The role of Ca-organic interactions in soil aggregate stability .II. Field studies with 14C-labeled straw, CaCO3 and CaSO4.2.H2O

Uniformly 14C-labelled straw with or without CaCO3 or CaSO4.2H2O was incubated in a leached, fine sandy loam in the field. The addition of both Ca salts increased the residual 14C in the soil after several months decomposition, CaSO4.2H2O being more effective than CaCO3 in this respect. Addition of the Ca salts decreased the amount of dispersible clay and increased the proportion of particles 50-250 µm diameter. The addition of 14C-labelled wheat straw (with or without CaSO4.2H2O or CaCO3) increased the stability of aggregates >2000 pm diameter. Addition of Ca during decomposition of straw resulted in a synergistic stabilization of aggregates >1 mm. Moreover, the stabilization was prolonged in the presence of Ca.