The slow reaction of phosphate with aggregated particles of ferrihydrite, after initial rapid phosphate sorption, was investigated by measuring the changes, with time and temperature, in the amount of phosphate sorbed, and the extractability of the sorbed phosphate. The ferrihydrite was, subsequently, recovered and examined by infra-red spectrometry (IR) and electron probe micro-analysis.Phosphate continued to react with ferrihydrite for at least 90d at 2 5 T , but was completely recovered by extraction with 0.1 M NaOH. The IR spectra of sorbed phosphate was insensitive to the temperature and duration of the reaction. Electron probe microanalysis of the aggregates showed that phosphate migrated to surface sorption sites within the aggregated particles of ferrihydrite.There was no evidence for the formation of surface coatings of ferric phosphate, for changes in the type of bonding, or for penetration of phosphate into the crystal lattice. The slow reaction was attributed to the migration of phosphate to surface sorption sites of decreasing accessibility within aggregates.

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Many studies have been conducted on ecosystem services and double counting is a frequent problem that causes uncertainty and poor reliability of estimating the value of ecosystem services. By referring to previous studies of ecosystem service valuation, our research has identified the basic causes of double counting. These include ambiguous definitions and inconsistent classifications of ecosystem services, poor understanding of ecosystem complexity, inadequate recognition of exclusiveness and complementarities of individual ecosystem services, spatio-temporal scale dependence of ecosystem services, and overlap and lack of cross-referencing between ecosystem service valuation methods. Measures for reducing double counting in ecosystem service valuation are proposed as follow: (1) identifying the spatiotemporal scales of ecosystem services; (2) valuing the final benefits obtained from ecosystem services; (3) establishing consistent classification systems for ecosystem services; and (4) selecting valuation methods appropriate for the study context.

In a laboratory experiment, samples of 18 soils, which are known to be flooded in the field, were flooded for up to 32 days. Both untreated and phosphate-treated (50 mg P kg-1) soils were studied. It was attempted to identify which chemical properties measured on the dry untreated soils, and the changes in pH, Eh and extractable Fe and Mn over the flooding periods, controlled the changes in sodium acetate buffer (pH 3.0) extractable phosphorus during flooding. It was shown that the reduction of iron(III) oxides was the dominant source of the P released during flooding. However, the amount of P released was strongly inhibited by re-sorption. Direct measurement of the amount of iron(III) reduced during flooding and measurement of phosphate sorption were required to predict the amount of P released during flooding. Organic matter contributed toward the P released during flooding. Its contribution appeared to be by mineralization, rather than by accelerating FeIII reduction. The reduction of MnIII and MnIII was a minor source of P in the untreated soils. Changes in soil pH during flooding were responsible for desorption of freshly applied P, but did not appear to affect P release in the untreated soils. The Vertisols and some of the Alfisols showed very little, or no release of P during flooding.

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Decreases in nutrient availability after loss of soil-water saturation are significant constraints to productivity in lowland rainfed rice soils. The effectiveness of soil amendments like lime and straw in ameliorating these constraints are poorly understood. This pot experiment was conducted in Cambodia to investigate changes in soil chemical properties and nutrient uptake by rice after applying lime or straw to continuously flooded or intermittently flooded soil. In continuously flooded soils, exchangeable Al decreased to below 0.2 cmolc/kg. Liming (pH 6.5-6.8) the continuously flooded soil decreased the levels of acetate extractable Fe and P, plant P uptake and shoot dry matter, but had no effect on either Bray-1 or Olsen extractable P values. By contrast, the addition of straw (3.5 g dry straw/kg soil) increased Bray-1, Olsen, and acetate extractable P, plant P uptake, shoot P, and shoot dry matter. The non-amended soils became strongly acidic after loss of soil water saturation: extractable Al increased to 1.0 cmol c /kg, a potentially harmful level for rice. By contrast, extractable P decreased markedly under loss of soil water saturation as did plant P uptake, shoot P, and shoot dry matter. With loss of soil water saturation, liming substantially depressed the levels of Al but it did not increase plant P uptake, shoot P, and shoot dry matter. Straw addition not only decreased extractable Al levels to well below 0.6 cmol c /kg under loss of soil water saturation, but it also increased extractability of soil P, plant P uptake, shoot P, and shoot dry matter. Thus, in rainfed environments, the incorporation of straw may be more effective than liming to pH 6.8 for minimising the negative effects of temporary loss of soil-water saturation on P availability, P uptake, and growth of rice.

The environment and the natural resource base have been severely degraded in Alxa League, western Inner Mongolia, China, over the past half-century. This study reports surveys that reveal farmers' perceptions of environmental degradation and their adoption of improved management practices in this poor and remote desert region. Surveys were made in villages that had been engaged in a large environmental rehabilitation and management project [Alxa League environmental rehabilitation and management project (ALERMP)] and those that had not. The survey results showed that farmers perceived environmental degradation in terms of increased frequency and severity of sandstorms, movement of sand dunes, deterioration of pasture quality and declines in groundwater depth and quality. Farmers had low adoption rates for improved management practices, ranging from zero to a maximum of 28Á5 per cent for the most adopted practice. A Tobit model analysis showed that the education level of farmers, the availability of extension services and whether farmers had participated in ALERMP were highly significantly correlated with the farmers' perception of degradation. The farmers' adoption of improved management practices was found to be significantly correlated only with whether they had participated in ALERMP. This shows that specific extension activities of the type possible in large and well-funded projects are required if farmers are to recognise degradation and adopt improved management practices. The promotion of farmer education and strengthening of extension services are recommended as the best policy strategies for improving environmental management in this region.