No description available.

No description available.

The overall objective of the work presented in this thesis was to investigate roles of arbuscular mycorrhizal ( AM ) fungi in growth and phosphorus ( P ) nutrition of wheat ( Triticum aestivum L. ) in a highly calcareous soil from the Eyre Peninsula, South Australia. The soil used for this study is one of the main soil types used for wheat production in South Australia. It is severely P - deficient, but plant responses to conventional fertiliser application are poor. Although the total P and Colwell - extractable P contents of the soil are high, the resin - extractable P content is very low. Resin - extractable P is better able to predict P availability for plant growth than Colwell - extractable P. The soil is also strongly P - fixing. Moderate levels ( about 20 mg kg [superscript minus 1] ) of resin - extractable P for wheat could only be achieved by adding high rates ( up to 100 mg kg [superscript minus 1] ) of CaHPO4 in this soil. A bioassay with wheat showed that it can be highly colonised by AM fungi in the soil. AM fungi have been shown to improve P nutrition of plants, particularly in nutrient poor soils. They may thus be important for wheat grown in the soil with low amounts of plant - available P such as the one used. The first part of the work involved conventional pot experiments. Effects of AM fungi on wheat were compared between sterilised soil and non - sterile soil, sterilised soil inoculated with non - sterile soil or with Glomus intraradices or noninoculated, with different soil / sand mixes. Colonisation of wheat at 8 weeks was high, with about 75 % of root length colonised for indigenous fungi and 55 % for Glomus intraradices, regardless of the soil treatments. Growth and P uptake of wheat were significantly increased by both indigenous fungi and G. intraradices, irrespective of soil / sand mixes. Effects of indigenous fungi on plant growth were larger in sterilised and inoculated soil than in non - sterile soil. In sterilised soil, increases of plant growth by AM fungi were higher with G. intraradices than with indigenous fungi. Dilution of the soil by mixing with sand reduced plant growth and P uptake of both AM and non-mycorrhizal ( NM ) plants. In another experiment, responses of wheat to AM fungi and P supply were compared with those of clover. Plants were inoculated with four different AM fungi. Colonisation of wheat was lower than clover. Although suffering from P deficiency, NM wheat ( 6 weeks ) grew relatively well with no added P ( P0 ) and application of P at 100 mg kg [superscript minus 1] ( P100 ) increased the dry weight ( DW ). Shoot P concentrations increased with P application and there were positive effects of all AM fungi at P100. In contrast, NM clover ( 8 weeks ) grew very poorly at P0 and did not respond to P application. Clover responded positively to all AM fungi at both P levels, associated with increases in P uptake. The results showed that responses of wheat to AM inoculation and P supply were quite different from those of clover, and emphasized the different abilities of the two species to access P in the very high P - fixing soil used. Responses of two wheat cultivars ( Brookton and Krichauff ) to AM fungus ( G. intraradices ) were also evaluated with different P supplies at two developmental stages ( vegetative and maturity ). Colonisation by G. intraradices of both cultivars was well established at 6 weeks ( ~ 50 % in P0 plants ) and continued to increase up to