CHANGES IN THE CHEMICAL NATURE OF SOIL ORGANIC PHOSPHATE DURING PEDOGENESIS

Summary In two chronosequences of soils, total organic phosphate (P0) accumulated rapidly during the first 50 years of soil development, when organic matter increased and pH decreased. The rate of P0 accumulation then declined with age of soil until a ‘steady state’ was reached. The amounts of phospholipid, inositol phosphates and humic acid—P0 followed the same trends as the total P0. Parent materials and very young soils contained largely citric acid-soluble P0, but after less than 50 years, surface horizons accumulated sufficient organic matter to complex a considerable proportion of the P0. An upper limit of 20–5 per cent citric acid-soluble P0 and 70–80 per cent NaOH-soluble P0 was attained within 50 years of soil formation in the surface layers, and this slowly extended down the profile so that, after 10000 years, the soil had 20 per cent citric acid soluble-P0 and 70 per cent NaOH-soluble P0 to a depth of 1 m.