School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemHand-held decision support tool for estimating nitrogen requirements for food production and environment protection( 2008)Concentration of nitrogen (N) in plants reflects the supply of N in the root medium, and crop biophysical variables increase as internal concentration of N in plants increases. This is useful in assessing how crop biophysical variables can be improved through proper fertiliser application rate. The ability to successfully determine N deficiencies in crops and soil is highly dependent on visual symptom examinations, plant analysis, and soil analysis. Using these methods, information on N deficiencies or excess in the soil will be made available to farmers by the end of the cropping season. Therefore correcting N deficiency or efficiency at this stage is a waste as crops are harvested or are in a condition where interference is of no value. Accordingly, there is a need for improved methods, and available technology could be applied. Chinese cabbages responded significantly (p<0.05) at urea rate of 100 kg ha-1 compared to rates lower or higher than 100 kg ha-1. Relatively, water stress are insignificant (p>0.05) in its response to chinese cabbage growth, however N and water stress together have a significant impact on growth. In addition, crops irrigated every 2 days have higher variables mean than crops irrigated every 5 days. This study found that N rate of 100 kg ha-1 with irrigation every 2 days performed better than other treatments measured. The N uptake pattern was very rapid between 200 and 400 degree days after transplanting and fertiliser application is recommended at this stage. Fertiliser rate should be minimised before and after this phase as crops N uptake is reduced. SAVIgreen VF had a positively good correlations with Leaf Area index (LAI) (r2 = 0.91, p<0.001), above ground biomass (r2 = 0.86, p<0.001) and N uptake (r2 = 0.75, p<0.001) in the first glasshouse experiment. Similarly, the second glasshouse experiment supported these findings where VF correlated positively to LAI (r2 = 0.84, p<0.001), above ground biomass ((r2 = 0.73, p<0.001) and N uptake (r2 = 0.69, p<0.001). VF correlated negatively with soil total mineral N in the first and second glasshouse experiment, r2 = 0.31, p<0.001 and r2 = 0.61, p<0.001 respectively. In addition above ground biomass (r2 = 0.62, p<0.001) and N uptake (r2 = 0.60, p<0.001) in the field also indicated better correlation with VF, however plant N was poorly correlated (r2 = 0.0, p>0.05). These correlations were greatly reduced when crops were exposed to N and water stress. VF was reduced at lower N rates (0 and 50 kg ha-1) and at higher N rates (200 and 400kg ha-1) with irrigation every 5 days. Optimum VF (0.2 – 0.4) is obtained at 100 kg ha-1. Consequently VF is a good predictor for LAI, above ground biomass and N uptake probably because canopy photosynthetic capacity increases with increasing N concentration only to an optimum level. As determined from this research, higher concentration of N in leaves was found when N rate of 400 kg ha-1was applied. The crops become N saturated and VF was greatly reduced, hence crops may have not optimally photosynthesised. Knowledge of N accumulation in the soil, leaching can be determined from levels of N accumulated in plant tissues. Therefore digital camera an invaluable remote sensing tool is cheaper and appropriate for estimating responses of VF to crops biophysical variables to determine N requirements and, hence, it may aid in predicting N losses to the environment. Modeling using Denitrification Decomposition (DNDC) model indicated that crop N uptake (90 kg ha-1) did not meet crop N demand (120 kg ha-1), even though soil N mineralisation from organic and inorganic pool of N (900 kg N ha-1 yr-1) and anthropogenic activities were very efficient. Much of N was lost through leaching (approximately 100 kg ha-1 yr-1), gas emissions (close to 400 kg ha-1 yr-1) and weeds (approximately 300 kg ha-1 yr-1). These N loses may contribute to environmental pollution. Therefore predicting crops biophysical and chemical variables using VF coupled with modeling improves knowledge on N dynamics in soil-plant-environment systems.
