What are the long-term impacts of soil erosion on the Langhe’s of Piedmont vineyards?
The Langhe of Piedmont in north-west Italy is an area famous for its wines and truffles, particularly for the wine of Barolo and the white truffle of Alba. Which is considered the capital of Langhe. While Barolo’s wine it has been said to be the “Wine of kings, the king of wine”. The Langhe area is in the hilly north-west of Italy, south of the Italian Alps. Historically Julius Caesar, coming back from Gallia, stops in this area to taste the famous wines of Langhe.
The Langhe is divided in Bassa Langa (Lower Langa) and Alta Langa (Upper Langa) this is because starting from south of Alba the scenery changes dramatically. By replacing the vineyards with hazelnuts, oak woodlands, and meadows. Alta langa is located on higher hills often toward the alps.
The Langhe are also famous for their historical heritage of medieval architecture blended with the renaissance style. Old churches with fine quality frescos and solitary monasteries.
All of this is affected by soil erosion and degenerative agriculture practices, caused by intensive agri-business applied to ancient vineyards. Periodic landslides are not only affecting the vineyards but also the local communities infrastructures like roads, cemeteries, farms, hospitals. The environment is affected, particularly by leaching big quantities of phosphates and nitrates from artificial fertilizers into watercourses, together with soil debris accumulating at the bottom of the rivers causing floods.
Historically, major events linked to soil erosion in the Langhe area have been recorded since 1705, with periodic events occurring every 50 odd years. Since 1839, there has been an increase of major hydrogeological events, on average one every 12-15 years. And, only since the 1900’s, there have been major hydrogeological events, one every 10 years with two in 1977, one in 1993 and one in 1994. In the 21st century, there has been only one major event in 2000. Anyway, small events affecting the soil stability are taking places every year such: road blocked by debris, landslides affecting cemeteries (Scagnello 2011), the stability of retaining walls and houses, flooding of small rural areas etc.
For the map of monthly soil loss, on the website of the Land management and natural hazard unit of the European commission:
The months more at risk of soil erosion events are the winter months, between November and December, with an exception for part of March and April. This is because those months are characterised by heavy rainfall, snow, and snow melting between the end of March and the first two weeks of April. But also because there is less vegetation during winter months due to the deciduous kind of vegetation present in the area, the so-called C-factor (Cover management factor). Vegetation help, with their leaves, to protect the soil from heavy rainfall, slowing down the speed of the impact of the raindrops on the top soil.
The European Soil Bureau estimate the soil loss occurring already every year in the Langhe area between 5 and 40 tonnes per hectare. (https://eusoils.jrc.ec.europa.eu/esdb_archive/serae/grimm/italia/eryear_large.htm)
But the potential of soil erosion, predicted by the European Soil Bureau, in the Langhe could rich between 40 and 200 tonnes per hectare a year. We know that soil forms at a rate of approx. 1 tonne per hectare a year (https://www.seafriends.org.nz/enviro/soil/geosoil.htm) so soil erosion will exceed between 40 and 200 times the soil formation every year.
Soil erosion is a natural activity, happening during geological times, and it is a process that is necessary to form the soil. With regard to soil degradation, most worries about erosion are associated to fast erosion, where the natural rate of erosion has been increased largely by human activity. Soil erosion by water is a common problem throughout Europe.
The physical process of soil erosion imply a separation of material by two processes, rain impact and flow friction; and transported either by natural action through the air or by land water flow. Runoff is the most important driver of intense soil erosion by water and processes causing runoff play a crucial role in the investigation of soil erosion levels.
By taking away fertile topsoil, erosion decreases soil productivity and, where soils are superficial, may produce a permanent loss of agricultural land. Even where soil depth is good, loss of the topsoil is not dramatic but potentially very detrimental. Serious erosion is associated with the establishment of temporary or permanently eroded channels that can fracture farmland. The soil removed by runoff from the surface, for example during heavy rainfall, piles up below the eroded areas, sometimes blocking roadways or watercourses and flooding buildings.
The erosion rate is sensitive to climate and land management, as well as to particular conservation practice at agricultural level. The Langhe are particularly predisposed to soil erosion because it is subject to lengthy dry periods followed by heavy erosive rain, falling on steep slopes with fragile soils. This means no water absorption by the soil because sand and silt have very high drainage values. In contrasts with NW Europe where soil erosion is lower because rain falls on gentler slopes and it is more evenly distributed throughout the year. Therefore, the area affected by soil erosion is less considerable than in southern Europe. Nevertheless, soil erosion is still a severe problem in NW and central Europe and is on the increase. In parts of the Mediterranean region, erosion has come to a stage of irreversibility and in some places like Greece, has virtually ceased because there is no more soil left.
The agricultural methods used in the last 50 years in the Langhe area is reflective of the industrial practices used in major industrialised countries. Use of deep plow, use of chemical fertilisers and pesticides, removing the vegetation groundcover like grasses and uses of heavy machinery for cultivation and harvest.
