Tesis sobre el tema "Soils South Australia Phosphorus content"

The effects of 40 years of integrated field management on soil organic phosphorus and its forms was evaluated on a highly organic B.C. soil supporting high value vegetable crops. This project was undertaken to study the effects of cultivation on the soil content of organic phosphorus, as a predictor of overall degradation effects of the soil organic matter. Organic carbon, total nitrogen, soil pH and total and inorganic phosphorus were also evaluated, due to the strong relationship of organic P and these other soil chemical properties. The forms of organic P that were evaluated were the phytic acid, inositol polyphosphates and the soil biomass phosphorus. The biomass P was used as a predictor of the effects of cultivation on nucleic acids since the soil methods for nucleic acid determination were very complicated and time consuming. In this study, attempts were made to find a shorter soil analytical method for phytic acid, the largest pool of soil organic phosphorus. Due to chemical structure of phytic acid and its higher negative charge, it was believed that this molecule is highly stable in the soil environment due to its adsorption and/or precipitation on mineral surfaces through cation bridging at low soil pH particularly by Iron and Aluminium salts and hydrous oxides which bear pH-dependent positive charge or through P chermsorption, and hence its turnover rate due to cultivation could be used to predict the behaviour of the rest of soil organic P and hence the organic matter in the same soil environment. It was however realized that P analysis in soils was very cumbersome and there was a need for a shorter and precise quantitative analytical technique for this element in the soil. ³¹P NMR spectroscopy was thought to be the solution and its possibilities were evaluated in this project. Therefore the objectives of the study were; a) To determine the effects of 40 yrs of integrated field managements on organic P and its forms. b) To develop a shorter method for soil phytic acid analysis. c) To attempt the use of ³¹P NMR for qualitative and quantitative determinations of soil phytic acid. It was found that soil pH was significantly increased from pH 4.46 to 5.28 due to liming and the increased degree of organic matter decomposition. Total nitrogen was significantly decreased by 24% with larger significant decrease of 42% in the shallow organic cultivated soil site, and only 8% significant decrease in the highly organic, deeper cultivated soil site. The decline in soil nitrogen was attributed to mineralization of organic nitrogen followed by crop uptake and leaching losses. Organic carbon was significantly decreased by 22%. There was a 40% decrease in this organic carbon in the cultivated shallow organic cultivated soil site, but there was no significant effect of cultivation on organic carbon (hence the organic matter) in the highly organic deeper cultivated soil site. There was no significant effect of cultivation on the C/N ratio. However, the highly organic deeper soil site had significantly wider C/N ratio than the shallow organic cultivated soil site. This observation was attributed to the degree of decomposition of soil organic matter in the two sites. There was a significant 20% decrease in P total in the highly organic deeper cultivated soil site. There was no significant effect of cultivation on P total in the shallow organic cultivated soil site, however there were indications of 33% accumulation in total P in this soil site as determined by ignition method. There was 179% accumulation of inorganic P in the shallow organic cultivated soil site, but there was no significant effect of cultivation on inorganic P in the deeper highly organic soil cultivated site. Organic phosphorus was significantly decreased by 4 0 yrs of integrated field management by 31% on a soil basis and 25% on an ash free basis. The percentage of organic P in total soil P was significantly decreased from 66% to 45%. The C/orgnic P was increased significantly from 394 to 439. This reflected greater effects of cultivation on turnover of organic P than organic carbon in the organic matter and that P has a geological cycle which organic carbon does not have. The results further showed that before the field was placed under cultivation, the shallow organic soil site had a significantly larger amount (73%) of organic P in the soil total P. However cultivation had a significant decrease in organic P by 23% in the deeper highly organic soil cultivated site and 40% in the shallow organic cultivated soil site. The study soil sites started with same the amounts of biomass P (the most labile form of organic P) , however it was found that 40 years of cultivation had no significant effects on this biomass in the highly organic soil site, but there was a significant decrease in biomass P by 86% in the shallow organic cultivated soil site. Soil phytic acid, the largest pool of organic P was significantly decreased by 28% due to 40 yrs of integrated field management. Its turnover rate was found to be equal to the turnover rate of the other forms of organic P. It was however noted that the study soil sites started with same amount of phytic acid before the field was placed under cultivation. Phytic acid was significantly decreased due to cultivation in the shallow organic cultivated soil site by 35%, but there was no significant effect of cultivation on phytic acid in the highly organic cultivated soil site. Inositol polyphosphates were not significantly affected by 40 years of integrated management. This form of organic P was found to have the same turnover rate as the rest of soil organic P. The slower turnover rate of inositol polyphosphates assayed by the barium acetate precipitation method of McKercher and Anderson was attributed to methodology. In the present study, there were no significant differences in results obtained by various methods for total P determination except in a few cases where the ignition method was thought to have over-estimated total P. A tentative new method for phytic acid analysis was developed in the on-going research. This method was proposed to be applicable in all soils. However, further research is required to confirm the purity of the phytic acid determined by this method. ³¹P NMR spectroscopy showed potential possibility for qualitative and quantitative analysis of soil phytic acid. However, it was emphasized that care should be exercised particularly during sample concentration step. It was concluded that organic P and its forms, organic carbon, total nitrogen, soil pH and phytic acid were significantly decreased by 40 years of integrated field management more in the shallow organic cultivated soil sites than in the deeper highly organic soil sites. This observation was found very interesting and was in contrast to existing soil literature and further research was proposed in this direction to investigate this phenomenon.<br>Land and Food Systems, Faculty of<br>Graduate

