Extraction methods in soil phosphorus characterisation : Limitations and applications

The quantification and characterisation of soil phosphorus (P) is of agricultural and environmental importance and different extraction methods are widely used to asses the bioavailability of P and to characterize soil P reserves. However, the large variety of extractants, pre-treatments and sample preparation procedures complicate the comparison of published results. In order to improve our understanding of the behaviour and cycling of P in soil, it is crucial to know the scientific relevance of the methods used for various purposes. The knowledge of the factors affecting the analytical outcome is a prerequisite for justified interpretation of the results. The aim of this thesis was to study the effects of sample preparation procedures on soil P and to determine the dependence of the recovered P pool on the chemical nature of extractants. Sampling is a critical step in soil testing and sampling strategy is dependent on the land-use history and the purpose of sampling. This study revealed that pre-treatments changed soil properties and air-drying was found to affect soil P, particularly extractable organic P, by disrupting organic matter. This was evidenced by an increase in the water-extractable small-sized (<0.2 µm) P that, at least partly, took place at the expense of the large-sized (>0.2 µm) P. However, freezing induced only insignificant changes and thus, freezing can be taken to be a suitable method for storing soils from the boreal zone that naturally undergo periodic freezing. The results demonstrated that chemical nature of the extractant affects its sensitivity to detect changes in soil P solubility. Buffered extractants obscured the alterations in P solubility induced by pH changes; however, water extraction, though sensitive to physicochemical changes, can be used to reveal short term changes in soil P solubility. As for the organic P, the analysis was found to be sensitive to the sample preparation procedures: filtering may leave a large proportion of extractable organic P undetected, whereas the outcome of centrifugation was found to be affected by the ionic strength of the extractant. Widely used sequential fractionation procedures proved to be able to detect land-use -derived differences in the distribution of P among fractions of different solubilities. However, interpretation of the results from extraction experiments requires better understanding of the biogeochemical function of the recovered P fraction in the P cycle in differently managed soils under dissimilar climatic conditions.

Functional limitations and quality of life in schizophrenia and other psychotic disorders

There is substantial evidence of the decreased functional capacity, especially everyday functioning, of people with psychotic disorder in clinical settings, but little research about it in the general population. The aim of the present study was to provide information on the magnitude of functional capacity problems in persons with psychotic disorder compared with the general population. It estimated the prevalence and severity of limitations in vision, mobility, everyday functioning and quality of life of persons with psychotic disorder in the Finnish population and determined the factors affecting them. This study is based on the Health 2000 Survey, which is a nationally representative survey of 8028 Finns aged 30 and older. The psychotic diagnoses of the participants were assessed in the Psychoses of Finland survey, a substudy of Health 2000. The everyday functioning of people with schizophrenia is studied widely, but one important factor, mobility has been neglected. Persons with schizophrenia and other non-affective psychotic disorders, but not affective psychoses had a significantly increased risk of having both self-reported and test-based mobility limitations as well as weak handgrip strength. Schizophrenia was associated independently with mobility limitations even after controlling for lifestyle-related factors and chronic medical conditions. Another significant factor associated with problems in everyday functioning in participants with schizophrenia was reduced visual acuity. Their vision was examined significantly less often during the five years before the visual acuity measurement than the general population. In general, persons with schizophrenia and other non-affective psychotic disorder had significantly more limitations in everyday functioning, deficits in verbal fluency and in memory than the general population. More severe negative symptoms, depression, older age, verbal memory deficits, worse expressive speech and reduced distance vision were associated with limitations in everyday functioning. Of all the psychotic disorders, schizoaffective disorder was associated with the largest losses of quality of life, and bipolar I disorder with equal or smaller losses than schizophrenia. However, the subjective loss of qualify of life associated with psychotic disorders may be smaller than objective disability, which warrants attention. Depressive symptoms were the most important determinant of poor quality of life in all psychotic disorders. In conclusion, subjects with psychotic disorders need regular somatic health monitoring. Also, health care workers should evaluate the overall quality of life and depression of subjects with psychotic disorders in order to provide them with the basic necessities of life.