Exploring profit - Sustainability trade-offs in cropping systems using evolutionary algorithms

Models that implement the bio-physical components of agro-ecosystems are ideally suited for exploring sustainability issues in cropping systems. Sustainability may be represented as a number of objectives to be maximised or minimised. However, the full decision space of these objectives is usually very large and simplifications are necessary to safeguard computational feasibility. Different optimisation approaches have been proposed in the literature, usually based on mathematical programming techniques. Here, we present a search approach based on a multiobjective evaluation technique within an evolutionary algorithm (EA), linked to the APSIM cropping systems model. A simple case study addressing crop choice and sowing rules in North-East Australian cropping systems is used to illustrate the methodology. Sustainability of these systems is evaluated in terms of economic performance and resource use. Due to the limited size of this sample problem, the quality of the EA optimisation can be assessed by comparison to the full problem domain. Results demonstrate that the EA procedure, parameterised with generic parameters from the literature, converges to a useable solution set within a reasonable amount of time. Frontier ‘‘peels’’ or Pareto-optimal solutions as described by the multiobjective evaluation procedure provide useful information for discussion on trade-offs between conflicting objectives.

The effects of holding space on growth and survival of individually reared three-spot crab (Portunus sanguinolentus).

The problem of cannibalism in communally reared crabs can be eliminated by separating the growing crabs into holding compartments. There is currently no information on optimal compartment size for growing crabs individually. 136 second instar crablets (Portunus sanguinolentus) (C2 ca. 7-10 mm carapace width (CW)) were grown for 90 days in 10 different-sized opaque and transparent walled acrylic compartments. The base area for each compartment ranged from small (32 mm × 32 mm) to large (176 mm × 176 mm). Effects of holding space and wall transparency on survival, CW, moult increment, intermoult period and average weekly gain (AWG) were examined. Most crabs reached instars C9-C10 (50-70 mm CW) by the end of experiment. The final survival rate in the smallest compartment was 25% mainly due to moult-related mortality predominantly occurring at the C9 instar. However, crabs in these smaller compartments had earlier produced significantly larger moult increments from instar to instar than those in the larger compartments (P < 0.05). Crabs in the smaller compartments (<65 mm × 65 mm) also showed significantly longer moult periods (P < 0.05). The net result was that AWG in CW was 5.22 mm week-1 for the largest compartment and 5.15 mm week-1 in smallest and did not differ significantly between compartment size groups (P = 0.916). Wall transparency had no impact on survival (P = 0.530) but a slight impact on AWG (P = 0.014). Survival rate was the best indicator of minimum acceptable compartment size (?43 mm × 43 mm) for C10 crablets because below this size death occurred before growth rate was significantly affected. For further growth, it would be necessary to transfer the crablets to larger compartments.

Space allowances for confined livestock and their determination from allometric principles

The amount of space provided to animals governs important elements of their behaviour and, hence, is critical for their health and welfare. We review the use of allometric principles and equations to estimate the static space requirements of animals when standing and lying, and the space required for animals to feed, drink, stand-up and lie-down. We use the research literature relating to transportation and intensive housing of sheep and cattle to assess the validity of allometric equations for estimating space allowances. We investigated these areas because transportation and intensive housing provide points along a continuum in terms of the duration of confinement, (from hours to months) and spatial requirements are likely to increase with increasing duration of confinement, as animals will need to perform a greater behavioural repertoire for long-term survival, health and welfare. We find that, although there are theoretical reasons why allometric relationships to space allowances may vary slightly for different classes of stock, space allowances that have been demonstrated to have adverse effects on animal welfare during transportation correlated well with an inability to accommodate standing animals, as estimated from allometry. For intensive housing, we were able to detect a space allowance below which there were adverse effects on welfare. For short duration transportation during which animals remain standing, a space allowance per animal described by the allometric equation: area (m^2) = 0.020W^0.66, where W = liveweight (kg), would appear to be appropriate. Where it is desirable for all animals to lie simultaneously, then a minimum space allowance per animal described by the allometric equation: area (m^2) = 0.027W^0.66 appears to permit this, given that animals in a group time-share space. However, there are insufficient data to determine whether this allowance onboard a vehicle/vessel would enable animals to move and access food and water with ease. In intensive housing systems, a minimum space allowance per animal described by the allometric equation: area (m^2) = 0.033W^0.66 appears to be the threshold below which there are adverse effects on welfare. These suggested space allowances require verification with a range of species under different thermal conditions and, for transportation, under different conditions of vehicular/vessel stability. The minimum length of trough per animal (L in m) required for feeding and drinking can be determined from L = 0.064W^0.33, with the number of animals required to feed/drink simultaneously taken into account, together with any requirement to minimise competition. This also requires verification with a range of species. We conclude that allometric relationships are an appropriate basis for the formulation of space allowances for livestock.

