylenchus                         399      515      59       84 

Tylenchorhynchus/Merlinius             0       --       0        0 

Paratylenchus/Gracilacus              26       31     150       89 

Heterodera                             0       --       0        0 

MeloidoWrne                            0       --       0       -- 

Enrichment index                      58       15      52        7 

Structure index                       46       20      56        9 

Channel index                         31       19      31        8 

                                                 Biochemical 

Microbial activity                   1.2      0.4     2.8      0.2 

  ([micro]g FDA/g.min) 

Microbial biomass C (mg/g)          0.03     0.02    0.09     0.02 

Labile C (mg/g)                      1.9      0.6     3.2      0.3 

Total organic C (mg/g)              18.0      5.3    32.5      3.9 

Total N (mg/g)                       1.4      0.5     2.6      0.3 

                                                 Chemical 

pH(Ca[Cl.sub.2])                     5.7      0.4     4.8      0.2 

pH(water)                            6.5      0.3     5.7      0.2 

EC (ds/m)                           0.05     0.03    0.07     0.01 

P retention index                   36.4     26.9   108.7     31.9 

P (mg/kg)                           59.3     55.9    29.0      5.9 

K (mg/kg)                           67.8     31.7    95.9     28.3 

S (mg/kg)                            4.5      1.2     6.6      0.9 

DTPA Cu (mg/kg)                      0.4      0.3     0.6      0.1 

DTPA Zn (mg/kg)                      1.0      0.2     0.8      0.1 

DTPA Mn (mg/kg)                      3.9      0.4    11.6      2.6 

DTPA Fe (mg/kg)                    159.6    153.7   468.7     68.1 

Exchangeable Ca (cmol/kg)            5.6      1.8     4.8      0.8 

Exchangeable Mg (cmol/kg)            1.0      0.5     1.2      0.4 

Exchangeable Na (cmol/kg)            0.1      0.0     0.2      0.1 

Exchangeable K (cmol/kg)             0.2      0.1     0.3      0.1 

Exchangeable Al (cmol/kg)           0.01     0.01    0.32     0.11 

                                       Perennial 

                                       ryegrass        Phalaris 

                                       (n = 8)         (n = 6) 

Factor                              Mean   95% CI    Mean   95% CI 

Herbage mass (kg DM/ha)             2448     1061     933      306 

                                               Nematodes 

Total free-living nematodes         3366      666    3396      660 

Total plant-parasitic nematodes      565      838     125      237 

Pratylenchus                         379      456     120      251 

Tylenchorhynchus/Merlinius            67      113       5        9 

Paratylenchus/Gracilacus              14       31       0       -- 

Heterodera                             0       --       0       -- 

MeloidoWrne                            0       --       0       -- 

Enrichment index                      48       12      41       13 

Structure index                       71       11      73       17 

Channel index                         29       15      10        7 

                                                 Biochemical 

Microbial activity                   3.3      0.3     2.2      1.1 

  ([micro]g FDA/g.min) 

