Ec Lefroy

Emergy evaluation of three cropping systems in southwestern Australia

Wind erosion and rising water tables are serious threats to the ecological sustainability of annual plant-based farming systems on deep, infertile sandplain soils in southwestern Australia. In this study, an annual cropping system was compared with two novel perennial plant-based systems designed to address these threats in terms of their use of renewable indigenous resource, their use of non-renewable indigenous resources, their purchased inputs of energy and materials, and profitability. The farming systems were an annual lupin/wheat (Lupinus angustifolius L./Triticum aestivum L.) crop rotation, a plantation of the fodder tree tagasaste (Chamaecytisus proliferus L.) and an alley cropping system in which the lupin/wheat rotation was grown between spaced rows of tagasaste trees. Flows of energy and materials between the environment and the economy were identified for each farming system and the natural and human activity involved in generating inputs as goods or services then valued in terms of the equivalent amount of solar energy required for their production using the emergy method of Odum [Ecological and General Systems: An Introduction to Systems Ecology. University Press of Colorado, revised edition of Systems Ecology, 1983, Wiley, New York, 644 pp.; Environmental Accounting: Emergy and Environmental Decision Making. Wiley, New York, 370 pp.]. The results showed that the two largest energy flows in the conventional lupin/wheat cropping system were wind erosion and purchased inputs of phosphate. The renewable component of production was 15% of total flows in the lupin/wheat system, 30% in the alley cropping system and 53% in the tagasaste plantation. The annual net income from the plantation system was nearly four times higher, and from alley cropping 45% higher, than from the lupin/wheat rotation. This analysis suggested that once the two agroforestry systems were fully established, the tagasaste plantation was the most efficient at transforming natural resources into goods and services and the most profitable, while the lupin/wheat system was the least energy efficient and the least profitable.

Improving the use of species distribution models in conservation planning and management under climate change

Choice of variables, climate models and emissions scenarios all influence the results of species distribution models under future climatic conditions. However, an overview of applied studies suggests that the uncertainty associated with these factors is not always appropriately incorporated or even considered. We examine the effects of choice of variables, climate models and emissions scenarios can have on future species distribution models using two endangered species: one a short-lived invertebrate species (Ptunarra Brown Butterfly), and the other a long-lived paleo-endemic tree species (King Billy Pine). We show the range in projected distributions that result from different variable selection, climate models and emissions scenarios. The extent to which results are affected by these choices depends on the characteristics of the species modelled, but they all have the potential to substantially alter conclusions about the impacts of climate change. We discuss implications for conservation planning and management, and provide recommendations to conservation practitioners on variable selection and accommodating uncertainty when using future climate projections in species distribution models.

Agroforestry for water management in the cropping zone of southern Australia

Agroforestry has been advocated as a means of managing excess water that has accumulated in the agricultural landscape of southern Australia since clearing of native vegetation. This article examines the feasibility and profitability of agroforestry systems designed to manage rising, saline watertables. A framework for Australian conditions is described that considers the interactions between trees, crops and their below ground environment and how they influence water use, crop yield and profitability. Data is presented from a study of a commercial scale agroforestry system under ideal conditions where trees have access to a shallow fresh water table. The discussion is then broadened to encompass soil, relief and ground water conditions more typical of the southern Australian cropping zone. The relative merits of segregating, integrating and rotating trees with crops are then examined. It is concluded that, in most cases, trees would need to be widely dispersed over a significant proportion of the landscape to manage deep drainage and salinity. Agroforestry is therefore only likely to be an effective solution to water management where trees can compete directly on commercial terms with conventional agriculture. Given the generally low rates of biomass accumulation in semi-arid woody species, this presents a significant challenge for agroforestry in the cropping zone of southern Australia.

Trees and shrubs as sources of fodder in Australia

Experience with browse plants in Australia is briefly reviewed in terms of their forage value to animals, their economic value to the landholder and their ecological contribution to landscape stability. Of the cultivated species only two have achieved any degree of commercial acceptance (Leucaena leucocephala and Chamaecytisus palmensis). Both of these are of sufficiently high forage value to be used as the sole source of feed during seasonal periods of nutritional shortage. Both are also leguminous shrubs that establish readily from seed. It is suggested that a limitation in their present use is the reliance on stands of single species which leaves these grazing systems vulnerable to disease and insects. Grazing systems so far developed for high production and persistence of cultivated species involve short periods of intense grazing followed by long periods of recovery. Similar management may be necessary in the arid and semi-arid rangelands where palatable browse species are in decline.

