Queensland Soils Research Articles

A validation test of WEPP to predict runoff and soil loss from a pineapple farm on a sandy soil in subtropical Queensland, Australia

Monthly runoff and soil loss simulated by WEPP (Water Erosion Prediction Project) were compared with field observations on a pineapple farm in south-east Queensland for a 3-year period. The soil at the site is sandy. Slope length and steepness are 36m and 5.5%, respectively. Three treatments, namely bare, farmers’ conventional practice, and mulching of the furrows, were used. Infiltration and erodibility parameters were determined using WEPP-recommended equations and measurable soil properties. These parameters were also calibrated using the runoff and soil loss data for the bare plot only. Apart from the soil loss prediction for the mulching treatment, for which WEPP did not perform well, the average coefficient of efficiency in runoff and soil loss predictions was –0.02 using soil property-based parameter values and 0.66 using calibrated parameter values. The corresponding r 2 values are 0.57 and 0.81, respectively. On the whole, WEPP is able to reproduce the trend and variations in runoff and soil loss among different treatments for the site. Parameter values based on measurable soil properties would greatly under-estimate the runoff and soil loss for the site. Thus, use of WEPP outside its US database requires calibration with locally obtained data. It was also found that WEPP does not seem to model effectively the situation where there is considerable flow impediment with the furrows covered with mulch. We are unable to reject WEPP because the statistical performance indicators are reasonable for the site, and because the model is so complex that it is nearly impossible to pinpoint the source of discrepancy and articulate the model deficiency on physical grounds.

Field Tests of Formulated Products Containing EitherVerticillium chlamydosporiumorArthrobotrys dactyloidesfor Biological Control of Root-knot Nematodes

Abstract Granular formulations containing either Verticillium chlamydosporium or Arthrobotrys dactyloides were applied at 55–880 kg/ha in seven field trials on a range of soils in Queensland, Australia. Granules were incorporated into soil prior to planting tomatoes and the effectiveness of the formulated fungi in reducing damage caused by root-knot nematodes was compared to an untreated control and a granular formulation of fenamiphos. Formulations of V. chlamydosporium were used in three experiments but the fungus did not increase egg parasitism or reduce galling or nematode numbers at harvest. Formulations containing A. dactyloides were more effective, as galling was reduced 4–8 weeks after planting in four of five experiments. However, these effects generally disappeared later in the season, as significant reductions in galling were only observed in one of seven experiments at harvest. Fenamiphos generally reduced galling both at 4–8 weeks and at harvest. Yield increases due to fenamiphos or any of the biological treatments were not obtained in any experiment. The results suggested that formulations of A. dactyloides applied at 220–440 kg/ha substantially reduced the number of nematodes present in roots 4–8 weeks after planting. Since tomato is relatively tolerant of nematode damage under the crop management systems used in northeastern Australia, such formulations could provide useful nematode control, particularly if used in conjunction with other control measures. However, formulations with greater biological activity will be needed if the level of nematode control obtained with chemical nematicides is to be achieved with A. dactyloides.

Field amelioration of acidic soils in south-east Queensland. I. Effect of amendments on soil properties

Replicated field trials with rates of lime ranging up to 8 t/ha were conducted at each of 27 sites in south-east Queensland. At 16 of these sites, single rates (2 t/ha) of gypsum or phosphogypsum were also applied. Soil samples (0-10 cm) were collected from each plot and analysed for pH in both water (pHw) and 0·01 M CaCl2 (pHCa), for electrical conductivity, exchangeable cations, and extractable Al and Mn. Gypsum application resulted in either a general trend for, or significant (P < 0·05), reductions in pHw but had no significant effect on pHCa. The relationship between rate of applied lime and soil pH at each site permitted the calculation of pH buffer capacity for a wide range of soil types and properties. The pH increase per t applied lime ranged from 0·14 to 0·82 and from 0·16 to 0·63 for pH measured in water and 0·01 M CaCl2, respectively, reflecting the range in pH buffer capacity which was significantly correlated with organic carbon. Multiple regression indicated that organic carbon and clay significantly contributed to the variation in pH buffer capacity but only around 40% of the variation could be accounted for. The pH values at which Al saturation was reduced to 10% ranged from 4·82 to 6·02 (pHw) and from 4·26 to 4·93 (pHCa) and indicated that if neutralising exchangeable Al is the basis for liming, then no single target pH value will be appropriate for all soils. However, the target pH at which Al saturation would be reduced to 10% could be predicted from the initial pH and initial Al saturation. The effective cation exchange capacity (ECEC) was increased by liming at all sites and the additional exchange capacity was occupied by Ca. This increased Ca saturation was not necessarily at the expense of exchangeable K and Mg, which were significantly (P < 0·05) reduced at only a few sites. The increase in ECEC for a unit increase in pH ranged from 0·5 to 9 cmol(+)/kg and at some sites represented a doubling of the soil"s cation exchange capacity.

