| Popis: |
The accumulation of phosphorus applied as superphosphate over a 25-year period to pastures growing on sand over clay soils was measured in three areas of different rainfall in the south-east of South Australia. Total soil phosphorus levels increased in the 0-10 cm, 10-30 cm and 30 cm-clay layers for all areas, but no accumulation occurred in the clay layer. For every 100 kg ha-1 of single superphosphate (9.6% phosphorus) applied, 2.0, 3.2 and 3.5 kg ha-1 of phosphorus accumulated in the 0-10 cm layer for the Hundreds of Coles, Willalooka and Senior respectively. The recoveries of applied phosphorus in the sand layer for the three areas were 42, 57 and 75% for Coles, Willalooka and Senior respectively. The annual accumulation rates of organic phosphorus in the top 30 cm of soil ranged from 2.4 to 3.5 kg ha-1. By using a 'balance sheet' approach, the annual maintenance phosphate requirements for the three areas were calculated. These ranged from 60 to 165 kg ha-1 of superphosphate, and were associated with differences in leaching losses, stocking rates and organic phosphorus accumulation. |
