Northern Grain Research Articles

Fusariumspecies associated with stalk rot of grain sorghum in the northern grain belt of eastern Australia

Recent revisions in taxonomy have led to significant changes in our understanding of the Fusarium species associated with sorghum worldwide. To reassess the Fusarium species associated with stalk rot of grain sorghum in Australia, a survey was conducted in two different agroclimatic areas in the northern grain belt of eastern Australia (Goondiwindi and Quirindi). Across three sites in each of the two areas, 288 grain sorghum stalks were sampled from which a total of 324 Fusarium isolates were recovered. Species diversity and eveness was higher in the Goondiwindi area, which is hotter and dryer than the Quirindi area. Fusarium andiyazi and F. thapsinum were the most frequently isolated species overall, comprising 61% and 82% of the isolates from the Goondiwindi and Quirindi areas, respectively. The dominance and relative abundance of these species was associated with agroclimatic areas, with F. thapsinum more abundant in the Goondiwindi area and F. andiyazi more abundant in the Quirindi area. This study represents the first formal report of F. andiyazi and F. thapsinum in Australia.

Do spring cover crops rob water and so reduce wheat yields in the northern grain zone of eastern Australia?

During the 14-month-long fallow that arises when moving from summer to winter crops, stubble breakdown can denude the soil surface and leave it vulnerable to erosion. Cover crops of millet have been proposed as a solution, but this then raises the question, how often is there sufficient water in the system to grow a cover crop without reducing the soil water reserves to the point of prejudicing the following wheat crop? An on-farm research approach was used to compare the traditional long fallow (TF) with a millet fallow (MF) in a total of 31 commercial paddocks over 3 years. Each treatment was simulated using the simulation-modelling framework (APSIM) to investigate the outcomes over a longer timeframe and to determine how often a millet fallow could be successfully included within the farming system. The on-farm trials showed that early-sown millet cover crops removed before December had no effect on wheat yield, but this was not true of millet cover crops that were allowed to grow through to maturity. Long-term simulations estimated that a spring cover crop of millet would adversely affect wheat yields in only 2% of years if planted early and removed after 50% cover had been achieved.

Fertiliser N and P applications on two Vertosols in north-eastern Australia. 2. Grain P concentration and P removal in grain from two long-term experiments

Within north-eastern Australia’s grain-production region there are few reports outlining nitrogen (N) and phosphorus (P) fertiliser effects on grain P concentration and P removal in grain. Two long-term N × P fertiliser experiments with different cultivation durations were conducted, one at ‘Colonsay’ on the Darling Downs in southern Queensland (commencing 1985 after 40 years of cultivation), and the other at ‘Myling’ on the north-west plains of New South Wales (commencing 1996 after 9 years of cultivation). Applications of N and P fertiliser independently influenced both grain P concentration and P removal for a range of summer and winter cereal and legume crops. Generally, if N fertiliser application increased grain yield, the grain P concentration decreased as grain yield increased; however, if grain yield did not respond to N fertiliser, grain P concentration was unaffected. P fertiliser applications typically increased grain P concentration. Wheat and barley grain P concentrations were generally higher in this subtropical region than reported values from temperate regions in Australia. Grain sorghum values were similar to those from subtropical areas overseas, but were greater than reported values from more tropical production zones. Mungbean and chickpea grain P concentrations were consistent with other reported values. Experimental results indicated grain P concentrations for estimating grain P removal in the northern grains region of 3400 mg/kg for sorghum, 3500 mg/kg for wheat and barley, and 4000–4500 mg/kg for mungbean. At both sites, grain P removal was greater with summer and winter cereals than with legume crops. Larger grain yields with N fertiliser application had the largest influence on grain P removal at the Colonsay site, with an additional 23.3 kg P/ha removed from plots with 80 kg N/ha applied compared with nil N over 5 analysed crops from 1998 to 2003. Grain P removal was 20.9, 17.1, and 19.7 kg P/ha in the 3 sorghum crops at this site in this period. Thus, application of P at 10 kg P/ha.crop for this 5-crop study period did not replace P removed. In the predominantly winter-cropped Myling experiment with a shorter duration of cultivation and smaller N fertiliser response, cumulative removal was more influenced by P fertiliser, with 10 kg fertiliser P/ha.crop generally sufficient to provide replacement P. These results support findings of negative P balances recently reported for grain production in this region and suggest a need for further investigation into the implications of a continuing negative P balance on the sustainability of grain production.

