Soils Of South-eastern Australia Research Articles

Optimizing water management in young almond orchards with heavy clay soils in southeastern Australia using proximal and remote sensors

Optimizing water management in young almond orchards with heavy clay soils in southeastern Australia using proximal and remote sensors

Lime, phosphorus and stocking rate of an extensively managed permanent pasture affect feed-on-offer, sheep growth rate, carrying capacity and wool production

Context Soil acidity constrains pasture productivity, limiting production from grazing animals. Lime application can ameliorate acidity, although the rate is increased when incorporated rather than surface applied. Soils in south-eastern Australia are generally highly erodible, containing valuable native grasses that might be lost if disturbed. Surface application is, therefore, the only option, but the extent to which lime can ameliorate acidity and increase pasture and animal production requires research. Aim This 10-year experiment studied three rates of surface-applied lime, two of superphosphate (P) and two stocking rates (SR) on continuously grazed sheep on acidic soils. Two flocks were studied, one from May 1999 to December 2002, and the second from August 2005 to July 2008. We hypothesised that wool production and animal liveweight would increase as (1) lime rate increased, (2) P rate increased, and (3) peak animal productivity would occur under the combination of the highest rates of lime and P. Key results The experiment coincided with the Millennium Drought reducing forage production, and slowing lime movement into the soil and consequent amelioration. During Flock 1, effective SR (dry sheep equivalents (DSE)/ha) of the low P, low SR and limed treatment became higher by 1 DSE/ha for 10 months during the final flock measurement months, as drought intensified. During Flock 2, effective SR of both high P, high SR and limed treatments were greater by 2 DSE/ha than non-limed counterpart for the first 9 months of 2006. Trends of higher animal production under lime became clearer with time, so were more apparent in Flock 2 than Flock 1, and at higher SR. High lime, high P and high SR had the greatest wool production. High P, low SR and nil lime was initially highly productive, but declined sharply when legumes disappeared, associated with soil aluminium toxicity. Lime maintained superior ground cover under drought, reducing the danger of sward death and soil erosion, demonstrating its sward preservation, sustainability and ecosystem service benefits. Implications With the ever-increasing price of land, farmers must increase their land’s productivity. This trial demonstrated production and environmental benefits associated with acid soil amelioration through lime application.

Delaying nitrogen fertiliser application improves wheat 15N recovery from high rainfall cropping soils in south eastern Australia

Improving nitrogen (N) fertiliser uptake of crops growing in soils susceptible to waterlogging could potentially reduce fertiliser input costs and harmful losses of N to the surrounding environment. The fate of 15N labelled urea applied to wheat cv. Bolac was studied on brown chromosol soils at Hamilton and Tarrington, in the high rainfall zone of south western Victoria, in south eastern Australia. Wheat was fertilised with 15N-urea solution, either deep banded 0.1 m below the seed at sowing or top-dressed with or without the nitrification inhibitor DMPP (3,4-dimethylpyrazole phosphate or ENTEC®) later in the crops development. Daily temporal topsoil (0–0.1 m) water was monitored, throughout the growing season, and at physiological maturity the recovery of 15N-urea in straw, grain and soil (to 0.4 or 0.6 m depth) was measured. Delaying untreated 15N-urea application until top-dressing at mid-tillering to first node stage of growth resulted in significantly (P 2.8 %) and the potential for large rates of mineralisation during the growing season.