Potential of current perennial plant-based farming systems to deliver salinity management outcomes and improve prospects for native biodiversity: a review

Existing perennial plant-based farming systems are examined within 4 climatic zones in southern Australia (western winter rainfall, south-eastern low to medium rainfall, south-eastern high rainfall and northern summer rainfall) to assess their potential to improve the management of dryland salinity. If profit is to be the primary driver of adoption, it appears that the available options (lucerne and other perennial pastures, farm forestry, saltland pastures and forage shrubs) will fall short of existing hydrological targets with the exception of the higher rainfall zones. In the 3 eastern zones, the need to preserve fresh water flows to permanent river systems places limitations on the use of perennial plants, while the higher proportion of regional groundwater flow systems increases response times and heightens the need for regional coordination of effort. In the western zone, the prevalence of local and intermediate ground water flow systems increases effectiveness of individual action. Research into new perennial land use systems has been characterised by an emphasis on water use over profit resulting from poor dialogue between paddock, farm and catchment scales. Exploring the water use implications of land use systems that are potentially viable at farm scale is a more promising approach than focusing on the opportunity cost of catchment scale intervention. Perennial plant-based farming systems present both threats and opportunities to native biodiversity. The major threat is the introduction of new environmental weeds. The opportunities are potential improvements in vegetative cover, food sources and habitat for the native biota, but only where nature conservation goals can influence the structural complexity, composition and location of new land use systems.

The influence of tagasaste (Chamaecytisus proliferus Link.) trees on the water balance of an alley cropping system on deep sand in south-western Australia

Components of the water balance of an alley cropping system were measured to assess the extent to which tree rows 30 m apart with access to a fresh, perched watertable at 5 m depth were able to capture deep drainage from an inter-cropped cereal–legume rotation. Neutron probe data showed that the 4-year-old trees, cut back to 0.6-m high at the beginning of the experiment, depleted soil water to 2, 4, and 8 m laterally from the tree rows in their first, second, and third years of coppice regrowth, respectively. Combining data from soil water depletion in summer and comparisons of deuterium: hydrogen ratios of groundwater, xylem sap of trees, and herbaceous plants, it was shown that tagasaste trees drew on soil water for 80% of their transpiration in the first winter and 40% in the second, while switching to near total dependence on groundwater each summer and early autumn. Tree water use on a whole plot basis was 170 mm in 1997 (68% from groundwater) v. 167 mm in 1998 (73% from groundwater). Recharge to the perched watertable was estimated to be 193 mm under sole crop in 1998 (52% of rainfall), reducing to 32 mm when uptake of groundwater by trees was included. The degree of complementarity between tagasaste trees and crops in alley cropping used for water management is quantified for 1998 by calculating the ratio of the distance over which trees reduced drainage to zero to the distance over which they reduced crop yield to zero. It is concluded that segregated monocultures of trees and crops would be a more appropriate strategy than a closely integrated system such as alley cropping in this case.

Integrating economic and ecological considerations; a theoretical framework.

Previous chapters have described the fragmentation of the Western Australian wheatbelt environment over the past one hundred years. Ecological disintegration has been apparent in the form of the extinction of plants and animals (Hobbs et al., Chapter 4), the loss of topsoil and decline in soil properties (Nulsen, Chapter 5), and an annual increase in the area of land affected by salinity (McFarlane et al., Chapter 6). Social disintegration has been apparent in the last third of that period, with a decline in populations in small towns to the point of collapse of the social infrastructure (B.Y. Main, Chapter 3). In economic terms, however, agricultural land use in the region as a whole has remained viable over this period. This viability has been maintained partly at the expense of social values through the amalgamation of family farm businesses. The trend toward further amalgamation, which saw an eightfold increase in the amount of farmland controlled per farmer in the 50 years up to 1971 in Australia generally, continues (Mauldon and Schapper 1974; Australian Bureau of Statistics 1990). The primary cause of the social disruption of farm amalgamation has been the long-term decline in the terms of trade in agriculture; the prices received for farm produce have been increasing at a slower rate than the costs of inputs.