Canola residues do not reduce establishment, growth, and yield of following summer crops

Sowing of summer-growing species (e.g. grain sorghum, cotton, mungbeans, maize) into the stubble of recently harvested winter crops (e.g. wheat, barley, chickpea, canola) is practised widely in the north-eastern cropping zone of Australia. With the recent increase in canola area in the region, there are concerns that canola crop residues may be antagonistic to the germination, establishment, growth, and yield of summer crops, in addition to the well documented non-host effect of Brassica species on vesicular-arbuscular mycorrhizae (VAM). We report five field studies conducted at two locations in the north-eastern grains region of Australia where grain sorghum and mungbean were grown after canola, Indian mustard, and wheat. The experiments included treatments that varied residue removal and retention, irrigation, and time between winter crop harvest and sowing date of the summer crop. Non-host effects of brassicas on VAM and phosphorus nutrition were eliminated by conducting field experiments in soils of relatively high P status. This study failed to find consistent evidence that Brassica crops reduce the establishment, growth, and yield of following sorghum and mungbean crops. This is despite evidence from the literature on pot studies that extracts from Brassica residues can reduce germination and growth of a variety of crops, and anecdotal field evidence from farmers and the authors in the region. Based on our study, there does not seem to be a strong case for avoiding double-cropping summer crops into canola residues in the northern grains region.

A novel approach to planting grass - legume pastures in the mixed farming zone of southern inland Queensland, Australia

Reliable establishment of pasture systems with a desirable composition of grasses and legumes remains a challenge in the highly variable climates of the northern grain belt of southern inland Queensland. In this paper, an alternative system is proposed whereby legumes and grasses are planted simultaneously in alternative strips. A 4-year study tested the establishment, production, and botanical composition of the tropical legume species Macroptilium bracteatum cvv. Cardaga and Juanita, Lablab purpureus cv. Endurance, and Clitoria ternatea cv. Milgarra sown as pure stands or with grass strips. The grass strips, and a grass-only treatment, both contained a mix of Panicum maximum cv. Petrie, Dichanthium aristatum cv. Floren, and Bothriochloa insculpta cv. Bisset. L. purpureus was relatively unproductive, yielding ~2000 kg/ha dry matter (DM) produced in each of the first 2 years. M. bracteatum produced 2050 and 3300 kg/ha DM in Years 1 and 2, with declining plant populations and DM in subsequent years. C. ternatea produced 960 kg/ha DM in Year 1, 2730 kg/ha DM in Year 2, and continued to persist throughout the trial, albeit at low DM production levels. The grass-only treatment was dominated by the sown grass species, while the legume-based treatments were dominated by a colonising native species, Dichanthium sericeum, in the fourth and final year. Sowing grass strips adjacent to the legume areas proved a successful strategy, with the proportion of sown grasses in the legume strips increasing to >20% of total DM by Year 4. Soil carbon changes did not differ between treatments, but total C in the top 0.15 m increased from 0.99% in Year 1 to 1.13% in Year 4, representing a net gain of 6.5 t/ha in C over 3 years.

Fertiliser N and P applications on two Vertosols in north-eastern Australia. 1. Comparative grain yield responses for two different cultivation ages

Nitrogen (N) and phosphorus (P) are the 2 most limiting nutrients for grain production within the northern grains region of Australia. The response to fertiliser N and P inputs is influenced partly by the age of cultivation for cropping, following a land use change from native pasture. There are few studies that have assessed the effects of both N and P fertiliser inputs on grain yield and soil fertility in the long term on soils with contrasting ages of cultivation with fertility levels that are running down v. those already at the new equilibrium. Two long-term N × P experiments were established in the northern grains region: one in 1985 on an old (>40 years) cultivation soil on the Darling Downs, Qld; the second in 1996 on relatively new (10 years) cultivation on the north-west plains of NSW. Both experiments consisted of fertiliser N rates from nil to 120 kg N/ha.crop in factorial combination with fertiliser P from nil to 20 kg P/ha.crop. Opportunity cropping is practiced at both sites, with winter and summer cereals and legumes sown. On the old cultivation soil, fertiliser N responses were large and consistent for short-fallow crops, while long fallowing reduced the size and frequency of N response. Short-fallow sorghum in particular has responded up to the highest rate of fertiliser N (120 kg N/ha.crop). Average yield increase with fertiliser N compared with nil for 5 short-fallow sorghum crops was 1440, 2650, and 3010 kg/ha for the 40, 80, and 120 kg N/ha, respectively. Average agronomic efficiency of N for these crops was 36, 33, and 25 kg grain/kg fertiliser N applied. This contrasts with relatively new cultivation soil, where fertiliser N response was generally limited to the first 30 kg N/ha applied during periods of high cropping intensity. Response to P input was consistent for crop species, VAM sensitivity, and starting soil test P level. At both the old and new cultivation sites, generally all winter cereals responded to a 10 kg P/ha application, and more than half of long-fallow sorghum crops from both sites had increased grain yield with P application. At the old cultivation site, average yield gain for 10 kg P/ha.crop treatment was 480 kg/ha for all winter cereal sowings, and 180 kg/ha for long-fallow sorghum. Short-fallow sorghum did not show yield response to P treatment.