Field amelioration of acidic soils in south-east Queensland. II. Effect of amendments on the yield and leaf nutrient composition of maize

The yield of maize, grown on acidic soils with various rates of lime, was measured inreplicated field trials at each of 19 sites in south-east Queensland. Treatments comprising single rates of gypsum, phosphogypsum, and calcium silicate (as Portland cement) were incorporated into the trialde sign at selected sites. At 12 of the sites, lime significantly (P < 0·05) increased grain yield. Because Ca was applied as a basal nutrient the lime responses were attributed mainly to the amelioration of Aland/or Mn toxicities and this was supported by the observation that 90% maximum yield was attainedat pHw values of around 5·0-5·5. Soil pHw values of around 5·5 would appear to be adequate for optimal maize growth in the region and there was little evidence to support liming to higher pH values. High lime rates resulted in significant (P < 0·05) grain yield reduction relative to the maximum yield at 3 sites with concomitant soil pHw values of 6·7, 7·1, and 7·2, but leaf analysis did not provide a conclusive explanation for the yield reductions. Lime significantly (P < 0·05) increased leaf tissue P concentrations at 6 sites, whereas Zn and Mn concentrations were decreased at 7 and 10 sites, respectively. Across all sites, there were no consistent trends with respect to the effect of lime on N, K, S, and Mg concentrations. Although gypsum and/or phosphogypsum increased grain yield at 3 sites, there was little evidence that amendments other than lime or dolomite type products would have widespread potential for ameliorating soils where Al and/or Mn toxicities are limiting crop growth in the region.

Field amelioration of acidic soils in south-east Queensland. III. Relationships of maize yield response to lime and unamended soil properties

Maize (Zea mays) grain yield responses to rates of lime were measured at 19 sites onseveral soil types in south-east Queensland. At some sites, one rate of gypsum or phosphogypsum was also applied. Relative grain yield (100 mean yield of nil lime treatment/maximum yield) was correlated with each of soil pH (1 : 5 water and 1 : 5 0·01 M CaCl2), soil solution pH, exchangeable (1 M KCl) Al, exchangeable (1 M NH4Cl) Ca, Al saturation of the effective cation exchange capacity (ECEC), Ca saturation of the ECEC, and 0·01 M CaCl2 extractable Mn and Al. Across all soil types, Mitscherlich fits indicated that most of the variation in relative grain yield was accounted for by either Ca saturation (R2 = 0·62) or soil solution pH (R2 = 0·61), although soil pH(water) (R2 =0·53), Al saturation (R2 = 0·46), exchangeable Ca (R2 = 0·42), soil pH(CaCl2) (R2 = 0·40), and CaCl2-extractable Mn (R2 = 0·33) also accounted for significant (P < 0·05) amounts of variation. These results demonstrate that one or both of Al and Mn toxicities were having an impact on yieldat different sites. The contrast between the lack of responses to gypsum/phosphogypsum at mostlime responsive sites and the observation that Ca saturation was well correlated with relative grainyield suggested an ameliorating effect of Ca on Al toxicity. This effect was captured by an index,Al saturation/Ca saturation, which was well correlated with relative grain yield (R2 = 0·66 for a Mitscherlich fit). A step-up regression approach indicated that most variation in relative grain yield (RY) could beaccounted for by the following equation: The assessment of factors likely to limit yield on strongly acidic soils of the region will therefore needto include indices of Al and Mn toxicities as well as Ca status. Soil pH integrated the effects of these factors on yield, and as a single index, was shown to bean effective diagnostic tool. Relative grain yields of 90% were associated with pH values in the soil solution, 1 : 5 water and 1 : 5 0·01 M CaCl2 of 4·5, 5·2, and 4·4, respectively.

