Phosphorus fertilisation causes durable enhancement of phosphorus concentrations in forest soil

The duration of P fertiliser in acid forest soil was investigated in a Norway spruce (Picea abies Karst.) forest in southcentral Sweden. The fertilisation of the soil started in 1967, but no P has been applied since 1988. The N fertilisation is still continuing. Totally, 300 kg P per hectare, as superphosphate, and/or 1090 kg N per hectare, as ammonium nitrate, was applied. Concentrations of both 0.05M Na2SO4 + 0.02M NaF extractable P and 0.5M H2SO4 extractable P in the Of, Oh, E and top B horizons of fertilised soils were elevated compared to the control. The P fractions considered to be extracted are adsorbed and some Al-bound phosphate, in the case of Na2SO4 + NaF, and Ca phosphates, in the case of H2SO4. 3-4% of the added P was recovered as Na2SO4 + NaF extractable P, and 10-22% was recovered as H2SO4 extractable P in the soil profile down through the first 5 cm of the B horizon. Still continuing ammonium nitrate fertilisation has decreased the H2SO4 extractable P concentration in this soil. Cumulative P fertiliser application of 300 kg P per hectare has counteracted this decrease. (C) 2000 Elsevier Science B.V. All rights reserved.