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

Abstract

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.