Agronomic potential of earthworms in brigalow soils of south-east Queensland

The potential of earthworms to enhance the productivity of sown pastures was investigated in the brigalow region of Qeensland where such pastures are often devoid of earthworms. Wider surveys in eastern Australia recorded 75 native or exotic earthworm species and 27 of these were screened in a series of glasshouse trials to find candidates for field introduction. Whereas some earthworm populations declined in glasshouse soil cores, a maximum increase in numbers in six months was 10-fold. Increases in yield of oats or grass test crops associated with earthworm activity were as high as 60 or 80%, while yield of grain sorghum doubled. Not all species were equally effective: a few were found to depress plant yield. However, 12 species were selected for field trials. One year after earthworm introduction to brigalow pasture, plot yields had increased by an average of 64.4%, and survivors of Aporrectodea trapezoides, Eisenia rosea, Pontoscolex corethrurus and of a native Diplotrema sp. were recovered.

Nutritional constraints to growth of Australian red cedar (Toona ciliata) seedlings in five north Queensland soils

Summary Landscapes that are candidates for rehabilitation with tree species often include soils that are infertile, either inherently or as a result of previous agricultural, logging or mining activities. The potential nutritional constraints to the establishment of high-value cabinet timber species on five such north Queensland soils were evaluated in glasshouse nutrient omission experiments with seedlings of Australian red cedar (Toona ciliata M. Roemer). The soils, collected from sites now considered marginal or uneconomic for agricultural production but which had formerly supported tropical rainforest, were broadly representative of those available for plantation or agroforestry development in the region and differed in both parent materials and previous land-use histories. Within each soil there were marked differences in seedling dry matter production associated with the range of nutrient omission treatments that were imposed. Depending on the soil, single and multiple nutrient deficiencies were identified: phosphorus in a metamorphic soil from South Johnstone (Galmara series); nitrogen in a basaltic soil from Atherton (Pin Gin series); nitrogen and sulphur in a granitic soil from Feluga (Thorpe series); nitrogen, phosphorus, potassium, and sulphur in a basaltic soil from Innisfail (Eubenangee series); and phosphorus, potassium, and calcium, and possibly nitrogen and sulphur in an alluvial soil from Jarra Creek (Virgil series). This study demonstrates that there are potentially major nutritional constraints to the establishment and survival of tree species on many soils in north Queensland.

Production locality affects mango fruit quality

Summary. Differences in mango (cv. Kensington Pride) fruit quality under commercial and research conditions have been frequently noted. To assess the potential for production conditions to influence fruit quality, "Kensington Pride" mango fruit were obtained from 2 adjacent sites on an orchard on shallow nodular yellow podsolic soil in tropical North Queensland, 1 block of trees growing on soil with river gravel (site 1) and another without gravel (site 2). Fruit were also obtained from trees on a gleyed podsolic soil (site 3) in subtropical south-east Queensland. Fruit were harvested weekly for 4 weeks, with quality determined after ripening at 22°C and after storage at 10°C for 4 weeks. Eating quality and percentage dry matter increased, while days to eating soft decreased with later harvests. Fruit from site 3 (cooler growing conditions, rain during the harvest period) had acceptable eating quality at a lower dry matter than fruit from sites 1 and 2. The percentage of green colour on the skin (GS) at ripe was higher at harvest 2 in fruit from sites 1 and 2, but was lower at harvest 4 in fruit from all sites. Disease severity in fruit ripened without storage was higher in site 3 fruit, while body rots (caused mainly by Colletotrichum spp.) increased (site 3 only) and stem end rots (caused mainly by Dothiorella spp.) decreased with later harvests. Fruit firmness and GS decreased during storage at 10°C, but fruit from site 3 were generally softer, with higher GS, than those from the other sites. Chilling injury was also higher in fruit from site 3.

Change in infiltration characteristics associated with cultivation history of soils in south-eastern Queensland