Resistance to root-lesion nematodes (Pratylenchus thornei and P. neglectus) in synthetic hexaploid wheats and their durum and Aegilops tauschii parents

Root-lesion nematodes (Pratylenchus thornei Sher and Allen and P. neglectus (Rensch) Filipijev and Schuurmans Stekhoven) cause substantial yield loss to wheat crops in the northern grain region of Australia. Resistance to P. thornei for use in wheat breeding programs was sought among synthetic hexaploid wheats (2n = 6x = 42, AABBDD) produced through hybridisations of Triticum turgidum L. subsp. durum (Desf.) Husn (2n = 4x = 28, AABB) with Aegilops tauschii Coss. (2n = 2x = 14, DD). Resistance was determined for the synthetic hexaploid wheats and their durum and Ae. tauschii parents from the numbers of nematodes in the roots of plants grown for 16 weeks in pots of pasteurised soil inoculated with P. thornei. Fifty-nine (32%) of 186 accessions of synthetic hexaploid wheats had lower numbers of nematodes than Gatcher Selection 50a (GS50a), a partially resistant bread wheat. Greater frequencies of partial resistance were present in the durum parents (72% of 39 lines having lower nematode numbers than GS50a) and in the Ae. tauschii parents (55% of 53 lines). The 59 synthetic hexaploids were re-tested in a second experiment along with their parents. In a third experiment, 11 resistant synthetic hexaploid wheats and their F1 hybrids with Janz, a susceptible bread wheat, were tested and the F1s were found to give nematode counts intermediate between the respective two parents. Synthetic hexaploid wheats with higher levels of resistance resulted from hybridisations where both the durum and Ae. tauschii parents were partially resistant, rather than where only one parent was partially resistant. These results suggest that resistance to P. thornei in synthetic hexaploid wheats is polygenic, with resistances located both in the D genome from Ae. tauschii and in the A and/or B genomes from durum. Five synthetic hexaploid wheats were selected for further study on the basis of (1) a high level of resistance to P. thornei of the synthetic hexaploid wheats and of both their durum and Ae. tauschii parents, (2) being representative of both Australian and CIMMYT (International Maize and Wheat Improvement Centre) durums, and (3) being representative of the morphological subspecies and varieties of Ae. tauschii. These 5 synthetic hexaploid wheats were also shown to be resistant to P. neglectus, whereas GS50a and 2 P. thornei-resistant derivatives were quite susceptible. Results of P. thornei resistance of F1s and F2s from a half diallel of these 5 synthetic hexaploid wheats, GS50a, and Janz from another study indicate polygenic additive resistance and better general combining ability for the synthetic hexaploid wheats than for GS50a. Published molecular marker studies on a doubled haploid population between the synthetic hexaploid wheat with best general combining ability (CPI133872) and Janz have shown quantitative trait loci for resistance located in all 3 genomes. Synthetic hexaploid wheats offer a convenient way of introgressing new resistances to P. thornei and P. neglectus from both durum and Ae. tauschii into commercial bread wheats.

Developmental and physiological traits associated with high yield and stay-green phenotype in wheat

Water availability is a key limiting factor in wheat production in the northern grain belt of Australia. Varieties with improved adaptation to such conditions are actively sought. The CIMMYT wheat line SeriM82 has shown a significant yield advantage in multi-environment screening trials in this region. The objective of this study was to identify the physiological basis of the adaptive traits underpinning this advantage. Six detailed experiments were conducted to compare the growth, development, and yield of SeriM82 with that of the adapted cultivar, Hartog. The experiments were undertaken in field environments that represented the range of moisture availability conditions commonly encountered by winter crops grown on the deep Vertosol soils of this region. The yield of SeriM82 was 6–28% greater than that of Hartog, and SeriM82 exhibited a stay-green phenotype by maintaining green leaf area longer during the grain-filling period in all environments where yield was significantly greater than Hartog. However, where the availability of deep soil moisture was limited, SeriM82 failed to exhibit significantly greater yield or to express the stay-green phenotype. Thus, the stay-green phenotype was closely associated with the yield advantage of SeriM82. SeriM82 also exhibited higher mean grain mass than Hartog in all environments. It is suggested that small differences in water use before anthesis, or greater water extraction from depth after anthesis, could underlie the stay-green phenotype. The inability of SeriM82 to exhibit stay-green and higher yield where deep soil moisture was depleted indicates that extraction of deep soil moisture is important.