Microbial biomass C (mg/g)          0.13     0.05    0.13     0.08 

Labile C (mg/g)                      3.7      0.3     4.3      1.5 

Total organic C (mg/g)              41.4      2.6    47.1     11.5 

Total N (mg/g)                       3.6      0.4     4.2      1.2 

                                                 Chemical 

pH(Ca[Cl.sub.2])                     5.3      1.0     6.0      1.5 

pH(water)                            6.1      0.9     6.8      1.2 

EC (ds/m)                           0.10     0.07    0.28     0.18 

P retention index                   70.1     57.8   163.7     42.8 

P (mg/kg)                           30.1     12.1    78.8    112.9 

K (mg/kg)                           94.1     27.3   370.5    161.8 

S (mg/kg)                           10.2      4.1    13.7      5.6 

DTPA Cu (mg/kg)                      0.7      0.3     1.7      0.5 

DTPA Zn (mg/kg)                      1.3      0.7     1.9      2.9 

DTPA Mn (mg/kg)                     14.8      6.1    27.8     34.2 

DTPA Fe (mg/kg)                    471.2    210.0   263.7    269.9 

Exchangeable Ca (cmol/kg)            9.6      5.7   202.0     14.0 

Exchangeable Mg (cmol/kg)            2.1      1.4     8.0      3.4 

Exchangeable Na (cmol/kg)            0.4      0.3     2.2      1.1 

Exchangeable K (cmol/kg)             0.3      0.1     0.9      0.4 

Exchangeable Al (cmol/kg)           0.37     0.25    0.30     0.48 

Table 6. Correlation coefficients (r-values) between herbage mass 

(kg DM/ha) and a range of nematode, chemical and biochemical properties 

for different pasture types and rainfall zones in spring 2003 

Significant values (P = 0.05) are shown in bold. Values for nematodes 

are number/200 mL soil 

                                                Summer rainfall zone 

                                    Lucerne      Subterranean clover 

Factor                             (n = 18)           (n = 24) 

                                           Nematode 

Total free-living nematodes          0.68 *              0.09 

Total plant-parasitic nematodes      0.06               -0.17 

Pratylenchus                         0.10                0.44 * 

Paratylenchus/Gracilacus            -0.14               -0.38 

Enrichment index                     0.34               -0.16 

Structure index                      0.43                0.12 

Channel index                       -0.41               -0.12 

                                           Biochemical 

Microbial activity                   0.33               -0.19 

  ([micro]g FDA/g.min) 

Microbial biomass C (mg/g)           0.70 *              0.08 

Labile C (mg/g)                      0.65 *              0.27 

Total organic C (mg/g)               0.60 *              0.23 

Total N (mg/g)                       0.37                0.17 

                                           Chemical 

pH(CaC[I.sub.2])                     0.08                0.21 

pH(water)                            0.07                0.24 

EC (ds/m)                            0.04               -0.03 

P retention index                   -0.12                0.16 

P (mg/kg)                            0.69 *              0.19 

K (mg/kg)                            0.26                0.37 

S (mg/kg)                            0.51 *             -0.27 

DTPA Cu (mg/kg)                      0.22                0.26 

DTPA Zn (mg/kg)                      0.19                0.02 

DTPA Mn (mg/kg)                     -0.02                0.17 

DTPA Fe (mg/kg)                      0.15               -0.31 

Exchangeable Ca (cmol/kg)            0.13                0.43 * 

Exchangeable Mg (cmol/kg)           -0.04                0.32 

Exchangeable Na (emol/kg)           -0.12               -0.19 

Exchangeable K (cmol/kg)             0.07                0.35 

Exchangeable Al (cmol/kg)           -0.17               -0.36 

                                              Winter rainfall zone 

                                 Phalaris      Subterranean clover 

Factor                           (n = 18)            (n = 28) 

                                           Nematode 

Total free-living nematodes          0.37                0.53 * 

Total plant-parasitic nematodes     -0.46 *              0.23 

Pratylenchus                        -0.08                0.41 * 

Paratylenchus/Gracilacus            -0.44 *             -0.12 

Enrichment index                    -0.02               -0.28 

Structure index                      0.46 *             -0.53 * 

Channel index                       -0.24               -0.28 

                                           Biochemical 

Microbial activity                   0.35               -0.49 * 

  ([micro]g FDA/g.min) 

Microbial biomass C (mg/g)          -0.13                0.21 

Labile C (mg/g)                      0.13               -0.44 * 

Total organic C (mg/g)               0.12               -0.62 * 

Total N (mg/g)                       0.34               -0.67 * 

                                           Chemical 

pH(CaC[I.sub.2])                     0.41                0.47 * 

pH(water)                            0.30                0.47 * 

EC (ds/m)                            0.48 *             -0.19 

P retention index                    0.58 *             -0.64 * 

P (mg/kg)                            0.43                0.28 

K (mg/kg)                            0.96 *             -0.42 * 

S (mg/kg)                            0.28               -0.55 * 

DTPA Cu (mg/kg)                      0.30               -0.64 * 

DTPA Zn (mg/kg)                      0.24               -0.39 * 

DTPA Mn (mg/kg)                      0.78 *             -0.56 * 

DTPA Fe (mg/kg)                     -0.03               -0.62 * 

Exchangeable Ca (cmol/kg)            0.02               -0.27 

Exchangeable Mg (cmol/kg)           -0.13               -0.65 * 

Exchangeable Na (emol/kg)           -0.23               -0.56 * 

Exchangeable K (cmol/kg)             0.96 *             -0.43 * 

Exchangeable Al (cmol/kg)           -0.39               -0.43 * 

Note: Significant values (P = 0.05) are shown in bold indicated with *. 

