This is the second of a series of articles that will investigate the scientific basis of biodynamic viticulture and the effects of chemical agriculture.
The following review clearly illustrates that chemical inputs used in the past 50 years disrupt the subtle and complex balance that the vine has developed with the soil ecosystem and that humans have patiently fine-tuned to their senses along millennia
Does the idea of “terroir” also imply a quality concept? In viticulture, grape quality has been shown to be the consequence of the balance of above ground (canopy, as the energy synthesis organ) and below ground (root system, as the interface with the Earth) expressions of the grapevine (Lanyon et al. 2004).
Constantini and Buccelli (2013) review different mechanisms that govern soil’s effect on wine grape quality as mediated by canopy development. Nitrogen nutrition (Chone et al. 2001) and water supply (Seguin 1986) during critical phases of the vegetative cycle – between fruit set and maturity – have been shown to be essential factors in wine quality and primary determinants of the “terroir” effect.
Parent rock geology also plays an important role, as it influences soil texture and color (which modifies grape temperature) and provides most macro and micronutrients, therefore conditioning vegetative expression (phosphorus), pathogen resistance (sulphur), stress resistance (zinc), phenolic (manganese) and cell membrane integrity (calcium). It also determines root penetration and deep water-drainage, which can have a significant effect on quality (Lanyon et al. 2004).
Finally, human intervention interacts with these factors through surface management, cover crops or other cultivation. (Steenwerth and Belina, 2008).
Soil biology and soil structure bond these different mechanisms in a complex self-regulated ecosystem. In addition, bacteria provide micro-aggregates, fungi provide macro-aggregates and worms and invertebrates provide the break down, mixing and porosity required to create the soil structure which regulates soil water availability and aeration.
In spite of these well-known facts, after the “green revolution” and its compulsive drive towards land use efficiency in agriculture, viticulture became also dominated by a chemical approach to farming.
What conventional viticulture doesn’t tell you
Recent research is offering new perspectives on the effects of chemical agriculture. One example is provided by the collateral effects of glyphosate, the most widely used systemic herbicide. In viticulture, it is normally sprayed either on the under-vine area or on the whole row to prevent the growth of weeds that might compete with the vine for water or nutrients. Although it is common understanding that it has no non-target effects as it is easily degraded and adsorbed into the soil, Yamada et al. (2009) report that there is evidence that it is trans-located to the roots of target plants and released through exudates or dead material and can be taken up by the living roots of trees in an orchard (or vines in a vineyard).
The cation chelating ability of glyphosate can therefore create nutrient deficiencies in the soil due to immobilization of micronutrients (Johal et al., 2009). Also, its toxicity to beneficial organisms (i.e., rhizobia, Mn reducers as Pseudomonas and mycorrhizal fungi) and its stimulation of pathogens as fungi responsible for wood diseases in vines, among others, alters microbe population dynamics increasing disease pressure and reducing defense mechanisms (Yamada et al., 2009; Johal et al. 2009; Neuman et al., 2006).
As a consequence, increased root eating nematode infections, inhibition of root growth, reduced synthesis of flavonoids and reduced nitrogen fixation are also reported (Neuman et al., 2006).
Glyphosate is not the only chemical that disturbs ecosystem function. Synthetic fertilizers as urea and ammonia are regularly used in conventional viticulture to supplement vine nutrition. The addition of soluble forms of Nytrogen (N) overrides the control that vine roots perform on the soil eco-system creating all sorts of imbalances. Some reviews have shown that fertilizers may suppress microbial biomass in natural ecosystems (Treseder, 2008). In line with this finding, Kallenbach and Grandy (2011) have demonstrated that microbial biomass is 36% higher in microbial Carbon (C) and 27% higher in microbial N in soils treated with organic amendments relative to soils treated with inorganic fertilizers.
