Improving wheat simulation capabilities in Australia from a cropping systems perspective: water and nitrogen effects on spring wheat in a semi-arid environment

Systems approaches can help to evaluate and improve the agronomic and economic viability of nitrogen application in the frequently water-limited environments. This requires a sound understanding of crop physiological processes and well tested simulation models. Thus, this experiment on spring wheat aimed to better quantify water x nitrogen effects on wheat by deriving some key crop physiological parameters that have proven useful in simulating crop growth. For spring wheat grown in Northern Australia under four levels of nitrogen (0 to 360 kg N ha(-1)) and either entirely on stored soil moisture or under full irrigation, kernel yields ranged from 343 to 719 g m(-2). Yield increases were strongly associated with increases in kernel number (9150-19950 kernels m(-2)), indicating the sensitivity of this parameter to water and N availability. Total water extraction under a rain shelter was 240 mm with a maximum extraction depth of 1.5 m. A substantial amount of mineral nitrogen available deep in the profile (below 0.9 m) was taken up by the crop. This was the source of nitrogen uptake observed after anthesis. Under dry conditions this late uptake accounted for approximately 50% of total nitrogen uptake and resulted in high (>2%) kernel nitrogen percentages even when no nitrogen was applied,Anthesis LAI values under sub-optimal water supply were reduced by 63% and under sub-optimal nitrogen supply by 50%. Radiation use efficiency (RUE) based on total incident short-wave radiation was 1.34 g MJ(-1) and did not differ among treatments. The conservative nature of RUE was the result of the crop reducing leaf area rather than leaf nitrogen content (which would have affected photosynthetic activity) under these moderate levels of nitrogen limitation. The transpiration efficiency coefficient was also conservative and averaged 4.7 Pa in the dry treatments. Kernel nitrogen percentage varied from 2.08 to 2.42%. The study provides a data set and a basis to consider ways to improve simulation capabilities of water and nitrogen effects on spring wheat. (C) 1997 Elsevier Science B.V.

Engineering closure of an open pit gold operation in a semi-arid climate

Along with material characteristics and geometry, the climate in which a mine is located can have a dramatic effect on the appropriate options for rehabilitation. The paper outlines the setting, mining, milling and waste disposal at Kidston Gold Mine's open pit operations in the semi-arid climate of North Queensland, Australia, before focusing on the engineering aspects of the rehabilitation of Kidston. The mine took a holistic and proactive approach to rehabilitation, and was prepared to demonstrate a number of innovative approaches, which are described in the paper. Engineering issues that had to be addressed included the geotechnical stability and deformation of waste rock dumps, including a 240 m high in-pit dump: the construction and performance monitoring of a “store and release” cover over potentially acid forming mineralised waste rock; erosion from the side slopes of the waste rock dumps; the in-pit co-disposal of waste rock and thickened tailings; the geotechnical stability of the tailings dam wall; the potential for erosion of bare tailings; the water balance of the tailings dam; direct revegetation of the tailings; and the pit hydrology. The rehabilitation of the mine represents an important benchmark in mine site rehabilitation best practice, from which lessons applicable worldwide can be shared.

An evolutionary radiation of beeflies in semi-arid Australia: systematics of the Exoprosopini (Diptera : Bombyliidae)