Water use studies and implications for management of subtropical C4 turfgrasses in dryland and irrigated urban open space

A 2000-03 study to improve irrigation efficiency of grassed urban public areas in northern Australia found it would be difficult to grow most species in dry areas without supplementary watering. Sporoboulus virginicus and sand couch, Zoysia macrantha, were relatively drought-tolerant. Managers of sporting fields, parks and gardens could more than halve their current water use by irrigating over a long cycle, irrigating according to seasonal conditions and using grasses with low water use and sound soil management practices that encourage deep rooting. The use of effluent water provides irrigation and fertiliser cost savings and reduced nitrogen and phosphorus discharge to local waterways. Projected savings are $8000/ha/year in water costs for a typical sporting field.

Establishment and management of salt-tolerant amenity grasses to reduce urban salinity effect

This project built upon the successful outcomes of a previous project (TU02005) by adding to the database of salt tolerance among warm season turfgrass cultivars, through further hydroponic screening trials. Hydroponic screening trials focussed on new cultivars or cultivars that were not possible to cover in the time available under TU02005, including: 11 new cultivars of Paspalum vaginatum; 13 cultivars of Cynodon dactylon; six cultivars of Stenotaphrum secundatum; one accession of Cynodon transvaalensis; 12 Cynodon dactylon x transvaalensis hybrids; two cultivars of Sporobolus virginicus; five cultivars of Zoysia japonica; one cultivar of Z. macrantha, one common form of Z. tenuifolia and one Z. japonica x tenuifolia hybrid. The relative salinity tolerance of different turfgrasses is quantified in terms of their growth response to increasing levels of salinity, often defined by the salt level that equates to a 50% reduction in shoot yield, or alternatively the threshold salinity. The most salt tolerant species in these trials were Sporobolus virginicus and Paspalum vaginatum, consistent with the findings from TU02005 (Loch, Poulter et al. 2006). Cynodon dactylon showed the largest range in threshold values with some cultivars highly sensitive to salt, while others were tolerant to levels approaching that of the more halophytic grasses. Coupled with the observational and anecdotal evidence of high drought tolerance, this species and other intermediately tolerant species provide options for site specific situations in which soil salinity is coupled with additional challenges such as shade and high traffic conditions. By recognising the fact that a salt tolerant grass is not the complete solution to salinity problems, this project has been able to further investigate sustainable long-term establishment and management practices that maximise the ability of the selected grass to survive and grow under a particular set of salinity and usage parameters. Salt-tolerant turf grasses with potential for special use situations were trialled under field conditions at three sites within the Gold Coast City Council, while three sites, established under TU02005 within the Redland City Council boundaries were monitored for continued grass survival. Several randomised block experiments within Gold Coast City were established to compare the health and longevity of seashore paspalum (Paspalum vaginatum), Manila grass (Zoysia matrella), as well as the more tolerant cultivars of other species like buffalo grass (Stenotaphrum secundatum) and green couch (Cynodon dactylon). Whilst scientific results were difficult to achieve in the field situation, where conditions cannot be controlled, these trials provided valuable observational evidence of the likely survival of these species. Alternatives to laying full sod such as sprigging were investigated, and were found to be more appropriate for areas of low traffic as the establishment time is greater. Trials under controlled and protected conditions successfully achieved a full cover of Paspalum vaginatum from sprigs in a 10 week time frame. Salt affected sites are often associated with poor soil structure. Part of the research investigated techniques for the alleviation of soil compaction frequently found on saline sites. Various methods of soil de-compaction were investigated on highly compacted heavy clay soil in Redlands City. It was found that the heavy duplex soil of marine clay sediments required the most aggressive of treatments in order to achieve limited short-term effects. Interestingly, a well constructed sports field showed a far greater and longer term response to de-compaction operations, highlighting the importance of appropriate construction in the successful establishment and management of turfgrasses on salt affected sites. Fertiliser trials in this project determined plant demand for nitrogen (N) to species level. This work produced data that can be used as a guide when fertilising, in order to produce optimal growth and quality in the major turf grass species used in public parkland. An experiment commenced during TU02005 and monitored further in this project, investigated six representative warm-season turfgrasses to determine the optimum maintenance requirements for fertiliser N in south-east Queensland. In doing so, we recognised that optimum level is also related to use and intensity of use, with high profile well-used parks requiring higher maintenance N than low profile parks where maintaining botanical composition at a lower level of turf quality might be acceptable. Kikuyu (Pennisetum clandestinum) seemed to require the greatest N input (300-400 kg N/ha/year), followed by the green couch (Cynodon dactylon) cultivars ‘Wintergreen’ and ‘FLoraTeX’ requiring approximately 300 kg N/ha/year for optimal condition and growth. ‘Sir Walter’ (Stenotaphrum secundatum) and ‘Sea Isle 1’ (Paspalum vaginatum) had a moderate requirement of approximately 200 kg/ha/year. ‘Aussiblue’ (Digitaria didactyla)maintained optimal growth and quality at 100-200 kg N/ha/year. A set of guidelines has been prepared to provide various options from the construction and establishment of new grounds, through to the remediation of existing parklands by supporting the growth of endemic grasses. They describe a best management process through which salt affected sites should be assessed, remediated and managed. These guidelines, or Best Management Practices, will be readily available to councils. Previously, some high salinity sites have been turfed several times over a number of years (and Council budgets) for a 100% failure record. By eliminating this budgetary waste through targeted workable solutions, local authorities will be more amenable to investing appropriate amounts into these areas. In some cases, this will lead to cost savings as well as resulting in better quality turf. In all cases, however, improved turf quality will be of benefit to ratepayers, directly through increased local use of open space in parks and sportsfields and indirectly by attracting tourists and other visitors to the region bringing associated economic benefits. At the same time, environmental degradation and erosion of soil in bare areas will be greatly reduced.