Root-lesion nematodes (Pratylenchus thorneiandP. neglectus): a review of recent progress in managing a significant pest of grain crops in northern Australia

Two species of root-lesion nematode (predominantly Pratylenchus thornei but also P. neglectus) are widespread pathogens of wheat and other crops in Australia's northern grain belt, a subtropical region with deep, fertile clay soils and a summer-dominant rainfall pattern. Losses in grain yield from P. thornei can be as high as 70% for intolerant wheat cultivars. This review focuses on research which has led to the development of effective integrated management programs for these nematodes. It highlights the importance of correct identification in managing Pratylenchus species, reviews the plant breeding work done in developing tolerant and resistant cultivars, outlines the methods used to screen for tolerance and resistance, and discusses how planned crop sequencing with tolerant and partially resistant wheat cultivars, together with crops such as sorghum, sunflower, millets and canaryseed, can be used to reduce nematode populations and limit crop damage. The declining levels of soil organic matter in cropped soils are also discussed with reference to their effect on soil health and biological suppression of root-lesion nematodes.

Germination, persistence, and emergence of flaxleaf fleabane (Conyza bonariensis [L.] Cronquist)

Flaxleaf fleabane (Conyza bonariensis[L.] Cronquist) is a difficult‐to‐control weed in dryland minimum tillage farming systems in the northern grains region of Australia. Experiments under field and controlled environments were conducted to study the seed germination, emergence, and persistence of C. bonariensis. The base, optimum, and maximum temperatures for seedling germination were estimated at 4.2, 20, and 35°C, respectively, with light stimulating germination. The soil types and burial depths had significant effects on seed persistence and emergence. The persistence pattern showed an initial rapid drop, followed by a slow but steady decline over time. After 3 years of burial, there were ≈ 7.5%, 9.7%, and 1.3% viable seeds at 10, 5, and 0–2 cm soil depths, respectively. Conyza bonariensis predominantly emerged from the soil surface or from the burial depth of 0.5 cm. Very few seeds emerged from a depth of 1 cm and none emerged from ≥ 2 cm. The emergence was greater in lighter soils. On‐farm monitoring of the field emergence over time in a light sandy loam soil showed that 99% emergence occurred in late autumn, early and late winter, and a small fraction of 1% emerged in mid‐spring. The predominant emergence from the soil surface suggests that the fleabane problem is a result of weed species shift toward the minimum tillage systems that provide moist conditions for better emergence compared to conventional tillage systems. The seed longevity of at least 3 years in the soil and the prolonged emergence patterns between autumn and spring have posed great difficulties for the long‐term management of C. bonariensis.

Managing production constraints to the reliability of chickpea (Cicer arietinum L.) within marginal areas of the northern grains region of Australia

The poor reliability of chickpea yield produced in the marginal (<600 mm rainfall) areas of the northern cropping zone is a constraint to the wide adoption of the crop. Chickpea is a valuable rotation crop and is currently the only viable winter grain legume suitable to this region. This paper uses results from in-crop monitoring and crop simulation, to identify practical management strategies to improve the reliability of chickpea crops in this region. APSIM-Chickpea successfully simulated the commercial yields of chickpea crops monitored during the study. Soil water at sowing and sowing date were identified as key determinants of yield. A ‘rule of thumb’ was derived, which showed that crops sown with a starting plant-available water of ~100 mm at sowing had an 80% probability of producing a better than break-even yield for the majority of the region and this was independent of the soil’s plant-available water capacity or crop sowing date. The probability of accumulating 100 mm of stored water in this western region is 90% following harvest of a May–sown wheat crop. Increased plant population improved crop yields in 60% of years, but this only translated to improved returns in ~50% of those years. The use of these simple management approaches will improve the reliability of chickpea production and ensure that these marginal areas have the option of a viable winter grain legume in their rotations.