Eight years of annual monitoring of DNA of soil-borne potato pathogens in farm soils in south eastern Australia

Concentrations of DNA of the potato pathogens Rhizoctonia solani, Spongospora subterranea and Streptomyces scabies in surface soil (0–150 mm depth) from potato farm paddocks were monitored annually for 8 years in South Australia and Tasmania. A non-linear model was fitted to these data to test if changes in DNA concentrations could be explained by changes in land use in the paddocks, and so identify land uses with potential to either increase or decrease the risk of disease caused by these pathogens. Spongospora subterranea and R. solani anastomosis group (AG) 2.1 were the most prevalent pathogens in both states, followed by St. scabies and R. solani AG3, and R. solani AG4 in Tasmania. The fitted model showed prior crops of poppy and potato to be associated with increased R. solani AG2.1 DNA concentrations; and prior crops of carrot, fallow, poppy and ryegrass with increased R. solani AG3 DNA concentrations, while a prior potato crop was associated with increased concentrations of the DNA of Sp. subterranea and St. scabies. Prior potato crops resulted in average increases of Sp. subterranea DNA of 3300 (South Australia) to 7300 (Tasmania) pg DNA/g soil. Based on the average concentrations of Sp. subterranea DNA in the monitored soils, the model predicted that soils in which potato is grown at least once in every 5 years are likely to remain at high risk of powdery scab. Potato growers in these areas will need to take steps to minimize the risk of this disease, e.g. choose less risky paddocks, grow less susceptible cultivars, and where possible manage soil moisture to avoid wet soil at tuber initiation.

Influence of temperature and soil type on inhibition of urea hydrolysis by N-(n-butyl) thiophosphoric triamide in wheat and pasture soils in south-eastern Australia

Incubation experiments were conducted to assess the effectiveness of N-(n-butyl) thiophosphoric triamide (NBPT) for inhibiting hydrolysis of urea in three wheat-growing soils and one pasture soil in south-eastern Australia, under a range of temperatures (5, 15, 25°C). The effectiveness of NBPT decreased with increasing temperature and with increasing urease activity. In the acidic pasture soil with high urease activity (186 μg N/g soil.h) and high organic carbon content (11%), NBPT (0.1% w/w urea) had little impact on urea hydrolysis rates over all temperatures, with <1% urea remaining at Day 14. In the alkaline, wheat-cropping soils with lower urease activity (54–90 μg N/g soil.h) and lower organic carbon content (<1.5%), NBPT was able to effectively reduce urea hydrolysis over 14–15 days at 5°C and 15°C (>55% urea remaining). At 25°C in the wheat soils, NBPT slowed the rate of urea hydrolysis, but by Days 14 and 15, <2% of the urea remained. NBPT applied at a rate of 0.1% urea would be an effective tool for slowing urea hydrolysis in the wheat-cropping soils under cool-climate conditions. The delay in urea hydrolysis in the pasture soil still provides the opportunity for increased flexibility in farm management, such as irrigation scheduling.

Influence of sample depth on extractable nutrient concentrations, pH and the phosphorus buffering index of pasture soils in south-eastern Australia

Pasture soils of mainland Australia are routinely sampled to a depth of 100 mm, whereas pasture soils of Tasmania and New Zealand are sampled to a depth of 75 mm. Despite this difference, there are no published studies to allow accurate conversion between the 2 sampling depths. This study was undertaken to examine the effect of soil sample depth (75 and 100 mm) on soil nutrient analyses: Olsen phosphorus (P), Colwell P, Colwell potassium (K), KCl40 sulfur (S), pH (H2O and CaCl2), and P buffering index (PBI+ColP). Our findings suggest that on most soil types, Olsen P, Colwell P, and Colwell K soil test results could use a generic factor of 1.17 when converting between 75 and 100 mm samples. More detailed equations including direct or indirect measures of soil texture and P sorption capacity were also determined. We found there was no significant difference in P and K concentrations between the different depths in soils which had very low P sorption capacities, high sand contents, and were located in high rainfall zones. Additionally, soil sampling depth generally had no effect on extractable S concentrations, pH, or PBI+ColP, and therefore no conversion is recommended for these soil tests for any soil type.