Searching for common threads in threadfins: phylogeography of Australian polynemids in space and time

Proper management of marine fisheries requires an understanding of the spatial and temporal dynamics of marine populations, which can be obtained from genetic data. While numerous fisheries species have been surveyed for spatial genetic patterns, temporally sampled genetic data is not available for many species. We present a phylogeographic survey of the king threadfin Polydactylus macrochir across its species range in northern Australia and at a temporal scale of 1 and 10 yr. Spatially, the overall AMOVA fixation index was Omega(st) = 0.306 (F-st' = 0.838), p < 0.0001 and isolation by distance was strong and significant (r(2) = 0.45, p < 0.001). Temporally, genetic patterns were stable at a time scale of 10 yr. However, this did not hold true for samples from the eastern Gulf of Carpentaria, where populations showed a greater degree of temporal instability and lacked spatial genetic structure. Temporal but not spatial genetic structure in the Gulf indicates demographic interdependence but also indicates that fishing pressure may be high in this area. Generally, genetic patterns were similar to another co-distributed threadfin species Eleutheronema tetradactylum, which is ecologically similar. However, the historical demography of both species, evaluated herein, differed, with populations of P. macrochir being much younger. The data are consistent with an acute population bottleneck at the last glacio-eustatic low in sea level and indicate that the king threadfin may be sensitive to habitat disturbances.

Boronia heterophylla vase life is influenced more by ethylene than by bacterial numbers or vase solution pH

Bacterial proliferation in both vase solutions and in cut flower stems has been implicated in reducing the vase life of numerous genera. Boronia heterophylla F. Muell. (Red Boronia) vase life was assessed at two stages of floral maturity for nine vase solution treatments covering a pH range of 2.5-5.7. Vase life for advanced harvest maturity stems ranged from 4.2 d in 10 mM citric acid + 50 mg L-1 chlorine (pH 2.5) to 12.9 d after STS pulsing (pH 5.7). For normal harvest maturity stems, the corresponding range was 5.8-19.0 d, respectively. Vase solutions containing 50 mg L-1 chlorine biocide resulted in decreased longevity. In contrast, pulsing with the ethylene-binding inhibitor, STS, significantly increased vase life. The number of bacteria in the vase solutions after 11 d was determined in stems of advanced maturity. The solution with the greatest number of bacteria, 4.0 x 10(10) cfu mL(-1), was water used after STS pulsing and in which the flowers lasted longest. Vase solution bacteria were enumerated on days 0,3, 6, 9 and 12 of the vase period with stems of normal harvest maturity. There was no relationship between vase life and vase solution bacterial numbers ((R) over bar (2) = 0.000). Moreover, there was a negative relationship between numbers of bacteria in basal 0-5 cm stem segments and vase life. As no correlations were evident between longevity and either the pH or vase solution bacterial numbers, B. heterophylla vase life was evidently limited principally by ethylene action. (C) 2013 Elsevier B.V. All rights reserved.