Nitrous oxide emissions from a bermudagrass pasture: Interseeded winter rye and poultry litter

Adequate use of manure in grasslands may constitute an economical means of manure disposal and an abundant source of nutrients for plants; however, excessive nitrogen (N) additions to these soils could create new environmental risks such as increasing nitrous oxide (N2O) emissions. These potentially adverse effects in grasslands may be mitigated by improved management practices. In pasture systems, the combined effects of poultry litter applications and interseeded rye (Secale cereale L.) on N2O emissions are still not well established. This study was conducted to estimate the magnitude of soil surface N2O fluxes as affected by interseeded winter rye forage, annually spring-applied composted turkey litter as well as by weather and soil parameters. Fluxes were measured by vented chambers during 2 yr in a bermudagrass (Cynodon dactylon [L.] Pers.) pasture in moderately well-drained Tonti gravelly silt loam (fine-loamy, active, mesic Typic Fragiudault) located in northwestern Arkansas, USA. During the 60 d following turkey litter applications, N2O fluxes were frequently well correlated with soil nitrate (NO3−; r: up to 0.82, P's < 0.05) implying substrate stimulation on soil N2O production. Likewise, rainfall patterns strongly influenced N2O fluxes. Large rainfalls of 91 and 32 mm occurred within 6 d prior to the maximum N2O flux means (263 and 290 μg N m−2 h−1, respectively). Treatment effects on N2O emissions were significant only in spring periods following manure addition, particularly in the second year of our study. In the spring of 2000, additions of composted turkey litter resulted in 1.5-fold increase in seasonal cumulative N2O emissions (P = 0.04) which was directly associated to a numerically greater soil NO3−. In the spring of 2001, soils planted to rye exhibited a pronounced significant effect on mitigating N2O emissions (30 vs. 112 mg N m−2; P = 0.04). During the winter and early spring, rye growth also decreased quantities of both soil NO3− and water-filled pore space (WFPS) partly accounting for the lower N2O emissions in these fields. These results suggest that because poultry litter additions increased and interseeded rye diminished N2O emissions, the combined implementation of both management practices can produce environmental benefits while sustaining productivity in temperate pasture systems.