maturity ( ~ 70 % ), but decreased greatly at both harvests as P supply was increased ( up to 150 mg P kg [superscript minus 1] ). Addition of P significantly increased plant growth, grain yield and P uptake irrespective of cultivar and harvest time, and the optimum soil P for grain yield was 100 mg kg [superscript minus 1]. In both cultivars, a growth depression in AM plants occurred at 6 weeks at all P levels, but this disappeared at 19 weeks with added P. At P0, AM plants produced lower grain yield per plant, but with higher P supply, AM plants produced higher grain yields than NM plants. There was a significant positive effect of AM on grain P concentration at P0, but not at other P levels. Brookton was somewhat more P efficient than Krichauff, and the latter responded more to AM fungi. The results showed that responses of wheat to AM fungi and P supply changed during development. Growth depression induced by AM fungi in low P soil was overcome by addition of moderate amounts of P, resulting in significant increases in grain yield in AM plants. Additional approaches were used to help determine the roles of AM fungi in wheat growth and nutrition. The effects of plant density were tested, as it was expected that increasing density might decrease the negative effects of AM fungi on wheat growth. Large growth depressions were induced by both G. intraradices and Gigaspora margarita in wheat grown at low density, although % colonisation by G. intraradices was higher than by Gi. margarita. With increasing plant density, the growth depressions were smaller, indicating that competition modulates growth responses. Although there may be effects due to competition for soil P, it is clear that with increasing plant biomass per unit soil volume, the AM fungal biomass did not increase in proportion ; in fact, hyphal length density decreased. Accordingly, costs of AM in terms of organic carbon loss per plant decreased with increasing plant density, thus mitigating the growth depression. The results add to the increasing body of evidence that mycorrhizal growth responses of plants grown singly may not apply at the population or community level as in crops. Two compartmented pot systems were used to examine whether the fungal hyphae deliver the P into the plants even in the absence of positive growth responses. An experiment in which plants were constricted in a mesh bag, but hyphae of AM fungi could explore a large soil volume was carried out. Results suggested that AM fungi helped the plants acquire P, although mesh bags did not remove AM growth depression. The experiments in which AM fungi were supplied with [superscript 32]P in a small soil compartment to which only hyphae had access showed that a considerable amount of P was delivered to wheat plants via AM fungi. The original aim was to calculate the percentage of total P entering the plants via the AM pathway. However, realistic values were not obtained probably because of difficulties of determining plant-available P and uneven distribution of hyphae in the soil. It is also possible that plants and AM fungi access different P pools. This study demonstrated the potential roles of AM fungi in growth and P nutrition of wheat grown in the highly calcareous soil from the Eyre Peninsula, South Australia. Further studies on the effects of the interactions between AM fungi and wheat in the field are needed to assess the contribution of AM fungi to plant nutrition. / Thesis (Ph.D.)--School of Earth and Environmental Sciences, 2005.

