Cover Crops, Carbon Dynamics and the Ecological Intensification of Vineyards - A View From Under the Vine.

Abstract

There is mounting pressure to act more sustainably regarding agricultural land use, with viticulture no exception. How vineyard floors are managed can have broad ramifications, not only for grapevines but for the ecology of the vineyard and, importantly, for the soil beneath it. Traditional practices have often employed herbicides to maintain bare earth alleys, reducing grapevine competition with weeds. Many vineyards throughout the world have adopted some form of alternative management practice, at least in the vineyard mid-row, often revolving around the use of cover crops or a wild sward. The adoption of under-vine (or whole-floor) cover crop use has been somewhat slower, owing to apprehension over the perceived increase in direct competition between cover crops and grapevines for water and essential nutrients. It is hoped that by isolating and quantifying key vineyard floor variables we are better able to understand the influence of under-vine cover crop use and thus more accurately inform vineyard floor management practices. This thesis explores the theme of ecological intensification under-vine and thus how cover crops function as ecosystem service providers to the benefit of under-vine soil. Specifically, the following details experimentation conducted on two vineyards in South Australia, where seven treatments (five cover crop combinations, a straw mulch and herbicide-managed control) were established in 2014. Experiment one sampled soil under-vine and, through a pot-growth trial, aimed to determine whether cover crops increased the arbuscular mycorrhizal (AM) inoculum potential of both a leek trap plant and trial-based cover crops. In this, we were unable to distinguish differences in inoculum potential between different soils and concluded that AM inoculum may be buffered by the presence of other vineyard plants. Experiment two sought to quantify soil organic carbon (SOC) stocks and turnover in two vineyards, to a stratified depth of 0-10 cm and 10-30 cm. Results showed that SOC stocks were up to 23% higher under cover crop-managed treatments than the herbicide control. Experiment three employed a litter bag trial and laboratory incubation experiment to determine whether cover crop residues decompose more readily in their home soil, rather than their away soil. In this, we were unable to determine significant differences in decomposition in home vs away soils and concluded that the heterogeneity and frequent disturbance within vineyards were likely factors in dampening any homefield effects with regards to decomposition dynamics. In each hypothesis and subsequent experimental trial, we attempted to understand the role of undervine cover crops as providing ecosystem services to the benefit of the vineyard floor. The results suggest that cover crops sown under-vine can provide positive ecosystem services to the vineyard floor. Although we found non-significant results regarding AM inoculum potential and home-field advantage decomposition, there were no deleterious results of cover-cropping relative to herbicide use, and further experimentation may reveal significantly beneficial results. At a time when global CO2 emissions have reached detrimental levels, the planting of bare earth to draw atmospheric carbon into the soil is perhaps one of the most beneficial practices in agroecosystems. Moreover, the co-benefits of increasing SOC in vineyards are quantifiably numerous and are discussed in detail in chapter two.