Bibliography: leaves 164-193. This study aims to quantify the belowground input of organic carbon by barrel medic using techniques that account for root death and decomposition as well as root secretion and exudation. It also investigates the effect of defoliation on carbon allocation within the plant so as to determine the potential for optimising carbon input to the soil through grazing management.

Bibliography: leaves 131-153. This thesis investigates the mechanisms of manganese (Mn) efficiency (genetic tolerance to Mn-deficient soils) in barley (Hordeum vulgare L.) at both physiological and molecular levels.

"September 2001"<br>Bibliography: leaves 144-159.<br>xix, 159 leaves : ill. ; 30 cm.<br>Title page, contents and abstract only. The complete thesis in print form is available from the University Library.<br>The two main aims of this study were: 1) to determine if the presence of Calcium carbonate in soil was the reason behind soils from Yorke Peninsula having relatively high OC (organic carbon) contents, given local farming practices, and 2) to determine the effect that the composition of the soils' OC has on the mineralisation rates.<br>Thesis (Ph.D.)--University of Adelaide, Dept. of Agronomy and Farming Systems, 2002

Copy of author's previously published work inserted.<br>Bibliography: leaves 147-189.<br>xxi, 189 leaves : ill. (some col.) ; 30 cm.<br>Title page, contents and abstract only. The complete thesis in print form is available from the University Library.<br>This project examines the uptake of mineral N from the subsoil after anthesis and its effect on grain protein concentration (GPC) of wheat. The overall objective is to examine the importance of subsoil mineral N and to investigate the ability of wheat to take up N from the subsoil late in the season under different conditions of N supply and soil water availability. Greenhouse experiments investigate the importance of subsoil mineral N availability on GPC of wheat and the factors that contribute to the effective utilisation of N. The recovery of N from subsoil, the effect of split N application on GPC and short term N uptake by the wheat at different rooting densities are also studied.<br>Thesis (Ph.D.)--University of Adelaide, Dept. of Soil Science, 1997