Soil nutrient stratification and uptake by wheat after seven years of conventional and zero tillage in the Northern Grain belt of Canada

The distribution of NaHCO3-extractable nitrate-N, ammonium-N, phosphorus (P) and potassium (K) with soil depth (0 to 20 cm in 5-cm increments) at Fort Vermilion (58°23′N 116°02′ W), Alberta, was described in the 7th and 8th years of conventional and zero tillage following placement of red clover (Trifolium pratense) green manure (GM), field pea (Pisum sativum), canola (Brassica rapa) and monoculture wheat (Triticum aestivum) residues. Soil nitrate-N concentrations under zero tillage were greater than those under conventional tillage in the 0–5 cm soil layer, below which the concentrations were similar. Ammonium-N and K concentrations followed a similar pattern. However, soil P concentrations were usually not different between tillage systems in the 0–5 cm soil layer, but the concentrations decreased more under zero tillage than under conventional tillage at lower depths. A notable exception for soil phosphate was under canola residues, where the concentration was greater under zero tillage than under conventional tillage at all depths. Uptake of N, P or K by a subsequent wheat crop was usually greater (though not always significantly) under zero tillage than under conventional tillage, and there were no interactions between tillage and crop residue. Therefore, differences in nutrient stratification between the two tillage systems did not translate into differences in wheat nutrient uptake. Key words: Conservation tillage, crop rotation, nutrient uptake, soil nitrogen, soil phosphorus, soil potassium

Wheel traffic and tillage effects on runoff and crop yield

Traffic and tillage effects on runoff, soil water and crop production under rainfall were investigated over a period of 6 years on a heavy clay vertosols (vertisols) in Queensland, Australia. A split plot design was used to isolate traffic effects, while the cropping program and treatments were broadly representative of extensive grain production practice in the northern grain region of Australia. Treatments subject to zero tillage and stubble mulch tillage each comprised pairs of 90 m 2 plots, from which runoff was recorded. A 3 m wide controlled traffic system allowed one of each pair to be maintained as a non-wheeled plot, while the complete surface area of the other received a single annual wheeling treatment from a working 100 kW tractor. Mean annual runoff from controlled traffic plots was 81 mm (36.3%) smaller than that from wheeled plots, while runoff from zero tillage was reduced by 31 mm (15.7%). Traffic and tillage effects appeared to be cumulative, so the mean annual runoff from controlled traffic and zero tillage plots, representing best practice, was 112 mm (47.2%) less than that from wheeled stubble mulch plots, representing conventional cropping practice. Rainfall infiltration into controlled traffic zero tillage soil was thus 12.0% greater than into wheeled stubble mulched soil. Rainfall/runoff hydrographs show that wheeling produced a large and consistent increase in runoff, whereas tillage produced a smaller increase. Treatment effects were greater on dry soil, but were still present in large and intense rainfall events on wet soil. Plant available water capacity (PAWC) in the 0–500 mm zone increased by 10 mm (11.5%) and mean grain yields increased by 337 kg/ha (9.4%) in controlled traffic plots, compared with wheeled plots. Mean grain yield of zero tillage was 2–8% greater than that of stubble mulch plots for all crops except for winter wheat in 1994 and 1998. Increased infiltration and plant available water were probably responsible for increased mean grain yields of 497 kg/ha (14.5%) in controlled traffic zero tillage, compared with wheeled stubble mulch treatments. Dissipation of tractive and tillage energy in the soil is the apparent mechanism of deleterious effects on the soils ability to support productive cropping in this environment. Controlled traffic and conservation tillage farming systems appear to be a practicable solution.

Subsoil constraints to grain production in the cropping soils of the north-eastern region of Australia: an overview

In dryland agricultural systems of the subtropical, semi-arid region of north-eastern Australia, water is the most limiting resource. Crop productivity depends on the efficient use of rainfall and available water stored in the soil during fallow. Agronomic management practices including a period of fallow, stubble retention, and reduced tillage enhance reserves of soil water. However, access to stored water in these soils may be restricted by the presence of growth-limiting conditions in the rooting zone of the crop. These have been termed as subsoil constraints. Subsoil constraints may include compacted or gravel layers (physical), sodicity, salinity, acidity, nutrient deficiencies, presence of toxic elements (chemical) and low microbial activity (biological). Several of these constraints may occur together in some soils. Farmers have often not been able to obtain the potential yield determined by their prevailing climatic conditions in the marginal rainfall areas of the northern grains region. In the past, the adoption of soil management practices had been largely restricted to the top 100 mm soil layer. Exploitation of the subsoil as a source of water and nutrients has largely been overlooked. The key towards realising potential yields would be to gain better understanding of subsoils and their limitations, then develop options to manage them practically and economically. Due to the complex nature of the causal factors of these constraints, efforts are required for a combination of management approaches rather than individual options, with the aim to combat these constraints for sustainable crop production, managing natural resources and avoiding environmental damage.

