Terry Koen

Variations in soil organic carbon for two soil types and six land uses in the Murray Catchment, New South Wales, Australia

The aim of this study was to investigate variations in soil organic carbon (SOC) for two soil types and six common land uses in the New South Wales Murray Catchment and to explore the factors influencing those variations. Samples were collected from 100 sites on duplex soils (Ustalfs) of the Slopes region, and 100 sites on red-brown earths (Xeralfs) of the Plains region. Stocks of SOC (0–30 cm) across the study area ranged between 22.3 and 86.0 t ha–1, with means (± s.e.) of 42.0 ± 1.3 and 37.9 ± 0.8 t ha–1 for the Slopes and Plains regions, respectively. Higher SOC stocks were present in pasture-dominated land uses compared with mixed cropping in the Slopes region, with particularly high stocks found in pastures at positions on a slope of 7–10%. No significant differences in SOC stocks were identified between land-use groups (pastures or cropping) in the Plains region (<500-mm rainfall zone). Significant correlations were found between SOC and a range of climatic, topographical, and soil physico-chemical variables at both the catchment and sub-regional scale. Soil physico-chemical and topographical factors play an important role in explaining SOC variation and should be incorporated into models that aim to predict SOC sequestration across agricultural landscapes.

Diversity and abundance of biological soil crust taxa in relation to fine and coarse-scale disturbances in a grassy eucalypt woodland in eastern Australia

Over the last 200 years the box woodlands of eastern Australia have been considerably altered by European farming practices. These changes have been accompanied by a reduction in the size and number of patches of vegetation as well as the quality of the understorey vegetation and underlying soil surface. We measured diversity and abundance of soil crust taxa in relation to habitat complexity, remnant area and width, diversity of vascular plants as well as the number, size and separation of patches of vegetation and grass butts (coarse-scale patchiness), and an index of surface stability derived from measures of seven soil surface features of small microsites (patches of bare/crusted, litter- or grass-covered soil; micro-scale) on both coarse- and fine-textured soils at 35 sites in south-eastern Australia. Fifty taxa were recorded from the 35 sites, and there were more taxa from sites with fine-textured soils (12.7) compared with coarse-textured soils (4.4). The soil crust community was dominated by a few relatively common species, with many species occurring at only a few sites. Half the number of species accounting for <1% of total abundance. Bare and crusted microsites supported more species and greater cover compared with grassy microsites. Crust diversity declined with increasing coarse-level disturbances (i.e. declines in habitat complexity, remnant area and width, and diversity of vascular plants) but the results were not consistent between soil types. No measures of fine-scale disturbance were related significantly to any of the crust diversity or abundance measures, and there was no evidence of a recent grazing effect on crust composition. The fact that few sites had many species (and visa versa) suggests to us that many sites are probably required to conserve soil crust taxa in these highly fragmented landscapes

Measurement and estimation of land-use effects on soil carbon and related properties for soil monitoring: a study on a basalt landscape of northern New South Wales, Australia

There is a growing need for information relating to soil condition, its current status, and the nature and direction of change in response to management pressures. Monitoring is therefore being promoted regionally, nationally, and internationally to assess and evaluate soil condition for the purposes of reporting and prioritisation of funding for natural resource management. Several technical and methodological obstacles remain that impede the broad-scale implementation of measurement and monitoring schemes, and we present a dataset designed to (i) assess the optimum size of sample site for soil monitoring, (ii) determine optimum sample numbers required across a site to estimate soil properties to known levels of precision and confidence, and (iii) assess differences in the selected soil properties between a range of land-use types across a basalt landscape of northern NSW. Sample site size was found to be arbitrary and a sample area 25 by 25m provided a suitable estimate of soil properties at each site. Calculated optimum sample numbers differed between soil property, depth, and land use. Soil pH had a relatively low variability across the sites studied, whereas carbon, nitrogen, and bulk density had large variability. Variability was particularly high for woodland soils and in the deeper soil layers. A sampling intensity of 10 samples across a sampling area 25 by 25m was found to yield adequate precision and confidence in the soil data generated. Clear and significant differences were detected between land-use types for the various soil properties determined but these effects were restricted to the near-surface soil layers (0-50 and 50-100mm). Land use has a profound impact on soil properties near to the soil surface, and woodland soils at these depths had significantly higher carbon, nitrogen, and pH and lower bulk density than the other land uses. Soil properties between the other non-woodland land-use types were largely similar, apart from a modestly higher carbon content and higher soil acidity under improved pasture. Data for soil carbon assessment should account for equivalent mass, since this significantly modified carbon densities, particularly for the lighter woodland soils. Woodland soils had larger quantities of carbon (T/ha corrected for equivalent mass) than any other land-use type, and in order to maintain the largest quantity of carbon in this landscape, retaining trees and woodland is the most effective option. Results from this work are being used to inform further development the NSW Statewide Soil Monitoring Program.