Subsoil constraints to crop production on neutral and alkaline soils in south-eastern Australia: a review of current knowledge and management strategies

Crop yield variability and productivity below potential yield on neutral and alkaline soils in the semiarid Mediterranean-type environments of south-eastern Australia have been attributed, in part, to variable rooting depth and incomplete soil water extraction caused by physical and chemical characteristics of soil horizons below the surface. In this review these characteristics are referred to as subsoil constraints. This document reviews current information concerning subsoil constraints typical of neutral and alkaline soils in south-eastern Australia, principally salinity, sodicity, dense soils with high penetration resistance, waterlogging, nutrient deficiencies and ion toxicities. The review focuses on information from Australia (published and unpublished), using overseas data only where no suitable Australian data is available. An assessment of the effectiveness of current management options to address subsoil constraints is provided. These options are broadly grouped into three categories: (i) amelioration strategies, such as deep ripping, gypsum application or the use of polyacrylamides to reduce sodicity and/or bulk density, deep placement of nutrients or organic matter to overcome subsoil nutrient deficiencies or the growing of ‘primer’ crops to naturally ameliorate the soil; (ii) breeding initiatives for increased crop tolerance to toxicities such as salt and boron; and (iii) avoidance through appropriate agronomic or agro-engineering solutions. The review highlights difficulties associated with identifying the impact of any single subsoil constraint to crop production on neutral and alkaline soils in south-eastern Australia, given that multiple constraints may be present. Difficulty in clearly ranking the relative effect of particular subsoil constraints on crop production (either between constraints or in relation to other edaphic and biological factors) limits current ability to develop targeted solutions designed to overcome these constraints. Furthermore, it is recognised that the task is complicated by spatial and temporal variability of soil physicochemical properties and nutrient availability, as well as other factors such as disease and drought stress. Nevertheless, knowledge of the relative importance of particular subsoil constraints to crop production, and an assessment of impact on crop productivity, are deemed critical to the development of potential management solutions for these neutral to alkaline soils.

Effects of fire retardant on heathland soils in south-eastern Australia

A study was undertaken to assess the effects of fire retardant application, unmodified by heat of fire, on soil properties in 2 fire-prone heathland communities at Marlo and the Grampians in south-eastern Australia. Fire retardant (Phos-Chek D75-R at 0.144 g/L) was applied at rates of 0.5, 1.0, and 1.5 L/m2 and compared with control treatments of nil and 1.0 L/m2 of water. Monitoring of surface soils showed that pH at both sites decreased while soil salinity increased immediately after application followed by a rapid decline to pre-treatment values within 12 months. The impact of retardant on total carbon and nitrogen was minor and within the range of natural variation of C and N in surface soils at both sites. Levels of readily available or labile forms of N increased at both sites but declined rapidly to background values after 12 months. Applications of retardant progressively increased extractable P in the surface soil at Marlo, in contrast to the Grampians where a rapid increase was observed after two months followed by a decline after 12 months. These results showed a significant increase in labile P in the surface soil after 12 months and also indicated that a large proportion of the phosphate applied had leached into the subsoil. Likewise, fire retardant applied at the highest rate caused increases in labile sulfate after 2 months at both sites, followed by a rapid decline to background levels. It is expected that the elevated levels of soil phosphate in particular could have a long-term impacts on growth and composition of heathland vegetation known to be sensitive to elevated levels of phosphate in soil.

Crop damage caused by residual acetolactate synthase herbicides in the soils of south-eastern Australia

