The loss of phosphorus from sandy soils

Abstract

Leaching losses of phosphorus were measured in seven field trials. .Phosphorus was broadcast as superphosphate. Soils used were mostly loamy sands. Losses from the top 4 in. layer of soil ranged from 17 to 81% of the applied phosphorus. This seems to be the first report of such large losses from soil under pasture and receiving only 22 in. mean annual rainfall. Percentage losses remained fairly constant over a wide range of application rates. The surface 4 in. retained more applied phosphorus than did the lower layers. Phosphorus leached from the topsoil was removed beyond the reach of most clover roots. Mixing superphosphate with an equal weight of lime increased clover growth and phosphorus uptake in the establishment year only. It did not increase retention of phosphorus by the soil. The use of sufficient lime to raise the soil pH from 4.9 to 5.5 only increased phosphorus retention from 11 to 1676 of that applied. Applying phosphorus as slightly soluble rock phosphate increased soil retention from 56 to 850j,, but decreased phosphorus uptake by the pasture to only half that obtained if superphosphate were used. A close negative correlation was found between phosphate loss and both the native phosphorus content and the loss on ignition. Soils containing less than 100 p.p.m. native phosphorus or giving less than 6% ignition loss showed appreciable losses of phosphorus. Results show that the rate of accumulation of fertilizer phosphorus may be very slow in some soils unless steps are taken to prevent phosphorus from leaching.