South Australian Soils Research Articles

'Racy of the Soil': Ian Mudie, Right-Wing Nationalism, and the South Australian Soil Erosion Crisis

Abstract Ian Mudie was an Adelaide-based freelance journalist, short story and history writer, and most notably a passionate and political poet. During the 1930s and 1940s the degradation of South Australian agricultural and pastoral soil inspired Mudie to evoke soil in his poetry. Soil also proved a useful metaphor which Mudie could deploy in aid of his right-wing political stance. Critics and historians have described Mudie either as a 'nationalist or propagandist' and a 'hectoring' nationalist, or, alternatively, as an early conservationist and even a 'proto ecologist'; none address the intersection of environmental concern and right-wing nationalism in his poetry and politics. This article will interrogate the relationship between these two ideologies in Mudie's work. Despite echoes of Nazi 'blood and soil' ideology, Mudie's soil erosion poetry was primarily the product of his settler imagination, and resonated with 'cultural nationalists' in the Australian literary community.

Chronic and reproductive toxicity of cadmium, zinc, and lead in binary and tertiary mixtures to the earthworm (Eisenia fetida)

The presence of one metal can alter the toxicity of another metal by having an additive, synergistic, or antagonistic impact. Mixed metal pollution has clear ecological consequences. The importance of use of earthworms for ecological health monitoring is recognized widely. This study investigated the effect of binary and tertiary metal mixtures on the toxicity, bioaccumulation, and reproduction of the Eisenia fetida in different South Australian soils. The end points used in this 56-day reproduction study were avoidance behavior, worm mortality, weight loss, reproduction, and metal (Cd, Zn, and Pb) bioaccumulation. The three soils (acidic, neutral, and alkaline) were spiked with selected binary and tertiary concentration mixtures that considered the soil quality guideline values, EC50 and LC50 values for Cd, Zn, and Pb obtained from the previous single metal earthworm experiments done by the authors. In acidic soil, Zn and Cd constituted the most toxic metal combination to earthworms. However, in contrast to this observation, the same metal combination was the least toxic one to earthworms in neutral and alkaline soils. For Zn and Pb spiked soils, relationships between soil and internal metal concentrations were found with R 2 = 0.63, r = 0.8, and R 2 = 0.94, p < 0.01, respectively, for Zn and Pb. This study indicates that earthworms have high tendency to bioaccumulate heavy metals in their tissues and hence serves as ecological indicators of soil heavy metal contamination. The highest bioaccumulation factor (0–9) was evident for Cd in contaminated soils. This study demonstrated the role of soil edaphic factors and metal-metal interactions in the toxicity of metal mixtures to E. fetida. In Zn and Pb binary mixture spiked acidic soil, mortality of 60% was recorded even when the Pb and Zn concentrations were below the Canada and Dutch EIL (ecological investigational levels) values. This indicates the current guideline values are not safe for mixed metal toxicity. Therefore, care must be taken when predicting metal toxicities in mixed metal contaminated soils.

Adsorption and desorption characteristics of methamphetamine, 3,4-methylenedioxymethamphetamine, and pseudoephedrine in soils.

This work presents, for the first time, information on the adsorption-desorption characteristics of illicit drugs and precursors in soils and an estimation of their potential bioavailability. The experiment was conducted using a batch equilibrium technique for the parent drugs methamphetamine and 3,4-methylenedioxymethamphetamine (MDMA) and the precursor pseudoephedrine in three South Australian soils varying in physiochemical properties. The individual compounds exhibited different adsorption mechanisms in the test soils, and the results fitted better with the Freundlich isotherm model (r (2) ≥ 0.99). The maximum adsorption capacity was recorded for pseudoephedrine (2,000 μg g(-1)). However, pseudoephedrine recorded lower organic carbon normalized adsorption coefficient values (<250 mL g(-1)), lower magnitudes of Gibb's free energy change, and higher percent desorption (73-92 %) compared to methamphetamine and MDMA. The results thus showed pseudoephedrine to be the most mobile compound in the soils under study, to have the highest availability for degradation of the three compounds, and to have the highest susceptibility to biotic degradation in test soils.

