Tracking nitrogen transfer in grass-legume systems using enriched 15N2 during the warm season

Authors: QUEIROZ, LUANA - University Of Florida; DUBEUX, JOSE - University Of Florida; SOLLENGERGER, LYNN - University Of Florida; VENDRAMINI, JOAO - University Of Florida; LIAO, SUNNY - University Of Florida; CASAGRANGE, DANIEL - Federal University Of Lavras; SOUSA DE ABREU, DACIELE - University Of Florida; Jaramillo, David; SANTOS, ERICK - University Of Florida; RUIZ-MORENO, MARTIN - University Of Florida

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 11/15/2021
Publication Date: 11/15/2021
Citation: Queiroz, L., Dubeux, J., Sollengerger, L., Vendramini, J., Liao, S., Casagrange, D., Sousa De Abreu, D., Jaramillo, D.M., Santos, E., Ruiz-Moreno, M. 2021. Tracking nitrogen transfer in grass-legume systems using enriched 15N2 during the warm season. Meeting Abstract. ASA, CSSA, SSSA International Annual Meeting, Salt Lake City, UT.

Interpretive Summary: Legume inclusion in pastures can often improve delivery of ecosystem services. In addition, the inclusion of perennial legumes into C4-grass pastures can be an alternative to increase nitrogen supply via biological nitrogen fixation. Part of the nitrogen fixed by legumes can be transferred to grasses belowground via root decomposition, through association with arbuscular mycorrhizae, and root exudates. The objective of this experiment was to track the nitrogen transfer through roots using 15N2 as a tracer in rhizoma peanut (Arachis glabrata; RP) and bahiagrass (Paspalum notatum; BG) mixtures using H pots. The treatments were: BG and RP connected with the RP being enriched with 15N; BG and RP connected with the BG being enriched; BG and RP connected with none being enriched; BG and RP connected, however, with a membrane in each side impeding the connection of the roots and with the RP being enriched; BG and RP separate in which both were being enriched; BG and RP separate and no enrichment; and BG and RP in a mixture, connected, with no enrichment. Enriched 15N-gas was injected directly into the root zone for 10 consecutive days. Overall, we were able to track N transfer through the use of this technique, in which bahiagrass became more enriched whenever the rhizoma peanut received 15N2 gas.

Technical Abstract: Legume inclusion in pastures can often improve delivery of ecosystem services. The inclusion of perennial legumes into C4-grass pastures can be an alternative to increase nitrogen supply via biological nitrogen fixation. The objective of this study of was to track the nitrogen transfer through roots using 15N2 as a tracer in rhizoma peanut (Arachis glabrata Benth.; RP) and bahiagrass (Paspalum notatum Flugge; BG) mixtures using H pots. The experiment was conducted in a greenhouse environment, and it was set up in a randomized complete block design with four replications and seven treatments. The treatments were: BG and RP with the RP being enriched; BG and RP with the BG being enriched; BG and RP with no enrichment; BG and RP with a membrane impeding the connection of the roots and with the RP being enriched; BG and RP, both enriched; BG and RP, no enrichment; and BG and RP in a mixture, with no enrichment. The gas was injected directly into the root zone and 10 mL of 15N gas was provided for 10 consecutive days. Harvests occurred every four weeks. The harvested material and the roots were analyzed for 13C, 15N, root biomass, biological N2 fixation (BNF) and herbage accumulation. Results indicate the technique worked, in which the forage biomass became enriched in 15N, suggesting there was belowground transfer of N. In the treatments in which bahiagrass received 15N2 gas, bahiagrass became enriched, indicating an associative relationship with soil microorganisms that reduce N in the rhizosphere. Overall, the infusion of 15N2 directly into the root zone utilizing H-format pots can be used as a technique to track N transfer in grass-legume mixtures. Further studies are required to identify soil microorganisms responsible for nutrient transfer and N2 reduction, specially in grasses.