Change in soil infiltration characteristics with cultivation can result in reduced soil water storage, increased runoff and erosion, and reduced crop production. We measured changes in infiltration characteristics associated with years of cultivation for 5 soil groups in south-eastern Queensland. Soils were grouped according to soil type and texture into Sodosols, light and heavy Vertosols, Red Ferrosols, and Red Chromosols/Kandosols. Soil infiltration characteristics were determined from measurements of permeability and water-holding properties of the cultivated layer (0–0·1 m deep) and the layer immediately below the plough layer (0·1–0·2 m deep). A rainfall simulator was used to measure the hydraulic conductivity of surface seals and infiltration of bare, tilled soil in the field. Hydraulic conductivity of the soil matrix and macropores and water-holding properties of the 0·1–0·2 m layer were measured with disc permeameters and pressure plate apparatus. Hydraulic conductivity of surface seals decreased exponentially in all soil groups with period of cultivation; half of the decline occurred within 2–6 years of first cultivation. Hydraulic conductivity, macroporosity, and moisture characteristic of the 0·1–0·2 m layer were similarly affected by longer periods of cultivation in all but light-textured soils. Cultivation of light-textured, hardsetting soils (18% clay) did not adversely affect hydraulic conductivity or macroporosity of the 0·1–0·2 m layer and the loosening effect of tillage was somewhat beneficial for the water-holding properties of this layer. The low hydraulic conductivities of the surface or 0·1–0·2 m layer after long periods of cultivation reduced infiltration of rainfall in the field.

Chlorsulfuron residues are not accumulating in soils of southern Queensland

Chlorsulfuron persistence was measured in soils (to a depth of 150 cm) at 4 sites in the winter cereal region of southern Queensland. The residual herbicide had been applied 6-14 times in the previous 7-14 years. Residues here measured using a bioassay based on suppression of root growth of maize (Zea mays cv. GH5010). Less than 3% of the total applied chlorsulfuron (96-210 g a.i./ha) was detected 6-12 months after the last application, and residues were <0.7 ng/g soil in the surface 30 cm, and <0.3 ng/g below 30 cm. The limited vertical movement of residues was associated with the herbicide being applied in early winter, several months before leaching rains. Changes in residue concentration with time were also measured at a site in central Queensland, and in a fallow management experiment in southern Queensland. Persistence was greater at the cooler, drier site in southern Queensland than in central Queensland; 4544% compared with 3 4 % of applied dose remained 3 months after application respectively. Stubble retention had no effect on persistence, but tillage during the summer fallow increased persistence slightly. There was no evidence of chlorsulfuron residues accumulating and only limited leaching in these alkaline agricultural soils of southern Queensland. Persistence within a season was influenced by soil and climatic factors.

The effects of grazing pressure on soil animals and hydraulic properties of two soils in semi-arid tropical Queensland

A grazing experiment was used to examine the effects of high grazing pressure on soil Acari populations, and on termite populations and activity, at two sites in semi-arid north Queensland. Changes in soil hydraulic properties were also examined. Our investigations have shown that Acari populations were significantly lower in the heavily grazed treatments at one of the sites. Termite species diversity and activity were significantly lower in the heavily grazed treatments than in the lightly grazed treatments at both sites. The surface soils also had significantly lower steady-state how rates and hydraulic conductivities in the heavily grazed treatments than in the lightly grazed treatments. The deterioration in soil hydraulic properties in the heavily grazed treatments appears to be associated with both increased trampling by cattle and decreased termite activity in the top 25 mm of soil. The surface and near surface galleries constructed by detritiverous termites therefore have an important function in water movement in these semi-arid soils.

Amelioration of coarse textured acidic soils used for macadamia production. I. Tree growth, yield and leaf nutrient composition

Macadamia growers have responded to increasing soil acidity in plantations by applying ameliorants, but optimum pH for production has not been identified. The effects of lime applications on the growth, yield and leaf composition of macadamia (Macadamia integrifolia Maiden and Betch) trees were investigated at each of two sites (Pomona and Cootharaba) with acidic sandy soils in south-east Queensland. Trees at the Pomona site had been established for 6 years whereas, at Cootharaba, the trees had been recently planted. The effects of annual applications of nitrogen and nitrogen plus lime were also studied at the Cootharaba site. Tree parameters and soil properties were monitored each year for 5 years after treatment application in 1988. Treatments resulted in pH (water) values ranging from 4.6 to 7.5 and 4.3 to 6.5 at the Pomona and Cootharaba sites, respectively. with a concomitant range in soil Ca and A1 levels. Despite the wide range in soil properties, lime had no significant (P < 0.05) effect on nut-in-shell yield in any year, and the results suggest that macadamia is relatively tolerant of soil acidity. However, yields from treatments with pH values greater than 5.5 tended to be lower than those with more acidic pH values, suggesting that overliming may adversely affect long-term productivity. High lime rates also resulted in a marked reduction in the number of proteoid roots. At the Cootharaba site, nitrogen treatments significantly (P < 0.05) increased nut-in-shell yield despite the juvenile growth stage of the trees precluding nut yield until the 1993 season. Although lime applications at the Cootharaba site resulted in some increase in leaf Ca concentrations, treatments at the Pomona site, with older trees, had little effect on leaf nutrient composition.