Not All Phosphate Fertilizers Immobilize Lead in Soils

The effects of six phosphate (P) fertilizers in mobilizing and immobilizing water-soluble lead (Pb) were determined in a contaminated soil (Alfisol from Shaoxing) from China and four Australian soils (an Oxisol from Twonsville Queensland and three South Australian soils from Cooke Plains (Typic Palexeralf)), Inman Valley (Vertisol), and Two Wells (Natric Palexeralf). The fertilizers tested were single superphosphate (SSP), triple superphosphate (TSP), monoammonium phosphate (MAP), diammonium phosphate (DAP), monocalcium phosphate (MCP), and dicalcium phosphate (DCP) to produce an initial P concentration of 1,000 mg/L. The Chinese soil contained 16,397 mg/kg total Pb, but the Australian soils were uncontaminated. The four Australian soils were each spiked with 1,000 mg Pb/kg soil (as Pb(NO3)2) and incubated for a month. Single superphosphate treatments decreased total soluble Pb in soil solution to 2–14 % of those of the nil-P (0P) treatment in the four Pb-spiked soils and to 48 % in the Chinese Pb-contaminated soil. The DAP treatment followed by the MAP treatment greatly increased the total soluble Pb in soil solution up to 135–500 % of the 0P treatment, except in the Two Wells soil. MCP could decrease the total soluble Pb in Cooke Plains, Inman Valley, Shaoxing, and Two Wells soils while increase it in the Queensland soil; DCP decreased the total soluble Pb in Cooke Plains and Queensland soils while increased it in the Shaoxing and Inman Valley soils. There were close relationships between the total soluble Pb, total soluble Al, and total soluble Fe in the water extracts of each. Soluble Al and Fe ions in soil solution increased soluble Pb concentrations. We conclude that not all phosphate fertilizers immobilize Pb in soils equally well. SSP and TSP are excellent Pb-immobilizing fertilizers, while MAP and DAP are strong Pb-mobilizing fertilizers. MCP and DCP are either Pb-immobilizing fertilizers or Pb-mobilizing fertilizers depending on their reactions with individual soils.

Factors affecting ammonia-oxidising microorganisms and potential nitrification rates in southern Australian agricultural soils

Ammonia-oxidising archaea (AOA) have recently been described as having an important role in soil nitrification. However, published data on factors which influence their distribution and their impact on a soil’s potential nitrification rates (PNR) are sparse, particularly compared with the amount of information available regarding ammonia-oxidising bacteria (AOB). This study had two aims. First, to investigate which environmental factors affect the AOA : AOB ratio in soils from two agricultural regions, and second, to explore whether the abundance of either AOA or AOB correlated with PNR. Samples were collected from 45 sites within the cropping regions of Western Australia and South Australia. Soils were tested for pH, NH4+/NO3–, organic carbon (C), total nitrogen (N), C : N ratio, PNR, and electrical conductivity. Climate data were obtained from the Queensland Climate Change Centre for Excellence SILO website. Abundances of AOA and AOB were measured using real-time PCR quantification of the gene encoding the ammonia monooxygenase enzyme (amoA). Multivariate statistical analysis was applied to assess correlations between PNR, soil properties, and abundance of AOA or AOB. In the majority samples AOA were present, but their abundance, and the AOA : AOB ratio, varied considerably between sites. Multivariate analysis showed that the distribution of AOA and AOB and the AOA : AOB ratio were strongly correlated with climatic and seasonal factors. Sites where samples were collected during dry, hot periods tended to be AOA-dominated, whereas samples collected during cool, wet periods tended to be AOB-dominated or have equal abundances of AOA and AOB. The PNRs were correlated with total N content, organic C content, and soil pH. There was no clear correlation between AOA or AOB and PNR. This study shows that both AOA and AOB are widespread in Western Australian and South Australian soils and their abundance and ratio are affected by climate and season. It also shows that PNR is more strongly influenced by soil fertility factors than by the AOA : AOB ratio.

Fate of 1-(1′,4′-cyclohexadienyl)-2-methylaminopropane (CMP) in soil: Route-specific by-product in the clandestine manufacture of methamphetamine

We investigated the fate of 1-(1′,4′-cyclohexadienyl)-2-methylaminopropane (CMP) in soil. CMP is the major route-specific byproduct in the clandestine manufacture of methamphetamine (MAP) by the use of excess alkali metal (e.g., lithium) in liquid ammonia, which is commonly referred to as the “Nazi method”. This is one of the most common methods used in many countries for the illicit production of MAP. Knowledge on the fate of CMP in the terrestrial environment is essential to combat potential threats arising from illegal dumping of clandestine laboratory wastes. We report on the sorption–desorption, degradation, and metabolism patterns of CMP in three South Australian soils investigated in laboratory scale. CMP sorption in the test soils followed a Freundlich isotherm in the concentration range of 5 to 100μgmL−1. Degradation studies showed that CMP was fairly unstable in both non-sterile and sterile soils, with half-life values typically less than one week. The role of biotic and abiotic soil processes in the degradation of CMP also varied significantly between the different soils, and with the length of the incubation period. Interestingly, but not surprisingly, the results showed that the CMP was not actually degraded to any simpler compounds but transformed to more persistent MAP. Thus, the main concern with Nazi method is the potential hazard from MAP rather than CMP if wastes are disposed of into the environment.