EFFECT OF MICROAC ON NUMBERS OF SOYBEAN APHID, 2005

Infestations by SA can reduce the yield of soybeans and the efficacy of various biorational spray treatments need evaluation as alternatives to chemical insecticides for SA control. The efficacy of an entomopathogenic fungal formulation, MicroAC, against SA was compared to that of a distilled-water spray check and an untreated check. Two identical efficacy tests were conducted in growth chambers at the Northern Grain Insects Research Laboratory, Brookings, SD. Each test used a RCB design with 10 replications. In each test, 30 greenhouse-raised soybean plants, growing individually in separate pots, were infested in the late VE stage (unifoliate leaves fully expanded, first trifoliate leaves expanding) with five SA (adults or late third instars) on the underside of each unifoliate leaf (total of 10 SA per plant). The plants were placed in a growth chamber (16:8 L:D photoperiod; mean temperature and R.H. of 21.4 C and 45.9%, first test; 21.3 C and 73.9%, second test). Seven days after infestation, SA were counted on each plant. Sprays were then applied 20 cm from each plant using the wide-angle mist setting on the nozzle of a handpumped squirt bottle. Sprays were applied to run-off with eight squirts (about 9.2 ml) directed per plant, four with the nozzle horizontal and four with nozzle tip pointed downward at approximately 30-degrees. The number of spores contained in an 8-squirt volume of MicroAC was enumerated by direct observation of diluted product suspensions on a light microscope using phase contrast microscopy and a hemacytometer. Sporulation rate was measured as colonyforming units (CFU) in dilution-series cultures plated on Sabouraud dextrose agar with 2 % yeast extract under growth chamber conditions; CFU were counted after a 4-day incubation period when colonies were visible and separate. After spray application, clear 10-cm-diam × 40-cm-tall cylindrical acetate cages with 16-mesh screen tops were placed over each plant, and plants were returned to the growth chamber. At 10 days after treatment (DAT), (23 Jun, first test; 11 Jul, second test), plants were clipped at soil level, and SA were counted on each plant. For each test, SA counts were subjected to ANOVA and treatment means separated using Tukey’s HSD (P = 0.05). Post-spray SA counts were log (x + 1)-transformed before analysis.

Response of chickpea (Cicer arietinum L.) varieties to time of sowing in Mediterranean-type environments of south-western Australia

Chickpea has become an important grain legume crop in Australia over the last decade. New varieties with improved seed yield and quality are being developed in Australia with varied phenological and agronomic traits. This study examined the optimum time of sowing of several desi chickpea varieties (Dooen, T1587, Sona and Tyson) varying in phenology over a range of dryland Mediterranean-type environments in south-western Australia. Chickpea showed good adaptation, particularly in the northern grain belt of Western Australia where growing conditions are warmer than southern areas. Seed yields varied widely depending on the time of sowing, location and seasonal conditions. Mean seed yields greater than 1000 kg/ha and up to 2000 kg/ha were achieved, but in some cases seed yields were less than 800 kg/ha. In the northern region, seed yield was almost doubled by sowing in early-May (1625 kg/ha) compared with late-June (754 kg/ha). In contrast to this, seed yields were generally lower in the southern regions and greater from late-June sowings (865 kg/ha) compared to earlier mid-May sowings (610 kg/ha). Seed yields were not clearly increased by altering sowing time to match the phenology of the variety to the growing season rainfall and temperatures, except at the early sowing times (April and early-May) where Tyson out-yielded all other varieties. This is most likely due to the lack of photoperiod-responsive, long-duration varieties to match early sowing and low temperatures limiting vegetative and reproductive growth in all varieties, especially in southern areas. However, it is likely that early flowering varieties will show greater adaptation and yield performance in short growing seasons, while later flowering varieties will be better suited to longer growing seasons. The study found that there were significant differences in the optimum sowing time between northern, central and southern sites, based on differences in mean daily temperatures and length of the growing season. Generally, the greatest seed yields were produced by sowing between mid to late June at southern sites, and early May at central and northern sites.