Site preparation for Pinus establishment in south-eastern Queensland. 2. Effect of cultivation and cultivation width on growth

The standard site preparation practice used for Pinus plantation establishment on well-drained soils in south-eastern Queensland is blade (subsurface, wing rip) cultivation to a width of 2.0 m and a depth of 0.2 m. This operation requires high drawbar power and is difficult to achieve in high strength soils, or in soils where roots and stumps hinder progress of the blade through the soil. The aim of the study reported in this paper was to better define cultivation growth relationships for Pinus caribaea var. hondurensis plantations in order to determine if site preparation objectives could be achieved with a reduced cultivation effort. A highly significant 'soil type x cultivation' interaction was observed. In contrast to the growth responses observed on hardsetting soils, cultivation did not improve growth on non-hardsetting soils. There is an opportunity therefore to reduce reforestation site preparation costs by only cultivating soils that show a growth response. The cultivation response on hardsetting soils has increased throughout the study period, and is attributed to a reduction in soil penetration resistance. The response however shows diminishing gains with increasing cultivation widths. Blade cultivation widths of 1.2 m were found to capture 97% of the gains that could be expected from widths of 2.0 m. A significant 'family x soil penetration resistance' interaction was observed. An opportunity to increase plantation productivity by targeting better performing families to hardsetting soils is suggested.

A review of sodicity and sodic soil behavior in Queensland

The occurrence of sodic soils in Queensland is more related to soil genetic factors of the past than to the current rainfall pattern, with lower sodium accessions and smaller occurrence of saline lands than other areas of Australia. A soil sodicity map of Queensland is presented. On an area basis, 55% of soils in Queensland are non-sodic, 25% are strongly sodic and 20% are of variable sodicity. The map was prepared using exchangeable sodium percentage (ESP) values at 0.6 m depth from 2 009 soil profiles, as well as the soil boundaries of the 1:2000000 Atlas of Australian Soils maps (Northcote et al. 1960-68). There is general agreement with the earlier sodicity map of Northcote and Skene (1972). The relationships between exchangeable sodium and field-measured soil hydraulic properties and plant-available water capacity are discussed. Behaviour of sodic soils depends on the exchangeable sodium percentage, clay content, clay mineralogy and salt levels. The binary component particle packing theory has been used to explain soil behaviour and identify those soils most susceptible to sodium. Cracking clay soils with dominantly smectite mineralogy and high clay contents are less susceptible to a given ESP level, as determined by their hydrological behaviour, than soils of moderate clay content and mixed mineralogies. The sodicity and the salt content of an irrigation water are important in maintaining permeability of soils. The naturally occurring equilibrium salinity-sodicity relationships of a wide range of subsoils in Queensland is compared to the published relationships between stable permeability and decreasing permeability based on sodicity and salt content. Aspects of management of sodicity under dryland and irrigation are discussed.

Surface soil-pH map of Queensland

Surface soil pH can influence biological activity, nutrition and various chemical processes in the soil. Low pH or acidity is causing major concern in southern Australia, prompting requests for details on the extent, severity and distribution of acidic soils in Queensland. By creating a soil pH database, using an appropriate base map, rainfall isohyets and GIS technology, a coloured pH map of surface soils was produced at a 1:5000000 scale for the entire State. As most samples were from virgin or little disturbed sites, the map generally reflects naturally occurring soil pH. Developed horticultural, agricultural and fertilized pastoral areas are likely to have lower pH than that mapped. About two thirds (63.1%) of Queensland's soils have acidic surfaces, 9.5% neutral and the remaining 26.9% are alkaline. The major proportion (74%) of the > 1200 mm rainfall zone is strongly acid, and the remainder is medium acid or acid. Much of the sugar growing areas occur in this zone. Surface soil pH generally decreases as rainfall increases and to a lesser extent from subtropical to tropical climate. In addition to climate, identification of the soil type assists with predicting pH, as the organic, coarse and medium textured soils and massive earths are more likely to be acid and have low buffering capacity. Depending on the land use, such soils may require regular liming or minimizing of net acidifying practices for long term sustainability.