No description available.

The overall objective of the work presented in this thesis was to investigate roles of arbuscular mycorrhizal ( AM ) fungi in growth and phosphorus ( P ) nutrition of wheat ( Triticum aestivum L. ) in a highly calcareous soil from the Eyre Peninsula, South Australia. The soil used for this study is one of the main soil types used for wheat production in South Australia. It is severely P - deficient, but plant responses to conventional fertiliser application are poor. Although the total P and Colwell - extractable P contents of the soil are high, the resin - extractable P content is very low. Resin - extractable P is better able to predict P availability for plant growth than Colwell - extractable P. The soil is also strongly P - fixing. Moderate levels ( about 20 mg kg [superscript minus 1] ) of resin - extractable P for wheat could only be achieved by adding high rates ( up to 100 mg kg [superscript minus 1] ) of CaHPO4 in this soil. A bioassay with wheat showed that it can be highly colonised by AM fungi in the soil. AM fungi have been shown to improve P nutrition of plants, particularly in nutrient poor soils. They may thus be important for wheat grown in the soil with low amounts of plant - available P such as the one used. The first part of the work involved conventional pot experiments. Effects of AM fungi on wheat were compared between sterilised soil and non - sterile soil, sterilised soil inoculated with non - sterile soil or with Glomus intraradices or noninoculated, with different soil / sand mixes. Colonisation of wheat at 8 weeks was high, with about 75 % of root length colonised for indigenous fungi and 55 % for Glomus intraradices, regardless of the soil treatments. Growth and P uptake of wheat were significantly increased by both indigenous fungi and G. intraradices, irrespective of soil / sand mixes. Effects of indigenous fungi on plant growth were larger in sterilised and inoculated soil than in non - sterile soil. In sterilised soil, increases of plant growth by AM fungi were higher with G. intraradices than with indigenous fungi. Dilution of the soil by mixing with sand reduced plant growth and P uptake of both AM and non-mycorrhizal ( NM ) plants. In another experiment, responses of wheat to AM fungi and P supply were compared with those of clover. Plants were inoculated with four different AM fungi. Colonisation of wheat was lower than clover. Although suffering from P deficiency, NM wheat ( 6 weeks ) grew relatively well with no added P ( P0 ) and application of P at 100 mg kg [superscript minus 1] ( P100 ) increased the dry weight ( DW ). Shoot P concentrations increased with P application and there were positive effects of all AM fungi at P100. In contrast, NM clover ( 8 weeks ) grew very poorly at P0 and did not respond to P application. Clover responded positively to all AM fungi at both P levels, associated with increases in P uptake. The results showed that responses of wheat to AM inoculation and P supply were quite different from those of clover, and emphasized the different abilities of the two species to access P in the very high P - fixing soil used. Responses of two wheat cultivars ( Brookton and Krichauff ) to AM fungus ( G. intraradices ) were also evaluated with different P supplies at two developmental stages ( vegetative and maturity ). Colonisation by G. intraradices of both cultivars was well established at 6 weeks ( ~ 50 % in P0 plants ) and continued to increase up to maturity ( ~ 70 % ), but decreased greatly at both harvests as P supply was increased ( up to 150 mg P kg [superscript minus 1] ). Addition of P significantly increased plant growth, grain yield and P uptake irrespective of cultivar and harvest time, and the optimum soil P for grain yield was 100 mg kg [superscript minus 1]. In both cultivars, a growth depression in AM plants occurred at 6 weeks at all P levels, but this disappeared at 19 weeks with added P. At P0, AM plants produced lower grain yield per plant, but with higher P supply, AM plants produced higher grain yields than NM plants. There was a significant positive effect of AM on grain P concentration at P0, but not at other P levels. Brookton was somewhat more P efficient than Krichauff, and the latter responded more to AM fungi. The results showed that responses of wheat to AM fungi and P supply changed during development. Growth depression induced by AM fungi in low P soil was overcome by addition of moderate amounts of P, resulting in significant increases in grain yield in AM plants. Additional approaches were used to help determine the roles of AM fungi in wheat growth and nutrition. The effects of plant density were tested, as it was expected that increasing density might decrease the negative effects of AM fungi on wheat growth. Large growth depressions were induced by both G. intraradices and Gigaspora margarita in wheat grown at low density, although % colonisation by G. intraradices was higher than by Gi. margarita. With increasing plant density, the growth depressions were smaller, indicating that competition modulates growth responses. Although there may be effects due to competition for soil P, it is clear that with increasing plant biomass per unit soil volume, the AM fungal biomass did not increase in proportion ; in fact, hyphal length density decreased. Accordingly, costs of AM in terms of organic carbon loss per plant decreased with increasing plant density, thus mitigating the growth depression. The results add to the increasing body of evidence that mycorrhizal growth responses of plants grown singly may not apply at the population or community level as in crops. Two compartmented pot systems were used to examine whether the fungal hyphae deliver the P into the plants even in the absence of positive growth responses. An experiment in which plants were constricted in a mesh bag, but hyphae of AM fungi could explore a large soil volume was carried out. Results suggested that AM fungi helped the plants acquire P, although mesh bags did not remove AM growth depression. The experiments in which AM fungi were supplied with [superscript 32]P in a small soil compartment to which only hyphae had access showed that a considerable amount of P was delivered to wheat plants via AM fungi. The original aim was to calculate the percentage of total P entering the plants via the AM pathway. However, realistic values were not obtained probably because of difficulties of determining plant-available P and uneven distribution of hyphae in the soil. It is also possible that plants and AM fungi access different P pools. This study demonstrated the potential roles of AM fungi in growth and P nutrition of wheat grown in the highly calcareous soil from the Eyre Peninsula, South Australia. Further studies on the effects of the interactions between AM fungi and wheat in the field are needed to assess the contribution of AM fungi to plant nutrition. / Thesis (Ph.D.)--School of Earth and Environmental Sciences, 2005.

