Seasonal changes in the amounts of phosphorus and potassium dissolved from soils by dilute calcium chloride solutions

Variations during 12 months in the concentrations of soil P and K soluble in 0-01M CaCl2 solution were measured on several sites with contrasted histories at both Rothamsted and Woburn. Concentrations were always less in fresh than in airdried soils.

P concentrations in the heavy soils at Rothamsted were remarkably constant, seasonal variation only occurring where FYM or phosphate fertilizers had been applied during the year. At Woburn P concentrations were also constant in the poorer soils, but varied during the year in rich soils.

On Barnfield at Rothamsted the plots receiving FYM each year contained more soluble P than those treated with superphosphate. Where both FYM and superphosphate were applied, P concentrations were greater than the sum of values on plots receiving FYM and superphosphate separately because a given amount of P remained more soluble when FYM was regularly applied. P also remained more soluble on plots given ammonium sulphate. RESP-5309