Grain growers in south-eastern Australia have reported unexpected crop failures with theoretically safe recropping periods for acetolactate synthase herbicides in alkaline soils. This experience has led to the concern that these herbicides may degrade very slowly in alkaline soils, and herbicide residues have at times been blamed for unexplained crop losses. To address this issue, we established 5 recropping trials across Victoria and South Australia with 5 acetolactate synthase herbicides (chlorsulfuron, triasulfuron, metsulfuron-methyl, imazethapyr, and flumetsulam). The herbicides were applied to separate plots in years 1, 2 or 3, and sensitive crop species were sown in year 4 to measure the impact of herbicide residues. We observed that the persistence of the sulfonylureas (chlorsulfuron, triasulfuron, metsulfuron-methyl) varied between herbicides, but all persisted longer in alkaline soils than in acid soils, and were, therefore, more likely to damage crops in alkaline soil. Imazethapyr persisted longer in clay soils than in sandy soils and was, therefore, more likely to damage crops in clay soils. All herbicides persisted longer when rainfall was below average. Canola was more sensitive to imazethapyr than either pea, lentil or medic, but was less sensitive to the sulfonylureas. In contrast, lentil and medic were the most sensitive to sulfonylureas. Despite some damage, we found that safe recropping periods could be predicted from the product labels in all but one situation. The sole exception was that metsulfuron-methyl reduced dry matter and yield of lentil and medic sown 10 months after application in a soil with pH 8.5. We hypothesise that the real cause of crop failure in many situations is not unusual herbicide persistence, but failure to take full account of soil type (pH and clay content including variation in the paddock) and rainfall when deciding to recrop after using acetolactate synthase herbicides.

Persistence and leaching of sulfonylurea herbicides over a 4-year period in the highly alkaline soils of south-eastern Australia

The sulfonylurea herbicides are commonly used in the cereal belt of south-eastern Australia and there is concern that their persistence in alkaline soils is long enough to damage subsequent rotational crops such as legumes and oilseeds. In this study, we investigated leaching and persistence of 3 commonly used herbicides (chlorsulfuron, triasulfuron and metsulfuron-methyl) in alkaline soils of south-eastern Australia (pH range 7.4–8.6) for at least 4 years after treatment. In general, chlorsulfuron was predicted to persist for 3–5 years [time to degrade to 1% (DT99) of 33–63 months after treatment depending on the field site], triasulfuron for 1–3 years (DT99 of 13–37 months after treatment), and metsulfuron-methyl for less than 1 year (although data were insufficient for degradation estimates) after its application. However, this varied between sites and years of application. Although, the majority of residues remained in the top 20 cm of the soil profile throughout the study, leaching of a small fraction of the residue to deeper layers of the profiles (up to 1 m) was observed. Despite their slow rate of degradation, the herbicides did eventually dissipate, even in soils with very high pH (8.5). In most cases, the current product labels provide an adequate safety period to protect sensitive rotational crops from potential damage due to excessive persistence. However, in particular years at 3 of the 5 field sites, metsulfuron-methyl and triasulfuron persisted beyond the recommended recropping period (9 months for metsulfuron-methyl and 22 months for triasulfuron in soils up to pH 7.5 or 24 months in soils pH 7.6 and above). An accurate measurement of soil pH and its variability within the paddock is essential to minimise any subsequent crop damage by these herbicides.

Complementary ability of three European earthworms (Lumbricidae) to bury lime and increase pasture production in acidic soils of south-eastern Australia

Complementary ability of three European earthworms (Lumbricidae) to bury lime and increase pasture production in acidic soils of south-eastern Australia

Effects of resident rhizobial communities and soil type on the effective nodulation of pulse legumes

Communities of resident rhizobia capable of effective nodulation of pulse crops were found to vary considerably over a range of soil environments. These populations from soils at 50 sites in Southern Australia were evaluated for nitrogen fixing effectiveness in association with Pisum sativum, Vicia faba, Lens culinaris, Vicia sativa, Cicer arietinum and Lupinus angustifolius. The values for nitrogen fixing effectiveness could be related to soil pH as determined by soil type and location. It was found that 33% of paddocks had sufficient resident populations of Rhizobium leguminosarum bv viciae for effective nodulation of faba bean, 54% for lentils, 55% for field pea and 66% for the effective nodulation of the vetch host plant. Mesorhizobium cicer populations were very low with only 7% of paddocks surveyed having sufficient resident populations for effective nodulation. Low resident rhizobial populations (<10 rhizobia g −1 soil) of R. leguminosarum bv viciae and M. cicer were found in acid soil conditions. In contrast, Bradyrhizobium populations increased as soil pH decreased. Inoculation increased faba bean yields from 0.34 to 4.4 t ha −1 and from 0.47 to 2.37 t ha −1 for chickpeas on acid soils. On alkaline soils, where resident populations were large there was no consistent response to inoculation. Observations at experimental field sites confirmed the findings from the survey data, stressing the importance of rhizobial inoculation, especially on the acid soils in south-eastern Australia.

