Paul C. Smithson

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The effect of organic and inorganic sources of phosphorus (P) on soil P fractions and P adsorption was studied in a field without plant growth on a Kandiudalf in western Kenya. A high-quality organic source, Tithonia diversifolia (Hemsley) A. Gray leaves, and a low-quality source, maize (Zea mays L.) stover, were applied alone or in combination with triple(More)
Many soils of southern Africa are severely N deficient, but inorganic fertilizers are unaffordable for most subsistence farmers. Rotations and intercrops of legumes with crops may alleviate N deficiency through biological N2 fixation and redistribution of subsoil N to the surface. We monitored soil inorganic N dynamics for two seasons in a gliricidia(More)
Nitrogen deficiency is widespread in southern Africa, but inorganic fertilizers are often unaffordable for smallholder farmers. Short-duration leguminous fallows are one possible means of soil fertility restoration. We monitored preseason topsoil (0 to 20 cm) ammonium and nitrate, fallow biomass production and grain yields for three years in a relay(More)
Three experiments are reported using the 'negative priming' paradigm to investigate cognitive differences in normal schizotypal subjects. Lists of Stroop colour words were presented at different display times in a number of priming and non-priming conditions, in one of which the ignored colour name predicted the colour of the next target item. The increased(More)
Simple methods for the measurement of nitrogen (N) availability are needed to assess the effect of low-input, organically based land management systems on the N supply of tropical soils. Our objectives were to determine the effect of contrasting land-use systems (LUS) on soil N availability and to identify measures of N availability that correlated with(More)
One-season fallows with legumes such as Crotalaria grahamiana Wight & Arn. and phosphorus (P) fertilization have been suggested to improve crop yields in sub-Saharan Africa. Assessing the sustainability of these measures requires a sound understanding of soil processes, especially transformations of P which is often the main limiting nutrient. We compared(More)
BACKGROUND A recent national survey in Tanzania reported that mortality in children younger than 5 years dropped by 24% over the 5 years between 2000 and 2004. We aimed to investigate yearly changes to identify what might have contributed to this reduction and to investigate the prospects for meeting the Millennium Development Goal for child survival (MDG(More)
The Sentinel Panel of Districts (SPD) consists of 23 districts selected to provide nationally representative data on demographic and health indicators in Tanzania. The SPD has two arms: SAVVY and FBIS. SAVVY (SAmple Vital registration with Verbal autopsY) is a demographic surveillance system that provides nationally representative estimates of mortalities(More)
Low soil fertility and pest pressure are two causes of the decline in banana (Musa AAA) production in central Uganda. Foliar analysis by the Diagnosis and Recommendation Integrated System (DRIS) pinpoints K and Mg as the most limiting nutrients. This study tested the effects of K and Mg additions on plant performance and weevil damage for 2.75 yr, at(More)
Tropical upland regions have both the world's highest population growth rates and a preponderance of soils less suitable for agriculture. Nitrogen deficiency is almost universal, while acid infertility and the related problem of P deficiency affect more than 40% of tropical soils. Nutrient depletion, as opposed to inherent infertility, affects large areas(More)