Recovery of15N from ammonium nitrate and algal biomass-amended soil

Abstract

A greenhouse experiment was conducted to compare the effectiveness of blue-green algae (Anabaena flos aquae) produced in a simulated inorganic-wastewater medium and NH4NO3 as sources of N for bermudagrass (Cynodon dactylon L.) on a Decatur silt loam soil (clayey, kaolinitic, thermic Rhodic Paleudult).15N-labeled blue-green algae and15N-labeled NH4NO3 were used as N sources to supply up to 300 mg N per pot (3 kg of soil). Bermudagrass was clipped at 42, 63, and 102 d after planting and dry matter yield, total, and15N were determined at each clipping. Results indicated a highly significant increase in total dry matter (shoots and roots) and N uptake over the control for both algae and NH4NO3 treatments at all N rates. There were no significant effects of N source on bermudagrass yields, but total N uptake was significantly higher with NH4NO3. The net mineralization of N from blue-green algal biomass ranged from 36 to 59% of the total N applied and the corresponding net release for NH4NO3 ranged from 65 to 86%. From 29 to 54% of the total N applied as blue-green algal biomass and from 50 to 75% of the N applied as NH4NO3 were assimilated by bermudagrass plants. For N rates above 100 mg N pot−1, higher proportions of the labeled N in the shoots of the third harvest were derived from algal biomass than from NH4NO3. A large portion of the labeled N remained undecomposed or immobilized in the algae treated soil (41–64%) as compared to NH4NO3 treated soil (14–35%). More loss of N occurred in the NH4NO3 treatments from 3 to 15%, while the corresponding figures for algae treated soil were 2 to 8%.