Recent contraction of wet sclerophyll forest in the wet tropics of Queensland due to invasion by rainforest

Vegetation maps were prepared from aerial photographs taken in 1943?45 and 1991?92 of three, widely separated areas of sclerophyll forest adjacent to the western edge of rainforest on granitic soils in north Queensland. Nine types of sclerophyll communities could be discerned from aerial photos and characterized by field measurement. Two types of Wet Sclerophyll Forest (WSFa and b) were separated on the species of tree composing the tallest stratum and these were subdivided according to whether the ground layer was dominated by grass or young rainforest. A related type showed large, residual Eucalyptus grandis emergent from mature rainforest. Closed canopy sclerophyll forest with no emergents (SF), sclerophyll woodland and Acaciaforest were also discerned. WSF was defined as having more than 30 per cent of the closed crown cover contributed by trees more than 35 m tall. During the 50-year study period rainforest invaded 70 per cent of WSFa (tallest stratum dominated by E. grandis), which principally occurs as a narrow strip along the rainforest margin, and 57 per cent of the adjacent WSFb (tallest stratum composed of mixed species). Grass would be quickly excluded from invaded areas and thereafter they would only burn under extreme atmospheric conditions. Because sclerophyll trees are unable to regenerate in shade and usually require fire to provide the appropriate conditions, a long-term transition to rainforest may ensue. The final stages of this transition were observed in areas that exhibited full-stature rainforest with large, relictual E. grandis emergents in 1943, but had disappeared by 1992. The initial cause of this vegetation transition is a fire-free period of sufficient length for rainforest tree seedlings to establish and suppress the grass layer. It is not known whether these vegetation changes represent a trend, possibly caused by a change a century ago from fire management by Aboriginal people to management for the cattle industry, or whether it is a temporary phase in the fire-induced, dynamic relationship between rainforest and sclerophyll vegetation. The current loss of WSF probably endangers the survival of a range of genetically endemic biota. Most groups are poorly known but the marsupial Yellowbellied Glider Petaurus australis reginae is totally dependent upon WSF and a number of vertebrates would probably go locally extinct if WSF is replaced by rainforest. WSF is the wettest part of the sclerophyll communities and probably acts as a refuge in times of unusual aridity. To maintain the WSF habitat, fire management is clearly indicated, but the intensity of fire required to reverse the advance of rainforest may be socially unacceptable to instigate or impossible to control if it occurs by accident.

Time of nitrogen application and yield of Bengal lychee on a sandy loam soil in subtropical Queensland

Nitrogen (N) was applied over 4 years to 6-year-old lychee trees (Litchi chinensis Sonn. cv. Bengal) growing in subtropical Queensland (lat. 27�S.) on a sandy loam soil (0-15 cm) with 2.8 mg nitrate-N/kg, to determine the effect of time of N application on leaf N concentration, vegetative growth, flowering, and yield. Applications of N (equivalent to 750 kg N/ha in year 4) were made after panicle emergence in July, after harvest in January, or split between the 2 periods. Control trees received no N. Leaf N concentrations in April-June were, on average, about 0.1% lower after a single N application in winter than application in summer or split applications. Leaf N concentrations in November-February were about 0.1% higher after winter or split N applications than after summer applications. Timing of fertiliser application had no affect on yield. It took 4 years without N fertiliser to show significant reductions in yield compared with fertilised trees. In year 4, yield increased from 20 to 60 kg/tree on individual pairs of trees as leaf N in August increased from 0.95 to 1.56%. Lower yields in control trees in year 4 were associated with poor leaf growth in the previous 2 years, and with lower concentrations of N in the panicles, leaves, twigs, and small branches, as well as lower chlorophyll concentrations and net CO2 assimilation after fruit set, compared with trees receiving N.

Soil treatment, plant species, and management effects on improved pastures on a solodic soil in the semi-arid subtropics: 3. Improving cool season plant and cattle productivity

