Soil is not merely a mass of inert earth; on the contrary, it is one of the most complex and varied ecosystems in nature and, according to the Fao, it is home to a quarter of our planet's biodiversity. Within it lies an incredible variety of organisms that perform essential ecosystem functions: they are capable, for example, of modifying the physical structure of the soil and its water regime, and of sequestering carbon present in the ground. Soil erosion can compromise soil quality by stripping away its highly fertile surface layer; it therefore represents one of the principal threats to this fragile and complex ecosystem, and puts global food security and the supply of clean water at risk.

Soil health, according to the United Nations, is also fundamental to tackling climate change. Around the world, agriculture — particularly conventional agriculture based on monocultures — is degrading soil by accelerating its erosion process. The agricultural lands most at risk of erosion in Europe, especially in Mediterranean countries, are those where vineyards are cultivated. Italy is no exception; indeed, Italian vineyards appear to show the highest erosion rate — this is what emerges from a new study published in the journal Plos One, which analyses the impact that the growing production of Prosecco docg in the Veneto region has on the soil.

The impact of Prosecco

The aim of the study "Estimation of potential soil erosion in the Prosecco docg area (NE Italy), toward a soil footprint of bottled sparkling wine production in different land-management scenarios" is to estimate the potential soil erosion rate of the Veneto hills in the Prosecco Conegliano Valdobbiadene docg production area. Demand for this prized wine has been constantly increasing (since 2003 production has grown by 129 per cent) and, to meet it, production has risen and vine cultivation has undergone further intensification, bringing consequent changes in land use. The study's authors — Salvatore Pappalardo, Lorenzo Gislimberti and Massimo De Marchi, from the Department of Civil, Environmental and Architectural Engineering at the University of Padua, Francesco Ferrarese, from the Department of Historical, Geographical and Ancient Studies, and Paolo Mozzi, from the Department of Geosciences — have attempted to quantify the actual environmental impact of this wine production.

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How vineyards consume soil

Between 2000 and 2016, the expansion of vineyards in the area examined nearly doubled, rising from 4,000 to 7,000 hectares. This expansion came at the expense of other crops and, above all, of natural and semi-natural areas such as woodland and grassland. To estimate and map soil erosion, the researchers used the Rusle (Revised universal soil loss equation) model and drew on high-resolution topographic data, together with analyses of data on rainfall, land use and soil characteristics. The study highlights that erosion is mainly concentrated on steep slopes — that is, in "hilly agricultural areas where topography and rainfall regime are important factors predisposing erosion processes" — and that in the vineyards where grapes are grown to produce Prosecco, the average soil erosion rate is 31 times higher than the erosion tolerance threshold estimated for Europe.

More than 3 kilograms of soil lost per bottle

To grow the grapes needed to produce one bottle of Prosecco, according to the study, approximately 3.3 kilograms of soil are consumed. "Our geographical study represents a first quantitative estimate of erosion processes within the Prosecco docg wine-producing areas," explained Salvatore Pappalardo, one of the study's authors. "Conventional agriculture today can go as far as modifying the morphology and structure of slopes in order to optimise mechanisation and agricultural production, considerably increasing erosion processes." The scientists, who examined an area covering 215 square kilometres in the province of Treviso, estimated potential erosion by simulating various soil management scenarios; it emerged that for a conventional soil management scenario, "the potential erosion estimated in the docg area is just over 400,000 tonnes per year, with an average erosion rate of 19.5 tonnes per hectare per year."

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Lost soil will not return

The research findings, predictably, were not well received by winegrowers. Wine is undoubtedly one of the flagship products of Italian food and drink production — in 2018 exports reached a new record — and it is therefore necessary to preserve this resource. It is, however, both a duty and an imperative to counter soil erosion, which represents "a non-renewable resource that provides essential environmental services to the land and to communities: from carbon sequestration to water availability, from agricultural fertility to the mitigation of hydrogeological risk, to water purification," said Salvatore Pappalardo. The tools to do so, the study suggests, exist.

Combating erosion is possible

Among the scenarios simulated by the researchers there is indeed a more sustainable one, which involves the adoption of certain measures to drastically reduce erosion. "In vineyards with 100 per cent herbaceous inter-row cover, erosion is reduced by approximately three times, saving around 50 per cent of the soil in the cultivated area." This would involve using hedgerows and vegetated buffer strips around the vine rows, which would help contain soil erosion and would perform other important functions, such as mitigating polluting chemicals arising from agricultural activities. In this scenario, each bottle produced would consume 1.1 kilograms of soil rather than 3.3.

Towards more sustainable agriculture

The aim of the study is precisely to provide useful data and information in support of more sustainable management of the soil system. The research, the first ever carried out to estimate soil loss in the Prosecco docg production area, highlights the environmental impact of wine production in conventional vineyards and underlines the need to adopt a soil erosion monitoring system. If the necessary countermeasures are not adopted, the current erosion rate could seriously damage ecosystems in the medium to long term, with negative consequences for agricultural productivity and the entire territory.