The use of deep plow kills the soil micro and macro organisms because they get in contact with sunlight and ultra violet rays at which they are very sensitive. This will slow or in some cases stop the soil chemical processes like nitrogen fixation etc. Slowing down or stopping the vegetation growth that with their roots protect the soil from heavy rainfall, helping water penetrating deeply into the soil and creating humus with decomposing organic matter. Humus will hold more water and nutrients, including carbon, into the soil surface creating new soil.
The use of chemical fertilisers will accumulate different substances into the soil and when a heavy rainfall event will occur all those excess nutrients will be leaching through the soil in water courses causing eutrophication, which is the excess of nutrients in watercourses causing excessive growth in rivers,lakes etc. that will increase the decay of water plants by lack of light. Then, the bottom of water courses will be filled with decayed water plants causing the reduction in depth of the watercourse that it can carry less water and in the eventuality of a storm or just of snow melting it will be possible to have a flood.
The use of pesticides is killing the pests but also other beneficial insects and micro-organisms lessening the biodiversity also into the soil leaving the plants more expose to illnesses and pest attacks. Again, this will reduce the speed of biological soil processes reducing the amount of vegetation growth leaving the soil more exposed to weather events.
In some vineyards the soil under the vines is without any ground cover like grasses. This will leave the soil without any protection from rain,storms and wind erosion. Also, it has caused compaction because there are not plant roots aerating the soil.
The use of heavy machinery like tractors and harvesting machines are also compacting the soil under their weight, making it difficultto the organism living inside the soil and again leaving the land without any protection from weathering events.
The main reason of deforestation in the Langhe, used to be making more room to plant more vineyards. In fact, we can notice, all over the Langhe area, that there are very few trees left, if any. Normally grapes in Italy are planted south facing to maximize the exposure to sunlight to be able to have higher sugar content in the grapes. But in the Langhe grapes are planted everywhere even north facing. In some countries, usually the north face of the hill, where there is vineyard, it is covered with trees for many different reasons, but not in the Langhe. This kind of deforestation on hill tops, prevent the soil holding moisture and without the protection from sun-blocking tree cover soil is quickly drying out.
Trees also help perpetuate the water cycle by returning water vapor back into the atmosphere. Without trees to fill these roles, many former forest lands can quickly become barren deserts and on hill tops, this effect will be exacerbated even further thanks to the slope, that due to gravity speed up the process of surface run off. Also, trees they have big roots that hold the soil on the hill and the leafs protect the soil from the impact of rain drops. So, without trees and no roots, soil erosion will has increased by water run off and its route down a hillside as soon as a major weather event will take place.
The Langhe of Piedmont is also a very touristic area, this has resulted in the intense building of villas and touristic constructions (Hotels, B+B, agro-touristic compounds etc.).
Such buildings are often placed near vineyards or inside wine making estates removing big amounts of soil and constructing roads, paved areas etc. which inturn increases the rainwater runoff during weather events such storms. If the water runoff is directed inside or nearby vines areas can damage heavily the vineyards.
Long term impacts
• Permanent change of the morphology of the landscape
• Euthrophication of freshwater courses
• Periodic landslides
• Permanent loss of farmland
• Permanent loss of crop yields
• Economic damage
• Damage to the local community
• Soil compaction
• Loss of local wildlife habitat
• Permanent loss of soil biodiversity
• Disruption of streams ecology
• Increase of water treatment costs
• Damage to public health
• Recurrent flooding
Risks and uncertainties
Table 1.1. Human-induced Soil Degradation in Europe1 (M ha)
Best Management Practices to combat the effects:
• Construct diversion ditches to break up slopes and reduce water flow through your vineyard.
• Use grassed field borders and headlands of adequate width to filter out soil particles carried with runoff.
• Plant vineyard rows across the slope to break up water flow.
• Use grassed waterways in areas of concentrated flow.
• Subsurface drainage tiles may reduce surface flow.
• Subsoiling to break up compacted soil layers can increase infiltration and reduce surface ponding.
• Use permanent cover crops or straw mulch in row middles to absorb the force of raindrops hitting the bare soil.
• Avoid repeated tillage.
• In tilled row middles, use seeded cover crops to control erosion from fall to spring.
• Control gullies before they grow.
• Install temporary barriers during soil disturbance (e.g. following planting) to retard sediment flow.
• Consult with Soil and Water Conservation District (SWCD) and Natural Resources Conservation Service professionals (or other engineers) to identify potential problems before planting and laying out a vineyard.
• On irrigated sites, use drip irrigation and avoid over-irrigation by adjusting timing and rates to match vine demand and soil water-holding capacity.
JRC European commission- Land management and natural hazard unit,Soil erosion and risk assessment in Italy [online]. Available from: https://eusoils.jrc.ec.europa.eu/esdb_archive/serae/grimm/italia/start.htm [Accessed 14 May 2011]