Grain mineral concentrations and yield of wheat grown under organic and conventional management

AbstractOn the low‐P soils in southeastern Australia, organic crops differ from conventional ones primarily in the use of relatively insoluble, as opposed to soluble, P fertilisers and in the non‐use of herbicides. As organic management, particularly elimination of soluble fertilisers, is often claimed to enhance grain mineral concentrations, we examined grain from wheat on paired organic and conventional farms in two sets of experiments: (1) four pairs of commercial crops (1991–1993); and (2) fertiliser experiments on one farm pair where nil fertiliser was compared with 40 kg ha−1 of P as either relatively insoluble reactive phosphate rock or more soluble superphosphate (1991 and 1992). All wheat was grown following a 2–6 year legume‐based pasture phase. Both conventional management and the superphosphate treatment greatly increased yields but reduced colonisation by mycorrhizal fungi. While only minor variations occurred in grain N, K, Mg, Ca, S and Fe concentrations, conventional grain had lower Zn and Cu but higher Mn and P than organic grain. These differences were ascribed to: soluble P fertilisers increasing P uptake but reducing mycorrhizal colonisation and thereby reducing Zn uptake and enhancing Mn uptake; dilution of Cu in heavier crops; and past lime applications on the organic farm decreasing Mn availability. These variations in grain minerals had nutritional implications primarily favouring the organic grain; however, organic management and, specifically, elimination of soluble fertilisers did not induce dramatic increases in grain mineral concentrations. In addition, organic management was coupled with yield reductions of 17–84 per cent due to P limitation and weeds. The impact of large regional variations in the characteristics of organic and conventional systems on the general applicability of the results from this study and other similar studies is discussed. Copyright © 2004 Society of Chemical Industry

Effects of lime on the botanical composition of pasture over nine years in a field experiment on the south-western slopes of New South Wales

Two permanent pastures (annual pasture v. perennial pasture) were established in 1992 as part of the long-term field experiment, MASTER — Managing Acid Soils Through Efficient Rotations. The primary objective of the experiment was to develop an agricultural system that is economically viable and environmentally sustainable on the highly acidic soils in south-eastern Australia. This paper reports on the effects of lime on the botanical composition changes of annual and perennial pastures over 9 years. In general, lime increased the proportion of the desirable species, such as phalaris (Phalaris aquatica) in perennial pasture and subterranean clover (Trifolium subterraneum) in annual pastures, and decreased the proportion of the undesirable species, such as Vulpia spp., in both annual and perennial pastures, ultimately improving the quality of feed-on-offer to animals. As a result, the limed pastures carried 24% more sheep than the unlimed pastures, while maintaining individual animal performance similar for both limed and unlimed pastures. The phalaris-based perennial pasture was more stable in terms of maintaining the sown species than the annual pasture. Lime improved the persistence of phalaris and the longevity of the phalaris-based pasture should be at least 10 years. Lime changed the direction of plant succession of annual pastures. Without lime, Vulpia spp. gradually became more dominant while ryegrass and subterranean clover became less dominant in annual pastures. With lime, barley grass (Hordeum leporinum) gradually invaded the sward at the expense of ryegrass, thus reducing the benefits of lime, but this effect was less for the perennial pastures than for annual pastures. Liming perennial pastures should be more beneficial than liming annual pastures because of the beneficial effects on pasture composition. In addition, previously published work reported that liming perennial pastures improved sustainability through better use of water and nitrogen.