Landscape position moderates how ant nests affect hydrology and soil chemistry across a Chihuahuan Desert watershed

Ants moderate the supply of critical resources such as water and nutrients in desert environments by changing the physical arrangement of soils during nest construction. We measured water infiltration and soil physical and chemical properties on and off the nests of two ant species (Pogonomyrmex rugosus, Aphaenogaster cockerelli) across five sites at differing landscape positions within a Chihuahuan Desert watershed. Our aim was to test whether the effects of these long-lived ant nests on water infiltration and soil chemistry varied between ant species or across sites within a watershed. Water flow was generally slowest at the site with the highest silt and clay contents, and fastest at the site with sandy soils. Flow was generally greater through ant nest soils than adjacent non-nest soils, and we attribute this to increases in macropores in the nests. However, the effects of both ant nests and species varied among sites. Despite wide variation in soil chemical properties across all sites, ant nests had a consistent effect on soil chemical properties, with higher levels of carbon, nitrogen, sulphur, phosphorus and electrical conductivity on nests compared with non-nest soils. Our results demonstrate that while we can generalise about the effects of ant nests on water flow and nutrient levels, differences in soil type, nest density and ant species across sites are likely to moderate these effects.

Soil organic carbon stocks in saline and sodic landscapes

Increasing salinity (high levels of water-soluble salts) and sodicity (high levels of exchangeable sodium) are serious land degradation issues worldwide. In Australia, salinity and sodicity affect a large proportion of the landscape and often coincide with agricultural land. Despite the areal extent of salt-affected soils, both worldwide and in Australia, few data exist on soil organic carbon (SOC) stocks in these areas. For this study, the level of SOC was determined in scalded (bare areas without vegetation), scalded-eroded, vegetated, and revegetated (i.e. sown pasture) soil profiles from 2 sites in the Southern Tablelands region of New South Wales, Australia. SOC concentration was significantly higher in the profiles that were vegetated with native pasture (1.96-2.71% in the 0-0.05 m layer) or revegetated with sown pasture (2.35% in the 0-0.05 m layer), and lower in those profiles that were scalded (1.52% in the 0-0.05 m layer) or scalded-eroded (0.16-0.30% in the 0-0.05 m layer). These lower SOC levels are reflected throughout the profiles of the scalded and scalded-eroded soils. The soil carbon stocks to 0.30 m are also much lower in the scalded and scalded-eroded soils that have been affected by salinity and sodicity. The profiles that were vegetated with native pasture had carbon stocks to 0.30 m of 35.2-53.5 t/ha, while the sown pasture had 42.1 t/ha. This compares with the scalded profiles with 19.8 t/ha and the scalded-eroded profiles with 7.7-11.4 t/ha to 0.30 m. The presence of vegetation ameliorates several soil properties and results in the differences in SOC and other soil properties between scalded and vegetated profiles at the surface and at depth.

Effects of soil disturbance, weed control and mulch treatments on establishment of Themeda triandra (Poaceae) in a degraded white box (Eucalyptus albens) woodland in central western New South Wales

Temperate grassy woodlands are endangered ecosystems in Australia, and many degraded remnants are in desperate need of understorey restoration. This experiment compared the effects of soil disturbance, weed control and mulch treatments on establishment of the original dominant grass, Themeda triandra Forssk., in a degraded white box (Eucalyptus albens Benth.) woodland at Cowra in central New South Wales (NSW). Awned Themeda seeds were surface-sown into replicated plots treated as follows: soil scalping, soil disturbance (by ripping), herbicide (simazine) application and retention of natural mulch. Scalping combined with soil disturbance best promoted Themeda establishment (47.8% after 40 days and 28% after 518 days), and also reduced broadleaf-herb densities. By contrast, scalping without soil disturbance had the worst effect on Themeda establishment (5.2% after 40 days and 4.5% after 518 days). Disturbance significantly enhanced Themeda establishment and decreased the density of annual grasses and the basal cover of non-Themeda species. By contrast, the retention of 500–800 kg of natural surface mulch had no apparent effect on Themeda establishment. Contrary to expectations, simazine reduced the density and basal cover of all species, including Themeda, which is normally resistant to this herbicide. All combinations of the mulched, disturbed and herbicide treatments (i.e. all treatments except scalping) gave similar results, ranging from 10.7 to 22.0 Themeda plants m–2 after 518 days. These results suggest that Themeda stands can be established in degraded box woodlands by using awned seed materials, with minimal seedbed preparation and simple sowing techniques. Further studies are required to determine whether established swards can resist weed invasion in the absence of ongoing weed management, and whether establishment success varies with soil conditions and landscape position.

