Molybdenum sources and incorporation methods into urea granules: impacts on 15N-fertilizer recovery, photosynthesis-related parameters, and sugarcane growth

Abstract Background and Aims Sustaining and expanding the sugarcane ( Saccharum spp.) system depends on decreasing production costs and environmental impacts, improving nitrogen (N) use efficiency (NUE) has become a central challenge. In this context, molybdenum (Mo) is a cofactor of nitrate reductase and nitrogenase enzymes and may play a strategic role in enhancing plant N metabolism. Therefore, we hypothesize that adding Mo to urea might upregulate fertilizer N recovery by the plant and improve its NUE. Our goal was to assess the influence of Mo addition method and source on 15 N-urea granules regarding 15 N recovery, photosynthesis-related parameters, and plant N-cycle enzymes. Methods A 2 × 2 + 1 factorial experiment was carried out under controlled conditions for 140 d. The treatments comprised the Mo addition method to the urea granule (coated and incorporated) and Mo source (ammonium molybdate and nanoparticulated Mo trioxide). A Mo-unfertilized treatment, with the addition of conventional urea, was also employed. Fertilizers were granulated in the laboratory using a disk granulator. The 15 N recovery, N and Mo accumulation, leaf gas exchange and chlorophyll a fluorescence, and enzyme assays (nitrate reductase, glutamine synthetase, and urease) were measured in sugarcane plants. Results Mo addition to urea did not change 15 N recovery and net photosynthesis by sugarcane. However, Mo supply altered the stomatal conductance in situations of increased temperatures and influenced the activity of enzymes over plant growth. Conclusions Mo-enriched urea effectively supplies this micronutrient to sugarcane; nonetheless, it does not improve N acquisition or metabolism under the controlled conditions evaluated in this study.