Biotic and abiotic degradation of illicit drugs, their precursor, and by-products in soil

This study presents the first systematic information on the degradation patterns of clandestine drug laboratory chemicals in soil. The persistence of five compounds – parent drugs (methamphetamine, 3,4-methylenedioxymethamphetamine (MDMA)), precursor (pseudoephedrine), and synthetic by-products N-formylmethylamphetamine and 1-benzyl-3-methylnaphthalene) – were investigated in laboratory scale for 1 year in three different South Australian soils both under non-sterile and sterile conditions. The results of the degradation study indicated that 1-benzyl-3-methylnaphthalene and methamphetamine persist for a long time in soil compared to MDMA and pseudoephedrine; N-formylmethylamphetamine exhibits intermediate persistence. The role of biotic versus abiotic soil processes on the degradation of target compounds was also varied significantly for different soils as well as with the progress in incubation period. The degradation of methamphetamine and 1-benzyl-3-methylnaphthalene can be considered as predominantly biotic as no measureable changes in concentrations were recorded in the sterile soils within a 1 year period. The results of the present work will help forensic and environmental scientists to precisely determine the environmental impact of chemicals associated with clandestine drug manufacturing laboratories.

Effects of subsoil amendments on soil physical properties, crop response, and soil water quality in a dry year

In southern Australia the ability of field crops to extract soil moisture and nutrients from depth depends on the physical and chemical properties of the subsoil. In texture-contrast soils accumulation of water and nutrients in the E or A2 horizon, immediately above a clay B horizon of much lower hydraulic conductivity (herein called the interface), may generate lateral flows and enhanced nutrient and solute transfer to water bodies. Evidence that deep-ripping with addition of subsoil nutrients can increase crop productivity in regions having hostile, alkaline subsoils led to experiments to test whether this response was related to an increase in the use of water and nutrients in the subsoil. Our study measured the effects of deep-ripping with and without amendments on soil physical and chemical properties of the A and upper B horizons of 2 South Australian soils. Deep-ripping and deep-placement of nutrients increased grain harvest weight even in an exceptionally dry season. The greater yield was accompanied by significantly lower field-penetration resistance to 0.35–0.50 m depth, which we hypothesise enabled the crop to better access stored soil water and deep placed nutrients in the subsoil. Residual effects from deep-ripping were minimal after 4 growing seasons; therefore, ripping will need to be practiced at regular intervals to maintain treatment effects. The ripping and nutrient amendments had no significant effect on exchangeable sodium percentage, electrical conductivity, and readily extractable phosphorus and nitrate-nitrogen, despite changes in these soil properties between spring and harvest sampling.

Cullen australasicum (syn. Psoralea australasica): a review and some preliminary studies related to its potential as a low rainfall perennial pasture legume

This paper reviews the morphology, establishment, herbage quality, grazing tolerance, palatability, anti-nutritional compounds and rhizobial symbiosis of Cullen australasicum (Schltdl.) J.W. Grimes (syn. Psoralea australasica Schltdl.), a deep-rooted Australian native legume commonly known as tall verbine or native scurf-pea. Its natural distribution and the edaphic and climatic characteristics of germplasm collection sites within Australia are described. It also reports the results of three preliminary studies; two field studies on the establishment, persistence and herbage quality, and a glasshouse study to identify an effective Rhizobium strain for C. australasicum. In the field studies, C. australasicum established readily from seed and demonstrated similar persistence to Medicago sativa L. over a 3-year period in the medium rainfall wheat belt of southern New South Wales. The productivity of C. australasicum in year 3 was similar to M. sativa at one site but inferior at the second site. C. australasicum demonstrated superior persistence and higher herbage yields than Lotus corniculatus L. in year 3 at both sites. The mineral content of the leaves and stems of C. australasicum in these studies were similar to M. sativa and L. corniculatus for most elements except for Mo and Zn, which were significantly higher, and Na which was lower in C. australasicum. Organic matter digestibility of the leaves and stems of C. australasicum ranged from 79 to 89% and 62 to 72%, respectively, compared with 73–79% and 59–73% in M. sativa. Crude protein levels of C. australasicum leaves and stems were 22–28% and 15–27%, respectively, compared with 26–33% and 13–33% in M. sativa. The study of Rhizobium strains isolated from four South Australian soils identified a superior strain (SRDI 483) capable of establishing an effective symbiosis with C. australasicum. The potential of C. australasicum as a drought hardy perennial legume for extensive grazing systems where M. sativa fails to persist because of selective grazing is discussed. Its low palatability to sheep was seen as an advantage in assisting its survival in extensive low-input grazing systems.

