Sheep grazing as a strategy to manage cover crops in Mediterranean vineyards: Short-term effects on soil C, N and greenhouse gas (N2O, CH4, CO2) emissions

Abstract

Sheep grazing is increasingly being considered by winegrape growers to manage cover crop growth in Mediterranean vineyards, a practice that could contribute to reducing fertilizer inputs, coupling the cycles of C and N and increasing soil health. Nevertheless, short-term increases in available soil C and N could trigger the emission of greenhouse gases (GHG). We carried out a field experiment in a Mediterranean vineyard of the Central Coast of California to investigate the short-term effects of grazing in combination with tillage on soil C, N and GHG emissions. Tillage and grazing treatments were combined in a full factorial design with 16 plots. Gas samples were collected using static chambers during the main management events from the tractor row and the soil under the vines within each plot. Gas samples were collected through two years, including two wet and two dry seasons and analyzed to assess daily fluxes and cumulative seasonal emisions of N2O, CH4 and CO2. In spring each year we collected soil samples from 0 to 15 and 15–30 cm depths of the vine and tractor rows of each plot, and from 0 to 15 cm depth at the time of gas sample collection. We observed that sheep grazing did not produce an increase in available soil N and C, but resulted in sporadic and localized peaks in daily N2O, CH4 and CO2 emissions. Nevertheless emissions were not significantly larger than non-grazed soils when extrapolated to the cumulative emissions of the whole season. The combination of tillage and grazing increased N2O emissions from the soil under the vine potentially due to increased nitrification rates. Sheep grazing and tillage did not have a significant effect on the yield and quality of the grapes during the two years of the study.