School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemSoil physical and chemical properties under Casuarina cunninghamiana Miq. (river sheoak) shade trees in northern Victoria( 1994)Casuarina cunninghamiana Miq. (river sheoak) is an Australian native tree with a natural distribution throughout eastern Australia. It is one of the three Australian casuarinas being widely grown in many countries as an exotic multipurpose tree. This thesis reports on a study of soil physical and chemical properties under C. cunninghamiana shade trees in northern Victoria. The study aimed to assess whether the presence of the trees had any effect on soil properties (bulk density, organic matter and chemical properties) by comparing soil under the canopy with soil under the adjacent open pasture. The study was conducted at the Department of Agriculture Rutherglen research station which has a mean annual rainfall of 590 mm and moderately to strongly acid Rutherglen loam soil. The study involves two main treatments: under the tree canopy and under open pasture. The treatments were replicated in each quarter of the sample plot containing nine sample trees. Soil samples were collected only once for soil bulk density, organic matter and chemical properties. The results showed that the presence of C. cunninghamiana shade trees did not improve soil bulk density, organic matter content and chemical properties of the surface soil (0-15 cm depth) under the canopy. Soil bulk density and organic matter content under the canopy were not significantly different (1.12 g cm-3 and 4.44% respectively) compared with open pasture (1.19 g cm-3 and 4.07% respectively). Soil pH and total nitrogen were significantly less (pH 4.20 and 0.08% respectively) under the canopy compared with under the open pasture (pH 4.48 and 0.01% respectively). Available phosphorus and exchangeable potassium levels under the canopy (2.09 ?g/g and 4.22 cmol kg-1 respectively) were not significantly different compared with open pasture (0.773 .Lglg and 4.88 cmol kg- I respectively). The lack of improvement in soil bulk density and nutrients under the canopy is probably due to the inherent acidity of the soil. This may make conditions unsuitable for litter breakdown and nitrogen fixation. Low rainfall and seasonal flooding of the study site may also be influencing these soil properties. The results demonstrate that the potential of C. cunninghamiana to improve soil properties may be variable depending on the site conditions.
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ItemShelterbelt effects on microclimate and cereal crops( 1993)The 1980's saw a rapidly expanding community interest in re-establishing trees and other natural vegetation in the largely cleared rural environments in Australia. This culminated in Prime Minister Bob Hawkes' pledge to establish one billion trees in Australia by the year 2000. Tree growing became a major focus for many of the hundreds of Landcare groups which established in this period. The Landcare movement, which has at its foundation the objective of achieving sustainable land use, grew rapidly. Landcare encompasses a broad range of land management issues including soil erosion and salinity, pest plants and animals, declining soil fertility and nature conservation. Tree planting became one of the most popular landcare activities as trees are directly or indirectly related to the majority of landcare issues. Involvement in tree planting can lead an individual into a myriad of more complex aspects of land management. Indeed, many of today's Landcare groups started as Farm Tree groups. The motivation for people to re-establish trees varies greatly and reflects the heterogeneity of the population (such as their needs, their level of understanding and their values) and the multiple benefits that trees can provide. Some are motivated by what they see as the tragedy of the insidious loss, due to tree decline, of quintessential Australian rural landscapes which have resulted from the attractive combination of remnant eucalypts, acacias and other trees and shrubs with agricultural pursuits. Others recognise the importance of rural vegetation in maintaining the biodiversity of Australia's flora and fauna. There is increasing evidence that deep rooted perennial vegetation is important for sustainable agricultural production from many agro-ecosystems. Tree-establishment, in addition to the adoption of other conservation farming practices, is prominent in many strategies to control land degradation. For example, salinity management plans in Victoria are proposing the establishment of trees at low and medium densities over tens of thousands of hectares of land with high ground water recharge to control dryland salinity (Goulburn Broken Salinity Pilot Program Advisory Council 1989). Well planned, integrated revegetation programs may indeed provide combinations of these and other benefits (Burke and Voul 1988). Revegetation projects are generally costly with many long term benefits which are often difficult to measure in monetary terms. In recognition of the public benefit flowing from rural tree growing projects, state and federal governments have provided modest financial incentives such as those under the Tree Victoria Program, and the One Billion Trees Program. These programs at their current levels however only fund a small percentage of the tree growing component of the strategy needed to seriously address some of the land degradation problems present. Most farms in south-eastern Australia are family-owned small businesses. Regardless of the motivation for undertaking tree growing projects, given the modest level of financial incentives and subsidies available, these must largely be funded from the income generated from the farm. There is increasing recognition that "landcare should be able to pay for itself'. For this reason, tree growing projects are particularly compelling which have, at least as one of their benefits, enhanced short-term farm productivity. Shelterbelts are generally rows of trees and shrubs established to ameliorate the effects of the wind. Increased farm productivity from the provision of shelter is widely cited as one of the major benefits of trees on farms in the media and popular literature. This study aims to investigate some of the effects that shelterbelts can have on cereal crop production in south-eastern Australia and thereby help determine the feasibility of some tree growing projects to be at least partially "self funding".