Almost half of the 4822 described beeflies in the world belong to the subfamily Anthracinae, with most of the diversity found in three cosmopolitan tribes: Villini, Anthracini, and Exoprosopini. The Australian Exoprosopini previously contained three genera, Ligyra Newman, Pseudopenthes Roberts and Exoprosopa Macquart. Pseudopenthes is an Australian endemic, with two species including Ps. hesperis, sp. nov. from Western Australia. Two new species of the exoprosopine Atrichochira Hesse, Atr. commoni, sp. nov. and Atr. paramonovi, sp. nov., are also described from Australia, extending the generic distribution from Africa. Cladistic analysis clarified the phylogenetic relationships between the recognised groups of the Exoprosopini and determined generic limits on a world scale. Inclusion of 18 Australian exoprosopines placed the Australian species in the context of the world fauna. The Exoprosopini contains six large groups. The basal group I contains species previously included in Exoprosopa to which the name Defilippia Lioy is applied. Group II contains Heteralonia Rondani, Atrichochira, Micomitra Bowden, Pseudopenthes, and Diatropomma Bowden. Colossoptera Hull is newly synonymised with Heteralonia. Group III is a paraphyletic assemblage of Pterobates Bezzi and Exoprosopa including the Australian Ex. sylvana ( Fabricius). Ligyra is paraphyletic, forming two well-separated clades. The African clade is described as Euligyra Lambkin, gen. nov., which, together with Litorhina Bezzi and Hyperalonia Rondani, form group IV. The Australian group V is true Ligyra. The remaining monophyletic lineage of exoprosopines, group VI, the Balaana-group of genera, shows evidence of an evolutionary radiation of beeflies in semi-arid Australia. Phylogenetic analysis of all 42 species of the Balaana-group of genera formed a basis for delimiting genera. Seven new genera are described by Lambkin & Yeates: Balaana, Kapua, Larrpana, Munjua, Muwarna, Palirika and Wurda. Four non-Australian species belong to Balaana. Thirty two new Australian species are described: Bal. abscondita, Bal. bicuspis, Bal. centrosa, Bal. gigantea, Bal. kingcascadensis, K. corusca, K. irwini, K. westralica, Lar. collessi, Lar. zwicki, Mun. erugata, Mun. lepidokingi, Mun. paralutea, Mun. trigona, Muw. vitreilinearis, Pa. anaxios, Pa. basilikos, Pa. blackdownensis, Pa. bouchardi, Pa. cyanea, Pa. danielsi, Pa. decora, Pa. viridula, Pa. whyalla, W. emu, W. impatientis, W. montebelloensis, W. norrisi, W. patrellia, W. skevingtoni, W. windorah, and W. wyperfeldensis. The following new combinations are proposed: from Colossoptera: Heteralonia latipennis (Brunetti); from Exoprosopa: Bal. grandis (Pallas), Bal. efflatounbeyi (Paramonov), Bal. latelimbata ( Bigot), Bal. obliquebifasciata ( Macquart), Bal. tamerlan (Portschinsky), Bal. onusta ( Walker), Def. busiris (Jaennicke), Def. efflatouni ( Bezzi), Def. eritreae (Greathead), Def. gentilis ( Bezzi), Def. luteicosta ( Bezzi), Def. minos (Meigen), Def. nigrifimbriata ( Hesse), Def. rubescens ( Bezzi), K. adelaidica ( Macquart), Lar. dimidiatipennis ( Bowden), Muw. stellifera ( Walker), and Pa. marginicollis ( Gray); from Ligyra: Eu. enderleini ( Paramonov), Eu. mars ( Bezzi), Eu. monacha (Klug), Eu. paris ( Bezzi), Eu. sisyphus ( Fabricius), and Eu. venus (Karsch).

A simulation model of cereal-legume intercropping systems for semi-arid regions I. Model development

Cereal-legume intercropping plays an important role in subsistence food production in developing countries, especially in situations of limited water resources. Crop simulation can be used to assess risk for intercrop productivity over time and space. In this study, a simple model for intercropping was developed for cereal and legume growth and yield, under semi-arid conditions. The model is based on radiation interception and use, and incorporates a water stress factor. Total dry matter and yield are functions of photosynthetically active radiation (PAR), the fraction of radiation intercepted and radiation use efficiency (RUE). One of two PAR sub-models was used to estimate PAR from solar radiation; either PAR is 50% of solar radiation or the ratio of PAR to solar radiation (PAR/SR) is a function of the clearness index (K-T). The fraction of radiation intercepted was calculated either based on Beer's Law with crop extinction coefficients (K) from field experiments or from previous reports. RUE was calculated as a function of available soil water to a depth of 900 mm (ASW). Either the soil water balance method or the decay curve approach was used to determine ASW. Thus, two alternatives for each of three factors, i.e., PAR/SR, K and ASW, were considered, giving eight possible models (2 methods x 3 factors). The model calibration and validation were carried out with maize-bean intercropping systems using data collected in a semi-arid region (Bloemfontein, Free State, South Africa) during seven growing seasons (1996/1997-2002/2003). The combination of PAR estimated from the clearness index, a crop extinction coefficient from the field experiment and the decay curve model gave the most reasonable and acceptable result. The intercrop model developed in this study is simple, so this modelling approach can be employed to develop other cereal-legume intercrop models for semi-arid regions. (c) 2004 Elsevier B.V. All rights reserved.