In the semi - arid Mediterranean - type environments of southern Australia, soil and water resources largely determine crop productivity and ultimately the sustainability of farming systems within the region. The development of sustainable farming systems is a constantly evolving process, of which cropping sequences ( rotations ) are an essential component. This thesis focused on two important soil resources, soil water and nitrogen, and studied the effects of different crop sequences on the dynamic of these resources within current farming systems practiced on the upper Eyre Peninsula of South Australia. The hypothesis tested was that : continuous cropping may alter N dynamics but will not necessarily alter water use efficiency in semi - arid Mediterranean - type environments. Continuous cropping altered N - dynamics ; increases in inorganic N were dependent on the inclusion of a legume in the cropping sequence. Associated with the increase in inorganic N supply was a decrease in WUE by the subsequent wheat crop. Overall, estimates of water use efficiency, a common index of the sustainability of farming systems, in this study concur with reported values for the semi - arid Murray - Mallee region of southern Australia and other semi - arid environments worldwide. Soil water balance and determination of WUE for a series of crop sequences in this thesis suggests that the adoption of continuous cropping may increase WUE and confer a yield benefit compared to crop sequences including a legume component in this environment. No differences in total water use ( ET ) at anthesis or maturity were measured for wheat regardless of the previous crop. Soil evaporation ( E [subscript s] ) was significantly affected by crop canopy development, measured as LAI from tillering until anthesis in 2002, however total seasonal E [subscript s] did not differ between crop sequences. Indeed in environments with infrequent rainfall, such as the upper Eyre Peninsula, soil evaporation may be water - limited rather than energy limited and the potential benefits from greater LAI and reduced E [subscript s] are less. Greater shoot dry matter production and LAI due to an enhanced inorganic N supply for wheat after legumes, and to a lesser degree wheat after canola, relative to continuous cereal crop sequences resulted in increases in WUE calculated at anthesis, as reported by others. Nonetheless the increase in WUE was not sustained due to limitations on available soil water capacity caused by soil physical and chemical constraints. Access to more soil water at depth ( > 0.8m ) through additional root growth was unavailable due to soil chemical limitations. More importantly, the amount of plant available water within the ' effective rooting depth ' ( 0 - 0.8m ) was significantly reduced when soil physical factors were accounted for using the integral water capacity ( IWC ) concept. The difference between the magnitude of the plant available water capacity and the integral water capacity was approximately 90mm within the ' effective rooting depth ' when measured at field capacity, suggesting that the ability of the soil to store water and buffer against periodic water deficit was severely limited. The IWC concept offers a method of evaluating the physical quality of soils and the limitations that these physical properties, viz. aeration, soil strength and hydraulic conductivity, impose on the water supply capacity of the soil. The inability of the soil to maintain a constant supply of water to satisfy maximal transpiration efficiency combined with large amounts of N resulted in ' haying off ', and reduced grain yields. A strong negative linear relationship was established between WUE of grain production by wheat and increasing soil NO [subscript 3] - N at sowing in 2000 and 2002, which conflicts with results from experiments in semi - arid Mediterranean climates in other regions of the world where applications of N increased water use efficiency of grain. Estimates of proportional dependence on N [subscript 2] fixation ( % N [subscript dfa] ) for annual medics and vetch from this study ( 43 - 80 % ) are comparable to others for environments in southern Australia ( < 450mm average annual rainfall ). Such estimates of fixation are considered low ( < 65 % ) to adequate ( 65 - 80 % ). Nevertheless, the amount of plant available N present at sowing for subsequent wheat crops, and the occurrence of ' haying off ', suggests that WUE is not N - limited per se, as implied by some reports, but constrained by the capacity of a soil to balance the co - limiting factors of water and nitrogen.<br>Thesis (Ph.D.)--School of Earth and Environmental Sciences, 2005.

Bibliography: leaves 290-324. This thesis investigates two avenues suggested by Graham and Ascher (1993) for approaching the problems of subsoil infertility, with particular reference to zinc. Field experiments with wheat and barley were established at Minnipa, on Eyre Peninsula in South Australia to investigate the effects of applying nutrients (principally zinc, nitrogen and phosphorus) to the subsoil to a depth of 0.4 m with a modified deep ripper. A deep pot experiment was designed to measure the zinc efficiencies (in terms of dry matter production) of a range of species grown in siliceous sand. The effects of added zinc on root growth were compared. A pot experiment was also designed to measure the effects of zinc placement in the soil on the zinc concentrations and uptake in Excalibur, particularly with respect to concentrations in grain.