Seasonal analyses of grasses and legumes in a long-term experiment on a solodised solonetz soil (Natrustalf) in southern Queensland showed that the large liveweight losses of steers in the cool months (June-August) appeared to be broadly correlated with low plant nitrogen (N), phosphorus (P), and potassium (K) concentrations. Annual variation in the N, P, and K percentages of Rhodes grass (Chloris gayana) and volunteer grasses [medics (Medicago spp.) and siratro (Macroptilium atropurpureum)] as affected by soil and plant treatments were examined by fitting a Fourier series to the data. Cool season liveweight losses of steers ranged from 391 glday with sown grasses alone to 11 g/day with sown grasses and medics plus lime and gypsum. The N content of volunteer and sown grasses ranged from 0.56 to 0.70% in the cool months, which is below the accepted N requirement of 1%. The P concentration of volunteer grasses was only 0.08%, but where P fertiliser was applied, concentrations in Rhodes grass were 0.10-0.11%. Potassium levels were also low in the cool months, with values of 0.23-0.43% in grasses. Exchangeable magnesium (Mg) and sodium increased from 1.3 and 0.48 mLJ100 g at 0-10 cm depth to 8.5 and 5.2, respectively, at 40-70 cm. Exchangeable calcium decreased from 2.5 mL/100 g at 0-10 cm to 0.40 at 40-70 cm. The Mg levels in siratro (0.58-0.60%) were higher than those in Rhodes grass (mean 0.12%). Medics responded markedly to lime, resulting in a 54% increase in steer liveweight gains on Rhodes grass-medic pastures. The use of lime on solodic soils for reducing both surface soil acidity and exchangeable aluminium increased plant and steer productivity. The cost of lime transportation can be high in inland areas, but small limestone deposits have been identified on the Darling Downs and these merit closer attention.

Persistence and productivity of tropical pasture legumes on three cracking clay soils (Vertisols) in north-eastern Queensland

There are few commercial legumes available for sowing on the cracking clay soils of northeastern Queensland, where legumes are needed to improve quality of perennial native grass pastures and to arrest nitrogen decline in cropping land. To evaluate introduced legumes from heavy-textured soils, a replicated row experiment was established in 3 environments to assess the adaptation of 56 accessions from 37 species (22 genera). The sites were on 3 dark cracking clay soils supporting the following grasslands: Dichanthium -Bothriochloa- Astrebla; Dichanthium aristatum; and Cenchrus ciliaris on cleared Acacia harpophylla (brigalow) country.The main selection criteria during the 4-year evaluation were persistence, regeneration, production, and spread, with green leaf retention, nutrient concentrations, and pest susceptibility also being considered. The perennial legumes Clitoria ternatea (CPI 47 187 and CPI 49963), Desmanthus virgatus (CPI 78373), Leucaena leucocephala (CPI 61227 and cv. Cunningham), Stylosanthes scabra (CPI 55868), and Indigofera schimperi (CPI 69495), and annuals Centrosema pascuorum (CPI 55697), Desmodium dichotomum (CPI 47 186), and Vigna trilobata (CPI 47510), showed promise as pasture or short-term ley species for these clay soils (Vertisols) in subcoastal, north-eastern Queensland. Other species were identified that require evaluation of a wider range of genetic material. The role of perennial and annual sown legumes in pasture and cropping systems on these cracking clay soils is discussed.

Effects of fallow management and cropping history on aggregate breakdown under rainfall wetting for a range of Queensland soils

This paper reports changes in stability of soils to wetting under a range of fallow management/cropping treatments for eight experiment sites in Queensland. Because of its greater relevance to dryland soils, and its better correlation with field soil behaviour, wetting with high energy rain (HER) was used to wet samples and cause aggregate breakdown. The water-stable size fraction considered was that <0.125 mm, with the proportion of particles <0.125 mm referred to as P125. To study interactions between wetting method and tillage management, several other wetting methods were applied to some or all of the eight soils. These other methods were immersion (IMM), wetting by rainfall of low energy (LER) or under tension (TENS). Where fallow management treatments significantly reduced P125 under HER wetting, those reductions were generally small, and likely to increase steady infiltration rates of high energy rain into bare soil by only 2-6 mm h-1. In contrast, steady infiltration rates could be increased by 15-42 mm h-1 if those same soil surfaces were completely covered by stubble so that they received low energy rain. At least under Queensland conditions, retention of crop residues to protect soils from drop impact is therefore likely to be of much greater importance in improving water storage during fallows than any improvement in soil aggregation under 'improved' fallow management practices. Effects of fallow management and cropping history on P125 under HER varied across the sites. Three out of four virgin soils were more stable than corresponding cropped soils; stubble retention improved stability to HER wetting on three out of four sites where it was tested, and direct drill or reductions in tillage frequency improved stability at two out of eight sites. IMM showed responses to treatments that, for some soils, differed greatly from those obtained using HER. Neither LER nor TENS appeared useful, as LER gave occasional inconsistent results, and TENS caused little aggregate breakdown for most soils.