No abstract

This paper describes the accumulation of uranium in soils from superphosphate applied annually to arable and grassland soils. Rates of application of superphosphate were equivalent to about 33 kg P and 15 g U ha-' year-' in three experiments at Rothamsted and to about 37 kg P and 16g

A simple, sensitive method developed for the analysis of geostandards was used to measure the accumulation of Cd in soils from superphosphate applied annually to grassland and arable soils for many years. Rates of application were equivalent to 33 kg P and 5 g Cd ha-' yr-' for 95 yr in three experiments in England and to 37 kgP and 20gCdha-'yr-' for 30 yr in one experiment in New Zealand. Very little Cd accumulated in the surface horizons (0-22.5cm) of either of the arable soils from England; about one-quarter of the applied Cd was detected in the sub-soil (22.5-45.0 cm) of one experiment (Broadbalk) but none in the second (Barnfield). About one-half of the applied Cd was retained in the CL22.5 cm horizon of grassland soils from both England tnd New Zealand. The light ( <2.2 g C I T -~) organic-rich fraction of Park Grass soil from England contained about three times as much Cd as the heavier, mineral-rich fraction. This suggests that when Cd is incorporated into organic matter its mobility is decreased and soil pH then has smaller effects on its mobility. Uptake of Cd by grass-clover pasture in New Zealand averaged only 0.4 g Cd ha-' yr-' or 2% of the amount applied.

No abstract

Magnesium ammonium phosphate and iron-bearing magnesium ammonium phosphate (containing ferrous ammonium phosphate) were made in a pilot-plant, and pellets were prepared trom these products by bonding with 10% by weight of potassium sulphate. These rellets and a range of conventional water-soluble fertilisers were leached on soil columns for 3-6 months .at 23°c, 37°c, and 53°c. and the .leachates were analysed. Nitrogen, phosphorus, and magnesium leached slowly oyer long periods from the magnesium ammonium phosphate pellets, and aeration increased the leaching rate; only potassium was leached rapidly. Little iron was leached from iron-bearing pellets. In contrast, nitrogen, phosphorus, and potassium all leached rapidly from the soluble fertilisers. Magnesium ammonium phosphate therefore supplies essential nutrients to the soil over extended periods. The leaching rate from magnesium ammoni.um phosphat~was at a maximum in the temperature range 2rc-37°c, lind decreased considerably at 53 c. These results suggest that magnesium ammonium phosphate in soil is predominantly leached by an aerobic microbiological mechanism involving nitrification of ammonia. rather than by a solubility mechanism. '