Addition of aeolian dusts to soils in southeastern Australia: red silty clay trapped in dunes bordering Murrumbidgee River in the Wagga Wagga region

In southeastern Australia, aeolian dust deposits are very common and have a significant influence on soil properties and soil landscapes. However, the characteristics of the pure dust materials and the rates of dust-fall in the past are unclear because of the low overall rate of dust deposition and mixing with locally derived sediments. In the Wagga Wagga region, some dunes have functioned as dust traps. Thin (<1 cm thick) red clayey bands and thick (up to 2.5 m) red clayey layers within the dune sequences are likely to represent illuviated aeolian dust. These dust materials are characterised by a bi-modal particle size distribution, one mode in the clay and another in the coarse-medium silt. The clay minerals are dominated by kaolinite, illite and smectite. Both 14C and optical dating indicate the most recent period of dune formation was around 3–4 ka. In an example of these young dunes, there is a total of 2 cm equivalent thickness of dust materials, giving a deposition rate of 0.5–0.7 cm ka −1. All three samples from an elevated dune are saturated with respect to environmental radiation dosage, and give minimum optical ages in excess of 80 ka. In this higher dune, the total thickness of dust is 50–80 cm, similar to that (50–100 cm) of the Yarabee Parna, the youngest aeolian dust deposit in the Wagga Wagga region. This may have been deposited unevenly, being more concentrated during the period 25–16 ka, which has been identified as a major dust deposition period in the Tasman Sea. If this variation occurred, the dust deposition rate indicated by the 50–80 cm dust material in the dune could have been as high as 5 cm ka −1 for the period 25–16 ka.

Microbiological and chemical properties of soil associated with macropores at different depths in a red-duplex soil in NSW Australia

Some agricultural soils in South Eastern Australia with duplex profiles have subsoils with high bulk density, which may limit root penetration, water uptake and crop yield. In these soils, a large proportion (up to 80%) of plant roots maybe preferentially located within the macropores or in the soil within 1–10 mm of the macropores, a zone defined as the macropore sheath (MPS). The chemical and microbiological properties of MPS soil manually dissected from a 1–3 mm wide region surrounding the macropores was compared with that of adjacent bulk soil (>10 mm from macropores) at 4 soil depths (0–20 cm, 20–40 cm, 40–60 cm and 60–80 cm). Compared to the bulk soil, the MPS soil had higher organic C, total N, bicarbonate-extractable P, Ca+, Cu, Fe and Mn and supported higher populations of bacteria, fungi, actinomycetes, Pseudomonas spp., Bacillus spp., cellulolytic bacteria, cellulolytic fungi, nitrifying bacteria and the root pathogen Pythium.In addition, analysis of carbon substrate utilization patterns showed the microbial community associated with the MPS soil to have higher metabolic activity and greater functional diversity than the microbial community associated with the bulk soil at all soil depths. Phospholipid fatty acids associated with bacteria and fungi were also shown to be present in higher relative amounts in the MPS soil compared to the bulk soil. Whilst populations of microbial functional groups in the MPS and the bulk soil declined with increasing soil depth, the differentiation between the two soils in microbiological properties occurred at all soil depths. Soil aggregates (< 0.5 mm diameter) associated with plant roots located within macropores were found to support a microbial community that was quantitatively and functionally different to that in the MPS soil and the bulk soil at all soil depths. The microbial community associated with these soil aggregates thus represented a third recognizable environment for plant roots and microorganisms in the subsoil.

The influence of aeolian dust deposits on alpine soils in south-eastern Australia

Aeolian sediment collected from 2 locations across the ‘Main Range’ of Kosciuszko National Park, along with a series of soil profiles that were analysed for particle size, were used as a baseline from which to estimate the effects of aeolian sedimentation in this region. Laboratory analysis of the soil profiles indicated that the properties of the surface horizons of the alpine humus soils were heavily influenced by aeolian dust accumulation; however, the sub-surface horizons were mainly derived from the natural bedrock. The surface and subsurface horizons differed in texture bulk density, pH, electrical conductivity, exchangeable cations, and clay mineralogy. This study confirmed that the snow patch meadow soils exhibited particle size and mineralogy consistent with dust enrichment, with distinct bands being found in some profiles.