Thesis (M. Ag. Sc.)--University of Adelaide, Dept. of Soil Science, 1997. / Includes bibliographical references (leaves 159-177).

Thesis (Ph. D.)--University of Hawaii at Manoa, 2003. / Includes bibliographical references (leaves 94-99).

The adsorption of boron by Aiken clay loam and Vernal sandy loam was studied in the boron equilibrium concentration range of 0 to 40 ppm. Adsorption data were obtained at 11, 20 and 30°C. The data were analyzed by the application of the Langmuir adsorption isotherm. It was concluded that, in both Soils, the adsorption of boron occurred on three distinct sites or regions. The acid ferrigenous Aiken soil had a higher adsorption capacity for boron than the calcareous Vernal soil when compared on a unit mass basis. On the unit area basis, however, the Vernal soil adsorbed more boron than the Aiken soil. The isoteric heat of adsorption showed that boron reacted more energetically with the Vernal soil. The calculated 6H values were -7.6 K cal/M and -3.3 K cal/M for Vernal and Aiken soils, respectively. The capacity of both soils to adsorb phosphorus was higher than their capacity to adsorb boron. The presence of adsorbed phosphate did not greatly reduce the amount of boron adsorbed by either soil studied. In the Vernal soil, phosphate was three times more efficient in replacing boron than in the Aiken soil. Also, chloride was found to desorb more boron from the Aiken soil than phosphate. However, neither phosphate nor chloride was found to be effective in reducing to any great extent the adsorption of boron by the two soils studied.

Three greenhouse experiments were conducted with three phenotypes of alfalfa (Medicago sativa L.) obtained from a potassium (K)-deficient field and with their diallel crosses grown on low K soil. The first experiment was conduc ted to study the partitioning and broad-sense heritability of K a nd sodium (Na) between leaves and stems of the three phenotypes which were deficient in K and exhibited normal (N), marginal chlorotic (M), and white spot chlorotic (W) leaflets. The second experiment was conducted to study the partitioning of K and Na in leaves, stems, and roots as influenced by 32 alfalfa crosses obtained from diallel crossing of the mother plants of the three phenotypes. The objectives of the third experiment were to study the effects and interactions of nine alfalfa crosses and three soil K and Na levels on transpiration, biomass, and elemental composition of alfalfa components. The three phenotypes showed no variations in their leaf and stem K concentrations but varied in their ability to partition Na between the leaves and stems. Phenotype M accumulated more Na compared to N and W phenotypes. The Na trait was highly heritable in the broad sense. The K and Na concentrations varied among the diallel crosses. Crosses with M as the maternal parent had high Na concentrations in leaves while stems and roots accumulated lesser amounts. In contrast, the remaining crosses had higher Na concentrations in roots and lower and least amounts in stems and leaves, respectively. Significant genetic variation among alfalfa crosses from a single cultivar was observed for transpiration, biomass production, plant water-use efficiency, elemental concentrations, and K utilization efficiency. Leaf and stem biomass and K concentrations in alfalfa components increased in response to increasing soil K levels. The Na concentrations in stems and roots fell in response to increasing soil K levels and increased in response to Na application. The K utilization efficiency of alfalfa increased with increase in soil Na levels, indicating partial Na substitution for K. The differences among alfalfa phenotypes and crosses from a single cultivar in their Na accumulation and translocation were thought to be governed by plant genetics rather than the direct effect of K availability.

In soil science we shall always be confronted with reactions in soils that involve Ca. Early recognition of this led to experimentation in this area. Due to the fact that Ca deficiency is most common in acid soils, the majority of the experimentation has in the past been largely confined to acid soils and their soil-Ca-plant relationships. There has been relatively little research done with Ca and its availability problems associated with alkaline or sodic soils.