Animal foraging pit soil enhances the performance of a native grass under stressful conditions

Background and AimsIn line with the Stress Gradient Hypothesis, studies of facilitation have tended to focus on plant–plant interactions (biotic nurses), while the relative role of abiotic nurses has been little studied. We assessed the role of biotic and abiotic nurses, and their interaction, on soil enhancement and the consequential performance of a native annual grass, Dactyloctenium radulans.MethodsWe used a growth chamber study with two levels of water application to compare the performance of D. radulans growing in soil from foraging pits of the Short-beaked echidna (Tachyglossus aculeatus; abiotic nurse) and non-pit soil from either under tree canopies (biotic nurse) or surrounding open areas.ResultsAll measures of plant performance were more pronounced under the high than the low water treatment. The greatest differences between pit and surface Microsites occurred under the low water application, reinforcing our view that facilitatory effects are greater in resource-limited environments. Despite tree canopy soil having greater N, there was no significant effect on plant performance, nor any significant interaction with Microsite.ConclusionsOur study provides strong evidence that foraging pits enhance soil properties and this soil, in turn, facilitates plant growth; and supports previous work documenting the positive effect of nurse-protégé interactions under greater levels of abiotic stress.

The patterns of grazed pasture associated with scattered trees across an Australian temperate landscape: an investigation of pasture quantity and quality

Scattered paddock trees occur across agricultural landscapes in Australia. However, in the temperate regions of Australia their numbers are rapidly declining and they may be lost across much of the landscape in 200 years. Here we examined the spatial distribution of green (GDB), senescent (SDB) and total (TDB) dry pasture biomass, and nutrient status of the GDB fraction around scattered Eucalyptus trees on three parent materials (basalt, granite and meta-sediment) in native and sown pastures across a range of grazed temperate landscapes in northern New South Wales. We used a combination of destructive harvests and a handheld active optical canopy reflectance sensor (AOS) with an integrated GPS to examine pasture biomass around scattered trees. The harvested pasture biomass data indicated that under grazed conditions the presence of scattered trees did not introduce significant radial trends in TDB or GDB out to a distance of 3.5 canopy radii regardless of tree species or parent material. The red and near-infrared reflectance-based Normalised Difference Vegetation Index (NDVI), as measured by the AOS, did indicate a consistent azimuthal trend with larger GDB on the southern side of the tree and lower GDB on the northern side in the native pasture. However, this observation must be qualified as the regression coefficient for the relationship between NDVI and GDB was significant but weak (best r2 = 0.42), and SDB reduced its predictive capacity. We also found a higher percentage of GDB under the canopy than in the open paddock. We suggest that the combination of these results may indicate higher grazing pressure under trees than in the open paddock. Pasture nutrient concentration (P, K and S) was higher in both native and sown pastures beneath the tree canopy compared with the open paddock. This study indicates that, in this temperate environment, scattered trees do not adversely affect pasture production, and that they can improve some pasture nutrients.

Native couch grasses for revegetating severely salinised sites on the inland slopes of NSW

Perennial ‘couch’ grasses that reproduce from rhizomes and or stolons have some advantages on scalded saline sites where they can reproduce in situations that are often hostile to germination and establishment of obligate seeders. Promising couch grass species from an earlier evaluation at Wagga Wagga and Manildra were Cynodon dactylon, Paspalum vaginatum, Sporobolus virginicus and, to a lesser extent, Sporobolus mitchellii. This paper reports results of a subsequent evaluation of these species as well as Eragrostis dielsii and Distichlis distichophylla at 3 other saline sites (Burrumbuttock, Cudal and Cundumbul). All accessions were established vegetatively and assessed for vigour and survival (all sites), groundcover production and its relationship with EC and pH (2 sites), biomass production, forage value and the effect of regular cutting on groundcover (1 site). S. virginicus appeared the most tolerant to saline conditions and produced high levels of groundcover and biomass but was sensitive to regular defoliation. At the 2 alkaline sites, C. dactylon and D. distichophylla generally outperformed the other accessions in terms of persistence and groundcover but appeared to be relatively low in forage value, and D. distichophylla appeared to have significant weed potential. Paspalum vaginatum produced high groundcover and relatively high biomass of moderate forage value at Burrumbuttock but performed poorly at the other sites. S. mitchellii and E. dielsii persisted on the more benign sites producing only low amounts of dry matter and groundcover and may be useful for environmental plantings where low weed potential is paramount. Despite spatially intensive testing of the topsoil chemistry, there were no obvious relationships between EC or pH and plant performance at the 2 main trial sites – a possible consequence of vegetative propagation.

A Note on Tree Deaths during the Current (2001–?) Drought in South-eastern Australia

Abstract Tree deaths over large areas during droughts are uncommon. In the semi-arid zone of New South Wales (NSW) such events were last reported during the prolonged droughts of 1895–1903 and 1939–45, though whether caused solely by drought is open to question. Anecdotal and quantitative evidence during the current prolonged drought (2001–?) in NSWs sub-humid zone (where deaths are localised) and semi-arid zone (where deaths are more extensive) suggest that climatic conditions are comparable to, and perhaps more severe than, those of the earlier prolonged droughts. It is suggested that lack of access to deep soil moisture due to inherent shallow rooting, or due to site conditions, is the most likely cause; and that this may be associated with higher than optimal tree densities in cohorts of trees that arose from previous regeneration events during periods of well above average rainfall. A more thorough examination of the extent and severity of this event is warranted.