The effect of applied sewage sludge (SWS) at the rates, corresponding to 5 and 10 t/ha recalculated per dry weight, in combination with straw, spent kieselguhr, and sapropel on the phosphate status of leached slightly eroded chernozem was studied in a 3-month model experiment. The rise in the phosphorus content depended on the SWS rate and comprised 6–31% for the gross and 71–148% for mobile phosphorus. Its content was maximal on the sixth–eigtth week of composting. The additives to SWS exerted a slight effect on these parameters, but the application of spent kieselguhr and sapropel contributed to an increase in the phosphorus mobility by 50–220% at the rate of 5 t/ha and by 100–370% at the rate of 10 t/ha. The phosphate status of leached slightly eroded chernozem was in general improved in the sequence: (SWS + straw)–SWS–(SWS + kieselguhr)–(SWS + sapropel).
Gabbasova et al. (2025) studied this question.