Fertilizer P-derived uranium continues to accumulate at Rothamsted long-term experiments.

The application of phosphorus (P) fertilizers inevitably contributes to the accumulation of trace elements, such as uranium (U), in agricultural soils. The fertilizer-derived U accumulation was first reported in Rothamsted Research in 1979. In the present study, we expand this early key research by evaluating the fertilizer-derived U accumulation in topsoil (0-23 cm) from 1876 to the 2010s. We found that total U accumulation rates ranged from 2.8 to 6.1 µg U kg-1 yr-1 at the Broadbalk and Park Grass, respectively, being similar to those observed 40 years ago. This highlights that U accumulation is still an ongoing process in Rothamsted. Fortunately, the proportion of fertilizer-derived U did not significantly increase in the ammonium acetate extractable ('proxy' of plant-available) fraction over 130 years. In addition, we compiled an overview of the global rate of mineral P fertilizer-derived U accumulation in agricultural systems using existing literature (36 experimental trials, from 11 countries). The resulting dataset predicts an estimated mean U accumulation of 0.85 µg U kg-1 soil for an annual application of 1 kg P ha-1 in the topsoil of agricultural systems (0.26 µg U kg-1 per kg P ha-1 for arable land and 1.34 µg U kg-1 per kg P ha-1 for grassland). The annual U accumulation per applied kg P ha-1 being 0.08 (Broadbalk) and 0.17 µg U (Park Grass) corresponds to around one-third and one-eighth of the worldwide mean U accumulation for their respective agricultural systems, suggesting 'relatively' low U contents of the applied P fertilizers. Our study underscores that fertilizer-derived U accumulation is a persistent problem on the global scale, even if at different rates, and therewith suggests an evaluation of current regulatory limits and acceptable U input levels from P fertilization.

Facts and fiction about sulfur metabolism in relation to plant-pathogen interactions.

Sulfur deficiency developed into a widespread nutrient disorder in the 1980s because of the drastic decrease of SO(2) emissions in western Europe after Clean Air Acts came into force. It was observed that not only the yield and quality of agricultural crops were negatively affected by sulfur deficiency but also their health status. Since the mid 1990s the physiological background of this latter phenomenon in the sulfur metabolism has been studied by different researchers. From 2001 until 2006, field trials with different varieties of oilseed rape were conducted in Germany, and also from 2001 until 2003 in Scotland, to investigate the underlying mechanisms of sulfur-induced resistance and to develop fertiliser strategies which increase the health status of crops and minimise the requirement for chemical fungicides. A comprehensive disease assessment was conducted and a range of different sulfur-containing metabolites and enzymes were analysed in relation to sulfur nutrition and fungal diseases. H2S emissions from field-grown crops under different sulfur nutritional status were studied for the first time and a positive relationship was observed. Besides S fertilisation, fungal infection increased H2S emissions, too. The studies deliver new insight into the complex of sulfur-induced resistance but many questions still remain open. This contribution will show different possible strategies to solve some of the open questions.

Nutrient balances as indicators for sustainability of broiler production systems.

1. Flock balances of nitrogen, phosphorus, zinc and copper (N, P, Zn, Cu) were calculated in order to evaluate environmental effects of three different broiler production systems (intensive indoor, free range and organic). 2. Nutrient gain in birds per unit nutrient intake (retention) in intensive indoor production was higher than in free range and organic production. 3. Nutrient surplus relative to nutrient retention was higher in organic production than in free range and intensive indoor production. 4. The main reasons for differences in nutrient efficiency between intensive indoor, free range and organic production were duration of growth period, strain of broilers and feeding strategy. 5. The calculation of whole farm indicators (livestock density, N and P excretions per hectare of farmland) demonstrates how defining system boundaries affects the outcome of an evaluation: organic farms had the smallest livestock densities and the lowest N and P excretions per hectare of farmland. 6. In the efforts to reach a more holistic evaluation of agricultural production systems, the definition of adequate system boundaries must be discussed. In addition to nutrient balances, further indicators of sustainability, such as human and ecological toxicity, should be considered.

Organochlorine compounds in a Brazilian watershed with sugarcane and intense sediment redistribution.

Until 1985 persistent organochlorine compounds such as aldrin [(1alpha,4alpha,4abeta,5alpha,8alpha,8abeta)-1,2,3,4,10,10-hexachloro-1,4,4a,5,8,8a-hexahydro-1,4:5,8-dimethanonaphthalene] and heptachlor (1,4,5,6,7,8,8-heptachloro-3a,4,7,7a-tetrahydro-4,7-methano-1H-indene) were recommended and used as insecticides on a large scale in sugarcane (Saccharum officinarum L.) cropping in Brazil. The environmental impact of these applications was not investigated in the past neither prior to nor after their restriction of use in Brazil. In a case study conducted during 1999, organochlorine insecticides were investigated in soils, colluviums, submerged sediments, and organisms in a watershed located in a traditional sugarcane-growing region in the southeastern region of Brazil. The results indicated that past applications of organochlorine insecticides (prior to 1985) do not represent an environmental threat at the present time. Most insecticides applied in the past were not detected or were present only in amounts that were below the detection limit. The organochlorine compounds lindane [(1alpha,2alpha,3beta, 4alpha,5alpha,6beta)-1,2,3,4,5,6-hexachlorocyclohexane] and heptachlor that remained on the market after 1985 for purposes other than for soil application were still detectable in significant amounts in soils, sediments, and soil organisms (heptachlor in form of the epoxide metabolites). This may suggest that these residues were originated from applications after 1985. These compounds showed a capacity for accumulation in sediments and soil organisms. The enrichment ratio from soils to sediments was 2 to 3 times and from soils to organisms up to 20 times.

Uptake and metabolism of sulphur dioxide by Arabidopsis thaliana.

Arabidopsis thaliana (L.) Heynh. was exposed to various concentrations of SO2 during almost the entire life cycle. No negative effects of SO2 on shoot biomass production were observed. There was a linear relation between the deposition of SO2 and the atmospheric SO2 concentration. Sulphur accumulated substantially in the shoots upon SO2 exposure. SO2 was either oxidized to sulphate or converted into extra organic sulphur compounds in a sulphate to organic sulphur ratio of 3:1, independently of the atmospheric SO2 concentration. Exposure to SO2 resulted in an increase in water soluble non-protein sulphydryl content and a slight increase in the amount of glucosinolates, but both of these play a minor role as sinks for the excess sulphur. The ratio of total nitrogen to total sulphur decreased upon SO2 , exposure as a result of the increased sulphate content. The organic nitrogen to organic sulphur ratio did not change upon SO2 exposure, indicating no changes in the composition of sulphur-containing compounds.