Size, symbiotic effectiveness and genetic diversity of field pea rhizobia ( Rhizobium leguminosarum bv. viciae) populations in South Australian soils

Field pea ( Pisum sativum L.) is widely grown in South Australia (SA), often without inoculation with commercial rhizobia. To establish if symbiotic factors are limiting the growth of field pea we examined the size, symbiotic effectiveness and diversity of populations of field pea rhizobia ( Rhizobium leguminosarum bv. viciae) that have become naturalised in South Australian soils and nodulate many pea crops. Most probable number plant infection tests on 33 soils showed that R. l. bv. viciae populations ranged from undetectable (six soils) to 32×10 3 rhizobia g −1 of dry soil. Twenty-four of the 33 soils contained more than 100 rhizobia g −1 soil. Three of the six soils in which no R. l. bv. viciae were detected had not grown a host legume (field pea, faba bean, vetch or lentil). For soils that had grown a host legume, there was no correlation between the size of R. l. bv. viciae populations and either the time since a host legume had been grown or any measured soil factor (pH, inorganic N and organic C). In glasshouse experiments, inoculation of the field pea cultivar Parafield with the commercial Rhizobium strain SU303 resulted in a highly effective symbiosis. The SU303 treatment produced as much shoot dry weight as the mineral N treatment and more than 2.9 times the shoot dry weight of the uninoculated treatment. Twenty-two of the 33 naturalised populations of rhizobia (applied to pea plants as soil suspensions) produced prompt and abundant nodulation. These symbioses were generally effective at N 2 fixation, with shoot dry weight ranging from 98% (soil 21) down to 61% (soil 30) of the SU303 treatment, the least effective population of rhizobia still producing nearly double the growth of the uninoculated treatment. Low shoot dry weights resulting from most of the remaining soil treatments were associated with delayed or erratic nodulation caused by low numbers of rhizobia. Random amplified polymorphic DNA (RAPD) polymerase chain reaction (PCR) fingerprinting of 70 rhizobial isolates recovered from five of the 33 soils (14 isolates from each soil) showed that naturalised populations were composed of multiple (5–9) strain types. There was little evidence of strain dominance, with a single strain type occupying more than 30% of trap host nodules in only two of the five populations. Cluster analysis of RAPD PCR banding patterns showed that strain types in naturalised populations were not closely related to the current commercial inoculant strain for field pea (SU303, ≥75% dissimilarity), six previous field pea inoculant strains (≥55% dissimilarity) or a former commercial inoculant strain for faba bean (WSM1274, ≥66% dissimilarity). Two of the most closely related strain types (≤15% dissimilarity) were found at widely separate locations in SA and may have potential as commercial inoculant strains. Given the size and diversity of the naturalised pea rhizobia populations in SA soils and their relative effectiveness, it is unlikely that inoculation with a commercial strain of rhizobia will improve N 2 fixation in field pea crops, unless the number of rhizobia in the soil is very low or absent (e.g. where a legume host has not been previously grown and for three soils from western Eyre Peninsula). The general effectiveness of the pea rhizobia populations also indicates that reduced N 2 fixation is unlikely to be the major cause of the declining field pea yields observed in recent times.

