Phosphate State of Leached Chernozem under Applying Fertilizers Based on Sewage Sludge

In a 3-month model experiment, the effect of introducing sewage sludge (SS) in doses corresponding to 5 and 10 t/ha in terms of dry weight, in combination with straw, spent kieselguhr and sapropel on the phosphate state of leached, slightly eroded chernozem, was studied. The gross content of phosphorus increased depending on the dose of SS by 6–31%, and mobile phosphorus – by 71–150%, its maximum content was observed at 6–8 weeks of composting. At the same time, additions to SS had a slight effect on these indicators, but the addition of spent kieselguhr and sapropel contributed to an increase in the degree of phosphorus mobility at a dose of 5 t/ha by 50–220%, and at a dose of 10 t/ha – by 100–370%. In general, the phosphate state of leached, slightly eroded chernozem improves in the series: SS + straw < SS < SS + kieselguhr < SS + sapropel.