Less microbial biomass decreases the ability of soil to store and cycle nutrients. This requires that the timing and amount of soluble nutrition added to the vine are matched exactly to the vine needs, which puts the system in a state of permanent saturation if optimum nutrition is required (Drinkwater and Snapp 2007), thus creating the problem of leachates of soluble N and water table contamination. But this also creates problems to the vine, as the physiology of the plant is altered by the excess N: as Altieri and Nichols (2003) propose, this affects its vulnerability to diseases and pests due to reduced thickness of the epicuticle and increased N content of the tissue (which increases its acceptability to insects). Inorganic fertilizers also decouple C and N resources, impairing soil enzyme efficiency and suppressing key enzymes responsible for nutrient transformations (Kallenbach and Grandy, 2011).
In addition to herbicides and fertilizers, the effect of pesticides on non-target organisms is widely understood and recognized. This has led to the increasing adoption in viticulture of integrated pest management schemes (IPM) that base their mode of action on ecological principles. Even the use of permitted substances in organic viticulture as copper and sulphur have been shown to be strong biocides altering above ground and below ground biological communities.
The rebirth of Terroir
If water supply, nitrogen nutrition and soil geological characteristics are the key drivers of terroir expression and they are all critically mediated by soil biology and structure, is it reasonable to use conventional agriculture as a management system for the production of quality grapes?
Conventional agriculture bases its function on an oversimplified understanding of nature that destroys many of the feedbacks established in the soil ecosystem. It is no surprise that its results can only offer a glimpse of the potential of “terroir”. Fortunately, this fact is becoming progressively more evident to wine producers, consumers and journalists. On one hand there is a return to the idea that it is its origin what makes wine interesting and diverse (Costantini and Buccelli 2013; Goode and Harrop 2011). On the other, there is a renewed commitment of producers of premium growing areas to agro-ecological practices (organic, biodynamic, sustainable). As Viers et al. (2013) note with their “vinecology” concept, this can have a large impact in wine growing areas (traditional and new world Mediterranean), as the very environmental components that are perceived to produce quality grapes are also those that give rise to biodiversity and landscape conservation.
Altieri, M.A. & Nicholls, C.I., 2003. Soil fertility management and insect pests: harmonizing soil and plant health in agroecosystems. Soil and Tillage Research, 72(2), pp.203–211.
Costantini, E.A.C. & Bucelli, P., 2013. Soil and Terroir. In S. Kapur & S. Erşahin, eds. Soil Security for Ecosystem Management. SpringerBriefs in Environment, Security, Development and Peace. Cham: Springer International Publishing, pp. 97–133.
Choné, X., Van Leeuwen, C., Chéry, P., & Ribéreau-Gayon, P., 2001. Terroir influence on water status and nitrogen status of non-irrigated Cabernet Sauvignon (Vitis vinifera). Vegetative development, must and wine composition (Example of a Medoc Top Estate Vineyard, Saint Julien Area, Bordeaux, 1997). South African Journal of Enology and Viticulture, 22(1), 8-15
Drinkwater, L.E. & Snapp, S.S., 2007. Nutrients in agroecosystems: Rethinking the management paradigm. Advances in Agronomy, 92, pp.163–186.
Goode, J., & Harrop, S., 2011. Authentic wine: toward natural and sustainable winemaking. Univ of California Press.
Johal, G.S. & Huber, D.M., 2009. Glyphosate effects on diseases of plants. European Journal of Agronomy, 31(3), pp.144–152.
Kallenbach, C. & Grandy, A.S., 2011. Controls over soil microbial biomass responses to carbon amendments in agricultural systems: A meta-analysis. Agriculture, Ecosystems & Environment, 144(1), pp.241–252.
Lanyon, D.M., Cass, A. & Hansen, D., 2004. The effect of soil properties on vine performance C. LandWater, eds., pp.1–54.
Neumann, G., Kohls, S. & Landsberg, E., 2006. Relevance of glyphosate transfer to non-target plants via the rhizosphere. ZEITSCHRIFT FUR ….
Seguin, G., 1986: ‘‘Terroirs and pedology of vine growing’’, in: Experientia, 42: 861–873.
Steenwerth, K. & Belina, K.M., 2008. Cover crops enhance soil organic matter, carbon dynamics and microbiological function in a vineyard agroecosystem. Applied Soil Ecology, 40(2), pp.359–369.
Treseder, K.K., 2008. Nitrogen additions and microbial biomass: a meta-analysis of ecosystem studies. Ecology Letters, 11(10), pp.1111–1120.