Impact of Nitrogen Amendments on Soil Enzyme Dynamics under Simulated Wetland Ecosystem

Aims: To evaluate the influence of nitrogen amendments on soil enzyme dynamics in a long term incubation experiment.

Study Design: An in vitro simulated wetland ecosystem designed with rhizosphere soil was enriched with different N sources.

Place and Duration of Study: The study was conducted at Biocatalysts Laboratory, Tamil Nadu Agricultural University, Coimbatore, India. An incubation experiment ran for 150 days, to determine the temporal changes of soil enzyme activities.

Methodology: There were five treatments replicated thrice. The N enrichment included in the treatments were aerated except S1 as detailed below: rhizosphere soil (S1), rhizosphere soil without enrichment (S2), combined NH4Cl and KNO2 enriched rhizosphere soil (S3), KNO2 enriched rhizosphere soil (S4) and NH4Cl enriched rhizosphere soil (S5).

Results: The soil enzymes such as dehydrogenase (24.59 μg TPF g-1 soil day-1), urease (49.27 μg NH3 g-1 soil) and acid phosphatase (38.57 μg PNP g-1 soil h-1) were observed maximum in NH4Cl enriched rhizosphere soil (S5) on 70 DAI (days after incubation). While, highest alkaline phosphatase (53.40 μg PNP g-1 soil h-1) and fluorescein diacetate (7.57 μg fluorescein g-1 soil h-1) were registered on 70 DAI in KNO2 enriched soil (S4) and KNO2 + NH4Cl (S3) respectively. However, all the enzyme activities, irrespective of treatments, showed an increasing trend up to 70 DAI and thereafter, declined gradually.

Conclusion: Enzyme activities registered maximum in NH4Cl enriched rhizosphere soil (S5) than other enrichments. Basal N application as ammoniacal form (NH4+) triggers efficient trade-offs between soil functions in the wetland ecosystem whereas, combined sources contribute to microbial biomass and redox status of soil.