A simulation model of cereal-legume intercropping systems for semi-arid regions II. Model application

Smallholder farmers in Africa practice traditional cropping techniques such as intercropping. Intercropping is thought to offer higher productivity and resource milisation than sole cropping. In this study, risk associated with maize-bean intercropping was evaluated by quantifying long-term yield in both intercropping and sole cropping in a semi-arid region of South Africa (Bloemfontein, Free State) with reference to rainfall variability. The crop simulation model was run with different cultural practices (planting date and plant density) for 52 summer crop growing seasons (1950/1951-2001/2002). Eighty-one scenarios, consisted of three levels of initial soil water, planting date, maize population, and bean population, were simulated. From the simulation outputs, the total land equivalent ratio (LER) was greater than one. The intercrop (equivalent to sole maize) had greater energy value (EV) than sole beans, and the intercrop (equivalent to sole beans) had greater monetary value (MV) than sole maize. From these results, it can be concluded that maize-bean intercropping is advantageous for this semi-arid region. Soil water at planting was the most important factor of all scenario factors, followed by planting date. Irrigation application at planting, November/December planting and high plant density of maize for EV and beans for MV can be one of the most effective cultural practices in the study region. With regard to rainfall variability, seasonal (October-April) rainfall positively affected EV and MV, but not LER. There was more intercrop production in La Nina years than in El Nino years. Thus, better cultural practices may be selected to maximize maize-bean intercrop yields for specific seasons in the semi-arid region based on the global seasonal outlook. (c) 2004 Elsevier B.V. All rights reserved.

Improving wheat simulation capabilities in Australia from a cropping systems perspective - II. Testing simulation capabilities of wheat growth

To simulate cropping systems, crop models must not only give reliable predictions of yield across a wide range of environmental conditions, they must also quantify water and nutrient use well, so that the status of the soil at maturity is a good representation of the starting conditions for the next cropping sequence. To assess the suitability for this task a range of crop models, currently used in Australia, were tested. The models differed in their design objectives, complexity and structure and were (i) tested on diverse, independent data sets from a wide range of environments and (ii) model components were further evaluated with one detailed data set from a semi-arid environment. All models were coded into the cropping systems shell APSIM, which provides a common soil water and nitrogen balance. Crop development was input, thus differences between simulations were caused entirely by difference in simulating crop growth. Under nitrogen non-limiting conditions between 73 and 85% of the observed kernel yield variation across environments was explained by the models. This ranged from 51 to 77% under varying nitrogen supply. Water and nitrogen effects on leaf area index were predicted poorly by all models resulting in erroneous predictions of dry matter accumulation and water use. When measured light interception was used as input, most models improved in their prediction of dry matter and yield. This test highlighted a range of compensating errors in all modelling approaches. Time course and final amount of water extraction was simulated well by two models, while others left up to 25% of potentially available soil water in the profile. Kernel nitrogen percentage was predicted poorly by all models due to its sensitivity to small dry matter changes. Yield and dry matter could be estimated adequately for a range of environmental conditions using the general concepts of radiation use efficiency and transpiration efficiency. However, leaf area and kernel nitrogen dynamics need to be improved to achieve better estimates of water and nitrogen use if such models are to be use to evaluate cropping systems. (C) 1998 Elsevier Science B.V.