Species abundance of earthworms in arable and pasture soils in south-eastern Australia

Earthworms play an important role in soil ecology and can serve as practical indicators in land quality evaluation. The abundance and distribution of earthworms were determined in 84 cropping and pasture soils in north-east Victoria and southern New South Wales (NSW), Australia. Overall, an average density of 89 earthworms m −2 was found, with an average species richness of 1–2 per site, indicating relatively low abundance and species poverty. Introduced lumbricid earthworms, Aporrectodea trapezoides and A. caliginosa were the most widely distributed (88% and 61% of all sites, respectively) and numerically dominant (respective population densities of 35.8 and 32.1 m −2). Soils under pasture supported on average 3.2 times more earthworms than those under cropping. The age structure of populations varied with species, introduced lumbricids and acanthodrilids displayed an adult-dominant structure and the native megascolecids displayed a juvenile-dominant population. Indigenous earthworms belonged to a single genus, Spenceriella. Whilst not occurring in high densities these indigenous earthworms were widespread in their distribution and their numbers were negatively correlated with soil P, K, and Mg suggesting an adaptation to low levels of soil fertility. Although the relationship between earthworm densities and mean annual total precipitation (MATP) was not close ( r 2 = 0.35), of the 33 sites containing >100 earthworms m −2, 25 received MATP in excess of 600 mm. Correlations between earthworm densities and a range of physical and chemical parameters were generally poor. This may highlight the short-comings of these parameters in describing distribution patterns.

Mobility and persistence of three sulfonylurea herbicides in alkaline cropping soils of south-eastern Australia

Biologically active residues of the herbicides metsulfuron-methyl, chlorsulfuron and triasulfuron were estimated with field pea bioassays in soil samples to 80 cm depth from 4 field trials in south-eastern Australia situated on neutral to highly alkaline soil. Residues were both mobile and persistent at low levels. Leaching occurred beyond the lowest sampling depth during the winter–spring growing season. Metsulfuron-methyl was the most mobile of the 3 herbicides. Plant-back experiments involving susceptible crop and pasture species on 2 of the sites showed that the rates of decline of these residues in the sampling zone were slower than might be inferred from label plant-back recommendations in 1 of 2 seasons.

Influence of earthworms, Aporrectodea spp. (Lumbricidae), on lime burial in pasture soils in south-eastern Australia

The relative abilities of 3 exotic lumbricid earthworms, the endogeic Aporrectodea caliginosa and A. trapezoides and the anecic A. longa, to bury surface-applied lime and help ameliorate soil acidity were measured in cages in 7 pasture soils in south-eastern Australia. All 3 species buried lime, mostly within the top 5 cm of the soil profile, but A. longa buried it deeper than A. caliginosa and A. trapezoides. A. longa significantly increased soil pH at 15–20 cm depth at some sites within 5 months (winter–spring, the earthworm ‘season’ in the Mediterranean climate of south-eastern Australia). Lime burial varied markedly between sites. These site differences were explained, at least in part, by variations in rainfall. Lime burial increased with earthworm density. A minimum density of 214 A. longa/m 2 was needed to significantly enhance lime burial within one season. Higher densities were required for the other two species. However, per unit of biomass, A. caliginosa and A. trapezoides were generally more able to bury lime in the upper soil layers (2 . 5–10 cm depth) than A. longa. Agricultural soils in south-eastern Australia are dominated by shallow burrowing species such as A. caliginosa and A. trapezoides. Deeper burrowers such as A. longa are rare. Introduction of A. longa to soils in high-rainfall regions of south-eastern Australia, where it does not presently occur, should enhance lime burial and help reduce soil acidity.