Fusarium species and Fusarium wilt pathogens associated with native Gossypium populations in Australia

Fusarium isolates were extracted from stems and rhizosphere soils of 79 populations of four Gossypium species native to two regions of inland Australia in 2001. Six Fusarium species were isolated from 31 (3%) of the 919 stem samples. F. semitectum was predominant, occurring mostly in G. bickii populations and accounting for 81% of the isolates recovered. Twenty Fusarium species were isolated from 68 (87%) of the 78 composite soil samples, with F. solani (71%), F. compactum (8%), F. oxysporum (5%), F. graminearum (3%), and F. crookwellense (3%) being the most prevalent. Significant differences in the relative densities indicated that F. solani was more common in the soil from G. sturtianum populations than from G. bickii populations, and that F. crookwellense was more common in South Australian soils than in Queensland and Northern Territory soils. Fusarium oxysporum had a relatively greater relative density in the rhizosphere soils of G. australe plants than in that of sympatrically growing G. sturtianum plants. Fifteen (17%) of the 89 F. oxrysporum isolates produced typical Fusarium wilt symptoms on cultivated cotton (G. hirsutum cv. 'Siokra 1-4'), therefore they were classified as wild Fov. Soil samples collected from G. sturtianum populations in the Arkaroola-Leigh Creek region in South Australia had the highest incidence of wild Fov (24%). Two wild Fov isolates were similar in virulence to a cotton field Fov isolate in the glasshouse experiments, indicating that they could incite Fusarium wilt disease in cotton fields. The presence of wild Fov in native Gossypium populations suggests that the Fov occurring in Australian cotton fields may be of indigenous origins.

Earthworm population responses to cultivation and irrigation in a South Australian soil

Summary The changes in the population of earthworms, predominantly Aporrectodea trapezoides , induced by cultivation and cropping of Brussels sprouts, followed by a return to pasture, were monitored for a period of more than 2 years in a South Australian soil. Worms were hand-sorted from 0.5 m 2 areas at monthly intervals during 3 winter/spring periods, and during irrigation of the crop throughout one summer. Peak numbers in pasture reached 240 m −2 (biomass 66 g m −2 ) during winter/spring of 1999, were reduced to a very few individuals (13 m −2 ) by cultivation in late September 1999, but increased to 578 m −2 (biomass 62 g m −2 ) from January to April 2000 (the warm summer months) under irrigation in a similar manner to a normal winter and spring period (June to October). The loose matrix of the cultivated soil and abundant organic matter provided excellent conditions for reproduction, hatching and growth of earthworms. Ploughing in crop residues reduced the earthworm population to 32 m −2 , then there was a steady increase in the number and size of the earthworms during the following winter to 168 worms m −2 in October, with a mean weight of 450 mg and a biomass of 75 g m −2 . No earthworm activity occurred during the very hot dry summer of 2000–2001. However, in June 2001 after opening rains, the number of earthworms found was very similar to that of the previous late spring (178 vs. 168), but the average weight had practically halved (451 mg vs. 238 mg). Nearly all the earthworms had survived the summer months despite a loss of almost 50% of their body weight. During the winter of 2001, the population increased in average weight, with frequent appearance of large breeding adults, indicative of a mature population.

SORPTION OF FIPRONIL AND ITS METABOLITES ON SOILS FROM SOUTH AUSTRALIA

This paper reports on the sorption of fipronil [(±)-5-amino-1-(2,6-dichloro-α,α,α-trifluoro-p-tolyl)-4-trifluoromethyl-sulfinylpyrazole-3-carbonitrile] and its two main metabolites, desulfynil and sulfide derivatives on a range of soils from South Australia. The Freundlich sorption coefficient (Kf) values for fipronil on the soils ranged from 1.94 to 4.84 using a 5% acetonitrile/water mixture as the soil solution. Its two metabolites had a higher sorption affinity for soils, with Kf values ranging from 11.09 to 23.49 for the sulfide derivative and from 4.70 to 11.77 for the desulfynil derivative. Their sorption coefficients were found to be better related to the soil organic carbon than clay content. The presence of cosolvents in soil solutions had a significant influence on the sorption of fipronil. The Freundlich sorption coefficients showed a log linear relationship with the fractions of both acetonitrile and methanol in solutions. The sorption coefficient of fipronil on Turretfield soil in the aqueous solution was estimated to be from 13.80 to 19.19. Methanol had less effect on the sorption of fipronil than acetonitrile. The Kd values for fipronil on the eight soils using a 5% methanol/water mixture were from 5.34 to 13.85, which reflect more closely the sorption in the aqueous solution. The average Koc value for fipronil on the eight South Australian soils was calculated to be 825 ± 214.