Nitrogen isotope fractionation in the fodder tree legume tagasaste (Chamaecytisus proliferus) and assessment of N2 fixation inputs in deep sandy soils of Western Australia.

Nitrogen (N) isotope fractionation and symbiotic N fixation were investigated in the shrub legume tagasaste, growing in the glasshouse and field. In a pot study of effectively nodulated plants supplied with 0, 1, 5 and 10 mM nitrate [stable isotope 15N (δ15N) of 3.45‰], the δ15N of dry matter N of fully symbiotic cultures indicated a greater isotope fractionation during distribution of N between nodules, stems, leaves and roots than for N2 fixation itself, with whole-plant δ15N being near zero (–0.46 to 0.42‰). Regardless of whether plants were field-grown, pot-cultured, fixing N2 or utilising mineral N, woody stems were depleted in 15N relative to all other plant parts. The similar orders of ranking of δ15N for plant components of the nitrate-treated and fully symbiotic plants, and a general increase in δ15N as plants were exposed to increasing concentrations of nitrate, indicated that N isotope fractionation can be accounted for, and thus not undermine 15N natural abundance as means of measuring N2 fixation inputs in tagasaste trees. In pot culture the percentage of plant N derived from the atmosphere (%Ndfa) by symbiotic N2 fixation fell from 85 to 37% when the nitrate supply was increased from 1 to 10 mM, with evidence of nitrate N being preferentially allocated to roots. δ15N natural abundance assessments of N2 fixation of 4-year-old trees of field-grown tagasaste in alley (550 trees ha-1) or plantation (2330 trees ha-1) spacing were undertaken at a study site at Moora, Western Australia, over a 2-year period of shoot regrowth (coppicing). Cumulative N yields and %Ndfa were similar for trees of alley and plantation spacing, with much less coppice N accumulation in the first compared to the second year after cutting. Scaling values from a tree to plot area basis, and using a mean %Ndfa value of 83% for all trees at the site, inputs of fixed N into current biomass plus fallen litter over the 2 years of coppicing were calculated to be 83 kg N ha-1 year-1 for the alley and 390 kg N ha-1 year-1 for the plantation spacing. Although the plantation tagasaste fixed 587 kg N ha-1 in the second year, close to the maximum value reported in the literature for any N2-fixing system, this should not be seen as typical where the trees are used for animal production, since grazing and cutting management will substantially reduce productivity and N2 fixation input.

Beyond threat- and asset-based approaches to natural resource management in Australia

Natural resource management (NRM) in Australia began as a series of campaigns against specific threats to agricultural and pastoral production, with war progressively declared on soil erosion, introduced pests and dryland salinity. Critiques of NRM programs in the 1990s coincided with a shift towards an asset-based approach. This approach emphasises the need for public investment to be focused on those parts of the landscape of high value, rather than defending large areas against broad-scale threats. The asset-based approach is more strategic, but runs the risk of sacrificing effectiveness for efficiency by overlooking the large-scale biophysical and social processes that underpin the viability of discrete assets. Further, the asset-based approach fails to sufficiently acknowledge the importance of engaging and building the human, social and cultural capital required to underpin longterm environmental management. A condition-based approach to NRM is proposed that builds on the best of the threat-based and asset-based approaches by setting targets based on environmental processes rather than perceptions of ideal states; borrowing systematic approaches to assessing value and condition from conservation planning; and investing in the social, economic, human and cultural capital required to support lasting change.

What can agriculture learn from natural ecosystems

In the preceding papers, the authors evaluate the usefulness of the proposition that mimicking characteristics of natural ecosystems, particularly patterns of resource capture and distribution, can lead to improved sustainability of agricultural systems. They approach this question from a diverse array of disciplines over a broad range of geographical settings and ecosystems and produce an equally broad range of views and conclusions. The aim of this paper is to draw out the major themes that have emerged concerning the usefulness of the mimic concept in generating radical solutions to the problem of agriculture. First, a brief summary of their scope and conclusions.