The influence of organic and mineral nitrogen fertilizers on microbial biomass nitrogen and extractable organic nitrogen in long-term experiments with maize

Microbial biomass nitrogen and extractable organic nitrogen in extractions by 0.05M K 2 SO 4 and 0.01M CaCl 2 were studied in a long-term experiment with successive growing of silage maize. The highest content of microbial biomass nitrogen was measured for manure treatment, by 38–133% higher than for the control. In treatments with applications of mineral nitrogen fertilizers microbial biomass N was lower on average by 22–30% against the control. Extractable organic nitrogen was also lower in treatments with mineral N fertilizers compared to the control: by 23% in ammonium sulphate treatment and by 29% in DAM. The highest content of extractable organic nitrogen was determined for manure treatment. There was a positive correlation (r = 0.44–0.9) between microbial biomass nitrogen and extractable organic nitrogen in the extractions by 0.01M CaCl 2 and 0.05M K 2 SO 4 .