Emissions of CO2 and N2O after termination of legume green manures at contrasting soil moisture conditions

Authors: SINGH, HARDEEP - Oklahoma State University; KANDEL, TANKA - Oklahoma State University; Gowda, Prasanna; KAKANI, GOPAL - Oklahoma State University; Northup, Brian

Submitted to: Grazinglands Research Laboratory Miscellaneous Publication
Publication Type: Proceedings
Publication Acceptance Date: 4/17/2018
Publication Date: N/A
Citation: N/A

Interpretive Summary: Abstract only

Technical Abstract: Legume cover crops grown as green manures may also contribute for increased emissions of nitrous oxide (N2O) after soil incorporation. However, N2O emissions from green manures largely depend on soil moisture at incorporation since soil moisture is the major controlling factor for biomass decomposition, nitrification and denitrification rates. In this mesocosm study, we measured N2O and carbon dioxide (CO2) fluxes from of fall-planted hairy vetch (HV; Vicia villosa) and spring-planted grass pea (GP; Lathyrus sphaericus) incorporated at two contrasting levels of soil moisture achieved by simulated rainfall. Early simulated rainfall treatments received 80 mm deionized water at soil incorporation while late rainfall simulated treatments received the same amounts after a week. Additional 20 mm water was added after two weeks of the first simulated rainfall in both rainfall treatments. Comparisons also included control treatments without the legumes under both rainfall treatments.. Biomass was incorporated at 0-10 cm soil depth of 25 cm soil cores at the rate of 8 Mg dry matter ha-1. Measurements of gas fluxes were taken with a closed chamber connected to a FTIR gas analyzer 2-3 times in a week during 28 days incubation. Soil NH4+ and NO3- concentrations were determined on spare cores at 1 week interval while soil temperature and moisture were also recorded at hourly interval. . CO2 emissions increased immediately after first simulated rainfall events and peaked around day 2-3. However, the emissions did not increase considerably after the second (20 mm) simulated rainfall. CO2 emissions from GP treatment were generally higher than HV treatment. N2O emissions from GP treatment were mostly higher than HV treatment under both rainfall simulations which was related to rapid decomposition rates, high N concentrations and low C/N ratio of GP biomass. N2O emissions from early rainfall simulation increased immediately but reached to peak level around day 8-10. Thereafter, the emissions declined with declining soil moisture. N2O emissions from late rainfall simulations increased after the first simulated rainfall and reached to similar peaks as the early rainfall simulation. The second rainfall simulation abruptly increased N2O emissions in both treatments but subsided to zero level within a week. In conclusion, the results indicate that both legumes can contribute for large emissions of N2O if soil moisture is not limited.