Relationships among climate, latitude and migration: Australian butterflies are not temperate-zone birds

We examined the distribution of butterflies over the mostly arid and semi-arid continent of Australia and analyzed the proportion of migrant species and species diversity with respect to an array of climatic and geographic variables. On a continent-wide scale, latitude explained virtually no variance in either proportion of migrants (r(2) = 0.01) or species diversity (r(2) = 0.03) in Australian butterflies. These results are in marked contrast to those for temperate-zone birds from three continents where latitude explained between 82 and 98% of the variance in frequency of migrants and also accounted for much of the variance in bird species diversity. In eastern Australia where rainfall regimes are similar to those in temperate Europe and North and South America, latitude explains 78% of the variance in frequency of butterfly migrants. In both eastern and central Australia, latitude also accounts for relatively high proportions of the variance in species diversity. Rainfall patterns and especially soil moisture are negatively associated with migration frequency in Australian butterfly faunas, both alone and in combination with other climate variables. Where moisture levels are relatively high, as in eastern Australia, measures of temperature are associated with migration frequency, a result consistent with findings for temperate-zone birds, suggesting latitude is a surrogate for temperature. The ultimate causes of migration in temperate-zone birds and Australian butterflies are the uneven temporal, and in Australia also spatial, distribution of resources. Uneven distribution is brought about primarily by temperature in temperate regions and by erratic rainfall over much of arid Australia. As a key determinant of productivity, especially in the tropics and subtropics, aridity is likely to be an important determinant of the global distributions of migrants.

The breeding-season diet of wedge-tailed eagles (Aquila audax) in western New South Wales and the influence of Rabbit Calicivirus Disease

A total of 2071 individual prey items were identified from 34 active and 55 inactive wedge-tailed eagle nests following the 1995, 1996 and 1997 breeding seasons. Overall, the eagle's diet was comparable to that reported in other studies within semi-arid regions, with rabbits, reptiles and macropods accounting for 47.8, 22.6 and 13.7% of prey items, respectively. In spring 1996 rabbit calicivirus moved into the study area, resulting in a 44-78% reduction in rabbit abundance (Sharp et al. 2001). An index was developed to enable the time since death for individual prey items to be approximated and a historical perspective of the eagle's diet to be constructed. Rabbits constituted 56-69% of dietary items collected during the pre-rabbit calicivirus disease (RCD) samples, but declined to 31% and 16% in the two post-RCD samples. A reciprocal trend was observed for the proportion of reptiles in the diet, which increased from 8-21% of pre-RCD dietary items to 49-54% after the advent of RCD. Similarly, the proportion of avian prey items was observed to increase in the post-RCD samples. These data suggested that prey switching may have occurred following the RCD epizootic. However, a lack of data on the relative abundances of reptiles and birds prevented an understanding of the eagle's functional responses to be developed and definitive conclusions to be drawn. Nevertheless, the eagles were observed to modify their diet to the change in rabbit densities by consuming larger quantities of native prey species.

Biodiversity conservation and vegetation clearing in Queensland: Principles and thresholds

Clearing of native vegetation is a major threat to biodiversity in Australia. In Queensland, clearing has resulted in extensive ecosystem transformation, especially in the more fertile parts of the landscape. In this paper, we examine Queensland, Australian and some overseas evidence of the impact of clearing and related fragmentation effects on terrestrial biota. The geographic locus is the semi-arid regions. although we recognise that coastal regions have been extensively cleared. The evidence reviewed here suggests that the reduction of remnant vegetation to 30% will result in the loss of 25-35% of vertebrate fauna, with the full impact not realised for another 50-100 years, or even longer. Less mobile, habitat specialists and rare species appear to be particularly at risk. We propose three broad principles For effective biodiversity conservation in Queensland: (i) regional native vegetation retention thresholds of 50910: (ii) regional ecosystem thresholds of 30%: and (iii) landscape design and planning principles that protect large remnants, preferably > 2000 ha, as core habitats. Under these retention thresholds. no further clearing would be permitted in the extensively cleared biogeographic regions such as Brigalow Belt and New England Tablelands. Some elements of the biota. however, will require more detailed knowledge and targeted retention and management to ensure their security. The application of resource sustainability and economic criteria outlined elsewhere in this volume should be applied to ensure that the biogeographic regions in the north and west of Queensland that are largely intact continue to provide extensive wildlife habitat.