Table 7. Mean and 95% confidence intervals (CI) for a range of soil 

nematode, chemical and biochemical factors for groups with different 

soil activities (3.0) 

                                       n = 16 

Factor                              Mean     CI 

                                     Nematodes 

Total free-living nematode          3308    773 

Total plant-parasitic nematodes      393    319 

Pratylenchus                         240    157 

Tylenchorhynchus/Merlinius             9     -- 

Paratylenchus/Gracilacus             348    144 

Heterodera                             0     -- 

Meloidogyne                            0     -- 

Enrichment index                      52      9 

Structure index                       67     10 

Channel index                         30     11 

                                    Biochemical 

Microbial activity                   3.4    0.1 

  ([micro]g FDA/g.min) 

Microbial biomass C (mg/g soil)     0.12   0.03 

Labile C (mg/g)                      3.6    0.2 

Total organic C (mg/g)              41.2    2.5 

Total N (mg/g)                       3.3    0.3 

                                      Chemical 

pH(Ca[Cl.sub.2])                     5.0    0.5 

pH(water)                            5.9    0.5 

EC (ds/m)                            0.1   0.03 

P retention index                  155.7   38.0 

P (mg/kg of soil)                   37.5   13.1 

K (mg/kg)                          140.2   38.4 

S (mg/kg)                           11.6    3.6 

DTPA Cu (mg/kg)                      0.9    0.4 

DTPA Zn (mg/kg)                      1.4    0.8 

DTPA Mn (mg/kg)                     19.9    9.9 

DTPA Fe (mg/kg)                    503.2   99.1 

Exchangeable Ca (cmol/kg)           13.3   10.5 

Exchangeable Mg (cmol/kg)            2.3    0.7 

Exchangeable Na (cmol/kg)            0.4   0.10 

Exchangeable K (cmol/kg)             0.4   0.09 

Exchangeable Al (cmol/kg)            0.5   0.18 

Table 8. Matrix of correlation coefficients (r-values) for selected 

soil biological and biochemical properties for all locations (n = 108) 

surveyed in winter and summer rainfall zones in spring 2003 

Labile C (mg/g), microbial biomass C (mg/g), total organic C (mg/g), 

total N (mg/g), microbial activity ([micro]g FDA/g.min) and total 

free-living nematodes (TFLN, number/200 mL soil). Significant values 

(P = 0.05) are shown in bold 

                                 Microbial      Total 

                      Labile C   biomass C    organic C   Total N 

                                   Summer rainfall zone 

Microbial biomass C     0.66 *       --           --         -- 

Total organic C         0.96 *     0.64 *         --         -- 

Total N                 0.87 *     0.74 *       0.83 *       -- 

Microbial activity      0.36 *     0.29 *       0.43 *     0.50 * 

Total free-living       0.48 *     0.39 *       0.53 *     0.38 * 

  nematodes 

                                    Winter rainfall zone 

Microbial biomass C     0.16         --           --         -- 

Total organic C         0.92 *     0.30 *         --         -- 

Total N                 0.99 *     0.45 *       0.99 *       -- 

Microbial activity      0.22       0.61 *       0.76 *     0.81 * 

Total free-living      -0.30 *    -0.22        -0.31 *    -0.32 * 

  nematodes 

                                        All locations 

Microbial biomass C     0.53 *       --           --         -- 

Total organic C         0.95 *     0.41 *         --         -- 

Total N                 0.93 *     0.39 *       0.95 *       -- 

Microbial activity      0.59 *     0.42 *       0.64 *     0.61 * 

Total free-living       0.33 *     0.16         0.21 *     0.18 

  nematodes 

Note: Significant values (P = 0.05) are shown in bold indicated with *.