Corrigendum to: Piggery pond sludge as a nitrogen source for crops. 1. Mineral N supply estimated from laboratory incubations and field application of stockpiled and wet sludge

Piggery pond sludge (PPS) was applied, as-collected (Wet PPS) and following stockpiling for 12 months (Stockpiled PPS), to a sandy Sodosol and clay Vertosol at sites on the Darling Downs of Queensland. Laboratory measures of N availability were carried out on unamended and PPS-amended soils to investigate their value in estimating supplementary N needs of crops in Australia's northern grains region. Cumulative net N mineralised from the long-term (30 weeks) leached aerobic incubation was described by a first-order single exponential model. The mineralisation rate constant (0.057/week) was not significantly different between Control and PPS treatments or across soil types, when the amounts of initial mineral N applied in PPS treatments were excluded. Potentially mineralisable N (No) was significantly increased by the application of Wet PPS, and increased with increasing rate of application. Application of Wet PPS significantly increased the total amount of inorganic N leached compared with the Control treatments. Mineral N applied in Wet PPS contributed as much to the total mineral N status of the soil as did that which mineralised over time from organic N. Rates of CO2 evolution during 30 weeks of aerobic leached incubation indicated that the Stockpiled PPS was more stabilised (19.28% of applied organic C mineralised) than the Wet PPS (35.58% of applied organic C mineralised), due to higher lignin content in the former. Net nitrate-N produced following 12 weeks of aerobic non-leached incubation was highly correlated with net nitrate-N leached during 12 weeks of aerobic incubation (R2 = 0.96), although it was <60% of the latter in both sandy and clayey soils. Anaerobically mineralisable N determined by waterlogged incubation of laboratory PPS-amended soil samples increased with increasing application rate of Wet PPS. Anaerobically mineralisable N from field-moist soil was well correlated with net N mineralised during 30 weeks of aerobic leached incubation (R2 = 0.90 sandy soil; R2 = 0.93 clay soil). In the clay soil, the amount of mineral N produced from all the laboratory incubations was significantly correlated with field-measured nitrate-N in the soil profile (0.1.5 m depth) after 9 months of weed-free fallow following PPS application. In contrast, only anaerobic mineralisable N was significantly correlated with field nitrate-N in the sandy soil. Anaerobic incubation would, therefore, be suitable as a rapid practical test to estimate potentially mineralisable N following applications of different PPS materials in the field.

Piggery pond sludge as a nitrogen source for crops. 1. Mineral N supply estimated from laboratory incubations and field application of stockpiled and wet sludge

Piggery pond sludge (PPS) was applied, as-collected (Wet PPS) and following stockpiling for 12 months (Stockpiled PPS), to a sandy Sodosol and clay Vertosol at sites on the Darling Downs of Queensland. Laboratory measures of N availability were carried out on unamended and PPS-amended soils to investigate their value in estimating supplementary N needs of crops in Australia’s northern grains region. Cumulative net N mineralised from the long-term (30 weeks) leached aerobic incubation was described by a first-order single exponential model. The mineralisation rate constant (0.057/week) was not significantly different between Control and PPS treatments or across soil types, when the amounts of initial mineral N applied in PPS treatments were excluded. Potentially mineralisable N (No) was significantly increased by the application of Wet PPS, and increased with increasing rate of application. Application of Wet PPS significantly increased the total amount of inorganic N leached compared with the Control treatments. Mineral N applied in Wet PPS contributed as much to the total mineral N status of the soil as did that which mineralised over time from organic N. Rates of CO2 evolution during 30 weeks of aerobic leached incubation indicated that the Stockpiled PPS was more stabilised (19–28% of applied organic C mineralised) than the Wet PPS (35–58% of applied organic C mineralised), due to higher lignin content in the former. Net nitrate-N produced following 12 weeks of aerobic non-leached incubation was highly correlated with net nitrate-N leached during 12 weeks of aerobic incubation (R2 = 0.96), although it was <60% of the latter in both sandy and clayey soils. Anaerobically mineralisable N determined by waterlogged incubation of laboratory PPS-amended soil samples increased with increasing application rate of Wet PPS. Anaerobically mineralisable N from field-moist soil was well correlated with net N mineralised during 30 weeks of aerobic leached incubation (R2 = 0.90 sandy soil; R2 = 0.93 clay soil). In the clay soil, the amount of mineral N produced from all the laboratory incubations was significantly correlated with field-measured nitrate-N in the soil profile (0–1.5 m depth) after 9 months of weed-free fallow following PPS application. In contrast, only anaerobic mineralisable N was significantly correlated with field nitrate-N in the sandy soil. Anaerobic incubation would, therefore, be suitable as a rapid practical test to estimate potentially mineralisable N following applications of different PPS materials in the field.

