Incubation experiments on net nitrogen mineralization in organic Greek soils

Abstract

Aerobic incubation experiments were conducted in organic surface samples collected from arable soils of Philippoi, in Northern Greece. Laboratory experiments were carried out to investigate the nitrogen (N) mineralized from soils and sugar beet residues incorporated into the soils. Cumulative mineralization of N, potentially mineralizable nitrogen (N-0), and mineralization rate constant k were estimated after 30 continuous incubation weeks at 35 degrees C. Total N content of soils ranged between 6.6 and 19.2 g ka(-1), total soil carbon from 119 to 309 g kg(-1), soil organic carbon ranged from 119 to 308 g kg(-1), and the C:N ratio varied from 13.5 to 18.3. The cumulative net mineralized N ranged between 132 and 426 mg kg(-1) for nonamended soil and between 165 and 586 mg kg(-1) for residue-amended soil. Nitrate was the main form of mineralized N. although appreciable amounts of ammonium were measured. Potentially mineralizable nitrogen (NO) varied between 254 and 1067 mg kg(-1) for nonamended soil and 311-1465 mg N kg(-1) in residue-treated soil. The mineralization constant k was between 0.052 and 0.068 (week(-1)). Close relationships between total soil N and soil organic carbon, and between cumulative mineralization and total soil N were found. Mineralization occurred rather rapidly, although the amount of mineralized N per week was reduced in the later weeks of incubation. Variation in net mineralization among soil samples can be attributed to soil organic matter content, origin, and state of decomposition, as well as differences in management histories, and soil and microenvironmental conditions. Monitoring of mineralization process may ensure a basis for increasing nitrogen use efficiency.