SOME EFFECTS OF FERTILIZERS AND FARMYARD MANURE ON THE ORGANIC PHOSPHORUS IN SOILS

The amounts of P applied cumulatively to a neutral arable soil (pH 7.1–7. in 0.01M CaCl₂) at Rothamsted, as farmyard manure, alone or with superphosphate, which were converted to organic P in 100 years ranged from 18 to 44 μg P/g of soil (0–23 cm). Superphosphate alone (3300 kg P/ha) slightly lessened the total organic P in the soil. Neither farmyard manure nor super-phosphate significantly changed the amounts (38 to 42 μg P/g) of inositol penta- and hexaphosphate in these soils. In the surface layers (0–7.5 cm) of soils from permanent grassland at Rothamsted, superphosphate (3370kg P/ha) increased organic P by 134 μg P/g at pH 4.5 and 19 μg P/g at pH 6.5, about 6 and 1 per cent respectively of the P remaining from superphosphate applied cumulatively since 1858. In the sub-surface layers (7.5–23 cm) superphosphate increased organic P by 93 μg P/g at pH 4.5 and 62 μg P/g at pH 6.2, about 18 and 10 per cent respectively of the P remaining from superphosphate. The sum of inositol penta- and hexaphosphates accounted for 32 per cent at pH 4.5 and 21 per cent at pH 6.5 of the increases in organic P in the surface layers and 45 per cent and 26 per cent in the sub-surface layers at pH 4.5 and 6.5 respectively. Superphosphate (1260–2100 kg P/ha) applied intermittently or cumulatively increased total organic P by 19 to 52 μg P/g and inositol penta- and hexaphosphates by 13 to 17 μg P/g in acid tea soils (pH 3.2–3.4) from Georgia, U.S.S.R. Rock phosphate (510–1020kg P/ha) applied cumulatively had no effect on either the total organic P or the inositol P in acid tea soils (PH 3.6–3.7) from Ceylon.