Laboratory study on leachability of five herbicides in South Australian soils

Norflurazon, oxadiazon, oxyfluorfen, trifluralin and simazine are herbicides widely used in the vineyards of the Barossa Valley, South Australia. The leaching behaviour of norflurazon, oxadiazon, oxyfluorfen and trifluralin was investigated on four key soils in the Barossa Valley. Leaching potential on packed soil columns and actual mobility using intact soil columns were investigated. On the packed soil columns, norflurazon was the most leachable herbicide. More of the herbicides were detected in the leachates from the sandy soils (Mountadam and Nuriootpa) than from the clayey soils (Lyndoch and Tanunda). Organic matter is generally low in soils in the Barossa region. Porosity and saturated conductivity significantly affect herbicide movement and in the sandy Mountadam and Nuriootpa soils, the water flux is greater than for the higher clay content Lyndoch and Tanunda soils. Increasing the time interval between herbicide application and the incidence of “rainfall”; reduced the amounts of herbicides found in the leachates. The use of intact soil columns and including simazine for comparison showed that both norflurazon and simazine were present in the leachates. Simazine was the first herbicide to appear in leachates. Sectioning of the intact soil columns after leaching clearly demonstrated that norflurazon and simazine reached the bottom of the soil columns for all soils studied. Greater amounts of norflurazon were retained in the soil columns compared with simazine. The other herbicides were mostly retained in the initial sections of the soil columns.

Nodulation and growth of pasture legumes with naturalised soil rhizobia. 1. Annual Medicago spp.

The ability of 11 species of annual medics (Medicago doliata, M. laciniata, M. littoralis, M. minima, M. orbicularis, M. polymorpha, M. praecox, M. rigidula, M. rigiduloides, M. tornata and M. truncatula) to nodulate and fix nitrogen with naturalised rhizobia from 28 South Australian soils was assessed. The number of rhizobia in the soils was estimated. Medic shoot dry matter production and nodulation were measured, after inoculation of medic seedlings with a soil suspension, in 2 glasshouse experiments. The number of medic rhizobia ranged from 0.4 10 2 to 1.5 10 6 per gram soil. Medicago laciniata was the only medic species tested which was not consistently nodulated by the soil rhizobia. While all the other species formed nodules, they varied widely in their ability to form an effective symbiosis. Symbiotic performance (which indicates how much growth the medic line achieved, when compared to an effective inoculation treatment) of the medic species ranged from 3% (M. rigiduloides) to 67% (M. praecox). Herald (M. littoralis) achieved a symbiotic performance of 49% and it was estimated that this would be insufficient to meet the nitrogen requirements of a Herald-based pasture during early growth. The symbiotic performance of Santiago (M. polymorpha) was low (17%) and erratic (from –6 to 72%). The ability of the rhizobia to form an effective symbiosis varied widely also between soil regions. For example, the rhizobia in Riverland soils resulted in only 31% of the shoot dry matter of those in Eyre Peninsula soils, in association with M. polymorpha. There are significant opportunities to improve the symbiotic performance of a number of the species of annual medics examined in this study. Options to improve the effectiveness of the symbiosis of medics with naturalised soil rhizobia are discussed.

Degradation of strychnine by pure bacterial cultures isolated from South Australian agricultural soils

Degradation of strychnine by pure bacterial cultures isolated from South Australian agricultural soils

Wear of Cultivator Shares in Abrasive South Australian Soils

Abstract In general, conditions for the seeding and cultivation of cereal crops in Australia vary from those in the northern hemisphere, resulting in higher wear rates of tillage tools. This wear reduces the efficiency of Australian farmers, costing millions of dollars annually. This paper details the wear rates of commercial sweep shares at different sites in South Australia. The life of the shares at the different sites in terms of distance travelled, ranged from 9 to 168 km with wear rate being strongly dependent on the gravel content of the soil. At the Mangalo site (sandy clay–loam), the wear rate was found to increase as the soil water content decreased. These results are discussed and compared with those published in the literature. The damage to the tools and the mechanisms of wear were also investigated by metallographic analysis. This investigation revealed abrasive particles embedded in the cutting edges of shares worn in dry, stony conditions. An investigation of polished share cross-sections revealed three distinct areas of deformation caused by the abrasive particles.