Weed species richness, density and relative abundance on farms in the subtropical grain region of Australia

Weed management is one of the most important economic and agronomic issues facing farmers in Australia’s grain regions. Weed species occurrence and abundance was monitored between 1997 and 2000 on 46 paddocks (sites) across 18 commercial farms located in the Northern Grain Region. The sites generally fell within 4 disjunct regions, from south to north: Liverpool Plains, Moree, Goondiwindi and Kingaroy. While high species richness was found (139 species or species groups), only 8 species occurred in all 4 regions and many (56 species) only occurred at 1 site or region. No species were observed at every site but 7 species (Sonchus spp., Avena spp., Conyza spp., Echinochloa spp., Convolvulus erubescens, Phalaris spp. and Lactuca serriola) were recorded on more than 70% of sites. The average number of species observed within crops after treatment and before harvest was less than 13. Species richness tended to be higher in winter pulse crops, cotton and in fallows, but overall was similar at the different sampling seasons (summer v. winter). Separate species assemblages associated with the Goondiwindi and Kingaroy regions were identified by correspondence analysis but these appeared to form no logical functional group. The species richness and density was generally low, demonstrating that farmers are managing weed populations effectively in both summer and winter cropping phases. Despite the apparent adoption of conservation tillage, an increase in opportunity cropping and the diversity of crops grown (13) there was no obvious effect of management practices on weed species richness or relative abundance. Avena spp. and Sonchus spp. were 2 of the most dominant weeds, particularly in central and southern latitudes of the region; Amaranthus spp. and Raphanus raphanistrum were the most abundant species in the northern part of the region. The ubiquity of these and other species shows that continued vigilance is required to suppress weeds as a management issue.

Low nodulation and nitrogen fixation of mungbean reduce biomass and grain yields

Apparent nodulation failures and associated low grain yields have been reported for commercial mungbean (Vigna radiata) crops in southern Queensland and northern New South Wales. We therefore conducted on-farm surveys of 40 commercial mungbean crops in the region in which symbiotic traits, i.e. nodulation and nitrogen fixation, and biomass and grain yield were monitored. Effects of bradyrhizobial inoculation and inoculation methods on mungbean and soybean (Glycine max) symbiosis and yield were determined in experiments at 3 sites in northern New South Wales. Thirty-four of the 35 mungbean crops assessed for nodulation were nodulated. The relationship between soil nitrate to a depth of 90 cm at sowing and mungbean nodulation was not significant. However, at low-to-moderate soil nitrate levels (<100 kg N/ha), the mean nodule score was 1.6, compared with 0.5 at high (>100 kg N/ha) soil nitrate levels. Soil nitrate had a negative effect on the percentage of mungbean nitrogen derived from nitrogen fixation (%Ndfa). Mean %Ndfa values for soil nitrate levels <50, >50–100 and >100 kg N/ha were 35, 22 and 19% respectively. Grain yields of the surveyed mungbean crops varied from 0.3 to 2.1 t/ha, and were correlated with shoot dry matter. Grain yield was not significantly correlated either with sowing soil nitrate, nodule score or %Ndfa. In the inoculation experiments, mungbean did not nodulate as well as soybean, producing about one-third the number of nodules. Both species responded to inoculation with increased nodulation, although data from one of the sites suggested that responses during early growth of mungbean were not maintained during pod-fill. Effects of inoculation on mungbean %Ndfa were marginal. Average increases were 9%, based on natural 15N abundance, and 6%, based on the ureide method. Soybean %Ndfa, on the other hand, responded strongly to inoculation, with increases of 56 (15N) and 77% (ureide). Inoculation increased mungbean crop N by an average of 10% and grain yield by 6%, compared with responses to fertiliser nitrogen of 31% (crop N) and 10% (grain yield). For soybean, inoculation increased crop nitrogen by 43% and grain yield by 7%, similar to responses to fertiliser nitrogen of 45 (crop N) and 5% (grain yield). These results suggest that inoculated mungbean was N-limited and that inoculation of mungbean using current technology may be somewhat ineffectual. We concluded that low nodulation and nitrogen fixation of commercial mungbean most likely results from the suppressive effects of nitrate and/or insufficient numbers of bradyrhizobia in the soil. When low symbiosis and low soil nitrate are combined, N is likely to limit crop growth, and potentially grain yield. Suggested strategies for improving mungbean nodulation and nitrogen fixation in the northern grains belt include selection of more symbiotically competent plant and bradyrhizobial genotypes and more effective utilisation of established soil populations of mungbean bradyrhizobia.