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ItemSalting in Victorian catchments: an investigation of soil salinity problems arising under non-irrigated condititons in Victoria( 1956)Salting, that is, the accumulation of excessive amounts of soluble salts in soils, is found in many parts of the world. In Victoria salting is associated with the presence of a permanently saline water table in irrigation districts, or with local accumulations of salt in catchment areas. The results of an investigation, carried out between April 1952, and December 1955, into this second problem, referred to here as catchment salting", are set out in this thesis. The introductory part of the thesis includes evidence regarding the incidence, and economic importance, of catchment salting in the state. The area affected is estimated as nearer 10,000 than 100,000 acres; it is mainly the better class land of valleys, and flats. Salting is extending, but at present its main importance lies in the severe erosion which it induces. In the second part of the thesis, the ecosystems, under which the accumulation of salt in the soils or a catchment can take place, are examined. The factors contributing to such an ecosystem are listed here, with summaries of the conclusions reached: i) Accessions of salt to the soil. In Victoria these salts are largely chlorides of oceanic origin, their presence in soils inland can best be accounted for by the cyclic salt theory. The evidence for this theory is reviewed, and reasons are put forward to account for variations in cyclic salt accessions at different sites. ii) A low precipitation/evaporation ratio. Such a ratio prevails in many parts of Victoria. iii) Vegetative cover with a high water usage. The catchments, in which salting now occurs, were formerly covered with Eucalypt forest, or woodland, making use of rainfall. iv) Soils having an impermeable horizon. at no great depth. Salting in Victoria is confined to catchments with soils of the solodic or solonetzic, type, characterised by a light textured A horizon overlying a heavy clay B horizon. In an undisturbed catchment of this type the hydrological equation can be expressed by: Precipitation = Evaporation + Transpiration. So that, with annual accessions of salt, some accumulation in soils of the catchment is to be expected. In these catchments, which are found chiefly in the 20” – 30” rainfall areas, drastic changes in the hydrological balance have followed settlement. All too frequently catchments have been overcleared, and overgrazed, and the resulting reduction in transpiration has produced a surplus of groundwater, with accelerated water movement downslope. The sub-surface flow over the clay horizon of solodic type soils carries down any soluble salts from the catchment; should this flow be impeded, and saline water brought to the surface, salt is concentrated by evaporation, and salting occurs. A knowledge of the factors responsible for salting will enable an assessment of salting liability in catchments to be made. Three types or salting, seepage, wetpan, and hardpan, found in Victoria, are described, with the types of vegetation which occur on each. The soils of seepage, and wetpan, areas are described as “saline”, and those of hardpan areas as "salinealkali", following the classification used by the U.S. Salinity Laboratories, Riverside, The compacted surface structure of hardpan soils, despite the high soluble salt content, is attributed to the compacting action of raindrops whilst the surface soil is temporarily washed : free of salt, and is in the “alkali” condition. Hardpan formation accounts for the characteristic shallow, and extensively dissected, pattern of erosion on salted land. In the third part of the thesis, the control of salting, and the reclamation of salted land, are dealt with. Correct catchment management, which ensures sufficient vegetative cover, is the surest control measure. Measures such as drainage, the establishment of trees and shrubs, and of improved pastures, are dealt with in a general way. Detailed results are given of trials with fertilizer, and soil improver, treatments; also of trials with some sixty species, and varieties, of grasses, and legumes, on salted land. In the final chapter the evidence, and conclusions, of previous chapters are reviewed, together with recommendations for the treatment of salted land; it therefore provides a more detailed summary, should that be required. Details of soil sampling, analytical methods, plot layout, statistical methods, and some lists, and photographs, of plants, are given in seven appendices.
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ItemSoil salting in the Lake Corangamite region of south western Victoria( 1983)In Australia soil salting occurs in irrigation and non-irrigation areas. The latter type, called non-irrigation or dryland soil salting, is a problem in drier Western and Central Victoria, but has until recently been thought to be insignificant in the Lake Corangamite Region. The method developed to identify saline areas in the Lake Corangamite Region appears suitable for use in other areas of Victoria. It relies on the identification of several salt-tolerant plants, and incorporates the use of aerial photographs, field observations and soil analyses. Mapping and quantification of soil salting in the Lake Corangamite Region showed that approximately 1% of the region’ s cleared land is affected by salting. Further, it seems that this percentage is increasing in some parts of the region. Possible control and reclamation methods do not appear to be available and research into this aspect is needed if the problem is to be reduced in the Lake Corangamite Region.