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In a field study, soils of four conventional free-range and organic broiler runs were analyzed for N and P concentrations in the years 2000 and 2001. Zones of different use intensity by broilers were identified on the free runs and mean zonal nutrient contents were compared with each other. Intensity of use by birds and spatial distribution of soil nutrient concentrations were found to be related to each other. Fecal N input by broilers resulted in accumulation of soil mineral nitrogen (N(min)) contents down to a 90-cm sampling depth. In highly frequented "hot spots," plant requirement as defined by the German "N-Basis-Sollwert" (110 kg/ha N(min)) for grassland was exceeded in all four cases. This implies an increased environmental risk of ammonia volatilization and nitrate leaching. Fecal P input by broilers resulted in accumulation of plant-available and thus mobile soil P (phosphorus extracted with calcium-acetate-lactate [P(CAL)] and phosphorus extracted with water [P(w)]) in the most intensely used zones. In these areas, soil P contents exceeded 90 mg/kg P(CAL) (upper limit of soil test P defined in Germany for optimum plant yield) by as much as 217 mg/kg, which indicates an enhanced risk of P loss from the soil via runoff or leaching. The conclusion might be drawn that, with regard to nutrient loss from free-run soils, intensive indoor production in a closed system may be more environmentally neutral than conventional free-range or organic production. However, to put this into perspective, the scope of the environmental risk connected with spatially limited point accumulation of nutrients should be considered. Furthermore, an environmental evaluation must also account for the fate and environmental effects of the broiler litter produced inside the broiler house.

A risk ranking model was developed to provide a systematic evaluation of the range and quantity of 28 elemental contaminants applied to land in New Zealand and applied to mineral P fertilisers. The methodology is transparent, flexible and robust and allows contamination issues to be ranked according to their real or potential impact. The quantitative ranking model is based on the relative importance of each element in relation to accumulation in soil, transfer to water or uptake by plants, toxicity to soil organisms, plants and people, and the contribution of any radioactive isotopes. The highest risk score for potential environmental significance of P fertiliser borne trace element contaminants was found for uranium, followed (in decreasing order) by cadmium, mercury, boron, fluoride, selenium, arsenic, silver and rare earth elements. The lowest score (rank 28) was attributed to strontium.