Sorption and desorption behaviour of strychnine rodenticide in soils

Strychnine (Strychnidin-10-one) was used as a rodenticide to control a mouse plague across southern Australia in 1993. Wheat grains were coated with a mixture (containing strychnine, sugar, flour, oil, and a dye) at a rate of 3 g strychnine/kg grain, and were spread as a bait for mice at a density of approximately 3 treated grains/m2. We examined the release of strychnine residue from the treated grains into soils and its sorption–desorption behaviour in 4 different South Australian soils, ranging from sand to clay in texture and acidic to alkaline in reaction. Release studies using treated grains showed that, unless the treated grains were buried in soil, the release of strychnine from the treated grain into soil was slow, requiring about 2 months for its complete transfer into soil. However, upon burial of the treated grain, such as during resowing, the transfer of strychnine from the treated grain to soil was rapid (&gt;90% within 7 days). The sorption of strychnine was found to occur rapidly (&gt;90% of sorption within 15 min). The sorption affinity of strychnine varied by almost 1 order of magnitude among the 4 soils studied. An acidic clay soil (Mintaro) sorbed nearly all (97%) of the applied strychnine, whereas the alkaline sandy soil (Bute) sorbed only 54% of the applied amount, when a strychnine solution 10 mg/L was equilibrated with the soil. Sorption was found to increase substantially with decreasing pHCa from 9 to 7. Indeed, in the 2 soils with relatively higher sorption capacities, nearly 100% of the applied strychnine was sorbed at pHCa 6·5. The pH dependency of sorption was found to follow the proportion of cationic species of strychnine base present in the soil solution. During desorption, hysteresis between the sorption and desorption isotherms of strychnine was noted. The study showed that except in very sandy, alkaline soils, the sorption of strychnine is likely to be high.

Effect of manganese-reducing rhizosphere bacteria on the growth of Gaeumannomyces graminis var. tritici and on manganese uptake by wheat (Triticum aestivum L.)

Five bacterial strains capable of Mn reduction were isolated from the rhizosphere of plants growing in different South Australian soils. They differed in their Mn-reducing capacity. The antagonism of these strains compared to the imported strain 2–79 (from the United States) against Gaeumannomyces graminis var. tritici was tested in agar and in a soil sandwich experiment at different Mn2+ concentrations in the soil. In addition, wheat seeds were coated with the different strains and with MnSO4 or with MnSO4 only in order to investigate their effect on plant growth and Mn uptake. With one exception, all strains inhibited the growth of G. graminis in agar, but to different degrees. In contrast, only two strains significantly inhibited the growth of the fungus in the soil. The hyphal density was decreased more than the hyphal length. The Mn2+ concentration in the soil also had a marked effect on fungal growth; low Mn concentrations slightly increased while high Mn concentrations strongly decreased the fungal growth. Seed treatment with MnSO4 only (+Mn) increased Mn uptake above that of the control (no seed treatment). Only the weakest Mn reducer on agar significantly increased plant growth and Mn uptake from soil in comparison with the Mn treatment. One strain was tested as seed coating without adding MnSO4; it increased the plant growth to an extent similar to the Mn treatment. Increasing the Mn uptake by plants may be one of the growth-promoting effects exerted by rhizosphere bacteria.

COMPARATIVE PREDICTION OF YIELD RESPONSE AND PHOSPHORUS UPTAKE FROM SOIL USING ANION- AND CATION-ANION-EXCHANGE RESINS

Phosphorus desorbed from 18 South Australian soils by anion-exchange resin (AER-P) and cation-anion-exchange resin (AER-P) at different periods was core-lated with yield response and P uptake by wheat (Triticum aestivum cv. Gabo). The relationship between the quantity of P desorbed by both resin systems and P uptake and grain yield was found to improve significantly as the period of desorption increased up to about 10 h; after that it improved only slightly (up to 21 d). The CAER-P was better correlated with P uptake and grain yield and predicted yield response more closely than AER-P. The quantity of the latter was less than the former at all desorption periods. The two-constant rate equation (C= Kt, where C, is CAER-P or AER-P (mg/kg soil), K is the initial desorption rate constant, t is the desorption period (s), and b is the rate coefficient) described P desorption from soils by AER and CAER at different periods (from 10h to 21 d) satisfactorily. The ratio of K (CAER-P)/K (AER-P) was primarily affected by exchangeable calcium and magnesium and clay content of the soil (R= 0.91). Thus, the capacity of AER to desorb P compared with CAER was decreased, possibly by the buildup of calcium and magnesium in soil solution and the reduced diffusion of P through soil. The CAER-P may be a better measure of available P than AER-P by its capacity to take up cations as well as P from the soil solution, thus better simulating cations and P uptake by plants.