Phosphorus distribution and availability within soil water-stable aggregates as affected by long-term fertilisation

A field experiment lasting 37 years was conducted to evaluate the applications of different rates of pig manure and mineral fertilisers alone or in combination impacts on total phosphorus (P-total) and Olsen phosphorus (P-Olsen) contents and phosphorus activity coefficient (PAC, percentage of P-Olsen to P-total) within soil water-stable aggregates (WSA) in a Mollisol of Northeast China. The contents of P-total and P-Olsen associated with different size classes of WSA significantly (P < 0.05) increased with an increasing rate of applied P. The application of manure alone or combined with mineral fertilisers significantly increased PAC value associated with different size classes of WSA. There were positive correlations between P-total and P-Olsen contents with soil organic carbon (SOC) content within soil WSA. As SOC content increased 1 g/kg, P-total and P-Olsen contents increased 0.06-0.10 g/kg and 7.69-22.2 mg/kg, respectively, and the increase was larger in smaller size classes of WSA. The results suggested that a high manure rate combined with mineral fertilisers is more beneficial for increasing soil phosphorus content and availability. SOC is a vital factor controlling phosphorus content and availability within soil WSA.